What Forces Contribute to the Torque on a Moving Robot?

[Granger]

Homework Statement

2. Homework Equations [/B]
So I basically have to establish the non linear differential equation that governs the movement of this robot (relates d and theta):

The Attempt at a Solution

So I know that we should have the sum of torques equal to:

$$I\frac{d^2\theta}{dt^2}$$

where I is the total inertia momentum.

Now I'm having trouble understanding what terms will figure in total sum of the torques.

One of the terms needs to be related to the distance d from the y axis. That term must be

$$I\frac{d}{dt} d(t)=IV\cos{\theta}$$

where V is the constant linear velocity.

However there must be additional terms right? Can someone help clarify the mechanics of the situation? Thanks!

 

[haruspex]

One of the terms needs to be related to the distance d from the y axis. That term must be

$$I\frac{d}{dt} d(t)=IV\cos{\theta}$$

where V is the constant linear velocity.

That has the wrong dimensions for a torque, and I don't see how you arrive at it.
Surely you should be looking for forces that create the torque, but you have not indicated how forces are being applied by the robot.