In our robot drivetrain we have a set of 20 DP (3/8" face width) gears with a 2-speed shifting mechanism. The gears (high grade steel, not hardened) are bored and reamed to .750" and have 4 semicircle cutouts90 degrees apart. Each semicircle is approximately .125" deep. The gears ride on a stainless steel shaft with 2 sets of holes 90 degrees apart around the shaft and the center of the shaft bored out approximately 1/2". Ball bearings ride in each hole on the shaft and a plunger is pulled back and forth inside the shaft. To engage a particular speed, the plunger is pulled into alignment with one set of holes and ball bearings (1/4" dia stainless steel, precision ground) are pushed out to mesh with the semicircles cut into the bore of the gear. The other gear that is not engaged free rotates on the shaft.
The problem we have been having is that on one of the gearboxes something has caused wear on the shaft which leads to the non-engaged gear unable to freely rotate. This leads to the equivalent of both speeds being engaged at the same time (not good) and effectively stalls the motor. We have taken apart the gearbox and replaced the shaft, gears, and bearings with spares, and made sure that both the gears and the shaft are clean and lightly lubricated. The gearbox is enclosed so there is no foreign material that could be getting into the gearboxes. The wear seems to be build up of metal from the gears onto the shaft. This is not a flaw in gearbox design, as the system worked for many hours of competition and testing earlier in the season. In addition, one gearbox has never had this problem, and the other gearbox has done this twice in two days.
I'd appreciate help from anyone who might have an idea as to why this wear is ocurring and what I might be able to do to prevent this from happening. We have a limited number of shafts and they are rather difficult to machine and so we don't want this happening if we can avoid it.
You can see the shaft, ball bearings, and gears in
Thanks in advance, Michael Los Altos High School Robotics Team "Eagle Strike" Los Altos, CA