Physics prismatic joints: cannot rorate connected objects - bug?

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ludicarts

- 54ad379c-2758-41db-bb0b-232ff73e64b9
- - Joined 1 Jan, 1900
  - 6 topics • 21 posts
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- 16 Mar, 2022
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Hi!

Im trying to make 2d sidescroller car game. I have truck body and wheels, then I connect each wheel with body by 2 joints - distant joint (to have a spring) and prismatic joint (to make this spring with by upper and lower limit and make it fixed by angle over truck body).

Then I move truck by left mouse button holding.

In this case, connected wheels do not rotate at all. Question: is this a bug with prismatic joint or am I wrong?

Check my example.

dropmefiles.com.ua/ru/s8LTP
Tagged:

joint
physics
prismatic
rotate
truck
- dop2000
- - Joined 26 May, 2016
  - 140 topics • 12,767 posts
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- 17 Mar, 2022
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Prismatic joint probably doesn't allow rotation. You can add an invisible WheelBase sprite connected with prismatic/distant joints, and then connect the wheel to WheelBase with a revolute joint.

I have a simple example of a car with suspension, check it out:

howtoconstructdemos.com/physics-car-with-suspension
- 54ad379c-2758-41db-bb0b-232ff73e64b9
- - Joined 1 Jan, 1900
  - 6 topics • 21 posts
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- 17 Mar, 2022
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But why it cannot be rotated? This makes no sense. I can surely pin sprite and rotate it but base wheel still has no rotation.

Hey, Ashley, can you please answer this question?
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- 54ad379c-2758-41db-bb0b-232ff73e64b9
- - Joined 1 Jan, 1900
  - 6 topics • 21 posts
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- 17 Mar, 2022
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dop2000, I saw this one earlier, thanks. But there are no prismatic joints at all :)
- dop2000
- - Joined 26 May, 2016
  - 140 topics • 12,767 posts
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- 17 Mar, 2022
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Why do you expect prismatic joint to rotate? It's not supposed to. Revolute joint should be used for rotation.

Like I said, you can connect another sprite to the car with prismatic joint, that sprite will not rotate, but will work as a spring or a shock absorber. And then you attach the wheel to that sprite using a revolute joint.
- 54ad379c-2758-41db-bb0b-232ff73e64b9
- - Joined 1 Jan, 1900
  - 6 topics • 21 posts
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- 17 Mar, 2022
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I expext it to rotate cause in 2011-2016 I was working on same kind of games. We used Flash and ActionScript and our programmer did good job with using Nape's physics engine in Flash.

So I was Level designer and I had same joints and connected objects did rotate thats why.

I think Ashley can give a clear answer. Anyway thank you.

Here you can see one of our games.

youtube.com/watch
- dop2000
- - Joined 26 May, 2016
  - 140 topics • 12,767 posts
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- 17 Mar, 2022
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Prismatic joint by definition does not support rotation.
- 54ad379c-2758-41db-bb0b-232ff73e64b9
- - Joined 1 Jan, 1900
  - 6 topics • 21 posts
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- 18 Mar, 2022
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Got it. Thank you for help.