"mouse encoders"
 

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?

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

I've thought about this before, and ran into the same problem that you described. Commercial mice are just not made for high speeds. Can it be done? Sure - but you will need a lot of expertise on the subject, not to mention the ability to fabricate optics.

I am, however, working on something similar for next years' control system using optical flow navigation from a downwards-pointing digital camera. With the processing power of the cRIO, it might just work. Basically, you take a picture of the carpet, then another picture a fraction of a second later. You can solve the optimization problem to determine the vector relating the movement between the two shots. At a high enough speed (I'm hoping for 15-30Hz), you can essentially get optical mouse-like results.

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

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

Re: "mouse encoders"
 

That was the other option I was considering however given the proximity of the camera to the ground if its on the bottom of the robot wouldn't the size of the picture be so small that the next frame could have none of the old picture?

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

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

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

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.

Re: "mouse encoders"
 

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 :D But yes, it can and does work when well-implemented.

Re: "mouse encoders"
 

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

(Photographic illustration of martschr's post above)

Re: "mouse encoders"
 

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