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Unread 11-01-2008, 23:08
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EricS-Team180 EricS-Team180 is offline
SPAM, the lunchmeat of superheroes!
AKA: Eric Schreffler
FRC #0180 (SPAM)
Team Role: Engineer
 
Join Date: Apr 2002
Rookie Year: 2001
Location: Stuart, Florida
Posts: 561
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Re: Gyroscope saturation?

Right On Kaszeta.

The first year we used an AnalogDevices 300deg/sec yaw rate sensor was in 2004. We had a holonomic chassis that year. At first, the chassis was not easy to drive. The wheels were small and on irregular surfaces, they would not all be in contact with the floor. This tended to make the 'bot spin and drift while trying to drive straight. The first thing we did was to use the yaw rate signal to add counter spin to our drive train, when the driver was requesting straight motion without rotation. (...just a simple proportional control...a gain times the sensed yaw rate )
Next, we used a trapazoidal integration to get orientation from yaw rate. That was in our drive code that we wrote to allow the chassis to move in the direction the driver moved the stick, regardless of which way the 'bot was oriented. The kicker here, is that we did all this in the 38hz main loop. ...really slow when I now read that Kevin Watson's talking about sampling rates over 1000hz

What we found was that our orientation was off about 1.5deg for each full rotation of the 'bot. We had a reset button on the OI that year. If it got too funky for the driver, he set the 'bot facing straight up-field and reset the orientation.

Now, we do see the sensor value drift around the neutral point. So we just put a small deadband around 0 yaw rate - say +/-5 counts and forget about the small loss in sensitivity.

The yaw rate sensor is your friend. Get a good zero yaw rate reading while in disabled mode, and for the next 2:15, have some fun!
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Last edited by EricS-Team180 : 11-01-2008 at 23:19.