Joint conected wheels falls off

[ivan]

SketchUp 7.1 Sketchy Physics 3

1. Created rectangle (body), pushed-pulled, grouped, SP shape - box
2. Created circle, pushed-puled, grouped, SP shape - convexhull
3. Copied wheels
4. Created 4 hinges, grouped each hinge with one wheel
5. Joint connected each hinge with body (click on joint connector toll, click on hinge, ctrl+click on body)

on play wheels fall off the body. What am I doing wrong?
Here is my file.

Thanks for any help

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5.skp

[phy]

Did you group the hinge and wheel or did you make them a component.

[Wacov]

Yeah, you need to group them, not make components. Here:
5.skp
I just exploded and grouped all the wheels.

[ivan]

it was so natural "G" for group.
Thanks a lot