View Full Version : Motor selection..

12-18-2011, 04:57 AM
I am making a wired car robot. can i use motors of same rpm but different torque?.? front two motors will have same rpm n torque, n back rear motor wil have same rpm n torque but torque of front motor wil be less than rear one.

12-18-2011, 06:34 AM
As long as you don't make the robot so heavy as to cross the back motor's torque capacity, you should be fine.

12-18-2011, 10:51 PM
As long as you don't make the robot so heavy as to cross the back motor's torque capacity, you should be fine.

wont i face difficulty in turning as the acceration of front and rear motors wil be different.

12-19-2011, 10:30 AM
If you need very precise movement, you will have to use identical motors. Turning will not be an issue with your current setup if you keep the weight low. I would suggest to use the higher torque motors up front and shift the weight bias of the car towards the front. This will give you more traction to the higher torque motors and increase the pulling power of your car. :)

12-19-2011, 01:05 PM
Let's do some basic physics here now.

Looking at an ideal system's horizontal components (i.e. excluding gravity and friction)

Torque(T) = Force(F) x moment arm(r) , which makes F = T/r
F = m x a (acceleration) ,which makes a = F/m
Replacing force with the torque based equation.

a = T/(m x r) .. Now if your maximum torque is known, and moment arm is known (fixed axle/wheel size) all you need to do is to know the mass to have a certain acceleration. If you are within an understandable ball park estimate of that acceleration for that mass, I believe you should be good to go.

Also, the torque will come into play when your motor has to fight resistances to have a certain acceleration ,which are mainly gravity and friction. As long as you control the mass of the robot, both gravity(mg) and Friction (u x N) will come down hence limiting the torque generated by the motor.

Finally, the lesser torque the motor generates, the lesser the current requirements.

Moral of the story: make your robot light and be a happy roboteer.

12-19-2011, 02:18 PM
well the motor with higher torque will accelerate faster so will reach the described RPM faster hence the robot wont go straight.