Failing NEO 550 in VersaPlanetary Gearboxes

Our team runs two NEO 550s in VPs, one for our intake and one for our colour wheel mechanism. Both experience the issue of the VP motor shaft clamp loosening from the motor shaft and causing slight damage to the shaft, presumably as it free spins. The damage got so bad on the intake that the motor had to be swapped out.

We have tried tightening the crib screw alot, locktight and aryldite epoxy but it always finds its way loose in anywhere from 3-30 minutes of runtime (best results with epoxy). This happens in both high load (intake) and low load (colour mech) use cases.

Yes, the shaft collar clamp is the correct one for 550 motors and yes we have tried multiple motors and collar clamps. Has anyone got a resolution for this issue?

We had this same issue during competition in 2020, and never found a quick fix. To help, we checked before every match, and tightened as necessary. After our first comp, we were planning to redesign plates to use UltraPlanetaries and their pressfit pinion(which we had no issue with). This never happened, since other things took priority.

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Do not do this.

The keyway is meant for CIM style motors. The keyway should only be used for this.

As for the original post, are you making sure that the coupling is oriented correctly in the VP coupler?
(Check Page 14)

If the slot in the coupling isn’t perpendicular with set screw, it doesn’t really clamp down on the shaft and will slip.

It also suggests adding Loctite to the set screw.

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What @orangemoore said. The groove in the little spacer is not supposed to be under the set screw, it’s supposed to be 90 degrees to it. The set screw is supposed to squeeze that spacer onto the shaft. It isn’t supposed to touch the inner shaft directly. (It wouldn’t grip well even if it could, and would likely mar the shaft.)

This is one reason why press-on couplers are more reliable. Last year Vex started offering press-on couplings for 775 motors. I wonder if they’ll do the same for 550 motors.

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Oop yeah I was incorrect on that. Theres no shaft key with the 550’s.

Yes, the slot is definately 90 degrees to the grub screw. We’ve literally dipped the entire assembly in locktite without too much improvement

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Can you post a picture or a video of how you have it set up? We’ve never had a failure like you mentioned in all the years we’ve use versaplanetaries and we adopted them when they first came out. It might be easier to see a fault if we have eyes on the problem, or identify a strange situation where they just aren’t working for you.

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Not only that, but no shaft other than CIM shafts use the shaft key with a VersaPlanetary, and the only shaft key you should use with the VP is the one that comes in the hardware kit. There is no longer or shorter shaft key available.

Not directly relevant to your issue, but loctite used in this manner won’t do much at all. You’d have better luck with cyanoacrylate (which isn’t saying much). Loctite is designed to cure in the absence of air found at the interface of a screw and mating thread. It’s also essentially useless for something like locking the rotation of a shaft to a collar, as the surface area is quite small, and the forces that end up actually applied are a fraction of those found in tightened screw threads due to geometric relationships (applying a point load to the side of a cylinder).

I will also add, you have to make absolutely certain that no grease from your gearbox assembly process makes it into your coupler or onto your motor shaft during handling and assembly. Also, when torquing the set screw, we typically use a high quality hex key with the short arm in the screw, fingers on the long arm, and torque until the hex key is considerably bending. I tell my students, right before when you think you’re going to break something or strip it out, that’s when it’s tight enough. I’ve never had a student overdo it in these. I usually end up teaching them to torque even a little beyond what they originally felt comfortable with. Anyhow, we have only very rarely had a failure as described in this thread, and we’ve used quite a number of these.

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I’ll grab a photo this weekend when we meet.

Definately no grease on the shaft or clamp.

It’s very tight, we’ve broken an allen wrench in the process (used a slightly oversized allen wrench, tapped it into the set screw and tightened until it snapped. Would not recommend). When not commiting machinist sins the grub screw was set definately tight enough, tighter just caused more damage to the NEO 550 shaft when it inevitable got loose again.

Something about this sounds very not right.

