joint flipping problem

i have created an arm and hand with an ik solver for control using the hand and foot tutorial. However, i am getting joint flipping when i rotate the arm half way around the main joint. Can anyone help ? (using version 2.37a)

IK solvers base their rotation on the editmode pose. Ideally, these should be at half flex in order for the calculation to come out right. You don’t have to model the joints in half flex though, you can model them however you like and just rotate them to half flex in pose mode. Then apply the IK solver. I think that’s how I used to do it.

I highly recommend going to 2.4 if you haven’t already. It has joint limitations that fix the joint flipping much more easily. For the lower arm for example, say you intend to rotate it around local x-axis, then just lock the other axis and set a limitation on the x-axis for 0 to 180 or whichever angle is appropriate. The display will show the range the bone can go in. This stops your joints flipping wrongly.

You should also make sure to reset your bone roll values - it helps to have your bones coplanar when you do this so the axes are well-defined.

It may still happen at extreme points but in that case, just use some FK on top of the IK. So say you move the IK on the arm and it flips at an extreme pose, then just move the IK back a bit and rotate the upper arm manually. Then the IK will go further.

If you do choose to use 2.4 and you get odd results, make sure the chain length is set correctly. That put me off initially. For an arm, the length should be 2.