ADXRS450 Gyro

[slibert]

Originally Posted by viggy96

Unfortunately, we don't have any potentiometers or encoders. We're trying to work with what we have.

If you don't have a potentiometer or an encoder, here are a couple of other approaches that could work, though they're not as straightforward (they're not the simplest thing that could possibly work, though the IR sensor approach below is pretty simple):

- Use an Infrared Proximity Sensor to measure the distance from the base (e.g., the robot chassis) where the sensor is mounted to a point at the end of the arm opposite from the fulcrum. Then, measure the distance from the fulcrum to the point where you are measuring the distance. Using the Pythagorean theorem, use the known distance of one side, the measured distance of another side to derive the angle the arm is at. We used this approach on our shooter in the Aerial Assist Game. We added some retroreflective tape onto the shooter underside and pointed the IR sensor up at it, so we got a good reading that was accurate to 1cm. It worked except for one match in which a Frisbee went into the robot and covered the sensor.

- Use an accelerometer to measure the tilt angle of the arm. Keep in mind that accelerometers measure acceleration due to gravity (which is good in this case, because it will tell you the angle away from horizontal of the accelerometer), as well as acceleration due to linear motion (as when your robot is moving). Accelerometers typically have an error of +/- 1 or 2 degrees. I think this will be a little more complicated than the IR sensor approach described above, but it should be doable if you calibrate the accelerometer and mount it firmly to the arm you are measuring the angle of.

[Sperkowsky]

Hey to all of the people recommending potentiometors I have a question. How do you mount these things. We bought a vex edr one and got it mounted to a 1/2 hex shaft with a 3d printed part and it broke immediately.

[Peter Johnson]

Originally Posted by Sperkowsky

Hey to all of the people recommending potentiometors I have a question. How do you mount these things. We bought a vex edr one and got it mounted to a 1/2 hex shaft with a 3d printed part and it broke immediately.

We turn down the end of the shaft to 1/4", then mount the pot to a plate, use two standoffs to offset it from the end of the shaft, and then use a 1/4"-1/4" flexible shaft coupler to connect the pot and the shaft. Note this requires good mechanical capture of the shaft and the ability to turn down the end. I've also seen teams use elastic tubing with zip ties as a cheaper flexible shaft coupler.