Hinge animation problem

Good morning,
I have a problem with a simple IK chain on Bongo, here is the file on wetransfer:

I’d like the top-rod (green) to be fixed to the blue point, but I’m not sure how to make it.

Thanks in advance!

Nice going Camillo,

Keep in mind:

  • Think linear
  • Use auxiliary object when it seems you need 2 pivots in 1 object.

You need to take following steps to solve your model:

  • Move the pivot of the “Top Rod (Green)” object to the other end (so that coincides with “Follower point”).
  • Make the “Blue point (Fixed)” child of the “Top Rod (Green)” (an auxiliary at the end of the Hierarchy).
  • Set up the “Blue point (Fixed)” as a ‘Constraint’ ‘Keep pivot location the same’.
    Hatch 001.3dm (914.7 KB)

That’s it.

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Hi Luc,
now it works, but I’d like the hinge to be pointing down at the end of the animation (so it remain hidden).
I am currently working with Rhino 5 files and I cannot open newer files. Thanks a lot,

Lucky for you; I still have Rhino 5 operational! It is surely worthwhile to upgrade. Rhino 7 is shipping.

To have the scissor hinge fold together pointing down, the configuration of mechanism has to comply to some geometrical rationality. Mind you I’m not specialized in this matter.
The “Blue point (Fixed)” must for sure be positioned somewhere in the middle of the board when it is rotated upwards – if not the scissor hinge can impossibly be ‘hidden’.
In Hatch 002.3dm (872.2 KB) the point coincides with the upwards position of the other end of the scissor hinge. Both scissor hinge arms have the same length. Folded they end up coinciding but remain a little bit slant. I guess that is because from the mathematical point of view of the IK solver this is the most logical solution. Technically in that position the collapsed scissor can turn freely wherever it likes and probably gravity would help out (but gravity … that is a matter for Bongo’s WIP)

The lengths of both scissor hinge arms needn’t necessarily have the same length though.
In Hatch 003.3dm (901.5 KB) the position of “Blue point (Fixed)” is shifted downwards. The length of both arms differ, according to the calculations noted in the model. Hence they are forced vertically down in closed position. Because very tiny angles occur in the end phase of the movement Bongo’s solver briefly mentions the ‘Constraint goal not reached’ message.

As you can see in both models the use of the constraint to the red circle (occurring in you initial model) is superfluous. The cyan line and magenta arc are merely illustrative.


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Dear Luc,
I find it amazing! I’ll use file 003 although I don’t understand the formula.
Have a nice weekend and thanks again,

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