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Published byMichael Doyle Modified over 9 years ago
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DEWBOT VII Arm Drive What to do, post-FLR?
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Situation status quo Arm is driven using a 15mm wide HTD5 synchronous belt – 500mm long – this is a “nothing special” belt We shredded two of these belts in playoffs – teeth sheared off Drive motor is 2011 FisherPrice with a 256:1 reduction Banebots 4-stage planetary gearbox delivering: 101 ft lb f torque at stall 1.35 rev/s unloaded speed There is 56/20 (2.8:1) pulley reduction from gearbox to arm The motor is too fast – slowed in software Deux uses an earlier FisherPrice motor. They are not the same. (could account for “jitters” in prime’s arm)
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Objectives Must - Adopt a more durable arm drive mechanism that the current one Desired – Increase the amount of mechanical reduction between gearbox and arm – relax software speed limits
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Constraints The arm pivot is 3.063” (CAD model) from the back of the robot frame – this constrains the diameter of any sprocket, pulley or gear used to drive the arm We should continue to use the FisherPrice motor and Banebots gearbox Gearbox shaft is ½” (keyed) Arm shaft is 3/8” (keyed) There is a need to be able to manually lower the arm with the robot powered- down
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Arm drive options Pulleys – status quo Type 35 steel chain & sprockets Spur gears Helical gears Worm gears
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Pulleys A significantly stronger belt would be needed There is room for a larger driven pulley than currently used Low probability of delivering needed durability Do not pursue
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Type 35 steel chain & sprockets Easy to execute Existing motor mount & tensioner should work Parts either on-hand or easily & inexpensively obtainable A 42:10 (4.2:1) reduction is feasible Well-known ground for the team Probably strong & reliable enough Chain drive will have some slop & nonlinearity – tensioner should limit slop & backlash. Probably fits in budget without compressor change
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Spur Gear Stronger More linear than chain – some backlash Requires precision fixed mount plate for arm pivot pillow blocks & motor 84/15 (5.6:1) reduction possible More costly – compressor change will be needed Parts are obtainable
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Helical Gears Stronger & smoother than spur gears for same contact area Most linear Requires precision fixed mount plate for arm pivot pillow blocks & motor (same as spur) Expensive (but probably in-scope after compressor change) Limited parts availability ~4:1 reduction seems to be limit, based on findings so far.
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Worm Gear Mounting would be challenging Generally cannot be back-driven – a problem for us High reduction possible Basically, doesn’t meet the problem’s needs Do not pursue
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