DC Motor

Community General Discussions
1

Hi, I am looking for a very specific DC motor.

I need it to be as “variable” as possible.

I want to be able to control the RPMs at a very high resolution. I’d like to slowly increase the RPMs and be able to measure this as accurate as possible.

Any suggestions?

2

google steppers

nick

3

Aye, steppers are great for projects like self-balancing bots.

4

You can pretty much do that with any DC motor. There is no magic motor out there thats going to do all that for you, it depends on the data acq and controls you are using.

Also stepper motors are AC, not DC.

5

great, so just about any typical DC motor will vary it’s speed depending on the power it is given?

Therefore, what I need then is

  1. A way to regulate the voltage to the motor.
  2. Count the RPM of the spin.

I know there are numerous Nuts & Volts issues that probably do this, does anyone have an issue off hand?

OR any suggestions on an idea.

I just need to spin a motor, count the RPM and have the ability to speed or slow down the motor from 0% to 100% capability.

Thanks Again
Clonus

6

topher,

there are dc steppers (ive never seen an AC but im no expert) i have six of them sitting on my desk right now.

nick

7

I think most (or all) steppers are really “DC”, but since they run on multi-phase pulses, you could argue that they’re AC…
If you want continuous rotation, I’m thinking that a stepper is not the best choice.

For regular DC motors, you probably want to control the speed via PWM, rather than by changing the voltage.
And either way, you will need a feedback system to know how fast the motor is turning. Two ways to do this are:

  1. An optical encoder wheel on the shaft.
  2. A Hall-effect sensor to monitor the rotation magnetically.
    Most industrial applications use a Hall sensor.

Pete

8

As saipan posted, I consider steppers to be AC because the current going into them is not continuous. It changes just like a brushless motor. It all depends on the way you think of them I guess.

Anyways all DC motors generally have a Kv rating. That is idealy they produce a certain amount of RPM for every volt applied to them. Since you want to do this to a DC motor I would not suggest using BEMF sensing, or a internal Hall sensor. I would just simply use a external motor encoder. You could easily attach some kind object that spins and records its speed with a optical sensor or something like that. You could use a external hall sensor but you might have to worry about impendance and such things at high RPMs. The way we measure motor RPM at work is with a strobascope. It works really well and gives RPMs accurate to the .1 decimal place.

9

Well for a canned solution you could look at this sprint-electric.com/200xlv.html or something similar. I seem to remember using one or two in a test fixture at work awhile back. I don’t remember them being inexpensive, but they were not prohibitive either. They can run open loop, with or without torque compensation, or with a feedback voltage they can do the whole PID loop thing. Somehow I doubt it would be nearly as satisfying as just making something from a motor driver board, a PIC, and some perf-boarded circuitry but it really depends on what your goal is I suppose.
EB
:mrgreen:

10

I think it’s quite funny that the menu sliding around on the left side of that site uses a really poor approximation of a proportional controller to keep the menu aligned. :slight_smile: