Acorn was one of the great IT giants that rose high and then fell to obscurity during the rise of personal computing. However, for many hobbyists these computers are as important and as loved as the Commodore 64. [Simon Inns] has made a great adapter to interface modern USB mice to these old boxes.
After thirty years of interaction with people, one might be hard pressed to find a working mouse for an older computer. On top of that, even if you did, these mice are likely a lackluster experience to begin with. They were made long before industrial designers were invited to play with computers and are often frustrating and weird. Cotton swabs and alcohol are involved, to say the least.
[Simon]’s box converts a regular USB HID compliant mouse to a quadrature signal that these 8-bit computers like. The computer then counts the fake pulses and happily moves the cursor around. No stranger to useful conversion boxes, he used an Atmel micro (AT90USB1287) with a good set of USB peripherals. It’s all nicely packed into a project box. There’s a switch on the front to select between emulation modes.
If you’d like one for yourself the code and schematics are available on his site. As you can see in the video below, the device works well!
You don’t need any fancy tools. A CNC machine is nice. A 3D printer can help. Laser cutters are just great. However, when it comes to actually making something, none of this is exactly necessary. With a basic set of hand tools and a few simple power tools, most of which can be picked up for a pittance, many things of surprising complexity, precision, and quality can be made.
Not as pretty, but worked just the same.
A while back I was working on a ring light for my 3D printer. I already had a collection of LEDs, as all hackers are weak for a five-dollar assortment box. So I got on my CAD software of choice and modeled out a ring that I was going to laser cut out of plywood. It would have holes for each of the LEDs. To get a file ready for laser cutting ook around ten minutes. I started to get ready to leave the house and do the ten minute drive to the hackerspace, the ten minutes firing up and using the laser cutter (assuming it wasn’t occupied) and the drive back. It suddenly occurred to me that I was being very silly. I pulled out a sheet of plywood. Drew three circles on it with a compass and subdivided the circle. Under ten minutes of work with basic layout tools, a power drill, and a coping saw and I had the part. This was versus the 40 minutes it would have taken me to fire up the laser cutter.
Today’s engineers are just as good as the ones that came before, but that should not be the case and there is massive room for improvement. Improvement that can be realized by looking for the best of the world to come and the one we left behind.
Hey kids! Let’s learn why the CE certifications exist!
Survivorship bias is real. When we look at the accomplishments of the engineers that came before us we are forced to only look at the best examples. It first really occurred to me that this was real when I saw what I still consider to be the most atrocious piece of consumer oriented engineering the world has yet seen: the Campbell’s soup warmer.
This soup warmer is a poor combination of aluminum and Bakelite forged into the lowest tier of value engineering during its age. Yet it comes from the same time that put us on the moon: we still remember and celebrate Apollo. It’s possible that the soup warmer is forgotten because those who owned it perished from home fires, electrocution, or a diet of Campbell’s soup, but it’s likely that it just wasn’t worth remembering. It was bad engineering.
In fact, there’s mountains of objects. Coffee pots whose handles fell off. Switches that burned or shocked us. Cars that were ugly and barely worked. Literal mountains of pure refuse that never should have seen the light of day. Now we are here.
The world of engineering has changed. My girlfriend and I once snuck into an old factory in Louisville, Kentucky. The place was a foundry and the only building that survived the fire that ended the business. It happened to be where they stored their professional correspondence and sand casting patterns. It was moldy, dangerous, and a little frightening but I saw something amazing when we cracked open one of the file cabinets. It was folders and folders of all the communication that went into a single product. It was an old enough factory that some of it was before the widespread adoption of telephony and all documents had to be mailed from place to place.
[Larry] has done this sort of thing before with Amazon’s EC2, but recently Microsoft has been offering a beta access to some of NVIDIA’s Tesla M60 graphics cards. As long as you have a fairly beefy connection that can support 30 Mbps of streaming data, you can play just about any imaginable game at 60fps on the ultimate settings.
It takes a bit of configuration magic and quite a few different utilities to get it all going, but in the end [Larry] is able to play Overwatch on max settings at a nice 60fps for $1.56 an hour. Considering that just buying the graphics card alone will set you back 2500 hours of play time, for the casual gamer, this is a great deal.
It’s interesting to see computers start to become a rentable resource. People have been attempting streaming computers for a while now, but this one is seriously impressive. With such a powerful graphics card you could use this for anything intensive, need a super high-powered video editing station for a day or two? A CAD station to make anyone jealous? Just pay a few dollars of cloud time and get to it!
We’ve all taken apart a small toy and pulled out one of those little can motors. “With this! I can do anything!” we proclaim as we hold it aloft. Ten minutes later, after we’ve made it spin a few times, it goes into the drawer never to be seen again.
It’s all their fault
It always seems like they are in everything but getting them to function usefully in a project is a fool’s errand. What the heck are they for? Where do people learn the black magic needed to make them function? It’s easy enough to pull out the specification sheet for them. Most of them are made by or are made to imitate motors from the Mabuchi Motor Corporation of Japan. That company alone is responsible for over 1.5 billion tiny motors a year.
More than Just the Specs
In the specs, you’ll find things like running speed, voltage, stall current, and stall torque. But they offer anything but a convincing application guide, or a basic set of assumptions an engineer should make before using one. This is by no means a complete list, and a skip over the electrics nearly completely as that aspect of DC motors in unreasonably well documented.
