This has been designed to take a single CIM motor’s peak torque output with an overall reduction of (50/14 * 50/14 * 50/14) or a totally reduction of 45.5 times. You could potentially apply more torque before your 40 A breakers trip if something down the line isn’t geared to peak out at 40 Amps.Ī roughly equivalent pinion in the FIRST kit drive train has a face with of 0.809 inches.The impact loading on the gears in your drive train isn’t too substantial.Run time of a FIRST drive train can typically be measured in hours (relatively short).I think you have a few factors to consider: I have this showing 38,266 PSI, or a factor of safety of 1.04 (at a megar 40,000 PSI) Lewis Form Factor (Y) for a 14.5 degree PA gear = 0.223įorce on Tooth (Wt) = 53.25 /. Using this number, and the standard AGMA gear equation After a 45:12 ratio, this becomes about 53.25 in-lbs. I’ll assume that you’ll design the max torque to be right around 40 Amps, which I calced out to be about 14 in-lbs from a pair of CIMs. Joe seems to have a bit more confidence, from experience in this working well than I do, I want to take another swing just to see what the numbers show.įirst step I think is to be a bit more conservative with the torque these gears should actually see. I confess that my ‘edit’ about the two CIMs working on different teeth had poor logic - they’re running on different teeth on the 45 tooth gear, but presumably the 13 tooth gear will have one contact point. I won’t make any promises, but assuming a standard drive train setup with slipping tires right around stall current, I’d say this gear, as is, is on on the edge. 40kpsi is pretty conservative for a heat-treated gear, though I’ve seen some of the Martin stuff out of Mcmaster run at 30kspi out of the box.Ĭalcs attached (EDIT: for 20 degrees, its what I had handy) for reference. (Perhaps even only 40% of the torque I used.)Ī few things you can do to reduce stress on the gear:Īlso note, a quality gear bought from some place like Stock Drive Products may not be your average strength steel. Is it possible for this geartrain to actually ‘Lock Up’? Are you doing anything fancy that could cause locking or braking down the line in your drivetrain? If not, and your gear the drivetrain properly to ensure you don’t trip breakers while pushing up against a wall, then the true peak torque on these gears will be less than what I used. (Estimated Stress: 58 kpsi for 20 degree Pressure Angle. This admittedly conservative equation is showing 0.68 factor of safety, assuming 40 kpsi yield stress on your ‘common cold rolled steel’. Hence, the applied force is 73.7 in lbs / 0.325 lbs or 226.8 lbs.Ī quick Lewis Bending Equation I’m showing says this is not fairing too well. This 13 tooth gear has a radius of (13/20) / 2, or 0.325 inches. They are applying stress on different teeth. Stall Torque on Two Motors Combined = 39.3 in-lbs. For now, let’s say the 13 tooth gear is made out of common cold rolled steel.Īssuming a worst case scenario (motors reach stall torque/current), will the 13 tooth gear be able to withstand the force? These gears are 20 pitch, 14.5 degree pressure angle, and 3/8" face width. On the same shaft as the 45 tooth gear is a 13 tooth gear. 2 small CIMs, with a 12 tooth gear on each that mate with a single 45 tooth gear on a separate shaft.
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