The folks over at PONTECH have just released a pretty impressive opensource PIC32 library for controlling a linear slide at speeds of 800 inches per minute!
PONTECH makes the Quick240 (Quick Universal Industrial Control Kard) which is based on the open source chipKIT platform. It was designed for industrial automation systems, where typically a ladder logic PLC might be used. The benefits to using a system like this is that because it is open, you are no longer stuck with proprietary hardware, and it is much more flexible to allow you to “do your own thing”. Did we mention it is also Arduino compatible?
Using this system they’ve successfully controlled two 8″ Velox slides at a whopping 800 inches per minute with a resolution of 0.00025″ — just take a look at the following video to appreciate how freaking fast that is.
The StepAndDirection library can be found over at GitHub for use with a PIC32 microcontroller.
What sort of horrible measurement is “inches per minute”?
.. and why do we keep having the discussion about accuracy versus resolution? ;)
because the real discussion should be accuracy versus precision.
Don’t get me wrong, I’m quite pleased to see something that’s not only open, but also finally getting away from stepper-only based control.
It would have been more helpful if they had quoted numbers in the video about the update frequency of the servo loop, otherwise all this tells me is that they’ve got really good encoders.
fuuuu… nevermind. Steppers.
No, it should be repeatability.
http://www.hostechsupport.com/request-a-call
Freedom units.
Just to be clear, I am joking. I actually get pretty embarrassed when I see imperial units in any type of scientific application.
Ha! Well, you’re not the only one. ;)
It’s pretty silly if you ask me..
Even better, is that google will convert silly units into relatively more sensible ones. It informs me that this is actually 2036 furlongs per fortnight to help you out putting it into more real-world amounts.
Well now.. this is INCREDIBLY more useful.
I was happy knowing that .00025 inches is just a tad over 6 microns. ;)
Ah yes – Furlongs-per-fortnight. If i remember correctly, that was one of Jerry Pournelle’s favourites back in the day when he wrote a regular column for Byte magazine. And of course the acceleration would be measured in furlongs per fortnight per fortnight. Who needs metric units anyway? :)
@medix yes a tad over six and a third microns actually One can express metric values in fractions too.
@pcf11: .. but we don’t. And never will.
@medix but I just did, so you’re wrong.
ooh ooh – someone on the internet is wrong.. :)
It’s also about 12.9 furshlugginer potrzebie per day.
Yeah you’re right. Leave metric in the impractical scientific world. When it comes to engineering use Imperial units. This is engineering too, not science.
one of of the data sheets I’ve poured over has dimensional units in Imperial. Every other one is metric.
Why does ‘thou’ get used then?
Base 10? Decimal? Sounds like one of them commie Metric things to me.
“thou” gets used by machinists, whose equipment measures in thousandths of an inch. It’s like being metric (i.e., using powers of 1000 instead of fractions), but without the silly French unit of length. The meter is no more a fundamental unit of length than the inch. Completely arbitrary, when you consider that both the inch and the meter were originally based on measurements of the Earth, but now a “meter” is defined as “the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second” (if you can believe what you read on Wikipedia). Totally arbitrary.
Next time somebody asks me how far away something is, I think I’ll try to answer in kilo-inches.
Still, “inches per minute?” Who measures how far a machine runs in a MINUTE? Sounds more like a unit for snail races. But again, the units of inches per minute ARE used in machine tool specifications, where you DO expect that it’s going to take minutes to gouge out a handful of steel chips.
It’s not arbitrary though,
Consider that 1 gram of water occupies 1centilitre of space, which is 1cubic centimetre, (i.e. 1cenitmeter in every direction.) It takes 1 calorie of energy to raise this 1 cl of water by 1 degree (which is 1% of the freeze to boil range).
If the gram were made of hydrogen rather than water, it’d be 1 mole of hydrogen.
You see all the Metric numbers and measure actually relate to real things, AND to each other.
Whilst imperial measurements are based on some unknown standard thought up from nowhere and at least twice in history rumoured to be based on the length of a kings arm.
However, it makes sense to use what you’re comfortable with. (which is they way that we in Britain have done for a long time).
Which is why we measure our weight in stones, (14 pounds).
We measure your height in feet and inches.
We measure our roads in miles.
And we measure our beer in pints, real pints not those tiny American “queen” pints.
Then we measure swimming pools in meters.
It makes sense to use the best measurement for the job.
if I was doing something in Metal I’d undoubtedly use millimetres as my point of measurement.
If I was making someone in wood I’d use feet and inches.
I guess as feet and yards, and inches relate well to the human body
(about one foot, about half an arm span, about the length from the knuckle to the tip of the thumb) making furniture using imperial measurements seems to make it more comfortable.
I think the most annoying comparative measurement I hear in the UK is xyz is being built/destroyed/would cover “n” football pitches.
Whilst there is no standardised football pitches -they are all different sizes in the UK (where we play football with our feet)
Quick! How is the length of an inch officially defined?
Imperial measurements do have their place. This is not a US vs. the world comment. Just because a 10cm x 10cm x 10cm volume of water at room temperature is the weight of 1 kilogram, does not mean it’s practical. coke is measured in ounces, as is maryjane. much more practical than grams. Just sayin’
Who cares?
Scientific? That looks more like an industrial or engineering application to me. I guess it depends what you are using the slide for.
There are a lot of great arguments for using metric everywhere. Unfortunately none of them do a real person any good when they live in a country that is stuck on imperial. I’m currently scratch building a Mendel 90. It’s easy to customize, I thought about converting all the screws, rods, etc… to imperial so that it would be easier for me to find parts here in the US. This is my first reprap however so I wanted to keep the build as close to the original design as possible. What a mistake!
Having to special order very single screw, nut and washer is great! Especially when I have access to local stores that would sell me the imperial ones by the pound for pocket change. I thought I would be smart and buy all screws of a type the same, longest length. A metric screw cutter cost me almost $50 on eBay! I couldn’t find any actual stores selling them! I’m still looking for metric drill bits. I will probably have to over-pay and wait a month for those too.
