Can you tell the wheel of a a wheel joint not to rotate?

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SoggyB
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Joined: Sun May 18, 2014 9:51 pm

Can you tell the wheel of a a wheel joint not to rotate?

Post by SoggyB »

I am playing with the idea of a soft body wheel without the use of a chain or revolute joints between pieces of the chain/tire. Part of what I need is a wheel joint where the wheel of the joint never spins. I have partially accomplished this by enabling the motor, setting the torque high, and setting the rotations per minute to a very small number. This creates a nearly undetectable rotation of the wheel. I want to accomplish the same thing without adding the overhead of an enabled motor.

Can you tell the wheel of a wheel joint not to rotate, but still let it allow to move along the axis of the joint?
iforce2d
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Re: Can you tell the wheel of a a wheel joint not to rotate?

Post by iforce2d »

You can set the rotation speed to zero - isn't that what you want, rather than a very small number?

If it's working ok with this method, I would probably not bother with searching for other arrangements. You could achieve the same result by using a combination of a prismatic and distance joint pair, but at the end of the day both methods need to do almost the same calculations, so you will not escape any imagined 'overhead' either way. The fact that you've completely removed the chain of revolute joints is a major win though.

The one possible advantage of a prismatic+distance joint pair is that the two joined bodies will always remain in the same relative rotation. With a wheel joint that has a large torque and zero speed, it's possible for a strong impact to turn the 'wheel' body a little, so over time the relative rotation between the two bodies could drift.

After making the video about soft body wheels, somebody commented that circles would be better, so I tried the setup you're talking about and I really liked the result. I tried it again just now (attached) if that helps as a reference.
Attachments
circleRims.rube
(66.87 KiB) Downloaded 707 times
SoggyB
Posts: 4
Joined: Sun May 18, 2014 9:51 pm

Re: Can you tell the wheel of a a wheel joint not to rotate?

Post by SoggyB »

Thanks, iforce2d.

I tried setting the joint motor speeds to 0, but they still rotate. I have attached my sample, as the shape of the treads of the tire make it easier to see what I mean.
Attachments
SoftWheelVariant00.rube
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SoggyB
Posts: 4
Joined: Sun May 18, 2014 9:51 pm

Re: Can you tell the wheel of a a wheel joint not to rotate?

Post by SoggyB »

Ah.. ok, I thought it was working in your example but not mine. However, if you let your sample run for a bit, you can see they rotate also:
softwheel.PNG
softwheel.PNG (35.22 KiB) Viewed 11115 times
In mine, I wonder if the facets of the 'treads' make it rotate sooner than your sample. I love how your sample feels though.. very smooth and capable vehicle.
iforce2d
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Re: Can you tell the wheel of a a wheel joint not to rotate?

Post by iforce2d »

That's right. If you wanted to prevent the angles from drifting like that over time, you would have to use a prismatic+distance combo.
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