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Hubs coming loose with mecanum drive

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  • Hubs coming loose with mecanum drive

    We are using (Vex) mecanums this year for the first time. They work great... for just a couple of minutes, then the gears start slipping. The screws in the hubs keep coming loose either from the vibration or vectored forces of the mecanums wheels.

    We are thinking maybe loctite, but which color/strength?

    Is there a hub with a D-shaped center, which may hold a little better? We see some at ServoCity that look like they would fit the Tetrix motor shafts, but do the 4 screw holes line up? It doesn't look like they have any that fit the Tetrix axles.

    Have you found another way to fix this?

  • #2
    Originally posted by FTC8767 View Post
    We are using (Vex) mecanums this year for the first time. They work great... for just a couple of minutes, then the gears start slipping. The screws in the hubs keep coming loose either from the vibration or vectored forces of the mecanums wheels.

    We are thinking maybe loctite, but which color/strength?

    Is there a hub with a D-shaped center, which may hold a little better? We see some at ServoCity that look like they would fit the Tetrix motor shafts, but do the 4 screw holes line up? It doesn't look like they have any that fit the Tetrix axles.

    Have you found another way to fix this?
    Actobotics (ServoCity ) parts have different hole pattern. I am not sure if it's any help but AndyMark has this Wheel Conversion Plate (am-2609a) http://www.andymark.com/product-p/am-2609a.htm

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    • #3
      Originally posted by FTC8767 View Post
      Is there a hub with a D-shaped center, which may hold a little better?
      Andymark has a product called nubs that have a D-shaped center. There's still a set screw but it's only needed to keep the hub from sliding sideways on the shaft. With mecanum wheels there are certainly more sideways forces but these hubs still work better than standard tetrix hubs.

      http://www.andymark.com/AndyMark-Nub-p/am-nub.htm

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      • #4
        For Tetrix hubs, we generally replace the small setscrews with socket head screws of the same thread size. Some finagling may be needed to allow space for the socket head, as in can't be used with the smallest Tetrix chain sprocket, etc. This allows a beefier Allen wrench to be used, along with purple loctite. Purple will hold while still allowing disassembly without damage at this screw size. Using a dremel to add a small (just enough to feel) divot in the flattened part of the shaft at the point of screw contact helps as well.

        We are using some of the Vex 276-1447 mecanum wheels with 3d printed adapters to go to Tetrix hubs and axles. So far these have held up well with no problems throughout practice and ten matches.

        If you are using the other Vex mecanum wheels, not sure what would be required.

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        • #5
          Oh, and you mention gears slipping. We gave up on gears for drivetrain use two seasons ago. We only use #25 steel roller chain and sprockets for drivetrain.

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          • #6
            Originally posted by mlwilliams View Post
            Andymark has a product called nubs that have a D-shaped center. There's still a set screw but it's only needed to keep the hub from sliding sideways on the shaft. With mecanum wheels there are certainly more sideways forces but these hubs still work better than standard tetrix hubs.

            http://www.andymark.com/AndyMark-Nub-p/am-nub.htm
            Does anyone else find it odd that the setscrews into the "nubs" set into the rounded portion of the shaft? Perhaps with the "D" shape it's not as critical but I've always had set screws into the flat to prevent excessive galling. Perhaps they are using pointed set screws? I'll have to take another look at the ones that came in our tilerunner gear kit.

            For more hold, you can use high hold pointed setscrews https://www.mcmaster.com/#catalog/122/3061/=15cake6 or knurled end https://www.mcmaster.com/#catalog/122/3055/=15cal75. We use blue loctite for a bit more vibration resistance. The team overlooked this with their tilerunner build and had a major failure during drive practice (set came loose on main drive gear, shaft worked free, gear fell down). Upon disassembly, every screw in the drive chain was sloppy loose requiring complete disassembly and retightening, this time with loctite). Do NOT use red loctite unless you never want to disassemble them again without a torch.
            Last edited by gof; 12-05-2016, 05:21 PM.
            Technical Coach, Newton Busters FTC 10138, FLL 3077
            Chicago 'burbs, IL

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            • #7
              My impression is that it's specifically to push the flat spot of the shaft against the flat spot in the hub.

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              • #8
                Lots of ideas here for us to try - Thanks!

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                • #9
                  You can use actobotics (aka ServoCity) D-profile (use clamping for extra strenght) together with an adapter. I am not sure wchi hole pattern Vex Pro wheels use, but Andy mark sells adapters from AndyMark pattern to Actobotics, and actobotics has adapters from Tetrix to Actobotics.

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                  • #10
                    We thought the nubs for 6mm axle (both single & double boss) https://www.andymark.com/products/nubs-options were very cool and ordered a bunch. They worked well with being attached to gears driving mecanum wheels. But, now we are seeing that when the set screw on the nub is tightened, the gear is being forced into a plane that's not perpendicular to the axle, therefore constantly causing gears to be misaligned. Any other team suing this?

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