Thread: Hand Ergometer
If you (or anyone else) can point me towards a gear profile calculator (can't find one that does the outer ring) I'll knock up something for a strength test.
Irving Can't seem to open that link. ....Clive
Strength calcs: Calculate for input gear as worst case (Ref: Spur Gears)
Input torque = power/revs = 90/6 = 15Nm, add 50% for safety = 22.5Nm
Tangential force on tooth Ft = 2 * torque/PCD = 2 * 22.5/.01875 = 2400N
Bending stress = K * Ft/(b * m * Y)
K=velocity factor, estimated at 1.03
b = face width = 6mm
m = module = 1.25
Y = Lewis Form Factor = from tables, for 15T 20deg gear = .289 @ tip .49 @ centre of tooth, use .289
stress = 1.03 * 2400/( 6 * 1.25 * .289) = 1140MPa = ~165kPSI
PLA = 500kPSI so should be OK!
Last edited by irving2008; 27-06-2013 at 11:32 AM.
I'd go for a timing belt drive for three reasons:
- It's not unlikely that we might find the ratio needs changing and to change the ratio you only need to change one pulley compared to two gears.
- The torque ripple will also be less with a belt, unless maybe someone wants to have a go at making helical gears!
Last edited by Jonathan; 27-06-2013 at 05:54 PM. Reason: Formatting
2. Not sure what you mean by torque ripple in this context, its an artifact of a motor due to bad pole design aka cogging...
3. Maybe, but plastic gears shouldn't be that noisy at these low speeds...
Epicyclic is elegant solution to problem. Belt drive would need to find a way to route belt past magnetic pole piece each end of magnet carrier, or carrier would need to be vertical or at least at an angle making use of the U-channel mounting more difficult and making the mounting of the loadcell more complex. Also belt drive might increase the footprint.
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