Velocity PID Programming: Terms dependent on time

[z_beeblebrox]

Originally Posted by Tom Line

Several of the simplified position PID's I've seen fail to mention you need to incorporate time into your formulas for the I and D terms.

So, it seems that would carry over to a velocity PID.

Let's say I have a simple velocity PID in pseudo-code.

Desired_Velocity - Actual_Velocity * Prop Gain = Prop_Term;
This_Velocity_Error - Last Velocity Error =Der_Term;
Sum_Errors * Int_Gain = Int_Term;
Last_PID_Output = Feed_Forward;

PID Output = Prop_Term + Der_Term + Int_Term + Feed_Forward;

Which of these terms need to be normalized by dividing them by the loop timing?

You're missing parentheses in the term for proportional gain. Anyway, if the loop is always run at the same frequency, dividing in the loop time is unnecessary, as the tuned gains can account for the loop time. If it is not constant, the I and D gains are divided by the loop time.