Bounce from ground produces opposite dependency

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1 comment, last by anders211 9 years, 2 months ago
Hi
I have a problem. I have left-handed system. And formulas/dependency for movement before bounce impact are:
Vz ~ r*Wx
Vx ~ -r*Wz
In other words: ball which goes into Z+,X+ direction has positive value speeds and positive angular Wx speed and negative value of Wz.
However during bounce ground impact equation gives opposite results:
Vz ~ -r*Wx
Vx ~ r*Wz
Here are details:
Some comment to picture: After bounce with top spin V speed decreases and W speed increases. Wx has to have negative value in order to increase.
You know I might tune in manual well formulas obtained from bounce ground impact and replace Wx1,Wx2 with Wz2,Wz1 and everything would be OK. However I am planning to reuse this piece of SW for bounce from wall, for bounce from some slippery slope, so I cannot afford on such workaround because earlier or later I will get lost.
Does anybody have idea how to solve this problem and where I made a mistake that I got opposite direction?
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First, it would be much better if you post the equations you're using in plain text, as it's very difficult to read your hand-writing (my eyes are old, anyway), so I'm not at all sure I'm correctly interpreting your question or the equations show in the picture.

My guess: In the diagram just below "calculate bounce from ground," it appears you have angular velocities Wx1 and Wx2 defined as positive** when pointing along the positive X direction (left-hand rule). However, your torque equation R x F is right-handed - i.e., R X Fz (left-handed) should result in a +X torque, not a negative X component, if R==(0, -r, 0) and Fz==(0, 0, -Fz).

**assumed because you show a CW rotation about the X axis.

E.g., ( 0, -1, 0 ) cross ( 0, 0, -1 ) = ( 1, 0, 0 ) [left-hand rule]

You must define torque, angular acceleration, and angular velocity all with the same handedness.

EDIT: If you want to use a right-hand rule for torque, then use F x R.

Please don't PM me with questions. Post them in the forums for everyone's benefit, and I can embarrass myself publicly.

You don't forget how to play when you grow old; you grow old when you forget how to play.

Yes, Wx1 and Wx2 is > 0.

I understood my bug. The bug was that I calculated RxF like (0,-r,0)x(Fx,0,Fz) instead (0,-r,0)x(-Fx,0,-Fz).

Thanks for help.

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