So, yah, you can argue for metric until you are blue in the face. I will probably agree with everything you say (in theory). In the real world though, if you are actually going to build something rather than just measure scientific phenomena it is much better to just go with whatever the locals use.
lowes carries metric drill bits and taps, and one metric tape measure.
Check the body size on tape measures, they’re mostly metric these days.
That is, your 3″ body is probably 75mm. Your inside measurements will be about 1/16″ out.
Well, this is engineering, not science. Scientific research primarily uses metric because the metric system is optimized primarily for inputing measurements into complex data models; but this this means that it’s *not* optimized for the in-situ practicality of measurement itself. Imperial units, by virtue of having developed organically and being refined through use, are a lot less arbitrary and better scaled to fit their context of application than metric units.
Imperial units, for the most part, are based loosely on proportions found in direct human experience, and adjusted to the constraints of the materials, instruments, and quantities people generally do practical work with. Metric units, conversely, are based on essentially arbitrary values defined by reference to quantities outside of most practical contexts: the meter is a one-over-nine-digits fraction of the distance light travels in a second; the kilogram is defined according to the mass of a physical artifact stored by the BIPM in France, etc.
That’s not to say that metric units are really ideal for anything, of course: SI has that very bizarre gimmick of reimplementing scientific notation via an arcane system of verbal prefixes that attach to the name of the thing you’re counting, instead of just using numbers to represent quantitative information.
What people should really be embarrassed about is the use of metric units in wholly inappropriate contexts. I’ve seen recipies and ads for furniture with measurements specified in metric, and everything was expressed in three- and four-digit numbers, because the scale of the units is just so poorly suited to the application.
Inches Per Minute is the standard measurement of axis speed in CNC machines so here it makes perfect sense as that is the sort of thing these would be used for. Most CNC’s the Feed rates are measured in IPM or MMPM.
no kidding. i prefer miles per hour.
60 +/-~5 mph is a pretty common speed limit where I live. I like it because it works out to 1 mile per minute. Miles are labeled on the sides of expressways. It’s realy easy to make pretty good estimates of how long one has until the exit.
60km/h is nearly residential speed. I had better either already be very near to my destination or have just left, on my way to the nearest faster road if I have to drive that slow. I guess the math wouldn’t be too bad if I could go 120km/h. Few roads near me go that fast however.
100 kph isn’t that difficult to math in your head, because the distance to be travelled can be understood as percentages of an hour, which is pretty intuitive.
If you need to actually calculate it, then it’s 1.66 km per minute. 17 km per ten minutes etc.
Try living in the UK! We have this mental mix and match approach.
I’m 5 feet 7 inches tall but I’d walk through a door that’s 2 metres high. My body weight is expressed in Stones! I don’t really know what Stones are but I know I’m 11 and a half of them.
All engineering/science is done in metric units. Welllll apart from pressure which is pounds per square inch.
Baking a cake could use 300 grams of sugar and a pint of milk.
No wonder we’re a bit special some times!
The Imperial system of measurement is useful for practical applications, like engineering. There is zero advantage to using metric in this specific example beyond prejudice. Unless that is you somehow think that 0.000635 is somehow a more useful measurement than 0.00025 is. Personally I don’t.
Engineering is one of the applications the Imperial system should never be allowed near of. 0.000635 is not more explicit than 0.00025 unless you add the friggin’ units, then 6.35um is enormously more explicit.
How does the units make any difference.
Funny but I worked a project to build a device at my last job. I used metric to start off but since the standards for things like the spacing between keys was exactly .1″ When I took my first drawing to the machine shop they told me that the only metal they could get was in inches.
I think you will find many machine shops still use inches and many metal suppliers still use gauge for sheet metal.
The units make the difference in engineering because metric allows you to pick the most suitable one.
In actual reality, engineering in metric doesn’t deal in different units. You pick one and you stick to it. If you’re making things that require millimeter precision, you use millimeters. If you need micrometer precision, you use micrometers.
If for example you’re building furniture, you’d use millimeters for everything. No fractions and halves, no point something – just millimeters. It has the advantage that you remember the numbers as sequences without breaks and there’s less ambiguity in the math.
Why should engineering be an application that the Imperial system should never be allowed near of? It got us to the Moon. What has the metric system done as impressive? Before you say the LHC realize that you guys just ripped that idea off of us. We scrapped our plans to build a bigger supercollider back in the 80s. We decided that being more powerful than every other country on the planet combined was a better goal. So we threw you a bone with accelerators. Officially the money was channeled into the shuttle program, but fully half of the shuttle missions were DoD classified. We weren’t just peppering the sky with rainbows then either dontchaknow?
You seem to like another DARPA project of ours quite a bit too. AKA The Internet! Back when we built it you’d better believe the industry standard component pitch was you guessed it, Imperial! A tenth of an inch on center spacing.
So, what have you got, anything? Now go back and enjoy your little metric life, in our Yankee Imperialistic world.
“What has the metric system done as impressive?”
Dunno, Sputnik? First man in space? First robot on the moon? First lander on Venus?
The Soviets used metric. Didn’t seem to bother them too much.
Technically speaking, the metric system got to the moon first with Lunokhod as far as getting there is concerned.
If you want to make the comparison between imperial vs. metric on that case, the metric system got there based on the math alone because remote control of the lander was impossible, whereas the imperial system had a man to steer it the last mile.
Ya: and lets not forget what happened when the new kids mixed meters and feet when we landed on Mars——several somethings below the surface.
OK all of you just stop. You’re nowhere until you’re actually there. So no unmanned missions count. No one has ever been to Mars for instance regardless of how many unmanned missions we may fly to there. As far as the Soviets getting anywhere first goes they only managed to do that because the USA never was, or even is interested in space. The Soviets were so far behind us regarding bomber tech that they decided to change the game they’d play. Realize that the B-52 was in service 3 years before Sputnik flew!
The only interest the USA has ever had in space was to make the Soviets look bad, which we did, again, and again! Just in case you kids don’t know we finally drove them to collapse as a nation. So we won utterly, and completely.
