How can I stop sideways motion of the robot?

I have heard there are ways to stop the sideways motion of the robot. I mean the sideways motion from the wheels who have the cylinder on them. I saw one time someone use a screw to stop this motion but I’m not sure how to do it. Does anyone know this method or some other method to stop the sideways motion of the robot.

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For the screws just shove them in like this, but the more the wheel is used the screws will fall out easier, to combat this just use zip ties

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Here is a video showing the concept of locked omnis in a little more detail. Locked omnis can be created from 4" wheels and 2.75" wheels with #8-32 screws. Additionally, you can use a custom traction wheel created by stretching a 4" high traction tire over a 30 tooth sprocket wrapped in chain. But for 3.25" and 2.75" wheels, it is easiest to use the already made traction wheels.
Traction wheels, when made correctly, will stop sideways motion of the robot, keeping you from being pushed from the side. The best configuration for them is generally 3 wheels on each side, 2 normal omnis on either ends and a traction in the middle, for smooth and predictable turning around the center of the robot.

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Additionally, traction and high traction wheels exist, but don’t have the competitive edge that locked omnis have. They are listed on the wheels page of the VEX website.

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Something I recently discovered is that for at least the 2.75" wheels, you can just slip a 1/16" spacer in between the roller and the hub and it will make a satisfying “click”. It secures the rollers even better than screws, it will never slip out on it’s own, and it will make your wheels much lighter. It also has the benefit of not increasing the profile of your wheels like the screws can.

You can get 1/16" plastic spacers from Robosource, although you could probably get away with using vex metal washers, but I would recommend putting the more rounded side facing out so the sharper corner can click into place.

I’ve tried it on 4" and it kinda works if you stack two washers a bit offset from each other but it’s more sketchy. 1/8" spacers are a bit too thick, but I think that 3/32" thick spacers/washers could work.

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i dont understand why someone would want to lock omni wheels, if you dont want the movement it provides why use them in the first place?

There are a couple things here.

  1. Omni wheels are much more grippy than traction wheels anyways, so a locked omni wheel will almost always be more useful than a traction wheel of the same size.
  2. If unlocked omni wheels are used on the outside of the chassis, and the center wheels are traction or locked omnis, the turning advantage that the omnis give are combined with the resistance to pushing granted by the traction tires.

On our robot we use 6 wheels, 3 per side. The four on the outside are omni wheels, and the two center wheels are custom-made from some gears and flex wheels. They work really really well to allow us to move around very easily while still retaining the ability to resist pushing.

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ah i see, thank you this is actually useful

If you are using 4 omni wheels try putting a normal wheel in between each side of the robot. This will allow you to turn the way you are supposed to with omni wheels but not allow others to push you from the side. Worked well for me.