Favorite Sensors

[Kauaibots2465jm]

Aloha,

Our team, the Kauaibots, has started using the SHARP IR Proximity Sensors that you can buy from Sparkfun.com. They come in various ranges like 3 to 30 cm and 10 to 80 cm. We found that if you bounce the IR beam off of some of the reflective tape provided in the KOP they provide easy, reproducible results. This year we used one to measure the angle of our Frisbee shooter and the height of our climbing hooks. The reflective tape appears to be as important as the sensor.

We have tried to use the accelerometer/gyro boards included with the KOP with poor results for our key desired feature: Field-oriented drive. One of our mentors made our own Inertial Measurement Unit (IMU) circuit board which we used this past year with a lot of success on our field oriented drive with swerve drive. In other words our omni-directional drive robot will go in the direction that the joystick is pushed no matter what the robot's orientation is. This makes our robot much easier to drive. We were encouraged to sell them as a fund raiser for our team so we had a batch made. Now we are looking for about 5 teams to be beta testers. We will provide the board, software, and instruction set for a price of $65 to beta testers. This is below our cost.

There were two main goals for this project. First we wanted something that would work reliably, with yaw rate drift of less than 1 degree/game (which was the part that required the complex algorithms), and secondly we wanted something easy to work with so that our students could do the programming (so it was designed to be programmable with the Arduino IDE, and have also provided source code showing how to access it from the cRIO). We've completed the work and think this could be helpful for other teams.

Here are some of the specs for what we will market as the iNAV9:

iNAV9 Technical Specifications

- Small circuit board (2.5" x 2")
- 3 axis accelerometer and gyro (Invensense MPU-6050)
- On-board Auto-calibration and Digital Motion Processing algorithms - yaw drift of only .15 degree/minute (max of about .5 degrees/per game) means no need to stop/reset in the middle of the match.
- 3-axis magnetometer (Honeywell HMC5883L) (Compass for reading initial alignment before match starts; after match starts the readings are not reliable due to electromagnetic interference). This allows the robot to start out not pointing at the head of the field, and still be usable for field-oriented drive.
- On-board microcontroller (Atmega328) which sends fused yaw/pitch/roll and compass direction to cRio via RS-232 cable. Update rate can be as high as 200Hz, we found 100Hz works great.
- Arduino-compatible and open-source board firmware so anyone can re-program the board using the Arduino IDE.
- RS-232 cable for connection to cRio.
- JST connector for direct connection to 12V unregulated supply from the Power Distribution Board.
- Example code for interfacing to the board from the cRIO via WPI Library.
Instruction set for mounting, checking , calibration and programming.

If you are interested in Beta testing please email us at james@Omaotech.com.