Magnetorheological brake control

I’m trying to control the magnetic field of a small electromagnetic coil based on the output from a rotary encoder. The angular velocity is calculated from the encoder output. If the angular velocity is high then the magnetic field intensity should me high. Can someone help me with this?

What is the range or maximum RPM that the encoder will be rotating at?


The maximum RPM will be 27.9 rad/s and that will be the set value. if the encoder reaches the set value then the current should be 2A or can be 3A.

27.9 radians per second, OK.

Let us use 300 RPM, or 5 rotations per second, as always check my maths…

Now I should also have asked how many pulses per rotation of the encoder, is a quadrature type or what, maybe supply the part number or a link.

It looks probable right now that you can measure time from pulse to pulse.

Is output magnetic field related to angular velocity, simply, or is this headed for some kind of control loop?

Sry, I don’t mean to sound like I know anything that could help, these just seem like obvious questions that bear in you solution.


Actually the encoder is connected the the elbow joint. A device which is a kind of brake that help to slow down the elbow flexion. Whenever the elbow joint extends from the initial position is 0 deg (held perpendicular to the upper arm) to the final position of 90 deg. The average time taken for the extension movement is 0.5s to 1.5s. when the angular velocity (max. limit 27.9 rad/s) increases, the current supply should increase proportionally (maximum limit 3A) which causes the braking.
Yes, it’s a control loop and I’m using the PID control.

How many encoder positions are there in 90 degrees?

What is your PID loop rate?

A simple experiment of letting the arm drop and recording the encoder data time stamped might show this:

I don’t think the encoder pulses will give enough resolution and immediacy.

I suggest you investigat other ways to determine angular velocity. I would look at how stabilised camera platforms detect and correct the gimbal motors.

Again, I am beyond the edges of my experience and knowledge, and write here only hoping to invoke that handy rule of the internet:

The quickest way to get the right answer is to post the wrong answer. With authority.

I don’t think this is a workable approach.

a7, ducking for incoming.

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.