When some object like cube fells on flow. It's starts to rotate but speed of rotation is very low and unrealistic. Same thing when I move some object to edge and make it fell.
I just compared what I seen on screen with cell phone felling from edge on table. When central mass of cell phone reaches the edge it rotates and fells but when I model similar thing in bullet it is much slow.
Why is that?
My box size is much larger then cell phone
It is 4x3x0.5
It still looks unrealistic.
Please, advise, Thanks
Low Torque on edge
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Re: Low Torque on edge
I set gravity 20 instead of 10. Slightly better but still not realistic.
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Re: Low Torque on edge
What's the mass and inertia of the object?
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Re: Low Torque on edge
mass is 1000, size 4x3x0.5 and initial inertia is (0, 0, 0)
I use localCreateRigidBody from demo to create most rigidBodies
Thanks
I use localCreateRigidBody from demo to create most rigidBodies
Thanks
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Re: Low Torque on edge
If you want to do a direct comparison with your cell phone then you would need to set gravity to around 500. This should result in relative motions being the same (i.e. the same amount of world time to rotate one revolution, or to translate by its own size).razer wrote:I set gravity 20 instead of 10. Slightly better but still not realistic.
Big things move like small things but on longer timescales...
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Re: Low Torque on edge
What you've got there is very roughly the size and mass of a car (a gravity of 10 indicates metric units, so 1000kg and the dimensions in meters), which will certainly act a bit different than a cellphone.razer wrote:mass is 1000, size 4x3x0.5 and initial inertia is (0, 0, 0)
I use localCreateRigidBody from demo to create most rigidBodies
Thanks
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Re: Low Torque on edge
Things that have small mass fall as fast as heavy.
I set mass to 1 and there is no difference in bullet as well.
May be size make thing fall slower.
But it is unrealistically slow. when gravity is 10 and I set gravity 20 now.
May be bullet has some tuning or I should change some constant.
I set mass to 1 and there is no difference in bullet as well.
May be size make thing fall slower.
But it is unrealistically slow. when gravity is 10 and I set gravity 20 now.
May be bullet has some tuning or I should change some constant.
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- Joined: Tue Feb 20, 2007 4:56 pm
Re: Low Torque on edge
In free-falling due to gravity, yes you are correct. But in your case you have to rotate the object in order to fall off the edge of something. It is more difficult to rotate a massive object, not to mention that the moments of inertia go up with the *square* of the dimensions.razer wrote:Things that have small mass fall as fast as heavy.
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Re: Low Torque on edge
bone wrote:In free-falling due to gravity, yes you are correct. But in your case you have to rotate the object in order to fall off the edge of something. It is more difficult to rotate a massive object, not to mention that the moments of inertia go up with the *square* of the dimensions.razer wrote:Things that have small mass fall as fast as heavy.
But force is higher also. Size is important mass is not so important.
Cell phone is bad example.
It is too slow and not realistic.
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Re: Low Torque on edge
Correct. The increase in mass is directly offset by the fact that the force increases with mass.razer wrote:bone wrote:In free-falling due to gravity, yes you are correct. But in your case you have to rotate the object in order to fall off the edge of something. It is more difficult to rotate a massive object, not to mention that the moments of inertia go up with the *square* of the dimensions.razer wrote:Things that have small mass fall as fast as heavy.
But force is higher also. Size is important mass is not so important.
So what you've got is the inertia vs. the torque (and torque arm, which at the initial state of this example is the lateral difference between the body CG and edge of the table). Removing the offsetting mass from both sides, you are left with the body dimension squared vs. the torque arm. So bigger objects, even if moved proportionally further off the edge, will still rotate slower because the squared term dominates.
Regardless, all we have established so far is that the cell phone vs. the car-sized object isn't a great comparison, which you've agreed.
If you provide the CG position vs. the edge of the table, and the full inertia properties (and current gravity coeff), we can determine exactly how fast it should start rotating.