Step response for a DC motor with a transient load

I'm attempting to find the step response for a DC motor with a position-dependent load.

i.e., the motor is driving an arm, there is no load until the position reaches a critical value (arm hits a wall), and then the motor is prevented from spinning.

I have tried opening up the step function in MatLab, but it seems to work by calling itself.

Does anyone have any possible advice about how to do this? Ideally I would write my own step function in a loop where the torque was updated.

Thanks in advance,

Answer 1

[Sebastian Castro]

Depends on how you want to model this system. Assuming you want to stay in MATLAB and are not looking at Simulink,

If you want your inputs to a time-invariant linear system to change over time, you can use the lsim function and provide your own input time history. [ documentation link ]

If you additionally want the DC motor model to have parameters/dynamics that change over time, you can take a more involved approach using linear parameter-varying (LPV) systems.

- Sebastian

[Tom]

Thanks! The second link you provided helped me figure out a solution.

As a side note, if I solve this system in it's state space form, is there anyway of modelling a PID controller without converting to a transfer function?

[Sebastian Castro]

Yes -- there is a pid function in MATLAB. You can connect the result of this with any other linear system representation (state-space, transfer function, etc.)