The control law for a PIDf controller is:

u(t) = K_p e(t) + K_i \int_{0}^{t} e(\tau) d\tau + K_d \frac{du}{dt} + F(t,\dots)

where u(t) is the control signal (i.e. the voltage given to the motors), e(t) = x-x_{setpoint} is the error, K_p K_i and K_d are constants, and F(t,\dots) is some feedforward function. If I’m understanding the question correctly, you’re suggesting a constant feedforward function

F(\dots) = K_f

This feedforward doesn’t make much sense, and I’ll explain why. Think about the case where we want the turret to settle at some setpoint. If the turret is sitting exactly at the setpoint with no velocity then we don’t want to give the motor any voltage or it will move away from the setpoint. In that case the P, I, and D components of the control law will all be zero, just as we want. But the feedforward will be K_f \neq 0.

The goal of a feedforward is to balance any known forces acting on the system so the PID part of the controller only has to deal with the unknown forces (aka disturbances). A feedforward like the one I described above would be good for some system with a spring where the force acting on the system is proportional to the system’s position. But for a turret, there are no major external forces acting on the system that need to be cancelled out, so there shouldn’t be a need for a feedforward term.

If you find that the effect of the relative motion from the robot base turning does affect the turret more than can be rejected as a disturbance, then you could consider adding a feedforward to cancel out that “force”. But the “force” will be proportional to the angular acceleration of the chassis, which will need to be measured by some sensor in order to be cancelled out.