Ultraplanetary Failure

Our team is using REV Ultraplanetary gearboxes on our first comp swerve. Recently during testing one gearbox got very stiff, incresing in resistance as one turned the steering motor. Turns out the gearbox had failed, a inner output faceplate screw had backed out into the thin sheet metal retaining plate for the second stage gear stack.

The screw ended up doing major damage to the metal sheet, basically shearing half a rotation around the sun gear. As can be seen in the photo below, the loading bent the tabs on the plate leading to it shifting around a little inside the gearbox, pulling the plastic stick-out tabs off the injection moulded housing.

^ next to an untouched gear slice

This gearbox slice is mostly a write-off, but I didn’t make this post to complain. The gearbox was not under large loads and supported at both the face mounting and a wrap-around bracked at the motor end. On the end of the gearbox is the steering pulley, which is bolted using the 5-bolt pattern on the output faceplate, snugly against the gearbox. While this pulley is only supported at one end I don’t think its much in the way of sideways loading. (CAD pictured below to show mounting)

The question is, has anyone else experienced this failure or know why it could have happened to prevent it in the future? My guess is that some amount of vibration caused the screw to back out a little, then the sharp countersunk profile led to it grabbing the metal sheet and pulling out further. In the future we may try to locktite these screws before use, as they are now essential drivetrain components. We have the option in the design to very easily swap for VP gearboxes, as the mounting holes and bracket are also there from a previous iteration that used it, but this would be heavier and more expensive. Not to mention that we’ve had problems with the clamping collar slipping on NEO 550 shafts.

Important clarification: the purpose of this post is to alert teams to a COTS part failure mode to encourage prevention or resolution. This post is not a go at REV or their products, as a team we are generally quite happy with the quality and performance of their gearboxes and motors likewise.


It looks like you were running the original, discontinued UltraPlanetary output plate and not the newer v2 plate. Click the third picture of each and you’ll see the difference. I’d bet the difference is bound to solve it, though [email protected] may be able to be more specific than an outsider like me. :slight_smile:


You may be able to tack the bolts in with a TIG welder (no filler) and grind the plate flat. Obviously you’re not taking the bolts out if you do that, but that’s what I’ve done on high reduction VersaPlanatary stages to keep the pins from backing out and creating this exact failure mode.


Thank you for this thread. It is very helpful. Also, thank you to Billfred for your explanation and possible fix. We have had this exact problem happen with our Vex VP gearboxes. We just began trying UP and MP because of it (and a few other reasons). Knowing what to look out for helps a lot.

1 Like

Yep probably the older ones, we bought these gearboxes mid 2020 I think. Just buying new ones isn’t really an option, as we live in Australia and don’t have the budget to buy and ship these at the moment.

Might try adding a little epoxy to the other undamaged gearboxes, to prevent failure.

Wouldn’t loctite blue or red be less permanent but work just as well?

1 Like

Maybe, I was just going to use the whatever we had lying around.


@VaSIMR200 as @Billfred said, you have v1 outputs on those gearboxes. We found that the tolerance for the depth of the countersink was not great when tied with the very short length of those screws, which is why we changed the output block in v2. I would appreciate it if you could send details of this to [email protected] and we can see how we can help your robot get back on its wheels.


Thanks for the confirmation of verison difference in regards to output slice, we’ll look at new ones in the future. Also thanks for the offer of support, but we do have a spare and shipping to Australia can be problematic so I’ll hold off on the ticket unless more failures occur.

This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.