Motors different speed

Well the problem is that if you pair up 2 motors to one output, it doesn't mean that both motors are going to get the same power applied to each (electrical properties).

If in theory that each side is going equally, meaning channel 1 travels at motor command 500 at speed of 50rpms, and channel 2 both motors spin equally at 60Rpms in same conditions, then the solution would be to set the channel 2 to a lower command.

But if all 4 motors are going their own separate speed when paired up, then it's harder to compensate.

maha wrote: what do u mean by this sentence:
" it doesn't mean that both motors are going to get the same power applied to each (electrical properties)."

what do u suggest for solving mu issue?
i get another SDC21xx and control each motor separately?

It means the controller is not responsible for 2 motors tied to one motor output to drive both motors exactly the same. Just because the controller says it is outputting a 50% PWM output signal to drive the motor output at half the full speed, doesn't mean it is going to drive both motors at half speed. The problem would like in the motors not being not electrically perfect.

Even if you were to use closed loop mode, it does not compensate for 2 motors on the same output. The solution is to get another controller and run the 4 motors using 2 controllers. Closed loop speed with an incremental encoder would work since you are doing it by speed and the encoder is sued for feedback.