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Unread 21-07-2014, 17:29
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Re: Baxter Bomb Squad 2014 ~ Nighthawk

Quote:
Originally Posted by Bryce2471 View Post
In some ways that sound like a cool solution, and thinking outside the box. But it also sounds like they're fixing a software problem with hardware.
Regardless of my mixed feelings about this. I'd be very interested to hear if it helped or not.
The Inherent problem with the gearboxes we can afford (weight as well as price) is backlash. The resolution and control should be sufficient to hold a precise position but mopping up deadband is very difficult. Some attempts include raising the gain to the point of oscillation to average out the slop. This small amount of error hasn't been noticeable for driving in teleop but can cause significant drift when driving across the field autonomously.

The cylinder was intended to improve two issues.
1. We currently calibrate the wheel positions by rotating them all straight and running a task to save the voltage from the encoders as the reference values. These are saved to a file and used as the offset from then on. The cylinders would allow more precise mechanical positioning for that.
2. We would use them to ensure home position at the start of the match. notches around the perimeter of the bearing plate could allow accurate re-positioning at 45 deg or 90 deg or other intervals.

The cylinders are not intended to force the module to a position. when extended, the module software would oscillate at low energy around the setpoint until the cylinder is seated in the detent. This would be detected by a cylinder mounted limit switch on each wheel.

Obviously this was not required for autonomous success this year. We are always trying to mop up limitations of the hardware and software for the next time precision is needed.