Calculating Torque for a Robot Wheel: Mass, Acceleration, and Constant Velocity

[elimenohpee]

Homework Statement

You are given a robot, and you are asked to design the torque needed for the driving motor. What is the torque to turn a wheel who's mass of the system connected to the rim is 3kg, and the diameter of the rim is 0.0381m?

What is the torque when the wheel accelerates at a rate of 1.47m/s^2? What is the torque when the wheel reaches a constant velocity of 5 m/s?

The Attempt at a Solution

I know torque = force * distance = mass * acceleration * distance

I figured the torque to turn the wheel would be:
torque = m*g*r = 3*9.81*0.0381 = 1.12Nm (but this sounds like a lot for such a small mass)

but I'm not sure what to do when the wheel is to accelerate. And I'm lost what to do when the acceleration is zero, aka constant velocity.

 

[popo902]

I know torque = force * distance = mass * acceleration * distance

I figured the torque to turn the wheel would be:
torque = m*g*r = 3*9.81*0.0381 = 1.12Nm (but this sounds like a lot for such a small mass)

but I'm not sure what to do when the wheel is to accelerate. And I'm lost what to do when the acceleration is zero, aka constant velocity.

sorry but...your torque equation is wrong
remember that torque is r X F not r * F
r X F is also rFsin(theta), with theta as the angle between them
also that r is not the diameter of the wheel
it's the distance from the point of force applied
since it is a wheel, u can tpretty much use the center for axis of rotation and the distance to where it spins is yyour r

 

[elimenohpee]

Yes I'm aware that, the angle between the vectors was assumed to be pi/2. And that distance given was the radius of the wheel, since the force is assumed to applied at the center of the rim.