slow motor response

[ahmedragia21]

hi, im trying to follow a straight line and i found my motor has a slow response when i do PWM , i dont know why ? is this cuz the motor is a used one or what ? and how do i solve this problem ..

thanks !

 

[NightFalcon90909]

It is probably just a matter of you using too little power or too small a motor for too heavy a robot. Anyway, that is what I would check first.

 

[Papabravo]

Basic priciples of motor drives

T = I * α

where T is torque, I is moment of Inertia, and α is angular acceleration
in radians/per second

T = Kt * i

where T is torque (again), Kt is a constant which is unique to each motor
and i is the current in the coil.

You can set the two expressions equal and solve for any one of the four quantities if you know the other three. Check on wikipedia for the moment of inertia for a cylindrical disc which is the easies thing to model that you can connect ot a motor shaft.

 

[second286]

Slow motor response:

ahmedragia21:

Do a simple test, connect the motor directly to your voltage source-if the rpm/torque is still not good-replace the motor. But if it runs good then you know your problem is from either, insufficient power into the motor and/or you may need to adjust the PWM to match your motor electrical time constant.

Power in test:
compare the direct and PWM connected, motor RMS input currents?

PWM test:
You may do this by trial and error-varying your PWM freq/dutycycle for acceptable motor rpm/torque. Or simply place in series with your motor circuit a 2 to 3 ohm resistor (Rs)-then energize your system with a step voltage input (or a slow repeating squarewave)-view on a scope this transient voltage across Rs to get an estimate of your motor time constant. This voltage plot across Rs will be in proportion to the motor current, just larger in amplitude.