Reply To: 3dioot’s polybook

[Phil Osterbauer]

@3dioot A knee pop is a spacing error that results in the leg going from a straight position to a bent position (or bent to straight) usually over a single frame. When played back it looks like the knee is popping in and out of place. It can also look like the characters knees are wobbling around. Its usually a sign that you have some body mechanics that aren’t quite right. When I trouble shoot knee pops I look at the hips first. Is there enough twist in the ZRotate? Is the center of mass moving from one foot to the next properly? Is there too much/little ZTranslate down in the down position? Is there too much/little ZTranslate up in the up position? Make sure the hips, or in this case the head, is correct. (in your shot I think the hips/head are fine)
When the hips are looking good I’ll take a look at the feet. Are the toes peeling off correctly? Is the gait of the character proportional? Is the ankle following the correct motion trail? Are the feet slowing down when they shouldn’t be? As you’ve pointed out, an over extended leg can cause these pops as well, so be careful you don’t have that happening.
All while you’re checking these things out, be sure to be tracking the knees and keep an eye on the motion trails.

For the situation that you are in, the hips are fine. The pop is happening to the leg in the air, so the hips have no influence on it yet. Tracking the left knee I can see starting at frame 10 and 11 the knee is sticking in the same position. Then it pops on frame 12. On frame 11 take the foot control and try to get the knee in between where it is on frames 10 and 12. It might only take some Ztranslate…you’ll have to experiment.
The same thing happens to the right knee starting at frame 22.

Making these changes might be a little bit easier if you widen the gait of the character. I usually use the characters feet as a measuring tool for this, try to widen it by another half a foots worth and see what happens. (for a vanilla walk I’m usually shooting for 1 or 2 foot lengths wide on the gait)

I hope this helped, let me know if there are questions and I’ll do my best to answer.