PSA: Falcon Failure Mode

We discovered an unfortunate failure with our Falcon motors today. One of our motors had completely locked up and would not spin even under hand power. When we opened up the case, we found that the shaft retaining screws had all loosened. One of them was so loose that the head of the screw was rubbing against the forward shaft bearing, and that friction sheared off the screw head and caused the bearing to self-destruct. The shrapnel then lodged itself in the rotor and locked the motor. When we disassembled our other Falcons we found that the same problem of the screws loosening was starting to happen; luckily we caught it in time before they also committed suicide. We did not replace the shafts on these motors; they have the factory shafts. We talked to another local team 1577 who is also using Falcons this year and found that they had the same exact problem: one of their motors broke completely and the others showed signs of this process beginning.

Here you can see the rotor with the sheared screw (we removed the other screws):


 
And here you can see the face plate of the broken motor compared to one that did not break yet. The loose screw seems to have gone through the bearing and rubbed the finish off of the face plate.

We contacted Vex support about the issue and they suggested removing all of the screws from the motors and securing them with loctite. Apparently this is also the solution 1577 used and they haven’t seen the problem come back. We are going to do this to all of our Falcons tomorrow. I highly suggest that any teams using Falcons this year take the time to make this repair so that they don’t end up with a $140 paperweight like we have.

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Did Vex recommend applying Loctite to factor installed shaft screws or only when changing shafts? Also, did they say what color Loctite?

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Yes, our shafts were all factory installed and Vex still suggested taking them apart to add loctite.

They didn’t specify what color to use, but I imagine something like a medium-strength thread locker should do the job. I’m not fluent in loctite flavors to be able to be more specific.

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Am I nuts or is this something Vex should be making a major announcement about? This sounds like a huge problem.
BTW, we love your calculator. Using it tonight.

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How much driving did you guys do to reach this failure point?

I can’t give you an exact number, but we’ve had this robot assembled for a bit more than a week now. It does have a few driver practice hours on it but most of that time was taken testing new mechanisms and tuning programming.

Edit: Certainly still in the “wear-in” stage of the motor’s life. They should not reasonably be seeing mechanical failures at this point

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Unfortunately, the same thing happened to our 3/4 Falcons on our drivetrain. We drove for about 10-15 hours.

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@Jon_Jack @DRow this is a pretty common failure mode several teams I’ve talked to have seen now. Has a communication to your customers gone out? Will one?

If we experience this issue, can we expect a replacement able to ship immediately?

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Would love to take the shaft off and fix this, too bad all our pinions were pressed fit on!

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After this failure, we re-installed all of our falcon shafts. Even in factory assembled shafts fresh out of the box, the screws were loose.
We re-installed the shafts using 243 loctite glue, after cleaning the screws with alcohol (cleaning the grease leftovers is mandatory when using loctite).

Honestly the mechanical design is quite off, attaching a shaft with screws is weird - you compromise concentricity and risk the shaft becoming loose.

Sadly, this cost us 140$ so far, and I hope vex will offer a solution to this issue.

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A puller to remove them is fairly easy to make. A slot the size of the spacers in a piece of CRS box tubing to go behind the gear with a threaded hole opposite it to push on a screw in the shaft. I can post a drawing and pictures of ours on Thursday night.
Kind of like this though.
image

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This is part of that discussion about there should be a deadline when vendors release a new product. We didn’t order any this year, because we don’t have the funds to drop on a part that was untested. We are building with some neos that teams tested last year.

This is not at all a jab at teams that pre-ordered. I hope you can get refunded for destroyed motors so far and have a backup for comps.

Between long shipping and untested parts, teams are the ones that take the hit when new product is released in the winter.

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teams are the ones that take the hit when new product is released in the winter

** Teams that decide to bite take the hit

Not everyone saw the situation and said “yep, marginal benefit worth risking robot working at all for”

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Yeah, that was discussed pretty in depth too. Do you risk a product failing, or do you risk it working and someone having an edge over you? Not a fun decision that teams have to make with late product releases.

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@AriMB’s motor is not a $140 paper weight. We’re RMA-ing the motor and they’ll get a new one.

This is the first I’ve heard of an issue with your motors. Please email prosupport@vex.com and we can get the RMA process moving. Unfortunately, we cannot issue RMAs through a CD thread, so if you have a problem like this, emailing (or calling if you prefer) is the best route to avoid having a $140 paper weight.

As I mentioned above, contacting us is the best way to not only starting the RMA process, but also making us aware of issues. Yes, several of us monitor CD - however, sometimes issues that are buried deep in threads can get lost in the noise, especially during the season. Threads titled like this one definitely catch our attention.

We have only been hearing about issues related to the shaft screws for a week or so. We’ve been looking into this and determining what, if any, kind of messaging needs to go out.

Yes, we do have a limited amount of motors in reserve for RMA purposes. Also keep in mind that not every instance of this results in a catastrophic failure. In most cases, this problem has been solved by sending the customer new screws and/or front end cap. Again, contact us and we can determine the best course of action (replacement parts or replacing the entire motor).

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Something about the Falcon is a little concerning to me. design decisions like this as well as the arguably misleading motor data (having much more power than other FRC motors but not at currents that you can get on an FRC robot) make me worry about how these motors are going to stand in FRC. I know that there are definitely some great upsides to their design (integrated motor controller what now?) but stuff like this is why many teams wait a year to watch products get released and tested in a competition environment. I’d love to play with some falcons next year, but for the time being only time will tell how robust these motors are.

P.S. always been a fan of Vex stuff, just a little skeptical of the Falcon for now. Good luck and best wishes to the teams using them!

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As a team that is using falcons on our drivetrain this thread has me taking second thoughts. Will loctite decrease the chance of the screws coming loose? And should I apply it?

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As a team who is depending on the success of our Falcon 500s on our drive train, should we be pulling them apart and applying loctite? We’ve only driven them for an hour at this point, is this something we should be doing on our robot today before our event?

We’ve always loved working with Vex support, and vex support has always offered very quick RMAs - however, not fast enough to RMA 4 falcons during Finals 2.

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Thank you for your reply.
We did not contact you yet because we thought it might be something we did wrong, but after talking to Ari and realizing its a recurring thing (also via checking our other motors) we’ll contact you soon.

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Would it be smart to take apart the motors and loctite the shaft screws, knowing that the failure mode exists? Yes. Why roll the dice otherwise, when you can be sure?

I’d also remove the cooling port and mounting set screws, because I’ve seen one or two reports that they came loose here on Delphi.

If I hear about even one failure on a product, I usually look to ensure it doesn’t happen to me.

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