# Position control of DC brushed motor.

#### BillM

Joined Feb 9, 2009
6
Hello all,

I have a brushed DC motor that works nearly good enough. I've been using a timer to control when to start/stop the motor. However, after a period of time, the error accumulates and becomes large.

I'd really just like a third wire on my brushed DC motor that pulsed everytime it did 1 revolution. I could then count the pulses on my microcontroller to determine when to stop.

The problem I have is the cheapest method I currently have found are continuous servo's, which run around 10 dollars, and I have to send commands to send it in different directions.

Does anyone know of a place that sells cheap brushed DC motors that has a built-in hall effect sensor or something?

Thanks!

Bill

#### thatoneguy

Joined Feb 19, 2009
6,349
What type of motor is it -Brand/model ?

does the shaft stick out a ways on both ends?

An optical encoder disk with an opto-interrupter is all that comes to mind for a permanent magnet, brushed DC motor.

What are the torque and RPM requirements? Sounds like you are on a budget, would something like a stepper motor out of an old printer work for you? Lots of torque and good control, feedback is available if one gets fancy with the driver. I believe there is a stepper driver IC that uses back EMF for position verificaton as well.

#### BillM

Joined Feb 9, 2009
6
Right now my DC brushed motor is this DC gearmotor from solorbotics.com

http://www.solarbotics.com/products/gm3/

It has just the right amount of torque, is cheap, and can operate at around 3.5V.

My only problem is I can't detect where it's at

I think a stepper would work, as long as I could ensure it had enough torque to move my load. I also haven't seen any that were cheap.

I need something that can spin 7 or so revolutions one direction, then come back 7 revolutions the other direction and be in the same place. Originally I was using a timer... but it kept getting way out of wack

Thanks for the help.

Bill

#### SgtWookie

Joined Jul 17, 2007
22,201
If you're looking for cheap steppers, here's a possibility for you:
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?jameco_page=42&langId=-1&productId=171601&catalogId=10001&freeText=PF35T-48L4&storeId=10001&search_type=mfgr&ddkey=http:StoreCatalogDrillDownView

Bill