I'm making a mobile robot with 4 wheels each 125mm in dia. which will carry around 10kg load but i dont know how to choose motors for such a robot . I know that it'll need dc geared motors but i don't know that how much Torque , rpm it needs to be. So please help me figure these specs for motors also how does rpm relates to torque and acceleration. if you help me you'll get a good gf by the end of this month : )
The relationship is found in the theory of physics at pre univercity level.
The actual numbers depend on Your specs for acceleration, speed.
Begin with time/distance/speed. How much distance do you want your robot to cover in a given time when it is at full speed?
Suppose your want the robot to travel 2 metres in 5 seconds at full speed. The circumference of your wheels is 0.125*Pi = 0.4m (approximately). So the wheels must turn 2/0.4 = 5 revolutions in 5 seconds, which is 60 RPM.
How quickly your robot accelerates to full speed will depend on many things including the weight/load. But you can get a crude estimate by ignoring those other factors.
Suppose you want your robot to accelerate to full speed (which is 2 metres in 5 seconds, or 0.4m/s) in 2 seconds. That's an acceleration of 0.4/2 = 0.2 m/s².
If the robot has a mass of 10Kg, then the force required to accelerate at 0.2m/s² is 10*0.2 = 2 Newtons.
Your wheels have a radius of 0.125/2 metres, so the torque of the motor required to create the necessary force at the circumference of the wheels would be 2*0.125/2 = 0.125 Newton-metres.
I hope I got all that correct! At least that will give you a minimum torque figure to look for. You will need more than that because of friction.
I think the first step would be to define the quantity of motors needed for this setup.
We are using 4 motors in our project.
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