Sensors

[Donut]

We only really used one sensor other than the camera this year, so I'll list that as well as a few past ones/ones we're looking at:

Gyro: The Analog Devices ADXRS300EB that other people have already mentioned is good, ~$50. The kit ones are just a slower model with the 80 degrees per second, but anything less than 150 degrees per second is (I think) unacceptable, so the 300 degrees per second this sensor can handle is nice. The gyro was used for autonomous turning, but more importantly a very simple piece of code can be written to use it to help make your robot drive straight (we programmed it to work based on the joysticks, so our robot would drive straight during driver operation as well).

Limit Switches: Very cheap (less than $15), can be found at just about any electronics store (Radio Shack sells them in spare parts drawers). These provide nice safety limits for rotating or sliding mechanisms (to make sure you don't break an arm) and if you use them cleverly can be used to tell linear position (we used them in an arm that elevated vertically by having a metal piece slide along a track with multiple limit switches in it, and wrote autonomous code to automatically go to certain switch positions).

Potentiometer: Still pretty cheap (less than $10), available at most electronics stores. Potentiometers provide nice rotational feedback if you want a position rather than just limits. There's an interesting whitepaper on using them in place of encoders as well.

Accelerometer: Can't name a good one as I haven't used them, but most sell for between $30 and $50 (I know analog devices sells a number of them, and one was included in the kit). Accelerometers can be used for inertial navigation, but this would require a nice amount of math for the processor and small errors grow rapidly due to the math (without a high price model, I haven't found a sensor with enough accurate resolution to use for this). They can be used as a sensor for the earth's gravity though, and with a tiny bit of math you can determine the current angle your accelerometer is at with the earth based on the acceleration it reads, so you can make a nice anti-tip function programmed in your robot.

Sonar: Most cost $25-$50, the newer Maxbotix Sonar sensor outperforms most of the others out and only runs around $25 (this is from word of mouth from other sources, I've never used it). The only useful thing sonar can give you is distance of an object in its field of view, so you can use it to avoid walls/find a wall or goal in autonomous. I'm looking into developing a robot-dodging (for offense) and robot-seeking (for defense) autonomous mode with them, but something like this may not be very feasible.

[Ken Leedle]

Slide Potentiometer: These come in various slide lengths and are useful for some applications where linear motion can be measured. We used one in a our control box for controlling the launch angle of the shooter.

IR Photointeruptors: These can either be used as limit switches, rotational encoders or anywhere else you want to see if something is there. We constructed one using a IR led pulsed at 38khz and a IR reciever for sensing if a ball was in our scoop. The effective range of this sensor is between 1 foot and 30 feet depending on the current through the LED.