Measure rpm with hall effect sensor

[inktomi]

Hi.

Would it be possible to measure the rpm of a dc brushed motor with a hall effect sensor? I don't want to attach a magnet with the motor. I was thinking of detecting the magnetic field of the coils on the rotor, and calculate the rpm from that.

Thank you

 

[3v0]

It has been talked about. There should be information on the web about this but it may take some digging. Some motors may work better then others. Give it a try.

 

[inktomi]

It has been talked about. There should be information on the web about this but it may take some digging. Some motors may work better then others. Give it a try.

Thanks for the reply. I'll try it then.
Presumably I could also sense the direction the motor is spinning in by using a current sensor. Right?

 

[colin55]

You can only detect the direction of rotation if the motor takes more current when it is rotating in the wrong direction. A motor takes the same current in either direction but with most motors you control the direction of rotation by supplying the voltage with the positive to one of the terminals for clockwise rotation or negative to the same terminal for anti clockwise rotation.
You really need to tell us the type of motor you are using as there are hundreds of different types. Yours could be an AC motor and different rules apply.

You can also detect noise from a motor (commutation noise) to provide constant RPM and this is a very simple circuit (for some motors).

 

[inktomi]

Hey Colin55.

The motor I'm going to use is a common 5V dc brushed motor. I'm not sure if I'm correct, but if I manage to find out the direction of the current wouldn't that correspond to a particular spinning direction?

Thank you for taking the time to reply

 

[colin55]

You measure the direction of the VOLTAGE. This is the easiest to measure.

 

[inktomi]

I'm setting the voltage so I know which direction it should spin at. The problem is if I change the direction abruptly the motor won't change the direction instantaneously. I'm primarily interested in the direction of the motor during this transition.

Now would the voltage indicate the direction at this instant?

Thanks again

 

[colin55]

That's where you need two hall effect devices. Simply put a tiny magnet on the shaft.

 

[plis]

Hi.

Would it be possible to measure the rpm of a dc brushed motor with a hall effect sensor? <...>

Hi!
I have it.
**broken link removed**
But it, may be not DC brushed motor. It is odds-on AC motor without brushed, but it can remake.

Best regards.
P.S. My english is not natural.

 

[tcmtech]

I'm setting the voltage so I know which direction it should spin at. The problem is if I change the direction abruptly the motor won't change the direction instantaneously. I'm primarily interested in the direction of the motor during this transition.

I'm pretty sure it will still be going the same direction until it reaches zero RPM then it will go the other way! If it does not go either of these directions you may need to publish a research paper on it! or get a new motor.

 

[Roff]

I'm pretty sure it will still be going the same direction until it reaches zero RPM then it will go the other way! If it does not go either of these directions you may need to publish a research paper on it! or get a new motor.

Inktomi said,

The problem is if I change the direction abruptly the motor won't change the direction instantaneously.

I think he meant, "The problem is if I reverse the voltage abruptly the motor won't change the direction instantaneously."

 

[inktomi]

Inktomi said,I think he meant, "The problem is if I reverse the voltage abruptly the motor won't change the direction instantaneously."

Yes, obviously that's what I had meant.