Improved actuators for SMMB

One of the major challenges SMMB had in Robogames 2016 was in overall walking speed.  It is using HerkuleX DRS-201 servos, which are roughly comparable to the Dynamixel servos that other entrants were using, but the physical geometry of the robot is such that is hard to get it to move quickly with that class of servos.  The center of gravity is too high, especially with the gimbal mounted turret. The R-Team bots all use very low slung machines that scoot along.  I could go that route, but why do things the easy way?

Instead, I’ve been working to take some ideas from fellow Boston-ite Ben Katz and build some actuators that would permit truly dynamic motion.  He got a leg jumping using Hobbyking brushless motors with some simple FOC control  The biggest differentiators vs the Dynamixel / HerkuleX class of actuators would be low mechanical inertia, high transient power, low backlash, and high speed.  I’m just getting started here, but have managed to build up a 5x planetary gearbox driven by a Turnigy Elite 3508 (so a fair amount smaller than what Ben did, but more appropriately sized for Mech Warfare), and a VESC 6 as an interim motor controller.  It is designed for electric skateboards, but has minimal position control support.  Although, as my bruised hand can attest, it isn’t super stable and flips out occasionally.

The first prototype is assembled and has been spun up, although a fair amount of dremel time and shims were required to get everything to fit together.

Some SDP-SI gears for the prototype
The 3508 with its stock shaft extracted
New shaft installed, with spur gear alongside
AS5047 wired up to the VESC
Shapeways arrived!
Housing mounted onto motor
Planet carrier assembled
Planet carrier inside housing
Final assembled gearbox

And finally, the pretty videos: