# What does the value of kA mean in feed forward control

I known it has something to do with acceleration but I don’t know what it does or how it is calculated. Especially in the simple motor feed forward class when you are passing in a velocity not acceleration.

The acceleration gain has dimensions of voltage per acceleration, and tells you how much driving voltage is needed to make your mechanism accelerate at a given rate.

There’s a two-velocity calculate method on the feedforward class to make using it a bit easier; you specify the current and next desired velocities and the controller figures out the acceleration.

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Essentially the equation describing the voltage required for a velocity of v, and an acceleration of a is:

V = kA * a + kV * v

In practice there’s usually a `kS` term as well, though if your motor is very powerful you can sometimes omit this. See the following article for more info:

I know about the equation it just didn’t make much sense to me because I was wondering how the acceleration was calculated because voltage is proportional to speed. I guess that the acceleration constant is there to speed that up.

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It’s proportional to both velocity and speed, simultaneously. If you leave out the acceleration term you’ll lag the profile because you’ll have the right voltage for steady-state velocity at each timestep but you’ll have left out the voltage that’s needed to drive the corresponding acceleration between them.

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