# Relationship between band and rise time in motor control

#### alpheratz

Joined Nov 10, 2019
8
Hello everyone, I'm not sure about the category I post this thread in but it's something that has to do with theory and I hope you don't ignore it because of that.
My problem is that I study DC motor control and I find from my lecture the case that you see in the image.

(it is transfer function of speed control), I have this general relation that can be applied to this system $$t_r \cdot f_B = 0.35$$. It's a type 0 system and you see the rise time and the crossover frequency indicated in the formula. It surprises me because in the past I studied that for this formula the cutoff frequency should be used. If this formula is right than it means that using a proportional controller I can reduce my rise time and it's again something new I've always thought I can control the regulation error only like that.

So which frequency should be used? Don't take the body diagram too seriously I put there some simple values only to make you get an idea

#### ericgibbs

Joined Jan 29, 2010
9,116
hi,
Welcome to AAC.