@VR so you like failed Mars missions do you? Then you should appreciate this page
http://mars.jpl.nasa.gov/programmissions/missions/log/
You might even notice that the USA has more success than everyone else put together. Far less failure too.
Well the crux goes something like this. How many meters in a kilometre? 1000/1=1000. Its easy to divide it in your head. So how many yards are there in a mile? Lets see. 5280/3. Quick! Fast and in your head.
@BG Quick, why do you need to know how many yards are in a mile? Heck, take you time and give me one valid reason. I’ll be here all week. Then you can tell me about all of the times it has been useful for you to know how many meters were in a kilometer.
*crickets*
Yeah, I thought so.
“OK all of you just stop. You’re nowhere until you’re actually there. So no unmanned missions count.”
Why? That’s just shifting the goalpost.
For the comparison of metric vs. imperial in engineering, it doesn’t really matter if it’s people or robots. The Soviets were quite superior in space technology, but they lacked the resources and money to have it at such a grand scale as the US.
“why do you need to know how many yards are in a mile?”
Maybe if you’re trying to navigate around and you’re counting your footsteps (2 per yard).
@Dax are you really winning the race when you’re the only one running? Because the USA didn’t even get involved until after Sputnik was launched. We had absolutely no interest in it. We did not even have a space program until after Sputnik was launched. But you make it sound like the Soviets were so far ahead of us despite our best efforts.
Forget that it was the USA that developed liquid fueled rocketry first. That is why we call it the Goddard Space Flight Center. If you want to go around flaunting firsts two can definitely play at that game.
Counting my footsteps? Is that all you really have? You really do have nothing. Counting my footsteps! That’s rich. Go home. You’re too stupid to even find your mouth in order to get drunk.
-“are you really winning the race when you’re the only one running? Because the USA didn’t even get involved until after Sputnik was launched.”
One acronym: ICBM
After WW2 both the Soviets and the US were racing neck to neck in secret to develop intercontinental ballistic missile technology to deliver nuclear weapons, based on the research and technology they both obtained from the Germans, including the V2 rockets used to bomb London. The US took most of the scientists and forced them to work for the military btw.
When Sputnik was launched, the US got caught with their pants down because the Russians had just in fact demonstrated their ability to launch a nuclear attack on the US with no means of retaliation. That’s when the space race and one-upmanship “offically” started, but in reality it had been going on ever since Hiroshima and Nagasaki.
>”Forget that it was the USA that developed liquid fueled rocketry first.”
And then promptly forgot all about it and didn’t do anything with it.
>”That is why we call it the Goddard Space Flight Center. If you want to go around flaunting firsts two can definitely play at that game.”
Only retroactively. The space race on the US side was started with imported technology and scientists from Germany, which were more advanced than Goddard’s work.
>”Counting my footsteps?”
Yes. It’s very useful when finding your way around with a map in the woods, because you count your steps to keep track of how far you’ve gone so you don’t lose track. Even with a compass, it’s easy to get lost because you’ve sidestepped and walk past your target, and then can’t figure out where you’re supposed to be. There’s even a sport called orienteering where you run with a map to find flags in the woods.
That’s one of the nice things about the metric system. Maps are really easy to work with because you can translate real world measurements onto the scale by simply shifting the decimal point in your head.
Another one might be to figure out how many square feet of housing you can fit in a plot of half a square mile. Quick! What’s the conversion factor? In metric it’s trivial.
Metric units are based on physical constants while imperial is arbitrary. This leads to a fundamental problem with conversion between the two. It’s made even more complicated by rounding error.
With metric units, you simply move the decimal point to convert from big units to small units. No error whatsoever.
With imperial, it’s a total mess. Yet, those who grew up with imperial find it much more intuitive, myself included. This is a social problem, not a math/physics problem.
That is a load of crap. Metric was an arbitrary choosing of materials (that is now just so slightly wrong by the way). Likewise imperial was an arbitrary choice. There is no one true measure for anything. It is all relative against a standard. Which standard that is used is merely a stylistic choice from an intellectual perspective. Practicality is usually the one to dictate which one to use. Whatever the suppliers of your given industry uses will likely win out.
One thing I think we can all agree on is fractions are, even though technically infinitely accurate, stupid and should be banned from the face of the earth.
@medix you really don’t want to play the Mars mission failure game with the USA. Because statistically no one even comes close to the USA’s overall success rate. You only heard about that one failure because it is something that doesn’t happen as often with the USA as it does for everyone else. So when it happened it was indeed big news. When metric losers fail that is par for the course.
Before you were even born I was down at the Cape watching the Viking Waldo they had setup in a corner of the assembly building kid.
Are you kidding in regard to fractions?
Fractional representation is (a) more intuitive: it’s necessary to understand how fractions work before you can understand decimal notations. (b) more precise: plenty of values can’t even be represented with decimal notation without rounding to the nearest multiple of a power of ten, or require an infinite number of digits to achieve equal precision, and (c) more clearly representative of what’s actually going on: “1/8” is a much more direct way to express the concept of dividing something into eight parts than “0.125”.
I’ll grant that decimal notation makes certain arithmetic operations a bit more straightforward — specifically, addition and subtraction — but, conversely, multiplication and division are far less cumbersome with fractions.
You just pointed out that fractions and decimals are fundamentally similar mathematically, then tried to make the argument that fractional values are somehow more precise.
Although 1/8th is a more intuitive representation than 0.125, how would you represent 0.1 as a fraction with a denominator that’s a power of two?
THIS! Who cares about the individual units. It’s the conversion that matters.
In real life converting rarely matters. When it does it might be a good time to exercise one’s brain anyways.
@pcf11: it sure did matter when the Mars Climate Orbiter burned up in the Martian atmosphere because of a telemetry error.
http://en.wikipedia.org/wiki/Mars_Climate_Orbiter
Metric is indeed based on physical constants which have constantly been changing too.
When better measurements of the constants are discovered, the changes made are many orders of magnitude smaller than what happens to the imperial standards sitting in their vaults.
