Quadrature encoders

[Max Lobovsky]

As a rookie team this year, we didn't have time to do much more than the basics with out control and programming system, but i have been reading about the hundreds of ways to improve them. I understand a quadrature encoder has two different striped rings so that two sensors can be used to tell which direction the thing is spinning.

What systems have you used that work effectively?
If you bought it, how did you adopt it to work for FIRST?
If you built it, how?

[Bobby Moretti]

No need to apologize, asking questions and learning this kind of thing is what FIRST is all about!

My team (492 from Bellevue, WA) used quadrature encoders on our robot this year. You have the basic idea right - they can be thought of as IR sensors that count the ticks passing by the wheel. This tells you roughly how far you have traveled along the field (assuming your wheels don't slip).

Our team also used a gyro for positioning. Rather than go into all the technical details here, fairly soon we're going to be adding a technicnal section to our website (http://titanrobotics.net) where we'll have white papers and good explanations of our robot's control feedback system.

I'll post back here when we get it up.
/me adds this to a growing list of post-shipping FIRST-related todo's

You can read it, and then ask any specific questions you might have.

Good luck-

[Ryan M.]

If you can do them, quadrature encoders are great. However, you often don't need to do them if you just read the direction that the motor is supposedly turning. Just a suggestion.

[Warren Boudreau]

Digi-Key has shaft encoders for sale. You have your choice of the number of lines (clicks) per revolution. We are using 2 64-lpr encoders, with quadrature, and are plugging them directly into the RC. The software guys claim that this works.

We'll find out this weekend.

[Ryan M.]

Originally Posted by Warren Boudreau

Digi-Key has shaft encoders for sale. You have your choice of the number of lines (clicks) per revolution. We are using 2 64-lpr encoders, with quadrature, and are plugging them directly into the RC. The software guys claim that this works.

We'll find out this weekend.

Our team didn't get nice premade shaft encoders this year, unforunately. Our encoders only have a resolution of 16 -lpr.

[Neal Turett]

Originally Posted by Texan

If you can do them, quadrature encoders are great. However, you often don't need to do them if you just read the direction that the motor is supposedly turning. Just a suggestion.

We tried this on this years robot, and after hours of debugging realized that it's not always reliable - if the motor suddenly reverses direction, mechanical lash will throw off your readings.

[Bobby Moretti]

Originally Posted by Neal Turett

We tried this on this years robot, and after hours of debugging realized that it's not always reliable - if the motor suddenly reverses direction, mechanical lash will throw off your readings.

You can prevent that sort of thing in software. That's why PID-type control laws are so great

There's plenty of information about PID control here:
http://www.chiefdelphi.com/forums/sh...ad.php?t=24340