Design calculations

Maximum speed

Motor has 5600 RPM at 6V no load. Gearing is 9.68:1 Wheel diameter is 6cm.

This gives a max speed of 5600/60/9.68*0.06*Pi = 1.8m/s

Encoder calculations

The encoder has 48 ticks per revolution. This gives 48*9.68 = 464.64 ticks per wheel revolution, or Distance per tick = pi*0.06/464.64 = 0.40568 mm/tick

Speed calculation

Speed is calculated based on time between encoder ticks

At max speed there should be approx 4.48 encoder ticks per ms, or 223 us between tics The timing base is pt. 10us, so velocity resolution is rather bad at high speeds. This is be improved by averaging if time between encoder is smaller than sample time.

Sample time is (pt.) 1ms.

At low speed the time between encoder ticks make the calculated wheel velocity delayed, resulting in poor controller performance (or even instability). A velocity estimator is implemented based on anchor voltage and current velocity. This is then high-pass filtered and added to the encoder based velocity.

Parameter estimation

Pololu say that at 6V stall current is 2.2A, or R_A = 2.7 Ohm

On this robot the total anchor resistance is estimated to 3.3 Ohm (including H-bridge and wires) based on current step responce.