Pololu TRex dual motor controller help 3rd motor output

hey guys!

i currently run 2 TReX motor controllers on my robot, and they both run like a dream, but i have one thing that needs some clearing up.
for the design of the robot, i need to run two motors on one motor output. naturally using a continuous series (positive to positive of one robot, continue the circuit to the next motor, fnish the circuit with the negative on the second motor to the motor controller) the motors do present a problem. as i am using up channels 1 and 2 (2 dc 12 volt motors, 2 dc actuators) on both motor controllers, i have to resort to using the 3rd channel on one of the motor controllers to power my continuous series motors. i have read through the manual for the TReX, and have noticed that i need to produce a diode and put them onto both leads of the motors. but do i really have to?
the motors i will be using are a very high RPM (around 2400RPM) but i have tested them before on the 1st and 2nd channels on an old TReX motor controller, and they work fine in a continuous series. the two motors i am using are desinged to only spin one way, so i have to set the 3rd channel to only neutral and (red?), as i am using the gear switch on my transmitter. all im asking is if i really need to put diodes on both motors, and what the use of the diodes really are for the motors.

Thanks for any help provided!


Yes, you really do need to put the diodes across your motors. The diodes give the motor current a loop to circulate around during the off portion of the PWM. Without them, the inductance of the motor will act to keep the current flowing, causing large and potentially dangerous voltage spikes in the process. These diodes are inherently present in an H-bridge, which is why you don’t need them when controlling a motor with an H-bridge. For more information, see this wikipedia article on flyback diodes.

- Ben