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1 wheeled ackermann robot

asked 2019-02-27 06:57:17 -0500

EdwardNur gravatar image


Can I use this local planner LINK for my 1 wheeled robot?

My robot has only 1 wheel and can move forward/backward and also rotate at the same time. My guess is that my wheel-base should be 0?

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I'm not sure how you would set this up in the planner. But to clarify you have a robotic unicycle? I would not describe this as ackermann steering, which would need at least two wheels like a motorbike.

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-02-27 08:03:06 -0500 )edit

@PeteBlackerThe3rd what about having 6 wheels? Where all of them can drive but only 2 of those are placed infront and can rotate whereas all other all at the back and simply drive at the same speed as front ones.

EdwardNur gravatar image EdwardNur  ( 2019-02-27 09:26:17 -0500 )edit

You're describing a 6 wheeled truck, yes that would be a case of ackermann steering. Is this related or your original question?

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-02-27 09:35:21 -0500 )edit

@PeteBlackerThe3rd Okay but is there a big difference if all wheels rotate instead of traditional RWD? It is related to my original question where I wanted to know if driving and rotating will create the same path as front rotation and back spinning (like a bike)

EdwardNur gravatar image EdwardNur  ( 2019-02-27 09:38:10 -0500 )edit

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answered 2019-02-27 10:21:25 -0500

Okay I think I know what you're asking now. Your wording describes a robot that only has a single wheel, not a robot with several wheels where only one drives and rotates.

The important thing to understand is that in a 2 wheel drive car (front or read) or a 4 wheel drive car none of the wheels rotate at the same speed when corning. This is why they have differentials to stop the wheels skidding on corners and wearing your tyres away in no time. If you are actually driving all the wheels at the same time then your robot will be skidding while cornering which makes it virtually impossible to accurately predict where it will end up.

So to answer your question in the case of two different car type chassis, one which is rear wheel drive and one which is front wheel drive. When the cars are cornering the rear two wheels are following smaller arcs than the front two wheels. So if you set a mean velocity for the front wheels you will end up travelling at a different speed than if you set a the same mean velocity for the rear two wheels.

Hope this makes sense.

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@PeteBlackerThe3rd Yes I understand that but would I be able to use the package above for AWD?

EdwardNur gravatar image EdwardNur  ( 2019-02-27 10:47:04 -0500 )edit

Yes you can use that package. But as described in section 2.2.2 of the page you linked to you may need to write your own code to convert the twist messages into the appropriate commands for the robot depending how it's driven (with differentials or separate motors)

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-02-27 10:58:02 -0500 )edit

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Asked: 2019-02-27 06:57:17 -0500

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Last updated: Feb 27 '19