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Hey, Be careful out there...
Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]
Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems. Posted on 2/1/2000 7:41 PM MST In Reply to: More gear questions posted by Justin Stiltner on 2/1/2000 7:09 PM MST: Justin, I can answer your question, but I am a bit afraid to. The Fisher Price gearbox is designed for the motor that it comes with. Specifically the Mabuci motor with a stall torque of about .36 N-m. I am far from convinced that the geartrain is sufficiently overdesigned to take the .65 N-m stall torque of the Johnson Electric motor used by Bosch. Also, there are other considerations. The Johnson Electric motor is much bigger and has a higher free speed. Both of these factors mean that more kinetic energy will be stored in the armature as the motor reaches high speeds. If the output shaft is stopped rapidly (e.g. your arm hits a hard stop or your robot runs into a diamond plate wall ;-), the much larger kinetic energy of the armature can provide very much larger impact loads to the gears in the gearbox. Bottom line: I STRONGLY urge you to reconsider using the drill motors on the Fisher Price gearboxes. But... in my spirit of giving teams the rope needed to hang themselves if they REALLY insist that they know what they are doing... The gear is basically a standard 'full depth,' 16 tooth, 20 degree pressure angle, 32 diametral pitch gear. Note: this is close to the 0.7 module (approx. 36 Diametral Pitch) gear on the drill motor, but is not the right pitch. While Raul tells me from experience that the drill motor pinion is sufficiently hard to 'wear in' a 28 D.P gear, I cannot in good conscience recommend it. Joe J. |
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