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  #1  
Old 04-04-2012, 10:53 AM
mcarames mcarames is offline
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potentiometer

If the angle changes from 0 to 90 degrees which would be the reading of the potetiomenter? Is there any calibration's possibilities?
Thank you.
manuel
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Old 04-12-2012, 06:54 PM
chris@aura chris@aura is offline
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Re: potentiometer

Every potentiometer is slightly different, so it is impossible to say for sure.
Best to put it on the robot, manually turn the mechanism to the locations you want to know the values for, and use the debugger to read them off.

Also be careful that you don't try and measure positions too close to the physical limits of rotation on the potentiometer - the values might not change at all until you've gone maybe 10 degrees in from either end
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Old 04-12-2012, 08:13 PM
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tabor473 tabor473 is offline
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Re: potentiometer

be sure not to raise your arm all the way through the limiter
we did
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Old 04-12-2012, 08:17 PM
jgraber jgraber is offline
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Re: potentiometer

Vex Pot has a physical range of ~270 degrees, and a useful range of ~250 degress.
Robots that need to measure an arm angle of only 90 degrees sometimes run a chain and sprocket from arm axle to pot axle to increase the rotation.
Robots that need 270 degree arm rotation have to gear down the pot to avoid hitting the stops.

Calibration is usually done by using a limit switch at one end of the arm movement to say "whatever the current pot value is, thats the bottom"

Alternately, you can put an additional hand-operated calibration pot on the robot, and compare the arm pot to the cal-pot to decide when to stop.
That lets you tweak the calibration pot as your robot sits on the field, sinking into the foam more or less than it does on the table.
That also lets the calibration pot vibrate to a different position during the match.
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Old 04-13-2012, 10:30 AM
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Team80_Giraffes Team80_Giraffes is offline
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Re: potentiometer

Sometimes a limit switch is not available space-wise.

Calibration is typically needed on these things. It's really a variable resisitor in there and we've seen variations from day to day for some reason. So before every comeptition we re-calibrate and re-download the porgam. It takes no more than 5 minutes once you've done it a few times.

Set the various key values in #define or const int variables at the top of your code and run it through the debugger with a tape measure or the goals and objects themselves. I am sure after unpacking you should recalibrate anyway. Who knows how loose that thing got in transit.

example off the top of my head....
#define TOP_GOAL (2010)
#define MIDDLE_GOAL (1490)
and so on.....

While the range of values is pretty big, you don't want to have your robot trying to fight through a floor limit or a physical stopping point or be short of that goal height. You also don't want floor being 0 as was mentioned above. Play in the middle of the range if possible. The Cortex gives a much wider range than the old PIC ones but it's all relative.
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