They are called constants for a reason. The only reason we ever have to adjust their understood values is because we do not have the tools of “god”. How do you suppose we actually _know_ whether a new measurement is better than the old one? Maybe you ought to do some independent research for your own sake.
Yes John just like the Standard Kilogram Sitting in it’s vault
http://en.wikipedia.org/wiki/Kilogram#International_prototype_kilogram
Maybe you should not fault other people’s research.
When the metric system was originally developed it was supposed to be the measuring system for the world so they took what they thought was the circumference of the world and used that number as their starting point. Too bad they were way off with their calculations because each pole is approximately 2 kilometers away from where they figured it was supposed to be. Meanwhile this planet itself is just a random bit of dust floating in space so why anyone would attach cosmic significance to its circumference in the first place escapes me.
It harkens back to a time when humans used to think the Earth was the center of the solar system, and everything revolved around it. Better known today as the Dark Ages.
But you go right on ahead and keep on taking the high philosophical road when it comes to defending the metric system. I find it rather amusing. The ancient Greeks got closer than the people who developed the metric system did when it comes to measuring the Earth and all they had was a well to look down! How’s that for the tools that God gave all of us?
“When the metric system was originally developed it was supposed to be the measuring system for the world so they took what they thought was the circumference of the world and used that number as their starting point.”
Actually, the first suggestion for the definition of a meter was to be a pendulum at 45 degrees of latitude with a half-period of 1 second (at standard gravity). That turns out to be very close to the modern meter.
It was supposed to tie together the units of time and gravity, but measuring such a pendulum exactly proved to be difficult and the apparatus too variable so they standardized on the surveying meter instead, since measuring things from the large scale down was less prone to random errors.
@Dax Less prone to errors you say? So what you’re really saying is that the metric system despite their best efforts is still flawed at its core and fraught with errors? I can go along with that.
Hey, if the metric system is so wonderful then how come we don’t have metric time too? How come we still use 60 seconds to the minute, 60 minutes to the hour, and 24 hours to the day? Why isn’t it base 10 like everything else? You brought it up. Time that is. You’re still using bad old Imperial time units!
New definition of Kilogram will be provided in 2018. Several potential methods are possible, like ‘The World’s Roundest Object’ measurement.
>” So what you’re really saying is that the metric system despite their best efforts is still flawed at its core and fraught with errors? I can go along with that.”
That was a contemporary problem of accurately measuring pendulums when you don’t have accurate clocks and you don’t know local gravity, and you don’t know how long a second really is. Measuring a long straight line on land was much easier and more accurate, so that was used instead.
>”then how come we don’t have metric time too?”
We do. It’s called the second and it’s counted in SI units. It’s different from the imperial second in that it’s not based on mean solar time, because that would make it change ever so slightly from year to year.
The hours and minutes etc. are what’s called “convenience units” which don’t actually belong to the metric system, but are allowed in conjunction with it.
>”You’re still using bad old Imperial time units!”
The US is actually metric because all the imperial units are now fixed and defined through the SI. All the imperial units are now convenience units to the metric system, and you simply choose not to use the proper ones.
@Dax Well there you have it then. The Imperial and metric scales are just two ways of looking at the same exact thing. My digital calipers are Imperial, or metric, but I only use them in metric when I am dealing with something that I suspect is metric itself, in order determine better what it is trying to be. Like say if I need to order a replacement part. Other than that when I am fabricating from scratch I use Imperial measurements. I use SAE hardware too because metric hardware sucks cock. I don’t really stock metric hardware like I stock SAE either. I have the full range from 2-56 up to 1-8 in SAE My metric collection is quite a bit more spotty than that. My metric hardware isn’t even really binned by size like I keep SAE, it it just in bins marked “metric”. I don’t even have a decent metric tap and die set for that matter. I just have some of the popular tools. I should get a decent metric tap and die set someday but I always find something else I’d rather have. Because I wouldn’t use metric for new construction anyways. I consider metric hardware to be vastly inferior to SAE. Like the measuring system the hardware just has a crappy dispersal in its range. Imperial is simply graduated more nicely for use.
0.00025 is just an “arbitrary” round number close to the real performance. The actual measured speed is probably more like 0.0002756 or something. It’s marketing blurb, meaning it’s not showing the ACTUAL speed but the “spec sheet speed”. Any engineer knows the first question to a supplier can be: “Ok, thats some impressive speeds. But what can I get if I turn it to 11?” And then expect to be sold a faster version for some “faster version” amount of extra dollars. (Which may or may not be the same thing with a different sticker)
0.00025″ is a nice round number, but no engineer would bat an eye if it showed 6 micrometer resolution. (Unless he was specifically looking for something with 6.35 micrometer performance.)
If your idea of engineering is carpentry in metal then the imperial system is fine. Once you start bringing accelleration into the game it all gets nasty (in my experience at least). I learned engineering back in the old days when the UK used a lot of foot pound second stuff. Force was measures in pounds in which case mass was measured in slugs unless you were measuring force in poundals in which case the unit of mass was the pound, or maybe you were using the engineering system where both force and mass were measured in pounds and you could never be sure of the accuracy of calculations.
Is it better in the USA, I hope so.
I let the computer plot my acceleration. I’ve never heard it bitch about the Imperial system either. It’s pretty good at math apparently.
Because fractions are a easy way to describe somethings? Threads for example?
A common one that can be compared machine to machine to derive useful information on performance.
I’ll admit I know nothing about any of this. Is this impressive because it is both fast and precise? Is that precision unusual? Is the speed?
Yes.
The most impressive thing we’re seeing here is that multi-start leadscrew that they’re running. That is some hot stuff right there. The screw and the nut probably cost a couple of grand. There isn’t a CNC motion control software package in use today that wouldn’t look good driving it either. The linear motion rails are meh. They should have went with THK. I mean if you’re going to blow your wad big time then you might as well go for the full bukaki effect. Spoogies all around!
The ass smoke is thick with this one.
