May 21, 2016

Documenting all the things

I've been saying I'll post my design files and such online for a while now, so here it is.  Use anything at your own risk.

I've been using mbed to store and compile my code.  Here's the version of the code that's running the jumping leg.  I'm not a software person, so please don't judge me too hard on my code.  I went into this project thinking it would be a good idea to make all the code modular, but I think I went a little too far with that.  At some point I'll condense it all down into something a bit more manageable, and just keep things like position sensor code modular.  The current loops should have enough stability margin to work for a fairly wide range of small motors without any tweaking of constants.

Here are the python scripts that send serial commands to the motor controllers.

Here are the eagle files, gerbers, and BOM for the motor controllers and sensor boards.  When I sent the boards to 3PCB, the text the motor controllers got all scrambled so keep that in mind.  At this point I've built up three of each board, and they all work.  I haven't even blown up a single FET yet, in all of my motor control derping so far.

Here are my CAD files for the motor, gearbox, motor module, and leg.  Requires Solidworks 2015-2016 to open.  Many of the gearbox files have HSMWorks CAM in them, so you'll need the full version of HSMWorks to view the CAM.  There's also a list of the gears I got from KHK and the post-machining I did on them.

What's Next
I'm taking a break from this for the summer, but don't worry, it's not getting abandoned.

Things I might do eventually:

Scramble the physical layout of everything to make it more robust.  No more sensors dangling off 3D-printed mounts, and I don't want to have to modify the motors in any way for the gearbox.  Probably move to a single-board design with both motor controller and position sensor on it.  Maybe get quotes for how much it would cost to get a bunch of the gearboxes made in China?  We'll see.

More motor stuff!  I'm in the process of building a motor dynamometer, so I'll be able to quantify dynamic motor performance.  This is something the MITERS circle of motor enthusiasts hasn't ever done.  Woo, science!

Thoughts on selling motor modules:  I've been asked a surprising number of times if I plan on selling these motor/gearbox/controller modules.  I definitely do not plan on it any time in the near future.  Maybe I'll give it more thought later, but right now I'm not interested.  Also, there's a lot more engineering that needs to be done to make this product-grade.

Oh, hey, I wrote a thing.  It's basically this blog half-assedly copy-pasta'd into Latex, and re-written in a slightly more formal tone.  There's fairly little that's not also somewhere in this series of blog posts, but hey, it exists.

Until next time,

May 5, 2016

Slow-Motion Jump

One more jumping leg post.  Bayley broke out his Photron high-speed camera last night, and we took some 500 fps video of the leg jumping.  Sorry it's so red, from a combination of incandescent bulbs and no IR filter on the lens:

Expect design files, code, etc.  to appear here in a couple weeks, when I'm done with classes.  Also, this is the 100th post on this section of my blog!  Only took ~4 years.

May 4, 2016

More Jumping

Last night I reworked all the communication to happen directly over serial, and hooked the leg up to a more capable power supply.  Performance was greatly improved.  Now the leg can max out the travel of the linear guide it's fixed to:

And the obligatory animated GIF:

That jump was actually still with a current limit set on the power supply.  Turning up the supply to max current, the leg can easily crash into the hard-stop at the top of the linear rail.  It actually managed to move the hard stop by a couple millimeters - I dialed back after that, because if the bearing manages to escape the rail, all the little recirculating balls will fall out.

I almost set it up for wireless control over XBee, but decided to take a nap instead.  Wireless communication with a small LiPo battery fixed to the leg, and no cables dangling off would be beautiful.