Fitting a DC Gear Motor with an encoder

Describe how you're using the motor. For example, you might be able to make an encoder disc and put it on a wheel, if that's how you're using the motor. The methods for attaching an encoder largely depend on the application.

Also provide your price range. Good DC gearmotors with encoders (or encoders added) can be fairly expensive.

-- Gordon Author: Robot Builder's Bonanza Budget Robotics:

I working with students in a college robotics club to make a fire fighting robot for the Trinity College Fire Fighting Contest. I would like to keep costs for each motor to a around a maximum of $50 each.

Looking at the gearmotors on the site you provided, none will be easy to mount an encoder on. My favorite place is on the shaft hanging out the back of the motor, before the gearcase. If you drive wheels via a belt drive, you might be able to hang an encoder on the output of the gearcase with an encoder wheel stuck on the flange of a toothed pulley or gear. If you mount the wheel directly on the gearcase output, you can stick a photo-reflective encoder on the side of the wheel. Photo reflective encoder wheels can be printed on a laser or inkjet printer and transmissinve wheels might be able to be printed on transparency material in a similar fashion. The detector's can be found at DigiKey or US Digital among many places. They are not difficult to make.

If the shaft is long enough, you can buy an encoder that fits the shaft and can be adhered to the motor face (this isn't necessarily cheap, however). If the motor is fitted with an aramture shaft (on the back) you can usually DIY an optical encoder or even a hall-efect encoder.

You can also make an optical encoder disk to fit on the inside face of the wheel, although the resolution won't be great. Really, there are lots of possibilities.

Hope that helps -- m

For the price you need to limit yourself either to the homemade reflective discs that the others have mentioned, or surplus.

For surplus try:

These are very nice motors and fit your price point extactly. The optical encoder is already attached to the ungeared side, and resolution is quite good. I know of several Trinity contestants who have used these. If this particular outfit is sold out you can probably find the same motor from another source with a diligent search on Google.

-- Gordon Author: Robot Builder's Bonanza Budget Robotics: