We are using the 326:1 P60s, to articulate our arm, being driven by an RS395 and the other driven by a FisherPrice motor
(For all you critics out there, this is not for power reasons but because we are limited to the number of BaneBot motors we can use - an RS395 will replace the FP and run the arm very happily). We have not experienced any failures yet but on both we have begun seeing signs
of the gearboxes failing and although we have spares, we elected to try and "bulletproof" them rather than risk a breakdown. I am pretty confident we have mitigated the major modes
of failure that we have been seeing from teams using these gearboxes.
The four "banes"
of the banebot P60 include:
1) Rounding
out of the output shaft and/or drive socket on the output carrier.
2) Bearing failure due to defective bearings (ungreased) and overloading the output shaft.
3) The roll pins acting against the flat sections
of the ring gear that hold the rign gear torsionally captive galling, snapping and rounding
out.
4) Binding
of the gear train due to axial bending
of the gearbox.
In order to rectify these we have:
1) Machined a new one-piece output shaft and final carrier from Stressproof steel to eliminate the interface between the output shaft and carrier.
2) Machined a new endplate with larger 1/4-20 mounting holes which houses larger (to accommodate the 1/2" output shaft) high quality NTN bearings spaced further apart to reduce loading caused by sideloads on the output shaft.
3) Bored sockets in the new endplate and stock ring gear to internally lock the ring gear to the end plate with 6 roll pins.
4) Replaced the non-graded 6-32 bolts which hold the assembly together with high strength socket head cap screws.
So far the end result is very promising. Obviously we have not been able to test it on our robot but we are hopeful this will eliminate the weak spots previously experienced with these gearboxes. All
of these parts were made with a bench-top milling machine and 9x11 lathe and are well within the capabilities
of even the most basic machine shops. The shafts for the planet gears on the final carrier are made from 1/8" hardened steel dowel pins. The output shaft is made
of Stressproof Steel(
http://www.niagaralasalle.com/product-stressproof.html) which is stronger than chromoly grades but machines like a dream (one
of my favorite metals!). The bearings are 1/2" ID 1-1/8" OD, 1/4" W double sealed NTN bearings. The end plate/bearing block is just regular 6061-T6. The pins are 3/32" heavy wall roll pins.
You all have made me think about this in a new way - which I appreciate. - aaeamdar [more] 
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