Alert! I’m at Maker Faire Bay Area all weekend in the Mech Warfare area in Zone 2 (May 17-19, 2019 for you time travelers from the future). Drop by and say hi!
If you were left in suspense last time, yes, the robot can walk! Getting it to do so in a minimal way was relatively painless. What I found, which hadn’t happened in earlier iterations, is that many types of dynamic motions would cause the lower leg belts to jump a tooth. Needless to say, this was nearly universally fatal, as there is no direct position sensing of the lower leg. This robot is heavy enough that my simulacrum 3d-printed timing belt pulleys just don’t cut it.
Well, there wasn’t enough time to actually get better pulleys now, so I just tuned the walking to be slow and gentle enough that nothing went awry. Here’s the first bit of a 13 minute video I took of it walking around and shooting targets.
Now, that that was over with, I had a few minor things to finish up before heading out to Maker Faire. I made some covers for the motors to keep BBs out.
And I made a bracket so that I could attach the front and rear target panels to shoulder joints:
And here’s a glamour shot of the whole thing in fighting form!
Now that it was all ready, time to take it all back apart and pack it for shipping.
And off to the airport I went!
3 thoughts on “Walking and Maker Faire!”
Congrats, I bet that was a hectic sprint. With the new geared shoulder and knee actuators, do you need the stilts anymore? What control models are you using/plan to use for gait locomotion?
I kept the stilts for now both so that I could keep using my canned stand up procedure, and also because I was having problems with the shoulder joint properly holding the timing belt pulley in place, such that under large loads it would skip. I’m reworking the shoulder joint and eventually will make a better stand-up procedure. Once I fix up both things, then the stilts will no longer be necessary.
At the moment, I am still using the same old open loop position gait that SMMB used previously, although with some “hacks” to allow it to command a feedforward torque and tweak servo gains at various points in the cycle. It’s on github at: https://github.com/mjbots/mjmech/blob/master/mech/ripple.h
I’ve been meaning to ask what you’re using for a controller? If you like, I can give you a few of mine at cost to experiment with? If you don’t care about form factor, then an ODrive should be fine and usable too.
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