I'm trying to simulate a DC motor with simulink. The problem is that I don't know how to take a load torque into account. If the DC motor drives a wheel with constant velocity, there will be a constant frictional force working against the DC motor. How would this be implemented in a DC-motor simulink simulation?
I have tried subtracting a load torque in between the two transferfunction blocks but then the simulated motor speed is always goes negative.