The controllers for the improved actuators for SMMB have a moderate amount of power to deal with.  During jump maneuvers they can put 60 amps of phase current into the motor, and I’ve applied for very short intervals over 500W of power to a motor.  The FETs on the board are relatively high performance, but there is still a fair amount of heat that has to be dissipated.

When getting started, I knew I would likely have to do something to get heat out of the board and had a two stage plan.  The first was to heatsink the back of the controller board and second, if that wasn’t enough, heat sink the front of the board.

Now that I have a mammal geometry leg moving, I wanted to get a better feel for what the overall performance would be in various gaits.  I had already derived position based inverse kinematics for Super Mega Microbot, but had no such derivation for force.  Here’s my jupyter notebook with derivations for both position and force (in 2D), along with average power consumption for various forms of straight walking gait with my current draft motor selections.

I got the mammal geometry leg up on the jump stand, then took it down, switched the femur motor to a BE8108, then took it down, and added a 3rd degree of freedom.  There is still a lot of work to do to get it performing well, and it is pretty clear it won’t have the same vertical jump of the 4 bar linkage, but I think it still might be an overall superior option.

Before committing to the side-by-side 4-bar linkage leg for SMMB’s new actuators, I wanted to give a try with a more traditional mammal geometry.  That was my preference to begin with, but my initial motor evaluation didn’t find any motors which had sufficient torque without a gearbox, and adding a gearbox in a simple way changed the dimensions enough that mammal geometries weren’t feasible.  I spent some time looking for new options, and I found at least one which was promising, the XOAR Titan 6008.

While testing SMMBs new actuator under load, I kept getting faults from overvoltage that I had not anticipated.  The firmware only samples voltage once per control cycle, and while that plot did look very interesting, it probably wasn’t representative.  I wired up the scope to be able to sample the voltage and FET control signals during operation and sure enough, the voltage ripple was way higher than I had predicted based on the original design.  Even at only 30A phase current, the voltage ripple on the main power bus was 4.2V.  Note that this was with a nominal operating voltage of only 13V!  I had been trying to operate at 40A, for which it must have only been worse.