Indeed, thus I am here consulting the CD knowledge base.

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It is likely to be permanent, but loctite bearing retaining compound applied to both the motor/collar and collar/hub. I would try either 620 or 638. These are somewhat different for the thread locker varieties.

We’ve been running NEO550s with VP gearboxes as our swerve steering motors as well as for our turret rotation motor for our 2020/2021 robot with no issues. We did a bunch of driving before our 2020 competition (probably the most practice driving we have ever done prior to our first competition), completed our 2020 comp, and have done a bunch of driving since (including the at home challenges) with no issues with any of these gearboxes.

I am not sure what we have done “right” or what you have done “wrong” to get such different results. I know you have stated that you have checked many of these things, but the most likely scenarios I can think of are:

  1. Wrong shaft collar: I know that there are several different size shaft collars for different size shafts in the VP kit. Some of them are hard to distinguish from the others. In particular, the collar for the RS-550 and the AM-9015 are very similar in size and you might be able to assemble the gearbox with the wrong collar. They look a little different, so you should be able to confirm visually, that you have the right collar. In some cases, I believe that if you select the wrong size collar, the gap in the collar will close before clamping tightly on the shaft. So, you may also want to look and see if you can still see a small gap in the collar after tightening the set screw. Also, can you look at the collar and see if you see any witness marks on the OD of the collar that would indicate that the collar was rotating relative to the splined gearbox coupler (hub)? If the collar was rotating inside the coupler, then you may have the wrong collar.

  2. Undersized shaft: You may want to measure the shaft diameter of the motor using a micrometer and make sure that the shaft size is correct for a 550 shaft. This seems like a longshot, but there could be a quality control problem with the motor that we have not uncovered before.

  3. Thermal expansion: I am not 100% sure what materials each of the pieces are made from. I suspect the motor shaft is steel. If the coupler is aluminum, then it is possible that if it gets hot, the auminum will expand more than the steel. This would be worst if the heat was coming from the gearbox instead of the motor. I have never seen this occur, but if the couper were rubbing on the motor plate (friction) or if the gearbox itself was not correctly lubricated and was heating up, the coupler could be heating up while the shaft is relatively cool resulting in the fit between the collar and the shaft loosening up. Can you tell if anything is getting hot or see any indications of rubbing in the parts involved?

  4. Loosening set screw: Can you mark the set screw in such a way to see if it is backing out? Seems unlikely, but it could explain what you are experiencing.

Good luck. I hope you find what’s causing this and can get it corrected. Sometimes these issues are hard to solve.

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I’m 98% sure that this is the issue. The 550 collar should be a snug fit on the shaft with no pressure from the set screw. It should need to be aligned properly to fit on with a little bit of effort to slide it on, then it will clamp tight when the set screw is tightened. If I remember right, you can turn the motor so the shaft is pointing toward the floor and the collar will stay on when you have the right one.

Here is a photo of the shaft. It is clear that some element of the collar has dug grooves into the shaft, this one was re-assembled a few times. The collar is smooth, this motor saw two collars with the same results. Epoxy and locktite were used on sepetate occasions.

Despite doing alot of high power work at the intake this shouldn’t happen. The collar is definately the one for 550 motors, it is a nice snug fit and is labeled as so on the vex documentation. We swapped it back to a 775pro for next week’s competiton as we have the weight but these are pieces of equipment we would like to use into the future.

Any ideas with this new info?

Sadly no… I can’t see a way that this should be happening without something being noticeably wrong. I guess the only other problem could be in how the set screw and collar align, but it sounds like you are confident in that arrangement.

If you want to show one more picture, just to verify, I’d love to see a shot or two that show the motor with the plate, collar, and hub on it. But I’m grasping at this point.

Ill see what I can get tomorrow (australian time, it’s 11:35 at night right now).

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I will say if it happens once, it will happen again. That motor is done. The outer diameter of it’s shaft has been reduced.

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