"mouse encoders"

[nickmagus]

I know it’s possible to convert an optical computer mouse into an optical encoder that you can mount on the bottom of your robot to tell how far you've gone, but I can’t seem to find any mouse sensors fast enough. (The fastest I've found has a top speed of about 5 ft/sec.) Is there any pre-existing encoder that functions like a mouse, or any optical mouse hack that would achieve a sufficient speed to go on a FIRST robot?

[Andrew Schreiber]

What about actually using a ball that ran on the ground to "gear down" the speed you are moving at. I think that would work... either that or a series of balls to do it. I cant say how efficient that would be.

As for a larger version of that system I cant say.

[nickmagus]

That could work but it might have slop or break if it hit a piece of debris on the field. Thats why I was hoping to avoid contact in the first place.

[Jared Russell]

Originally Posted by Damien1247

What about actually using a ball that ran on the ground to "gear down" the speed you are moving at. I think that would work... either that or a series of balls to do it. I cant say how efficient that would be.

As for a larger version of that system I cant say.

I think he was talking about using an optical mouse. Ball mice can work and I've seen them on robots with some modifications.

[Andrew Schreiber]

Originally Posted by Abwehr

I think he was talking about using an optical mouse. Ball mice can work and I've seen them on robots with some modifications.

I know, I was thinking read the ball, truth be told, that might help you with your camera thing, keep the issue of field debris away. Just put a fine checkerboard pattern on the ball and go from there.

[nickmagus]

Originally Posted by Damien1247

I know, I was thinking read the ball, truth be told, that might help you with your camera thing, keep the issue of field debris away. Just put a fine checkerboard pattern on the ball and go from there.

ya that could work i wonder if its possible just to avoid the ball all together though. That would be ideal.

[Gdeaver]

A couple of years ago some people looked into this. There are gaming mice that are fast enough. The problem is optics, illumination and the fact that optical mice are designed to work best on a laminate surface. Avago holds most of the patents on the algorithms used to detect the movement and are suing a bunch of other chip companies. Using a 1/2 VGA camera could work if you got the focus and lighting right. Then you would have to develop the algorithm and have enough processing speed. The good algorithms are closely guarded IP.

[Alan Anderson]

I need to warn anyone thinking of using a "telephoto mouse" or camera system of a real problem. The field of view, and thus the relationship between image motion and actual velocity, changes with height from the floor. Any bouncing of the system, or even significant vibration, will throw off the results.

[martschr]

Same thing for us.
We tried the optical mouse thing only to find out they are too slow. Instead we put encoders on omni wheels to accomplish the same task. One encoder for x axis and one for the y axis. It was accurate and accomplished our task. The only problem was by the end of everything the rollers in the omni wheels (ones for VEX) were not turning very well because of cuts and scrapes.

[FourPenguins]

I think a vision-based system (ie, optical mouse/camera) is probably more trouble than it's worth. As Mr. Anderson said, the potential for error due to vibration/bumps is pretty high (try bouncing your optical mouse and see what your cursor does).
MORT has used these on our drive shafts, and they don't seem to be a problem. Naturally, any time the wheels slip, there is slop.

[Jared Russell]

With a good Kalman filter, the optical flow path can work quite well. I've done it before.

Is it worth the trouble? Probably not But yes, it can and does work when well-implemented.

[David Brinza]

This approach is used by Team 16, the Bomb Squad...

(Photographic illustration of martschr's post above)

[danshaffer]

Originally Posted by David Brinza

Or how about this approach used by Team 16, the Bomb Squad?

That's what I suggested when Nick asked me about it after school today

[Alan Anderson]

Originally Posted by martschr

...we put encoders on omni wheels to accomplish the same task. One encoder for x axis and one for the y axis.

Our 2005 Triple Play robot had three miniature omniwheel "follower" encoders. There was one in front and one in back to measure sideways motion and turning, and one in the middle to measure forward motion. It worked great on carpet. On vinyl or tile or concrete, not so great.

[Andrew Schreiber]

How did you measure rotation with them? Ive been looking at a similar concept but couldnt come up with a way to do it without a ton of floating point math/look up tables.