Mcmaster has multistart acme rods and nuts for tens of dollars per. Or am I missing something?
What we’re seeing here is likely ballscrews.
Honestly, .00025″ is nothing to write home about. My cnc mill is currently set at about .0001 and the encoders will actually allow finer resolution but I use the built in pulse multiplier to make it more manageable and keep the speed up.
From their pages, it looks like step motors. It would be nice to get away from step motors.
In the comments of the Youtube video they say they’re Leadshire steppers.
I agree, stepper motors are nice and cheap and all, but they’re definitely not ideal for real machinery.
It seems like those Velox slides they’re using are some sort of mid-ground between a crappy 3d printer slide and a real, accurate industrial slide. The difference is really in the price… $420 for that Velox unit, and $2300 for a similarly specced Misumi ball screw slide unit. You could probably get away with a McMaster-Carr unit (6734K2) for $970, but that is really no better than the Velox unit.
Why are steppers undesirable? Because they’re open loop? I use steppers regularly in my work.
All motors are inherently open loop without encoders. Nothing technically stops anyone from closing control loops with stepper systems. Where stepper motors really fall down is in how they develop torque, or don’t as the case is, at higher speeds. Steppers have what can only be called a counterintuitive torque curve. They are at their strongest when they are holding still, and weakest at their top speed. Which is sometimes less than useful for motion control. Other kinds of motors develop their most power at the upper limit of their speed. This leads to a circumstance where we can have fast, and strong. As opposed to steppers where we have to choose between fast, or strong.
“a counterintuitive torque curve. They are at their strongest when they are holding still, and weakest at their top speed”
That’s pretty much how all electric motors behave.
Although some types of induction motors don’t develop much starting torque, or you may have to limit the current – but once you reach top speed you have essentially none. Otherwise it could go faster than that.
@Dax no that is not how all electric motors behave at all. Induction motors are rotor locked to the frequency that they run on, and the number of poles that they have. So if you want one to go faster then increase the frequency of the current. That is why at 60Hz you usually have either 1740 or 3460 RPM induction motors. If yo uwant to get technical, and something tells me that you do (I’m sure you’ll be furiously Googling to find some little piss assed thing to trip me up with because it is obvious now that you know jack shit about what you’re talking about), then they slip a little so 1740 is really 1725 and 3460 is 3450 but name plate specs do not always reflect this apparently folks that make motors care about as much about it as I do. Because those speeds are the result of two popular pole configurations. Duh!
Induction motors are so weak starting up in fact that they have to have special mechanisms just to get them going. But once they get going, then look out!
Now do you have any more brilliant insights you’d like to share with the world? You should start a YouTube channel and call it Ignorance is Dax or something. I’d subscribe just for the lulz which is the same thing that keeps me coming back to this site really.
You just proved yourself false.
The slip of the motor is why it develops torque, because it starts to lag behind the AC frequency and the difference in the angle of the mangetic fields between the rotor and the stator is what turns the whole thing.
Therefore, the more it slips – or the slower it turns – the more torque it makes, and the faster it turns the less torque it makes. When the slip grows too much, you get what’s called a breakdown where the torque of the motor starts to decrease sharply. Induction motors are operated between the breakdown point and full synchronous speed because in that region any increase in load will slow the motor down, which will automatically increase torque and prevent the motor from stalling.
Here’s a torque graph for a typical induction motor:
http://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/energy/images/energystar/figure-04.jpg
The reason they are weak to start is obvious from the graph.
@Dax How did I prove myself wrong? You just stated why the motors have torque. So you proved yourself wrong. Good job! it also hasn’t escaped me that you’ve completely backed off your first speed statement that you made in your previous comment. I don’t need a graph to see why the motors need an out of phase kick to start up either. I’ve been working with the things for long enough now. That is what is called first hand experience, in case you didn’t know. I’ve repaired more induction motors than I can even remember today. I can even make them reverse too. That is done by transposing the phase relationship between the start, and run windings on start up. Whichever way you kick one over is the way they run. Without that initial kick though all they do is the angry buzz. I’ve dealt with it countless times now. I’ll repair a broken internal lead but I won’t rewind them. That is where I draw the line. Too tedious for me. Kind of like you.
>”How did I prove myself wrong?”
By mentioning slip, which directly proves the point: induction motor torque increases as speed decreases and vice versa. That’s the general and desired property of all electric motors.
All electric motors have essentially zero torque at top speed and there’s nothing counterintuitive about that. Otherwise they’d go faster and that wouldn’t be the top speed, because if torque exists then acceleration exists, and without any applied load to counteract the torque the rotor must turn faster.
I also said that induction motors don’t make much starting torque, so I haven’t backed off from anything. You simply seem to be having comprehension problems. Below the breakdown point, the torque behaves more erratically because increase in load results in the motor losing speed and torque, which makes it impossible to start the motor and gain speed with the full load on, but it still has more torque at zero RPM than at max RPM, which is the general pattern of all electric motors which is supposed to be “counterintuitive”.
It’s not.
To be more specific:
>” Induction motors are rotor locked to the frequency that they run on, and the number of poles that they have.”
No, they’re not.
The actual speed depends on the amount of slip the motor experiences, which depends almost linearily on the amount of load you put on the shaft. Because of the inverse relationship between torque and speed, the motor is self-regulating like that above the breakdown point. Below the breakdown point, the motor becomes unstable and speed regulation becomes erratic until very low speeds where the torque curve becomes similiarily descending again.
Due to the slip, all induction motors are actually asynchronous: http://machinedesign.com/motorsdrives/difference-between-asynchronous-and-synchronous-motors
It sounds to me that you’re not very well informed on electric motors, despite claiming to have worked extensively with them. I guess that is the difference between a self-taught mechanic/tinkerer and someone who’s actually studied the theory.
