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Eddie Wheel Encoder Error? — Parallax Forums

Eddie Wheel Encoder Error?

TLCTLC Posts: 74
edited 2012-04-05 16:19 in Robotics
This is somewhat related to my "Eddie and RDS4" post but I've removed RDS for now to make things more generic to Eddie.

When I use the serial terminal to issue "turn b4 10" which (I believe) should be a 180 degree turn Eddie stops short. I have to enter "turn BC 10" which equates to 188 degrees but the turn is consistent.

After the turn I request "head" and receive B2, 178 degrees.

To get a 90 degree turn I have to specify hex 62 which is 98 degrees, but consistent.

Has anyone else seen this?

tlc

Comments

  • David CarrierDavid Carrier Posts: 294
    edited 2012-04-05 16:19
    When the Eddie stops, try lifting each side to see if the wheel spins a little more. It may be that it isn't turning all the way because it is slowing down too much as it approaches the point where it needs to stop. If this is the case, the motors will also vibrate a little, because they are running at a power level that is too low to break the static friction, and they will vibrate at the PWM frequency.

    Some Eddies have more friction in their motors than others, and different floor surfaces and load weights will also effect how fast or slow a slow speed is. The Eddie firmware can be tuned to be more aggressive when trying to reach an end point. Look for the following line in the firmware, and decrease the number '16' to make your Eddie try harder to go the last inch or two when it is traveling:

    Kp long Motors#MAX_ON_TIME / 16 ' Proportional error feedback gain

    — David Carrier
    Parallax Inc.
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