How to make gears not fall off

During our last regional, we had our gears come off a lot, we are currently using bolts to keep them on. Any suggestions on how we could improve this, or keep the gears on better for our next regional?
Also, is eight motor drive with mecanum reasonable?

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Can you please show us a photo of how you are holding your gears on now? It is always easier to help when we are not guessing about what things look like.

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8 motors is probably 2x what you need. With a current limit it’s probably fine, but overkill.

What brand of thread locker are you using on those bolts? How much?

It looks like they’re using bolts tapped into the end of the shafts.

@Hunter_Morgan You could probably try either loctite or extending your shafts to fit either e-clips, retaining rings, or shaft collars.

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You should definitely use Loctite if you retain them that way. If you still have problems use a plate and standoffs for a more proper fix.

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We currently aren’t using any thread locker

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Thank you so much, we’ll try that!

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If your gear ratio is appropriate for your robot weight, then a four NEO drive is -plenty- of power! I would expect that a 4 NEO drive with mechanum or omni would be -easily- able to break the tires loose and drift. You would need to turn down the current limits to control this.

Our swerve bot is driven by 4 NEOs. Last year’s tank bot was 6 NEOs and was kind of over-powered; we had to turn down the current limit quite a bit to kill brown out and keep the tires from slipping like crazy.

The 9mm shaft collars should do a good job on the NEO pinions. It looks like you used fender washers and large head screws in the end of a hex shaft. That should work well, as long as you loctite the screws. You could also run longer shafts and use shaft collars.

Which gears are coming off?

Cool. That’s almost certainly your problem.

This is my favorite thread locker: https://www.amazon.com/Loctite-506166-Medium-Strength-Threadlocker/dp/B0053ZNMDE/ref=mp_s_a_1_3?crid=2FGX5Y6HS09W6&keywords=blue+loctite+242+stick&qid=1679365885&sprefix=blue+loctite+242+stick%2Caps%2C224&sr=8-3

Apply to the retaining bolts, and you should no longer have this issue.

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Throw the design away after this season and use the kitbot. I’m not joking, this drivetrain isn’t winning you any matches. If anything it gets you on some DNP lists. You are likely worse off for using it. I am not saying this to be mean, I am saying this because I want your team to do well. The row of exposed gears is unnecessary risk. The mecanum wheels are not competitive in a drive system in FRC. You are having failures because of unnecessary complexity in the most important subsystem on a robot. I applaud and recognize the custom design and creativity, but you are less competitive with this drive system. This is how you improve it.

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You’ve taken that quote of context. The OP is looking to improve bolts falling out. Also, you’re being rather brusque with a robot that this team has liekly put a tremendous amount of effort in to. I’m not saying your wrong about how their competitiveness would compare if they were to use the KOP drivetrain as I’m really not qualified to say, but I am certain that your tone is not the most effective way to convey this. Also, there is a very real possibility that they would not be more competitive with a KOP base as they might not be able to get one in time for their next competition or would be frantically putting it together the night before. It is possible that an improvement could be switching to traction wheels and covering up those gears, but that can be phrased in a kinder way. Also, mecanum wheels do have advantages compared to tank. I would guess that this team is able to line up their game pieces ore effectively than a tank drive.

I’m not saying your points are completely inaccurate, but I’d recommend that you reconsider your delivery and think about who is going to be reading your response.

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Probably not.

It starts with thinking about what you expect to gain from using 8 motors in your mecanum drivetain.

Is it more “pushing power?” Well, with the NEO motors you’re using (and even with older motors like CIMs), you can already deliver enough torque to your wheels that they can cause your wheels to slip against the carpet in almost any situation you’ll experience in FRC. Remember that you’re bound by how much friction exists between your wheels and the carpet (which is determined by the coefficient of static friction between your wheels and the carpet multiplied by the Normal Force applied - typically your robot’s weight). So unless you are supporting lots of additional weight (such as carrying multiple robots or particularly heavy game pieces), there’s not much advantage to being able to generate additional pushing force beyond what it takes for your wheels to slip during normal operation.

You can gain some amount of acceleration with additional motors, but the benefits there are marginal. But the added weight, complexity, and potential points of failure of adding these additional motors likely provide more drawbacks than this small amount of acceleration provides.

95% of these super fast swerve drive teams you see are only using 4 brushless drive motors (either NEOs or Falcons). This generation of BLDC have more than enough power to provide the torque, speed, and acceleration demanded by recent FRC games.

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I’ll second all of what @Lil_Lavery says here. Three additional points to consider:

  1. It’s true that you’re really not gaining anything useful from the second motor on each wheel. You could eliminate several points of failure by getting rid of the inside motor set and that exposed set of gears. The loctite will fix the rest of your problems there.
  2. The point about friction between the wheels and the carpet is well made. You’d gain a lot more from improving your mecanum wheels to ones that have better contact with the carpet, like these from Andymark.
  3. You might be able to gain some traction by adding ballast to your robot. Looking at the picture, it looks like you might be well below max weight. If so, then adding some weights to the frame corners near the wheels will help. Though the gains will be small, it’s likely to be more than what you’re getting from the second set of motors.
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Don’t let mecanum haters get you down :slight_smile:

Looking at that picture, your mecanum wheels are installed incorrectly. When looking from the top they should point in forming an X pattern.

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Edit: Nope, I’m blind.

But agreed on don’t let mecanum haters get you down.

In addition to thread locker I would add a split lock washer for Tertiary retention in this case because there aren’t any simple additions to capture the end of the shaft.

I would not use split lock washers, they are worse than not having them in most applications. Link to a NASA study in this post.

Wedge lock washers are a little pricey but would be much better for this application.

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I was not familiar with that article but it doesn’t surprise me. In my industry we don’t use them, I only ever use them in FRC. I was going for something easy to get anywhere.

While I’m familiar with the wedge lock / Nord Lock style washers I don’t use them frequently.

My actual preferred solution would be these.

They are not the easiest thing to install with no experience and limited tooling but for this type of application they are the best secondary retention. For tertiary I would figure out how to use a tab lock washer or in the case of this design you could actually use safety wire by adding the attachment points, but again that is a tool/technique issue.

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Wait what, helicoils have locking features? Or are they reinforcing the threads which then allows for higher joint preload?

(OP: blue loctite is sufficient and should be in the kit of parts, don’t worry about this whole line of over-optimization)

Self locking Helicoils exist! Not all of them are self locking though. These have a crimped/distorted thread to create the locking feature. You can see it if you look down the middle of the helicoil.

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