I personally would have found this article to be more useful with the first link being their github page and NOT the youtube video which you just link to in the Read More section… I actually missed the github link several times as its really easy to miss a one liner RIGHT below the embedded video and the related hacks section…
That’s fast – I only managed 6″/sec slew to 0.001″ with a 10 lb wire guide head for a coil winder back in ’83. [2.5MHz Z80 powered]
Oh, I hope they don’t rely on software to stop the servos at the endstops – I had a software crash, and snapped an aluminum plate that was 1/2 thick and 2″ wide when my
software locked up. I put a pair of microswitches that when open, inserted diodes so that the servo could not drive past the limit switch, but could be backed off.
0.00025 inches is about x14 smaller than a human hair. Must be a lot of steps per revolution. Is 4000 steps/inch unusual?
If they are using 10 turns per inch rod and a 200 degree motor then they are only running in half step sequence mode. Half stepping a 200 degree motor one revolution takes 400 steps, then multiply it by 10 for the motion. You have to turn a 10 TPI rod 10 times to move an inch. They are more likely quarter stepping, so they have 5 TPI multi-start rod. Double the steps, and half the threads is the same total steps for the same move. That would be my guess if 4,000 steps is accurate, based on what it looks to be.
Seeing the coupling between the actual steppers and the leadscrews, I wonder if they are not using a backlash free armonic drive reduction stage, so they can use full step enhancing accuracy.
Let’s say they are using a 5 TPI leadscrew. That means they need to turn it at 800 (IPM) * 5 (TPI/RPI) = 4,000 RPM. That’s a tricky job for a stepper motor. I bet if you try it you’ll find all about inertia, momentum, resonance and lots of fun and difficult-to-overcome phenomena.
The difficult-to-overcome phenomena you allude to is called inductive reluctance. That is a stepper motor’s real Achilles heel. We overcome it to some extent by using high voltage PWM chopper drives these days, but they can only go as far as the input voltages they can handle. The higher voltage a drive can handle the faster it can run a stepper motor, and still manage to get torque out of it.
To run at 4,000 RPM I’d say run at least 80 volts input. Then it is no problem.
If you want to impress me then get the same performance using 1/2″ X 10TPI acme threaded rod. Because all we’re seeing here is how nice the leadscrew that they’re using is.
The best and only valid point here. Kudos pal!
All they’re demonstrating is a high helix leadscrew with good backlash parameters.
Heck an standard high torque nema 23 running 1/32 stepping (200 step) on the same leadscrew can do this.
They should have hired Shamwow Vince to do their demo.
It’s only proper since Billy Mays has since passed
So you’re experiencing leadscrew envy? Perhaps this whole thing was just so much compensation…
unless you use a dead slow cpu, speed and resolution is determined by the mechanical hardware not the software
I know what you mean but in order to achieve speeds, or relative accuracies it is a combination of both hardware, and software that achieves goals. Miss either one and you’re just not getting there. I’d like to see how their software performs running a drawer slide machine that uses hardware store all thread lead screws. 1/4-20 bitch yeah! Because it is the same diameter as the motor shaft dontchaknow? Gotta have gas line motor couplers too natch.
F-yeah! How you gonna build that CNC machine if you don’t have access to a CNC machine? 1/4-20 and gas line, ho’s!
Yes but what is the pitch and yaw like over its motion.
That’s 2,036 furlongs per fortnight.
how about using SI units, and these are meters and not babyboo or anything else.
we have si units and please use them also use maths better with those predecessor units like km for 1000 meters, …
it is nuts to write something with 0,00000000000234 where you have to count manually the zeros when there are things to defintely tell how many there are
e.g. 2.34 *10^-6 m makes more sense or even e.g. 35.23 nm ….
sadly you are unable to use proper maths units so its readable and understandable. or even express it with SI units. SAD FACE.
http://lmgtfy.com/?q=convert+800+inches+per+minute+to+m+per+second
@DAX, Whatever metric you use, I know the drive shaft I use is much larger than yours!
…I shall prove it thusly! (insert relative and biased reasoning here). I shall measure using an absolute superior standard!
Err wait… it don’t exist.
C’mon guys! Just use your calculator if you can’t float Imperial to metric conversions in your little head. a micron is pretty effin small. So is 39 millionths(.000039in).
But alas, into the wind you shall spit. (facepalm)
Inches per minute and 0.00025″ confuse people here??? I don’t understand at all. Surely some people here are machinists or operate even CNC machines.
I run a 5 axis HAAS mill all day. IPM, or inches per minute, is a basic measurement of material removal speed for any machinist. As is also IPR, or inches per revolution. 0.00025″ is just a measurement in inches, 2 and a half tenththousandths, measurable with a good micrometer. A machinist would say “2 and half tenths”. And yes, they know decimally speaking, it is not 0.25″, but 0.00025″, when they say that. Machinists call tenthousandths of an inch, or 0.0001″, “tenths”, and everyone who works in a shop generally knows this. Almost noone refers to 0.25″ this way, that is huge to us. That’s when fractional measurements are commonly used.
To people STILL using “human hairs” as a measurement- stop it. I find THAT ridiculous. No one actually references anything physically to how many hairs big it is. Noone. Ever. Anywhere. STOP IT. My beard hair varies between 0.004-0.005″. Hair is imprecise as a measurement for anything anyway, it compresses. Ditto for “Libraries of Congress” as a measurement. It’s just idiotic. How many people have ever even seen the physical size of that one anyway? It’s useless.
And for the record, I am not a papered machinist. But this is basic, basic stuff to me, and anyone who runs mills, lathes, and CNC equipment. Not meaning to insult anyone, but for a place where people who regularly make stuff congregate, these things not being known confuse me greatly. Don’t you guys use micrometers (mics) or calipers?
“No one actually references anything physically to how many hairs big it is. Noone. Ever. Anywhere. STOP IT.”
Actually, that is not true at all. There is a unit of human hair measurement commonly referenced in shops. It is usually referenced as a single unit, with the specific type of hair. I don’t mention the units here because it would be in poor taste.
Agreed, I know what measurement you are talking of too.
My comment too, btw, is not meant to offend or call others fools. I am genuinely surprised people don’t know!
Ever watch eevblog? How do you feel about measuring with half bees dicks?
