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Unread 12-03-2008, 00:10
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Kevin Watson Kevin Watson is offline
La Caņada High School
FRC #2429
Team Role: Mentor
 
Join Date: Jan 2002
Rookie Year: 2001
Location: La Caņada, California
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Re: Gyro Repeatability, Expected Drift ?

Quote:
Originally Posted by eugenebrooks View Post
Kevin's code implements a deadband. Although this is just fine
for using it to measure a turn, it is not so good for using the gyro
as a compass.

Using the gyro as a compass requires you to be entirely linear
with no deadband, and to carefully average the "no turn" output
(noise helps you here) and subtract the value using fixed binary
point arithmetic. Second order accurate time integration is also
a good idea in this case.

A drift of a couple of tenths of a degree during the 15 second
autonomous mode is achievable, but the drift is sensitive to
temperature and you either need to recalibrate, or compensate,
for that. What we do is check the drift now and then, and then
recompute the required average when the drift has picked up
due to temperature change.


Eugene
Yes, there is a deadband, but it only comes into play if the gyro's output is within a few DN of the bias point. As long as your 'bot rotates at a rate above a few DN, every sample is included in the integration (I would argue that every FRC 'bot rotates above this rate, which is less than a degree per second). So, unless I'm missing something (which is entirely possible ), I don't see how it's a problem.

-Kevin
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Kevin Watson
Engineer at stealth-mode startup
http://kevin.org