How to calculate Torque on the rear wheels of an RC car?

[Firedawn]

Hi guys,

I'm working on a project where I need to find the torque produced by the rear wheels of an RC car so that I can convert it into power and then into the current required by the motor.
So T=ω×P_mech → P_mech → P_elec → I_motor
Here are the details for the car:
1kg weight
Torque on each rear motor (need to find torque of each)
Radius of wheels is r = 0.03m
Voltage input to motors is 5V
Average velocity of car is 0.33m/s
Assume acceleration time of 2s (not sure if needed)

What is the torque at takeoff and at constant velocity on a flat surface?

 

[jedishrfu]

Have you thought of trying to measure the force by attaching various weights to the car and hang the weight to dangle off of a table while the car resting on the tabletop tries to pull it up?

 

[Firedawn]

No because I need theoretical values since I do not currently have the motors.

 

[jedishrfu]

This might help:

http://www.micromo.com/technical-library/dc-motor-tutorials/motor-calculations

 

[CWatters]

You could estimate the max possible torque by calculating the torque required to lift the front wheels off the ground...

Torque = (mass of car) * g * (distance from rear wheels to centre of mass)

 

[CWatters]

The torque at constant velocity is very hard to calculate because it depends on the rolling resistance and similar drag forces.

PS: That's the torque at the wheel. You need the gear ratio to calculate the torque at the motor.

 

[David Lewis]

So T=ω×Pmech

Torque = power/rotational speed
Current = torque/torque constant

 

[jack action]

The maximum force that can be handled by your car depends on the friction coefficient of your driven wheels. It doesn't matter if you use that force to accelerate, fight drag or rolling resistance or anything else.

This simulator should help define the power you need according to the performance you want.