[Jared Russell]

Talon SRX closed loop control implements PIDF. The "F" stands for feedforward - and this works in all of the available closed-loop control modes (current, velocity, position, profile).

However, the feedforward gain is constant until you change it, so compensating for an arm by using a cosine function would require some form of gain scheduling. The Talon SRX Software Reference Manual talks at length about a couple of ways you could do this.

I also believe that you can hack the motion profile control mode to do what you want. This control mode is fundamentally position control plus a feedforward velocity (voltage) command for each trajectory point. There is no requirement that the integral of the feedforward velocities be equal to the subsequent position command. So you could calculate a profile to move your arm from any angle to any other angle, and account for gravity, spring assistance, or up/down asymmetry by manipulating the feedforward part of each trajectory point to provide a voltage disturbance in the desired direction.