This video https://www.youtube.com/watch?v=WTtiTyZhMhE would be impossible to make with imperial units.
I can’t believe I fell for that.
I read many comments above, and it is obvious to me that some guys just don’t get it. NO ONE exept USA uses imperial as a main measurement system anymore. They don’t study it in schools and they shouldn’t either. It is a horrible mess of random multipliers, 12 inches in foot, 3? feet in a yard, ? feet in a mile, ? ounces in a pound, etc, etc. It is stuff good only for carpenters and various trades, because it is easier to remember “4 feet” than “122 cm”. And no, it didn’t get you to the Moon. Germans like Von Braun got you to the Moon, and he used … metric for designing V2, from which all later rockets descended. Hungarian and other Jews devised an atom bomb, and not because they were adding feet and pounds in Hungarian schools. Likewise for modern computer concept: Von Neumann was an European student (Hungary again). As Von Karman, as … Grow up already and smell the roses. 21st century is upon us. Drop the imperial, because imperials (Britain) themselves have dropped it like a giant turd that it is. USA is having STEM issues, and this is precisely one of the problems leading to that. The more you wait, the ruder the awakening is going to be.
@Miroslav You’re the one that needs to smell the roses. A friend of mine’s grandfather was all of those Jew’s boss on the Manhattan Project. I found that out when he showed me a paperweight he’d gotten after the first successful test. He’s in Who’s Who and everything but I’m not going to name names here. Another kid I went to school with his family was close personal friends with Von Braun too. I found out when I saw a picture hanging on their wall with all of them standing with him. He was like oh yeah, we know him. Ken was a weird kid, so hanging around old Nazis explains that. Anyways Braun used Goddard’s research to get going. Goddard of course was a decent American.
My grandfather was a founding member of his carpenter’s union, and likely far brighter than you are. So you’d better not speak ill of your betters. Von Neumann? Please, he only dreamed about a machine. They actually built it at the University of Pennsylvania though. I don’t recall Neumann being there for it either.
BTW the USA officially adopted the metric system in 1964 because of our NATO alliances. Not that our allies are much use, but we try to accommodate those weaklings as best as we can. It doesn’t help, but we do what we can do regardless.
As far as any STEM issues we may have go we still manage to win more Nobel Prizes than the rest of the world combined. So as the old saying goes, we’re number one, bitch.
Out of 853 nobels, 349 were awarded to people in the US (source: http://en.wikipedia.org/wiki/List_of_Nobel_laureates_by_country#United_States_of_America). That’s just about 40%. Or, in imperial units, 40%.
Now do it for Germany pre-1939.
A high percentage of Americans consider themselves to be of German descent. I’m better than half German myself. Although to look at me someone might guess I’m all German, or Scandinavian, or Nordic, or something like that. I have the whole tall, blond hair, blue eyed thing going on with the pale skin too of course. Once when I was visiting some relatives in Florida her kids accused me of glowing in the dark at dusk. Kids say the damnedest things. They were truly amazed, pointing, staring, and gawking at me. I guess they never saw someone as pale as I am though? She inherited the more Mediterranean genes in our family tree than I did. We don’t even look related.
I think all I got from that side of the family is my taste buds. I do love Italian cooking!
Only 40% these days? I stand corrected! heh still not bad.
@PCF USA number one, in what? Violent crime? Drug-related offences? Incarceration rates? God-believers? Illiterate people in western hemisphere? Invasion of foreign countries? The fact that Europeans, with American help, reduced Europe to ashes twice in 20th century helped you more than you will ever know. And all those Jews, Germans, Russians etc. that helped american science and technology came there directly or indirectly because of the wars. Wars, from which ultimately, only one non-european nation profited. Guess which one? America is number one in exporting wars and importing people running away from those same wars. There, said it for you.
Perhaps we are beginning to drift off-topic now?
>”because it is easier to remember “4 feet” than “122 cm”.”
Not really.
If you’re doing carpentry, a foot is not nearly enough precision and it becomes extremely confusing because you’re juggling feet, inches, and fractions of an inch at the same time. You’ll probably want just inches and fractions, just like metric uses just centimeters and millimeters in a similiar case.
Actually, metric carpentry often uses just millimeters because saying “something point something centimeters” becomes cumbersome after a while. Saying “1121” for 1 meter 12.1 cm is much easier. It’s “one one twenty one” and remembering four number sequences is easy because they’re like chants.
No-one uses meters or centimeters, it’s always millimeters. No fractions, no unit conversions, whole numbers. Dead easy.
Like in the OCC clip posted by @Coffeegeek, 2:30 minutes trying to figure out the difference between 6-7/8″ & 7-1/4″ is. In metric that’s “what’s the difference between 174mm & 184mm?”
(Actually, amateurs use centimeters; it’s the easiest way to spot them.)
You’re quite mistaken. Imperial measures remain in common use throughout the English-speaking world: Canada and the UK are only marginally more metric than the US. In fact, metric road signage is actually completely illegal in the UK, whereas it’s permitted, though rarely used, in most US states (there’s an interstate highway in Arizona with all signage in metric, for example, which would be illegal in the UK). Most people in Canada and the UK continue to use imperial units in most aspects of day-to-day life.
There are a few reasons why this is the case: the countries that adopted the metric system earliest, from the late 18th century, tended to be those that *didn’t* have a body of common units in widespread use. At the turn of the 19th century, throughout France, Germany, Italy, etc. the same traditional terms were used for units that might vary drastically between cities: a ‘livre’ in Nimes and a ‘livre’ in Nantes might have had very different values, as might a ‘Fuß’ in Hanover vs. Trier. When strong incentives finally emerged to use standardized unis, adopting the novel metric system was a good way of implementing a common set of units without prejudicing anyone’s pre-existing standard over anyone else’s. But English units generally had uniform values from the medieval era onwards; in 1800, ‘foot’, ‘pound’, etc. meant the same thing in London, New York, and Sydney, so the incentive to adopt the metric system in order to *have* common units never existed in the first place.
