Sharon Youth Robotics Association
Eagle OverDrive
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Sharon Youth Robotics Association Eagle OverDrive |
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The Eagle OverDrive - time to Go Straight! As most FLL teams, the Eagle Unlimited team had been challenged by the difficulty in convincing robots to go straight. Patrick, one of our team members, had done a Science Fair project that concluded that matching the motors and using wheels bound together with a fixed axle both helped to keep the robot going straight (the axle, of course, kept it from turning well). The dual differential drive design was tested by our team, but rejected for erratic behavior that seemed to be caused by a gear train that was too complex. The limited slip differential in the "Building LEGO Robots for FLL" guide (page 5-77) put out by the Minnesota FIRST LEGO League (a top quality organization!) was considered by our team, but that would not force the robot to go straight, only straighter. A locking differential was considered as well (page 5-78), but rejected because it would use the third motor output to control it, and that was usually needed by some FLL competition module. A NEW development is the design of the Eagle OverDrive, using a clutch gear to improve the straight tracking of a differential drive CoreBot. Using a clutch gear and an axle to link the left and right side gear trains, they will track together while in forward, as with a fixed axle connection. While differential turning, the opposing forces will exceed the torque capacity of the clutch gear, and allow the gear trains to turn in opposite directions without any linkage. The clutch gear will eventually wear out, but improved performance results in straight tracking without other aids. The Eagle OverDrive acts as if the axle actual bound the wheels together, so that they must turn at the same rate, discouraging turns. As the clutch slips when the motors turn in opposite directions, turns are allowed, where a bound axle would always resist turning. Note: if your gear-train has low torque (geared for greater speed), this drive may not function properly. There must be enough torque difference to slip the clutch gear. Note: some line-following turning techniques (free-wheeling on one side while powering the other) may also result in too little torque to slip the clutch gear. Note: you can use a clutch gear on both sides of the drive train, but the performance will not necessarily match well, as the clutch gears have a fairly wide torque range. We have found it to be just as well to use one clutch gear and a matching 24 tooth spur gear (same tooth count and diameter). We feel that this drive innovation will be of benefit to the FLL community, and we welcome all to make use of it, identified as the Eagle OverDrive.
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Sharon Team Unlimited FTC website Last modified: 07/26/08 All Rights Reserved © 2007 by Team Unlimited |
