Motor encoders - How do they work?

Lynxmotion Rovers, Sumo, and Tracked
1

Hello guys, I have been all over the internet looking for information on how motor encoders work and for some examples of its use but I turn up empty handed.

My question is, does it make the motor work more or less like a servo? can you get fairly accurate positioning with it?

2

Hi Mike,

For better results try searching for quadrature encoders. They provide very accurate feedback to a microntroller as to the direction and amount of movement the motor makes. Yes it can be used to make a servo from a gearhead motor. In the case of the 2WD Rover it has the resolution to control the vehicles position to less than a thousandths of an inch. The efective resolution will be less due to geartrain slop and other environmental issues, but it will be very accurate. :smiley:

3

Thanks very much for the information.

This is the solution I was looking for - for one of the many projects I have lingering around in my head. I want to make a back massage robot that has X and Y tables.

How this would work is just like a TV tray that you can use in bed. It would have 4 legs like a table and you would simply lie under it between the legs. Positioning does not have to be dead on but needs to be with in 1/2 to 1" accurate. I plan to have limit switches at the home location to have the thing reset to zero for each use. I looked at continuous rotation servos but the gear motors are stronger and more powerful. The motors would need to move the weight of the assembly back and forth.

When the day comes that I build this, I will have a back rubber that never complains and never gets tired!

4

Is it a requirement that you use two encoders?

If all you are concerned about is if the bot is moving and perhaps distance moved, wouldn’t one encoder be sufficient?

Kenny

5

I think he’s looking for an x,y coordinate on the back. For that, he’ll need 2 motors and 1 encoder on each.

6

yeah, I will need to encoders for that project.

7

Will the motor encoder work for both GHM series motors as well as the planetary gear motors?

For my X, Y table machine, I need stong powerful motors and one I am looking at is this one:

Voltage = 9.6vdc
RPM = 271
Reduction = 51:1
Stall Torque = 7.46 ft. lbs
Motor Type = 36mm OD LS-550S

Also, I could not find any brackets that would fit this motor and there was no spec sheet for mouting hole dimentions.

Here is a rough design of what I want to make using these motors:

Click image to enlarge
img336.imageshack.us/img336/8308/xydesign2ad.th.png

I appreciate any help

Thanks.

8

you may want to check out www.cnczone.com What you are describing is basically a two axis router. Fab people use stepper motors w/drives and such for 2D cutting/engraving. To me it looks like a similar objective except you probably dont want a machine bit cutting into your back.

9

Thanks Topher,

I might get one of those driver boards in the future, but right now, I am putting this project on hold because I am to interested in building the Lynxmotion Humanoid Biped.

Thanks for the link though.

10

Wow that’s a neat “machine bit”