Simulating a Compliant Dampened Spring with Current Control

I've built another test robot leg in the name of robotic development! I decided to experiment with using current control to make a joint that behaves like a spring, using a brushless motor with 2-stage belt reduction so it's back-drivable, and an ODrive motor controller using current limiting. However a robot with springs in it's legs will behave quite unpredictably, so we need to dampen the spring and make it complaint for it to be any use. I experimented with this by using a PID controller to drive the motor to its new position after the 'virtual spring' has stretched. The next stage will probably be to make another three legs and attach them to a frame to see of the robot is dynamically stable and compliant - with each leg returning to its home position. We can then see what needs to happen to openDog next in terms of its reaction when to tipping when the feet hit the ground. ① HARDWARE/SOFTWARE What more important hardware is there in life than the clothes on your back and the cup in your hand. You can get your own Robot X tee or openDog mug at the link below: Teespring: https://teespring.com/stores/james-bruton Below you can also find a lot of the typical tools, equipment and supplies used in my projects. Some of these links are affiliate links, meaning, at no additional cost to you, I might earn a little extra if you click and make a purchase. Lulzbot 3D Printers: http://bit.ly/2Sj6nil Lincoln Electric Welder: https://bit.ly/2Rqhqos CNC Router: https://bit.ly/2QdsNjt Ryobi Tools: http://bit.ly/2RhArcD Axminster Micro Lathe: http://bit.ly/2Sj6eeN 3D Printer Filament: http://bit.ly/2PdcdUu Soldering Iron: http://bit.ly/2DrNWDR Vectric CNC Software: http://bit.ly/2zxpZqv And don't forget the code for some of my projects is available on my GitHub here: https://github.com/xrobots ② GENIUS No MacArthur grant yet. But while I’m still waiting by the phone for that call, maybe you might patronise me with your Patreon-age or pick up some of my merchandise. Or, if you’re all out of digital cash just comment on one of my hilarious Instagram pics, pop me a Tweet or generally yell in my direction. Patreon: https://www.patreon.com/xrobots Teespring: https://teespring.com/stores/james-bruton Instagram: https://www.instagram.com/xrobotsuk Facebook: https://www.facebook.com/xrobotsuk/ Twitter: https://twitter.com/xrobotsuk Huge thanks to my patrons, without whom my standard of living would drastically decline. Like, inside out-Farm Foods bag decline. Plus a very special shoutout to Aleph Objects, Inc who keep me in LulzBot 3D printers and support me via Patreon. Why not join my community, who are mostly made up of actual geniuses. There’s a Facebook group and everything: https://www.facebook.com/pg/xrobots.co.uk/community ③ XROBOTS Former toy designer, current YouTube maker and general robotics, electrical and mechanical engineer, I’m a fan of doing it yourself and innovation by trial and error. My channel is where I share some of my useful and not-so-useful inventions, designs and maker advice. Iron Man is my go-to cosplay, and 3D printing can solve most issues - broken bolts, missing parts, world hunger, you name it. XRobots is the community around my content where you can get in touch, share tips and advice, and more build FAQs, schematics and designs are also available. ④ MUSIC AND SFX The majority of the music and SFX used in my videos is from Epidemic Sound http://share.epidemicsound.com/xrobots