Ask Hackaday: Auto Bed Leveling And High Temperature Force Sensitive Resistors

FSR

[Johann] over on the RepRap wiki has an ingenious solution for making sure a borosilicate glass bed is completely level before printing anything on his Kossel printer: take three force sensitive resistors, put them under the build platform, and wire them in parallel, and connect them to a thermistor input on an electronics board. The calibration is simply a bit of code in the Marlin firmware that touches the nozzle to the bed until the thermistor input maxes out. When it does, the firmware knows the print head has zeroed out and can calculate the precise position and tilt of the bed.

Great, huh? A solution to bed leveling that doesn’t require a Z-probe, uses minimal (and cheap) hardware, and can be retrofitted into just about any existing printer. There’s a problem, though: these force sensitive resistors are only good to 70° C, making the whole setup unusable for anything with a heated bed. Your challenge: figure out a way to use this trick with a heated bed.

The force sensitive resistors used – here’s a link provided by [Johann] – have a maximum operating temperature of 70° C, while the bed temperature when printing with ABS is around 130° C. The FSRs are sensitive to temperature, as well, making this a very interesting problem.

Anyone with any ideas is welcome to comment here, on the RepRap forums, the IRC, or anywhere else. One idea includes putting an FSR in the x carriage, but we’re thinking some sort of specialized heat sink underneath the bed and on top of the FSRs would be a better solution.

Video of the auto bed leveling trick in action below.

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MRRF: ARM-Based CNC Controllers

smoothie

8-bit microcontrollers are the standard for RepRap electronics, but eventually something better must come along. There has been a great deal of progress with ARM-based solutions, and of course a few of these made a showing at the Midwest RepRap Festival.

First up is [Mark Cooper], creator of Smoothieboard, the ultimate RepRap and CNC controller. It’s an ARM Cortex-M3 microcontroller with Ethernet, SD card, and up to five stepper drivers. It had a Kickstarter late last year and has just finished shipping all the rewards to the backers. In our video interview, [Mark] goes over the functions of Smoothieboard and tells us about some upcoming projects: the upcoming Smoothiepanel will feature a graphic LCD, SD card, rotary encoder and buttons, all controlled over USB by the Smoothieboard.

Next up is [Charles] with a whole bunch of CNC capes for the Beaglebone. By far the most impressive board was a huge I/O expander, motor driver, and everything controller for a Beaglebone featuring – get this – three parallel port interfaces. This was a one-off board costing thousands of dollars, but [Charles] did show off a few smaller and more practical boards for Beaglebone CNC control. Here’s a link to [Charles]’ capes.

Videos below.

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MRRF: 3D Printed Resin Molds

mould

Visiting the Midwest RepRap Festival, you will, of course, find a ton of 3D printed baubles and trinkets. A slightly more interesting find at this year’s MRRF was a lot of resin cast parts from [Mark VanDiepenbos]. He’s the guy behind the RotoMAAK, a spinny, ‘this was in the movie Contact‘-like device designed for spin casting with resins. At the festival, he’s showing off his latest project, 3D printed resin molds.

With the right mold, anyone with 2-part resins can replicate dozens of identical parts in an hour. The only problem is you need a mold to cast the parts. You could print a plastic part and make a silicone mold to cast your part. The much more clever solution would be to print the mold directly and fill it with resin.

[Mark] printed the two-part rabbit mold seen above out of ABS, filled it with urethane resin, and chucked it into his RotoMAAK spin casting machine. Six minutes later the part popped right out, and the mold was ready to make another rabbit.

Video below.

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Next Weekend: The Midwest Reprap Festival

midwest

Guess what next weekend is? It’s the Midwest Reprap Festival, in Goshen, Indiana. We’ll also be there keeping tabs on an absurd amount of new RepRaps and other 3D printers, new filaments, and distributing a ludicrous amount of Hackaday swag.

The highlights of the fest include the folks from Lulzbot and UltiMachine, [Prusa] showing off his i3, [Nick Seward] and the WallySimpson, and Lisa RepRaps, and hundreds of other RepRappers showing off their latest projects and printers.

Here’s the best part: it’s all free! It would be cool if you register before making the trip out, but any way you look at it, it’ll be an awesome weekend. It’s also the largest US gathering of 3D printer aficionados that isn’t on the east or west coast.

Solving Endstop Woes with a Simple Analog Filter

NoiseEndstop

You know what’s cool? Using your engineering knowledge to solve problems that you have while building something. This is exactly what [Reinis] did when his 3D printer’s endstop wasn’t working.

Many of us automatically go to a microcontroller when we run into a problem with a sensor, but often a simple analog filter will do the trick. The endstop in [Reinis’s] RepRap style 3D printer was giving off an unusual amount of noise when closed. When he hooked the endstop up to his oscilloscope, he was shocked to see how much noise there really was. In comes the low-pass filter. Unhappy with the response time of his low-pass filter, [Reinis] solved the problem using a pullup resistor. Two resistors and a capacitor was all that he needed to fix the problem. A great solution!

How have you used analog filters in your projects? Send us a tip and let us know!

The Stepper Driver Driver

KONICA MINOLTA DIGITAL CAMERA

The Stepstick and Pololu motor drivers are the heart of just about every Reprap electronics board, but they can go bad. The usual way of testing these things is to rig up a microcontroller on a breadboard, grab some cables, and wire something up. [Ken]’s Easy Stepper Motor Controller is a much simpler solution to the problem of testing these drivers and could, with a bit of practice, be constructed on a single-sided homebrew PCB.

The Easy Stepper Motor Controller is a very simple board with connections to a motor, a power supply, and headers for a single Pololu or Stepstick motor driver. Two buttons and a pot control the rotation of the motor with the help of an ATtiny10, and jumpers for up to 16x microstepping are right there on the board.

There’s a video after the break showing what this stepper motor driver driver can do. It’s not much, but if you’re just testing a driver, it’s all you need.
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We’re Going To The Midwest RepRap Fest

One month from now, Goshen, Indiana – deep in the land of Dairy Queens – will become one of the premier sites for RepRapping, 3D printing and everything involving open source manufacturing. It’s the 2nd annual Midwest RepRap Festival to be held March 14-16. Oh, Hackaday will also be there, cavorting around, distributing some swag, and doing some live videos and posts of the event.

Highlights of the Festival include [Prusa] giving a talk on the state of open source printing, [Sonny Monicou] discussing the challenges of his RepRap workshops, a roundtable discussion of the RepRap project, [Nicholas Seward] and his creations – the Wally, Simpson, and Lisa, along with a few folks from Lulzbot and UltiMachine. Basically, the only way to go to a bigger RepRap convention would be to visit a Maker Faire, and even that would only add a few hundred 9-year-olds astounded by printed Minecraft figurines.

If you’re willing to make the drive, there’s no fee to attend; just register, show up, and you’ll get a table for all that up-til-midnight RepRapping. There’s also a waffle breakfast on Sunday, along with me walking around makin’ it rain Hackaday stickers.