I’m trying to duplicate the computations given in the paper, and I can’t seem to get the same numbers for ka. Here’s what I have:
CIM_NOMINAL_VOLTAGE = 12 # volts CIM_FREE = (5310 / 60) # rps CIM_STALL_TORQUE = 343.4 # oz/in CIM_STALL_AMPS = 133 # amp CIM_FREE_CURRENT = 2.7 # amp wheel_diameter = (3.8/12.0) gearing = 6.1 nmotors = 3 robot_mass = 110 max_velocity = (CIM_FREE * math.pi * wheel_diameter) / gearing max_acceleration = (2.0 * nmotors * CIM_STALL_TORQUE * gearing) / (wheel_diameter * robot_mass) kv = CIM_NOMINAL_VOLTAGE / max_velocity ka = CIM_NOMINAL_VOLTAGE / max_acceleration print('vmax=%.3f amax=%.3f kv=%.3f ka=%.3f' % (max_velocity, max_acceleration, kv, ka))
And this results in vmax=14.433 amax=360.816 kv=0.831 ka=0.033 . However, the paper reports kv=0.83 and ka=0.1 … so something’s wrong with my acceleration numbers.
I assume I’m not using the right units for CIM_STALL_TORQUE, but I’ve tried a bunch of different units and none of them have worked out. I had expected the unit to be in ft/lb … but that yields amax=1.867 ka=6.427 which seems really off.