[KenWittlief]

In the past the teams I have mentored used the ADXRSxxx family of yaw rate sensors for two functions: to close the loop on steering with a PID feedback control system, and we integrated the turn rate to get a relative compass heading.

For both applications the yaw rate sensor works very well. We could spin the robot 360 degrees left, then 360 right and it came back to 0 degrees so well that we could not measure any error.

The two axis accelerometer in the KOP this year is also made by Analog Devices, its the same family of products. I looked into the part used, the ADXL311. This is an excellent device. Analog Devices literally sells them by the millions.

Maybe my last post gave the impression that all you have to do is hook up the wires and add some numbers together. OK, I admit that was over simplifying the entire design - that was only the starting point.

Ive read the data sheet for the ADXL311. Looks like this would be a good topic for a white paper. The device has a user selectable bandwidth, controlled by parts that are soldered on the board. I dont know the default bandwidth as the board is shipped in the KOP, but it would not be hard to set this device up to get a 10 or 20Hz bandwidth.

Bandwidth is the indication of what the device will let through to its outputs, and its also related to the noise-floor of the output signal. The lower the bandwidth you use, the less noise the sensor will have.

Im afraid I cannot give all the details of everything you would need to do to use these devices on your robot in the character limit of this post. Even if I could, that is part of what this program is all about - students and mentors on a team looking at the data sheet for the part, and the application notes that Analog Devices has on their website, and refining the response of the sensor, and the code that integrates it to get the results you want. I cant do that for you over the CD forum.

One key to success with these devices is getting the bandwidth set so that it integrates the acceleration for you between the times the uC reads the output signal. Keep in mind that your robot has a lot of mass, its not possible for your robot to be jerking around on the floor jumping from +2g to -2g to +2 gs at 5mS intervals. The force required to do that would be off the scale. (BTW: Jerk is accelerated acceleration). If you have the sensor solidly attached to a heavy part of your robot frame, the signal you get from it will be fairly smooth and noise (vibration) free.

These devices are excellent for measuring tilt and acceleration. They are also very good for calculating velocity. As Watson pointed out, going one integration further to get distance is pushing it somewhat, but all things considered, having more sensors on your robot is better than having no sensors.