Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: Littlejohn on March 01, 2010, 12:28:22 AM

Title: What kind of encoder to use on a DC motor driven base?
Post by: Littlejohn on March 01, 2010, 12:28:22 AM

Hello everyone, my first post so I hope I do it right.

I am building a 2 wheeled, 1 caster, robot base. For the drive I am using the gears and motors out of a Mattel Jeep at 12V DC. These are controlled by a Solarbotics L298, which I am in turn controlling with an Arduino, that will one day be controlled by an Apple IIGS motherboard.

The question I have is what would be the best/cheapest way to measure the rotation of the 2 8" lawn mower wheels. I need to compare the rotation with the Arduino because the 2 DC motors do not run at exactly the same speed. The wheels have a little wobble in them that I can't seem to remedy, but still works great.

I am including a video to answer (hopefully) all questions.

[youtube]fwtlwTWdHBc[/youtube]

Title: Re: What kind of encoder to use on a DC motor driven base?
Post by: chelmi on March 01, 2010, 09:28:52 AM

Quote from: Littlejohn on March 01, 2010, 12:28:22 AM

The question I have is what would be the best/cheapest way to measure the rotation of the 2 8" lawn mower wheels. I need to compare the rotation with the Arduino because the 2 DC motors do not run at exactly the same speed. The wheels have a little wobble in them that I can't seem to remedy, but still works great.

Rotary encoders: http://www.societyofrobots.com/sensors_encoder.shtml (http://www.societyofrobots.com/sensors_encoder.shtml)

Title: Re: What kind of encoder to use on a DC motor driven base?
Post by: waltr on March 01, 2010, 11:23:05 AM

I have used printed encoder disks with radial 'pie' shaped black and white bars that are glued to the wheels. Then use a reflective photosensor to 'read' the encoder bars.

Like this one:
http://www.acroname.com/robotics/parts/R253-WW02.html (http://www.acroname.com/robotics/parts/R253-WW02.html)

This is fairly easy to do your self for very little money. The disks can be created in various graphic programs and even in Excel then printed. reflective photo sensors can be bought at many electronic suppliers or build your own with an LED and a photo-transistor.

Title: Re: What kind of encoder to use on a DC motor driven base?
Post by: Soeren on March 01, 2010, 07:41:42 PM

Hi,

The easy way to create an encoder disc is by a postscript file Here's a bunch (http://www.google.dk/search?num=100&hl=en&safe=off&rls=com.microsoft%3A*%3AIE-SearchBox&rlz=1I7GGLJ_en&q=postscript+encoder+disc&btnG=Search&aq=f&oq=)

An online encoder drawing page (http://www.bushytails.net/~randyg/encoder/encoderwheel.html)

There also exists a few programs to generate the discs.