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I have a model that has a number of muscle actuators and I want to add another actuator that applies force on two segments of the model as a function of some of the state variables in the model. I reckon I should define an actuator and a controller for that additional actuator (similar to tugOfWar actuator). So I derive two classes – MyActuator from Actuators class and MyController from Controller class. Now I have two issues:

1. I want MyController to only be associated with MyActuator and not with the Muscle Actuators in the model. If I invoke addActuators() with an object of MyController, all the actuators, including the muscles are associated with MyController which is not what I want. If I invoke SetActuators with an object of MyActuators as an argument this does not work either because the argument of SetActuators is a Set<Actuators> type and not an Actuators type. How do I define a Set<Actuator> type different from an Actuator type or re-cast Actuators type to a Set<Actuators> type? The explanation in ClassNameMapping.pdf only takes me in a circuitous path.

2. Also, I was surprised to see that even though MyController is derived from class Controller, invoking the method setNumControls() with an object of MyController throws an error that only a controller can set its number of controls based on the actuators associated with it.
I will appreciate any help with these issues.

You're going down the correct path.

Use Controller::addActuator() (as shown in the README example: https://github.com/opensim-org/opensim-core) to tell your Controller that it should control your custom actuator. This only adds your one actuator to the controller, not all the other muscle actuators. This function is called *outside* of your controller, not inside the controller.

I don't think you should call setNumControls yourself. That seems like something handled internally based on the number of actuators that you added to the controller. Simly use addInControls() within your Controller::computeControls() function, as shown in the ControllerExample.

Thanks Chris. That works. But doesn't adInControls() add to the values already occupying the slot in the system-wide model controls? I just overrode Actuator_ setControls() in my Actuator methods to update my actuator control values and it seems to work fine. Thanks for the help.
Musa

Yes you're correct. What do you mean by overriding setControls()? That doesn't sound right. Is there another controller that's adding controls to your non-muscle actuator and you don't desire this? If you're using CMC, you can tell CMC to ignore certain actuators.

Chris,
Oops! Scratch that off! I had thought I needed to override those methods when I was getting some weird error messages; but got around them. Now I did not need to override them. Thanks for all the insight. Now my code runs well.
By the way, is version 4.0 now considered a stable release or is it still in beta phase?
Thanks.
Musa

Great to hear that you've got your controller working. OpenSim 4.0 is not released and is not yet in beta.