Re: Vex Versaplanetary gearbox repair
 

We grooved it to leave the shoulder while leaving a track to make it want to slide back into place if it move. It's more or less a measure to try and help realign it, if it slips.

Re: Vex Versaplanetary gearbox repair
 

Our machine this year had the same mechanism with a lead screw opening/closing our forklift arms and the shaft popped out match after match.

Our solution was to drill a hole in the output shaft and insert a roll pin. This prevented the snap ring from ever coming out. I don't think this gearbox was meant for the linear forces we were applying and will know to avoid this design in the future.

Re: Vex Versaplanetary gearbox repair
 

Could you show us a picture of this solution in curious how it looks.

Re: Vex Versaplanetary gearbox repair
 

I'm guessing they assembled the output side of the VP, then drilled a hole next to the retaining ring, on the side opposite of the bearing. Then put the roll pin in. Means you'd have to take the pin out to pull the shaft. Also, the clearances there are pretty tight. I think that would take up some/all of the axial play of the gears inside of the gearbox.

Re: Vex Versaplanetary gearbox repair
 

Kevin is right. I would take a picture, but taking apart that gearbox at this point would be a serious commitment (additional roll pin was used to affix our lead screw to the output shaft).

So if the shaft were to ever be stressed in the same way, the snap ring cannot pop off without breaking the roll pin. The snap ring is effectively sandwiched between the bearing and the roll pin.

Re: Vex Versaplanetary gearbox repair
 

O so you put the pin in the 1-2 mm gap between the bearings?

Re: Vex Versaplanetary gearbox repair
 

Pin goes right next to the retaining ring, on the side farther from the bearings, closer to the splined end. The ring will be trapped between the pin and the inside bearing. The pin will be between the ring and the last planet carrier plate.

Re: Vex Versaplanetary gearbox repair
 

You could try using a split "love joy jaw" style shaft coupling instead of a solid one. That way the coupling would separate a bit instead of transmitting tensile loads to the planetary output shaft.

We used one to connect the leadscrew in our spring pretension adjustment assembly to a versaplanetary gearbox last year and didn't have any problems with the snap ring.

Re: Vex Versaplanetary gearbox repair
 

What's the load on the output shaft? If one issue is space between the snap ring and the ring gear, once you've fixed the groove, remove the wave spring between the bearings. This gives a little more room to shim bearings away from the ring gear. Ive also found efficiency gains from removing the wave spring. With my teams use of vex planetaries, some times issues come from the pins in the gear Assembly portuding too far and then when the gearbox is clamped together, these pins lock into the other ring plate and the planetary seizes. Good to check each gear assembly.

Re: Vex Versaplanetary gearbox repair
 

Very interesting discussion. Thanks to all who contributed.

My experience with the VPs has been almost* uniformly positive. With 11 on Overclocked's robot we could be happier. But then I realized that loading condition in every case was primarily radial, not axial. I will keep this in mind when/if we ever decide that we need to have a VP carry an axial load.

Joe J.


*the only issue being that I think we got some early versions that had some quality control problems that made assembly somewhat difficult but once assembled they were fine.

Re: Vex Versaplanetary gearbox repair
 

So as an update:
We took the lead screws off and opened the gearboxes, I grooved the snap ring valley to be a little deeper and to have a some shaved down above it, as to give it a position to easily move back into if it ever moved.

We also moved the coupler all the way to the top right under the bearing in order to have it pull less on the output shaft.

Then we moved the top plate down a bit and made it apply pressure downward on the lead screw as well as have it have less of a gap of possibly moving up and down.

We ran some initial tests and had issues but then realized the coupler was to tight or the lead screw nut was going to far down and getting caught on the bottom which was then fixed.

At the demo we had today we ran it fast and slow with lots of strain and it didn't show any signs of failure even under the loads it had at competition minus the noodle, which wouldn't have been the tipping point in weight.