The paint mixers high running speed and infrequent use make it a decent candidate for hooking directly to the motor.
The first thing to note is that they really aren’t meant to drive anything directly. They are meant to be isolated from the actual driving by a gear train. This is for a lot of reasons. The first is that they typically spin very fast, 6,000 – 15,000 rpm is not atypical for even the tiniest motor. So even though the datasheet may throw out something impressive like it being a 3 watt motor, it’s not exactly true. Rather, it’s 3 N*m/s per 15,000 rotations per minute motor. Or a mere 1.2 milliwatt per rotation, which is an odd sort of unit that I’m just using for demonstration, but it gives you the feeling that there’s not a ton of “oomph” available. However, if you start to combine lots of rotations together using a gear train, you can start to get some real power out of it, even with the friction losses.
The only consumer items I can think of that regularly break this rule are very cheap children’s toys, which aren’t designed to last long anyway, and those powered erasers and coffee stirrers. Both of these are taking for granted that their torque needs are low and their speed needs are high, or that the motor burning out is no real loss for the world (at least in the short term).
This is because the motors derate nearly instantly. Most of these motors are hundreds of loops of very thin enameled wire wrapped around some silicon steel plates spot welded or otherwise coerced together. This means that even a small heat event of a few milliseconds could be enough to burn through the 10 micrometer thick coating insulating the coils from each other. Practically speaking, if you stall a little motor a few times in a row you might as well throw it away, because there’s no guessing what its actual performance rating is anymore. Likewise, consistently difficult start-ups, over voltage, over current, and other abuse can quickly ruin the motor. Because the energy it produces is meant to spread over lots of rotations, the motor is simply not designed (nor could it be reasonably built) to produce it all in one dramatic push.
Making Contact
Pololu has the clearest picture of the different kind of brushes inside these small motors.
This brings me to another small note about these tiny motors. Most of them don’t have the carbon brushes one begins to expect from the more powerful motors. Mostly they have a strip of copper that’s been stamped to have a few fingers pressing against the commutator. There’s lots of pros to these metal contacts and it’s not all cost cutting, but unless you have managed to read “Electrical Contacts” by Ragnar Holm and actually understood it, they’re hard to explain. There’s all sorts of magic. For example, just forming the right kind of oxide film on the surface of the commutator is a battle all on its own.
It’s a weird trade off. You can make the motor cheaper with the metal contacts, for one. Metal contacts also have much lower friction than carbon or graphite brushes. They’re quieter, and they also transfer less current, which may seem like a bad thing, but if you have a stalled motor with hairlike strands transferring the pixies around the last thing you’d want to do is transfer as much current as possible through them. However, a paper thin sheet of copper is not going to last very long either.
So it comes down to this, at least as I understand it: if bursts of very fast, low energy, high efficiency motion is all that’s required of the motor over its operational life then the metal strip brushes are perfect. If you need to run the motor for a long stretches at a time and noise isn’t an issue then the carbon brush version will work, just don’t stall it. It will cost a little bit more.
Take Care of Your Tiny Motors
Here is one of these motors being restrained properly. Only torque on the case is restrained. The motor is otherwise free to move.
To touch one other small mechanical consideration. They are not designed to take any axial load at all, or really even any radial load either. Most of them have a plastic or aluminum bronze bushing, press-fit into a simple stamped steel body. So if you design a gearbox for one of these be sure to put as little force as possible on the bearing surfaces. If you’ve ever taken apart a small toy you’ve likely noticed that the motor can slide back and forth a bit in its mounting. This is why.
Lastly, because most of these motors are just not intended to run anywhere near their written maximum specifications it is best to assume that their specifications are a well intentioned but complete lie. Most designs work with the bottom 25% of the max number written on the spreadsheet. Running the motor anywhere near the top is usually guaranteed to brick it over time.
These are useful and ubiquitous motors, but unlike their more powerful cousins they have their own set of challenges to work with. However, considering you can buy them by the pound for cheaper than candy, there’s a good reason to get familiar with them.
Built in 1969, the P6042 is pretty sparse transistor-wise when compared a modern sensor. The user would clip the current probe, permanently attached to the case since the circuit was tuned for each one, over a wire and view the change in volts on an oscilloscope. When the voltage division on the oscilloscope was set properly the current in a circuit could be easily seen.
The teardown is of a working unit so it’s not completely disassembled, but it also sits as a nice guide on refurbishing your own P6043, if you manage to snag one from somewhere. Aside from capacitors and oxidized switch contacts there’s not much that can go wrong with this one.
As for how it compares, the linear power supply, analog circuit design, and general excellent engineering has the P6042 coming in with a cleaner signal than some newer models. Not bad for a relic! Do any of you have a favorite old bit of measurement kit?
The build is pretty cool. She had to give up her passenger seat, but it’s a small price to pay for independence. He removed the door paneling on the passenger side. Then he welded on a few mounting points. Next he had to build the device.
The well-built device has a deceptively simple appearance. The frame is made from CNC milled panels and the ever popular aluminum extrusion. It uses a 12V right angle drive and some belting to lift the chair. There’s no abundance of fancy electronics here. A toggle switch changes the direction of the motor. There are some safety endstops and an e-stop.
Now all she has to do is strap the walker to the door. She picks the direction she wants the lift to go and presses a button. After which she walks the short distance to the driver’s seat, and cruises away.
