PSA: Falcon Failure Mode

I think the questions here are more asking “will this be enough” and “what else do I need to be checking for”

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Fair enough

We will likely be pulling the motors apart and adding the loctite here - we’ve already removed any grub screws on the motor as we actually managed to drop one into one of our Falcons on the first day - if you tighten them they jut keep going!

I sent an email to Vex Support to ask about the issue directly as well - the fact that they monitor Chief is wonderful, but as @Jon_Jack has mentioned the best course is to email them directly.

We’ve had very few issues with our Falcons, and have so far loved using them on our drive train! We’re really looking forward to seeing how well they perform in the coming weeks.

EDIT: Wow! What a fast response from Vex! It seems the recommendation is Loctite 243. We’ll be applying it tonight.

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Looking at the Falcon Shaft Docs & Downloads, I don’t see a torque spec for the M2.5 shaft bolts in particular (or any of the bolts in general). For something that small - somewhere around 7-8 in-lbs? I’d like the option to give our students a torque-controlled tool for this, rather than rely completely on loctite and “feels right”.

Can you add the bolt length to the manual as well? I’d like to buy some spare M2.5’s because I know we’ll manage to lose some of these in the process.

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**Unrelated desired product update: Torx drive on the M2.5s to match the back end; my students tried to use the same T10 driver on the 2mm hex and wrecked the T10 tip.
Or a T6/T8. Bonus: probably results in more torque/more bolt tension in the joint.

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This would have been nice to know before we built our robot so we could have done this beforehand

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VEX has updated the Falcon page with the following note.

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may not have had Loctite not properly applied

I had to read that 4 times…

Thanks for sharing, and thanks to VEX for adding the note.

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Thank you for making the public note on the product page. Appreciate that Vex is trying to get ahead of this and provide public guidance on the issue, underscores your commitment to customers.

Geeking out about fastener locking design for young engineers in this thread

“May not have had Loctite applied properly at the factory” - it sounds like Vex was shipping in bare bolts and applying wet loctite in the Falcon factory, which is a high risk difficult-to-control process and pretty far down my list of preferred solutions in work contexts.

With the fast ramp they pulled off for this product - I can imagine many ways to get that far down the solution list - but I didn’t know about pre-applied locking patches until I was working for a couple years. Products like this https://www.mcmaster.com/bolt-locking-patch will save you many many headaches.

Use pre-applied locking patches or mechanical locks in your professional designs. Avoid dealing with correct application of chemicals/curing/contamination on the final assembly line.

It’s possible Vex had a locking patch solution in place that failed - the relevant specification and QA testing would be on the “prevailing torque” created by the locking mechanism. The chemistry, patch thickness, etc, is hard to get right and I’ve dealt with my fair share of nonconforming (all non-name-brand, no issues with genuine Henkel) suppliers in that space.

The downside is leadtime, generally 1+ weeks in China & 3+ elsewhere - if this showed up late in ramp / late in qualification testing, Vex would need to keep the lines on with something and that something could be liquid-based.

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It’s great that they’ve acknowledged the issue on their website… but what are the odds a team that already has them in hand is going to browse the website and see it? I’d really like to see an email notification go out with that information.

This appears to be a relatively prevalent issue, from what I’ve heard. There were several different people from different areas that reported local teams with the problem on the weekly LRI call last night. I’m going to be taking all of my team’s falcon’s apart tonight to fix…

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As a further example for the students, there is a pre-applied locking patches on the 7 Falcon set screws.

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True!
(Which have also been reported to back in & out in much smaller numbers, which makes me wonder if there was prevailing torque acceptance testing in place…)

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Yeah, the set screw thing is tough because you can’t torque those to a proper level, they just float in there.

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Good catch to those who found the issue with the falcons, but before everyone goes and tears their falcons open, you might wanna consult with your local LRI.

R28 allows a mod to the Falcon 500 for remove plug screws but prohibits modifying the internals of the motor. I know it’s to prevent the motor from being compromised, but you might want to wait for FIRST to weigh in before messing with your motors!

Sincerely,

A Friendly Neighborhood Inspector

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You might be interested in Q122. Modifying the Falcon shaft is completely legal.

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Everyone should be aware that a degrease step is part of the official instructions for applying loctite (which typically nobody does), but it 100% should be done when loctiting these motor screws.

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Good find! Thanks for sharing that.

Does anyone know which number is the date code or where it is found? We see 2 different numbers that begin with 19#####, so we will be taking our apart regardless. We are assuming that 217-6515 is not the date code. :smirk:

Out of curiosity… was there a loud screeching/squealing noise (far louder than the Falcon’s stall whistle) prior to this failure?

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Ooh, I’m glad we bought those ThriftyBot output shafts, and had the kiddos Loctite all the screws when they installed them!

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19-708850 is the CTRE part number.

You should be looking at the bottom line of text which would start with a 19 or 20 and not have any dashes.

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