Need help with a Bongo animation

Hi everyone, I’m getting started with Bongo and I’m losing my head to make an animation with IK.
My goal is to simulate a steel cable that, coiling around a winch, pulls a shell until it closes.
How would you set the IK chain parameters?
The steel cable is the yellow one selected and as you can see from the pictures it should follo the arc’s trajectory until the shell closes completely. Obviously I don’t need the cable to really coil around the winch but I think the cable could just be scaled giving the impression that it coils around the cylinder.

Hi Lo,

Welcome to the Forum. Fine you used a lot of images to make the enigma clear.

It is indeed a bit of a brainteaser. A line that needs to rotate at both ends and scale…all of this while the line only has one pivot?
The answer lies in the use auxiliary objects.

I used lines in this model Lo.3dm (35.2 KB) because they are better visible in the image above, but point objects would also do nicely as well.


The IK chain starts with the Arch made rotating by keyframes. Attached to it is the ‘Hing’ing auxiliairy line. Follows the Cable-line. It is made a ‘Rubberband’. In order to get it scale properly its pivot is positioned (BongoMovePivot command) at one end (this becomes the origin of the scaling) and the pivot is rotated (BongoRotatePivot) so that the X-axis coincides with the Cable-line (thus the line will scale along its proper axis)
Finally the second auxiliary line, representing the end of the cable keeps the chain ‘Constrained’.


Have fun,

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Thanks a lot and sorry if I didn’t introduce myself here, but I was so into this thing that I forgot to do that.
Your solution works perfectly but since I’m a rookie it would be super nice if you could show me a video so I can repeat all the steps and do it by myself. I know I’m asking alot but I have difficulties understanding how you achieved this result.
Have a nice day by the way! ((:

Hi Lo,

Please excuse me… some nasty brain paralyzing side effects of my second Covid vaccination prevented me to reply earlier. But here it is finally the video you requested:

I suggest you to also have a peek on Bongo’s YouTube Chanel
or my personal channel
Luc Adriaenssen - YouTube

Have fun,