Question on wheel speed sensors

[Lil' Lavery]

Nobody is saying wheels on carpet don't benefit from sensors, but rather, they don't benefit from a "land speed" sensor as you were proposing. Almost every competitive team uses some form of sensors in their drivetrain, but usually just to monitoring their driven drive components. They'll mount a shaft enconder to their drive shaft or the output shaft on their gearbox, for example. They trust that the slip effects are small enough that any error they induce will not effect their gameplay.

If you want "external", field-oriented input, you don't always have to base it off the playing surface. Your GPS comment is on the right track. There have been games in the past with non-moving optical targets (such as the lights in 2004 and 2006) that can be incorporated into navigation software. While there hasn't been a game with enough stationary vision targets to triangulate your position on the whole field, using these points can certainly be helpful in many other ways.

[Ether]

Originally Posted by TroyCDH

Sounds like many people think that wheels on carpet would not benefit from sensors...

That's too much of a generalization of the responses.

If the only purpose of the sensors is to control wheel slip then that might be a fair generalization.

But if the purpose of the sensors is to improve autonomous accuracy then even on carpet - with minimal wheel slip - if you have no feedback of wheel position your accuracy is at the mercy of drivetrain friction and battery voltage and manufacturing tolerances of the motors.

Originally Posted by TroyCDH

...compared to the large amount of time it would take during the build season.

It doesn't take a large amount of time to put the KoP-provided sensor(s) on the wheel(s) and use that feedback in autonomous to improve the accuracy.

[Dave Scheck]

Originally Posted by TroyCDH

Thinking along the same lines, but more general now, what can be done during autonomous mode to keep straight directions actually straight and "X" degree turns really "X" degrees?

As has been mentioned, a gyro or wheel encoders will be your best bet. The tuning of your PID loop will determine how accurate your turn really is.

As far as driving straight goes, you can use those same sensors to make adjustments to your motor speeds to try to maintain a heading.

The tricky part to both of those problems is the experimental tuning of your PID loop(s). (This assumes that you can't get close mathematically). If you need a good C++ PID library, the Simbotics wrote a good one that we've been using for a couple years now. You can download it from their website