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[DPRG] Turning methods

Subject: [DPRG] Turning methods
From: Ed Paradis legomaniac at gmail.com
Date: Wed Jul 30 00:02:13 CDT 2008

Hello everyone!

Tonight at the RBNO I got Tankbot to run a UMBmark test.  It was more
a proof of the robot's ability to navigate to way points than a true
attempt to measure the performance.

One thing Tankbot did incorrectly was that it would occasionally hit a
way point and turn 'the wrong way', inducing a large amount of
slippage error. Essentially it would execute a -270 degree turn
instead of a 90 degree turn.

I know this is a problem in the code, but instead of fixing this
problem, I'd like to jump straight towards what I feel is the heart of
the matter: how to execute turns.

What are the methods that any one has used to execute turns in a list
of way points?  Does anyone look ahead to the next way point and try
to 'get clever' with the turning?  Because of the geometry and general
restrictions of the frame of Tankbot, I'd like to execute beautiful
sweeping turns, instead of coming to a dead halt, scratching and
scraping as it spins in place and racks up huge errors in encoder
counts.

They're really not that huge, because the 'bot can do a pretty good
square, considering no tuning.

For the record, here is the raw data from the test.  Notice that it
performs much much better clockwise than anticlockwise.

clockwise
turn #, X, Y
1, 2, 3
2, -2, 6
3, -5, 10
4, -7, 10
5, -5, 18

anticlockwise
1, 4, 15
2, 3, 26
3, 13, 36
4, 19, 42

The X and Y values are in inches from the starting point.  The square
was 60 inches on each side.  This is rather small for Tankbot, because
it is almost 2.5 feet long!

The anticlockwise numbers are so far off because the robot would
always "do a spin" on the second turn.  It keeps track of its movement
no matter what, but what it is recording begins to deviate quickly
when spinning in place.  Track speed is varying with battery voltage,
although it shouldn't.   This is due to the control system hitting
"max" and letting the PWM sit at 100%.

In other news, the networking issues with the on-board wireless router
have been fixed, and you can log into the robot about 30 seconds after
power on.

Ed

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