Motor module prototype is ready!

A project log for BLDC Walker

Brushless driven four leg quadruped

Peter WasilewskiPeter Wasilewski 08/14/2020 at 09:024 Comments


I finally managed to mill all the parts of the motor module I showed you in the earlier log. The material used is PA6 2017 T4511 aluminum bought at my local materials shop. Its great for milling, no clogged endmills etc, and at the same time it has great mechanical properties. I purchased it in 70mm cylinder slices, which were cut on a band-saw. Afterwards I faced each slice and mounted it to the table using screws. Machining of the module took me about 5-6 days, considering I machined one part a day. The amount of time the endmill was cutting the material was actually really short - the most time was spent on preparing the gcodes and making adjustments or fixing the material to the table. Only one part required probing, but it turned out really well. If you want to read more detailed description: 

Right now I'm improving the motor controller's code and making FDCAN communication to work (the bootloader is now functional)


dekutree64 wrote 08/16/2020 at 09:04 point


Have you given up on cycloids, or doing some joints with cycloid and some with gears, or just trying both to see which is better?

For milling lubricant, try Anchorlube. It has a consistency sort of like whipped cream, so it doesn't make too much of a mess. I use a syringe with a piece of plastic hose on the end to apply it as the machine runs. You do end up with your cutter spinning in a pool of aluminum soup, but it doesn't seem to be a problem. Much smoother and quieter cutting than running dry.

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Peter Wasilewski wrote 08/16/2020 at 09:21 point


Actually I'm trying both, but I kind of know the outcome already. Cycloids have to be manufactured perfectly, with tight tolerances to work well. Also without bearings (at least plain bearings) on each outside pin the gearbox has a lot of friction when loaded. I guess these drawbacks could be mitigated with some careful machining and thought-through construction, but this time I wanted to use planetary gears from cordless drills I've bought as they fit perfectly in my application ;) 

Thanks for the recommendation regarding the lubricant! 

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dekutree64 wrote 08/16/2020 at 10:32 point

Yeah, given the success of Ben Katz's design, gears are probably best. Easier backdriving, too. Just not quite as flashy :)

I, on the other hand, am working on flapping wings which need gear ratio in the 30-50 range, so cycloid is the obvious choice. I'm going to try one with a simple 2mm pin ring, and one with roller pins (2mm tubes over 1.5mm bearing pins). I'll get a project page up once I have something half way functional. Though at the rate I've been progressing, it could be a while. Currently waiting on a new ballscrew for my CNC, because my Y axis is a dud. It felt a bit rough to begin with, and has about .02mm backlash... which doesn't sound like much, but is still enough to give me headaches. But at $25 a pop, I can't complain.

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Peter Wasilewski wrote 08/16/2020 at 13:58 point

Can't wait to see the project!  I'm curious about the comparison between tubes and pins alone :)

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