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Originally Posted by Charlie675
Our team has an arm driven by two cim motors. The motors are obviously strong enough because the arm can fly up in a fraction of a second (no one dead yet!).
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This high speed indicates the motors are not sufficiently geared down.
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but we need to hold the arm in a constant position to score. when the motors are set to a value that holds them in a specific place, they work for a few seconds and then the arm suddenly drops.
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If you are using Jaguars, they are probably shutting down to prevent damage.
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I assume this is because the motors aren't meant to apply torque without moving
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Yes, and the Jags aren't meant to supply that level of sustained current.
Gear the motors properly. ideally, you want to select a gear ratio that provides about 45 to 90 degrees per second of arm rotation at a motor speed of half its free speed.
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would pulsing the motors help?
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No.
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our whole design is based on this working!
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You have at least 3 options:
1) add a brake to hold the arm in position so you don't have to apply high levels of sustained current
2) add a spring or surgical tubing to support some of the weight of the arm
3) gear the motor properly
Quote:
Originally Posted by ttakashima
Or use the Jaguar/Victor in Brake mode where it shorts the motor and prevents it from back driving
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The "brake" mode you refer to is dynamic braking, not static braking. Without improving the gear ration this is not likely to help.