Very weird behavior of IK


(IVELIN PEYCHEV) #1

Hi All,

I’m just a piece of fresh meat sucked into the Bongo scene.

I do have a big issue though. Could you please take a look at the video and tell me why on Earth is this happening?

Joints dislocating, motion not according to the given constraints.

I have to mention here that the objects are not oriented according to the global axes, but it’s as the anchor will be placed on the ship. Even rotations about X, with ‘Rotate in world space’ disabled, don’t work properly.

Is there some kind of limitation of Bongo making it unusable for arbitrary objects or grouped objects? Surprisingly, though, the Point on Curve motion, and the telescoping motion of the swivel work properly, only the hinges are completely messed up.


#2

No video or link that I can see.


(IVELIN PEYCHEV) #3

yeah I noticed something and I deleted it to do it again :), now it’s there.


(Marika Almgren) #4

Would you be able to send me to the model. I’d like to have a look at what’s going on?
You can send it using the following page:
https://www.rhino3d.com/upload
Just put me marika.almgren@mcneel.com in as the recipient.


(Luc Adriaenssen) #5

Hi Ivelin, welkom into the wonderful world of animation.

Based on your video I feel that lots of the objects which are made Hinge do NOT play any role in the IK-chain. Hence the random spinning.
These are: Crown, Object 0, Object 10, Object 13, Object 14, Object 3, Object 4, Object 5, Object 6, Object 7, Object 8 and Object 9.

When you switch to IK-view in the Animation Manager (after the constraint is set and the IK-decorations (telescope, hinges, etc…) appear in the Viewports) you’ll notice that only Swivel, Rod, Object 1 and Object 549 are listed. The other(list above) do NOT show up.

image

Only Swivel, Rod, Object 1 and (point) Object 549 form the actual active IK-chain. When you want the other Objects (0 to 14) all to move simply together with Object 1 it’s enough to make them child of Object 1. Making them all Hinges is superfluous - it only causes random spinning. Because Object 1 is a Hinge all of its ‘bare’ children (and grandchildren) will happily rotate along. In more complex models an even better option is to unify the objects working together in a Rhino Block. A Block instance is treated by Bongo as being one single object, given only one single pivot. That makes thing more uncluttered. The pivot is by default situated at the Block’s base point but can be relocated.

Furthermore I see that the pivot of Object 549 (the ‘end’ of your IK-chain) is NOT located at the point itself - you made it coinciding with the pivots of Objects 0 till 14.
When an object (point or other) is “constrained” the object’s PIVOT makes the connection (not the object/ point itself ). To make Object 549 itself follow Object 550 you should relocate its pivot to the point itself. Use the ‘Reset’ option in the BongoMovePivot-command.

BTW an IK-constraint to another object automatically relaxes rotation. So there is no need to make Object 549 a ‘Joint’ (Universal or other).

As far as I can make out this would/could solve your disfunctional model. If not, please to send it to Marika.
Of course she is right: a posted model is easier for us to examine than a video.


(IVELIN PEYCHEV) #6

Hi Marika, Hi Luc,

Thank you for your replies. I understood how important creating blocks instead of groups is for Bongo.

I believe due to my lack of knowledge on how Bongo works I may have also made other mistakes in that model. Later on I saw that I can’t really do that with IK and I abandoned the idea and I created the animation motion by motion.

I decided to purchase Bongo2 so now I’ll have more time to investigate the capabilities of IK.