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# How can I make 2 wheels on the same shaft counter rotate? Answered

Hi, I'm looking to take 2 wheels of the same size, placed next to each other on a shaft, and gear them in such a way that they rotate in opposite directions but at the same speed. Any gearing that takes place has to happen right in the center. Does anyone have any ideas as to how to accomplish this in the most efficient way?

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It is called gears.
But if space is an issue you might revert to two indepent drive trains for each wheel.

The gears part was sort of a given. I've considered having the central shaft consist of an inner and outer shaft with one of the wheels connected to each. What I'm mainly looking for is the configuration of gears that would allow this to work. Maybe an example of an existing design.

A differential style gear mechanism would work, you could make it with 3 or 4 bevel gears. In a car diff, you have a situation like this |_| your drive is applied to the _ bit, in the config you want, your drive is applied to one side of the |_| and the other | rotates in the opposite direction.

And there are epicyclic diffs too, which could be very small, if the mechanism has to be well hidden.

I like the idea of the lawnmower diff - I guess they are quite inexpensive ?

Yea I had to put new bushings and axles in one once people forget to grease them and they wear out quickly.

You don't give a lot of design information about the system you want to build but this will work.. A friction drive to concentric shafts

Thanks Rick, I think concentric shafts would work very well. The image you posted is pretty much exactly how I'd like the two wheels to be placed in relation to each other. The remaining issue would be how exactly to gear them so they can be run off a single motor (for simplicity) and run at the same speed. It's been a while since I took a math class involving gear ratios. I'll have to look into that a little bit.

Thanks, I probably should have mentioned I will be 3d printing everything, which sort of the leaves the options wide open. I'm leaning towards the idea of using a differential. Each of the wheels can have bevel gearing and maybe i can get the middle gear onto the shaft. We'll see where this goes.

OR You could mount 2 electric motors back to back attach the wheels and run the motors in opposite directions!

You may want to look at how the hands of a clock are mounted and moved.