Additionally, the UK and US were the first countries to industrialize; by the time metric usage began to spread beyond France, there was already quite a large industrial sector in the English-speaking world that was operating very effectively with imperial/customary units, so not only was the major incentive *to* adopt metric not present in these countries, there was also a major *disincentive* that wasn’t present elsewhere, in the form of significant costs associated with altering the installed base of industrial technology. This is still a very present factor, especially in the US.
Finally, there’s a significant cultural factor at work: English-speaking cultures generally tend to prefer standards to develop via organic, bottom-up emergence, rather than by top-down design. This is evident in a lot of contexts. For example, most European languages have a regulatory body that decides on official spellings and meanings of words; but not only does no such body exist for English, lexicographers of English-language dictionaries are today almost all hard-line descriptivists, carefully documenting established usage instead of trying to prescribe official definitions. Most countries tend to have civil-law systems which give supremacy to statutory law created by legislatures, but most English-speaking countries use a common law system, where the meaning of the law is authoritatively developed by the judicial process itself, via the accretion of precedents established by real-world cases. Measurement naturally fits into this pattern: the customary units used in the US, UK, Canada, and other countries have evolved through an emergent process, and have been refined against the constraints and necessities of real-world application, rather than, as with metric, designed in the abstract and optimized with respect to conceptual ideals.
5.51181102 x 10-7 inch semiconductor manufacturing process
On 12″ wafers.
So, are all the comments about the unit system being used? I’d like to see more discussion about the actual hardware.
@BG Quick, why do you need to know how many yards are in a mile?
Whoosh. Missed the crux by a mile. Ok. The example isn’t hard (didn’t take a long time). World war 2 naval gun range was rated in yards, distance between ships in miles (and not miles but nautical miles), but that again is missing the point. So why is it 5280 feet in a mile? 5280. Not 5000 or something else. Why not 5213.556? Its just as useful as 5280. When converting to the next unit 1) you need to remember how many units of what are in the other, 2) then you need to go through mathematical hell (no quick head conversions here). So you have 5280 and 3 and the result is 1760. But 16 ounces. Why 16? When squaring for area or cubing for volume, you are almost certain to wind up with decimals. And I can see the “imperial” temperature being 180 degrees between freezing and boiling (like degrees in a half circle), but the 32 degree offset? What the hell! And 12 inches, not 10, and 3 feet not 2 or 4 (no easy dividing by two here)! In the entire system the number of what that relates to the next smaller or larger unit is some oddball number that usually demands either a calculator or a pencil and paper. But its better…..nope. Maybe it was better in the 16th century. They made pyramids in cubits and they have lasted at least 4 millennia, but I wouldn’t brag about cubits either.
Gunnery? Really? They used tables, which they made using calculators, and pencil, and paper. Whole office rooms of girls would sit there and prepare those gunnery tables. They did it for every field piece used. Then eventually built computers which they called the firing table to figure that out. So you failed again to say why you’d need to do the conversion. See what happens when you pick a topic that I know more about than you do? You’d think you’d learn by now. I’m a huge WW2 buff. I have been ever since I was a kid. So don’t dream about going there. I got to see one of the Missouri’s naval rifles last year while they were moving it to a park by me. Wow, was I excited! Being an Iowa class battleship it was the first ship to have a firing computer. That made it the first CNC gadget in the world! It could fire a shell that weighed as much as a VW bug 23 miles. When one of those babies landed it left a crater in the ground you could hold a ball game in too. Now that is my idea of awesome.
The problems begin when you have to direct the fire of more than one gun onto the same target, from different ships or artillery positions, because your gunnery tables quickly become inadequate and your early computers overwhelmed by the number of calculations.
The metric folks solved that problem. Ever heard of the guy Vilho Nenonen? During WW2 he developed a method to direct artillery fire so that one spotter can aim an unlimited number of arbitrarily placed guns simultaneously by calling out distances relative to a known point from his own perspective, without any of the guns knowing the location of the spotter. All they knew was in which compass direction the spotter was looking at. If all the guns are first aimed at some known location on a map, let’s say a bend in a road, then the spotter can say “heading 245, 500 m out, 200 m left” and all the guns hit that target.
I don’t know the procedure how they calculated it at the other end, but I know it involved a board covered in millimeter grid paper and a cleverly designed ruler. No computers or tables of numbers necessary. It wouldn’t have worked if they also had to convert between miles and yards and feet.
In the Mars fubar the problem was degrees vs. radians confusion which is not directly metric.
Time and those confusing degrees are not imperial units unless you consider Sargon or some Babylonian ruler. Base 360 based on the year-day factor. Old stuff. We’re stuck on Earth with it.
Most kids in the US are partly stunted by the shadow of Roman numbering with the time notation having no zero as well as all rulers.
The slew rate of this device is in decimal units. Like volts, amps, etc. Time (Babylon) not withstanding.
https://www.youtube.com/watch?v=pikrntjcbyw
Good one :)
The metric version: “what’s the difference between 174mm & 184mm? Oh, never mind.”
Just read this and decided to click through my rss reader to get to the site to complain again about you damn Americans insisting on using absurd units of measure. Looks like you’re all right on top of it anyway. Furlongs per fortnight FTW!
Look at the lead screw. That’s where the speed is coming from.
Feeling sorry for those who can only multiply by moving a decimal. I use both systems every single day, as most engineers do. Not a big deal to keep two things in my head.
Metric vs Imperial…hogwash to all… we need a real warriors unit
Klingon..
0.01016 kellicam per min
Qapla’!
Ha! It went there.
I love this forum. I started reading the comments to learn about the motion control and I learned so much more….about something I never thought twice about.
I am a prototype mold maker and see designs daily that make no reference to a standard measurement. I think a lot of newer fresh from design school “engineers” haven’t got a clue how to measure or care. It is the design…does it have nice curves….they can’t measure a compound curve- it just looks good.
I do a lot of work on old Honda motorcycles (metric) and am never suprised to find a 1/4-20 screw jammed into an M6 threaded boss.