The root locus is only good for find where the poles will be as ONLY a proportional gain is changed.

What systems use only a proportional gain? Only mechanical systems like a speed governor or some spring based hydraulic devices.

Teaching root locus is almost useless. There are many threads on YouTube that show how to calculate the root locus and various related items.

I once asked a college instructor why he taught the root locus. The answer is that is is part of the curriculum that was always taught.

I think learning root locus it is a waste of time.

What is important is knowing where the break away point is. After that the rest is useless.

Root locus could be useful to mechanical designers that need to make sure their speed governors or spring type hydraulic control devices will work.

However, after 30+ years of control I have yet to see where any mechanical engineer knows how to calculate an open loop transfer function.

Look at the videos on YouTube. They all assume one knows an open loop transfer function to work with. This is definitely NOT the case in real life.

The root locus is useless unless one first has an open loop transfer function. The root locus is useless when using modern controllers capable of PI, PD, PID or leadlag closed loop control.

I submit that colleges and universities are wasting students time and money learning about the root locus. There are better things to learn that make learning the root locus obsolete.

This is my finger in the eye of those who continue to waste time and money teaching root locus.

Don't bother to object unless you have a very good argument for root locus.

Peter Nachtwey

Delta Computer Systems