Problem with HingeConstraint limits

[gabba]

Hi,

It seems that HingeConstraint (and other constraints involving an angle limit) doesn't like at all limits that are near or above PI (i.e. 180 degrees).

I tested this in ConstraintDemo.cpp. This works:

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spDoorHinge->setLimit( 0.0f, M_PI_2 );

However this doesn't work at all: the door starts spinning like mad once it crosses the 180 degrees angle:

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spDoorHinge->setLimit( -M_PI, -M_PI_2 );

this has the same problem:

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spDoorHinge->setLimit( M_PI_2, M_PI );

I've found a workaround by inverting the axis:

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 btVector3 btAxisA( 0.0f, -1.0f, 0.0f )

That allows me to define constraints in the quadrant that's otherwise problematic. But the workaround is unintuitive and complicates my code - you may want to consider it as a bug...

Is there a way to define the angular limits relative to the referential of the object, instead of having them be absolute/"relative to the world"? I'd like to be able to place a door (or pinball paddle, in my case) in any position without having to recalculate the limits every time.

Thanks!

Edit: I'm using Bullet 2.74

[rponomarev]

Yes, there is a problem when angle limits are close to -PI or PI
We added an issue http://code.google.com/p/bullet/issues/detail?id=217 and will fix it in future.

As a workaround you could create a dummy static body (without mass and shape) and set hinge limits relative to its frame instead of using world coordinate system

Thanks for pointing on that,
Roman

[gabba]

As a workaround you could create a dummy static body (without mass and shape) and set hinge limits relative to its frame instead of using world coordinate system

Would you mind pasting a few lines of code to give an example of setting hinge limits relative to the frame of another static body? While I understand what the axis and anchor do, I purposedly avoided using the methods that take a frame or frames as parameters, since I don't understand very well what frames are or do.

[gabba]

Bump.

[Erwin Coumans]

You could check out some of the constraint demos in the Bullet SDK. There should be some constraints using two constraint frames, frame in A and frame in B.

Hope this helps,
Erwin

[gabba]

Thanks. I still don't understand very much how to use the functions that use frameInA and frameInB as arguments, but the one that builds a HingeConstraint from an axis and pivot has a boolean that helps with this, and that I missed at first.