Rotating a scissor movement


I’ve been using Rhino for awhile now but didn’t start learning Bongo until a couple of weeks ago. Some of the IK components make sense, but I’m at a loss as to how to tie them together for a moving object.

In the attached document, I’m trying to have a V shaped armature open and close as two ends are rotated around different orbits. Thanks for any pointers, suggestions, hints, or sections of the manual for me to read again.

bongo-question.3dm (17.1 MB)

These two tutorials should help you get started with your IK animation:

Here’s one way to solve the model:
bongo-question.3dm (17.3 MB)

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Thanks, I’ll take a look at your solution and re-read the tutorials. I feel like I’m one or two “aha!” or “d’oh!” away from understanding how IK really works.

Ok, I see my first problem – I thought this could be done without adding points to the models.

can we expand on this a little, I was trying this and also drew a wire frame of a simulated ram. So I was able to get it to work ( a little sloppy) I know I am probably doing it the hard way…adjusting angles and distances manually. I also have a grouped object I Was making a child of the rotated part.

parallelogram W ram.3dm (94.0 KB)

Yep, a little IK could help smooth this model out as well. Here’s what I whipped up. Instead of the group animated to push I have the their parent rotating and make that a telescopic joint. Then there are two goals, one at each end of the bottom link. Everything else is a hinge rotating to meet those goals.

Let me know if you need any more help.

parallelogram W ram IK.3dm (77.8 KB)


looks great. I will check that out. I am going to watch a few more turtorials. Thank you.

Apart from the transcendent IK Bongo has other tools to help out in this. In some models Expressions and Simple Constraints (which in my opinion are easier to implement) can do which is not so easily done manually.

The equality of the angles within the parallelogram is used in the Expression set for Objects B and C. Hence editing the motion of Object A is automatically transmitted to B and C.
In order to animate the piston (hardly impossible to do manually) the Simple constraint ‘Look At’ comes in very handy. And yes … again … 2 auxiliary points are needed to act as target.

parallelogram W ram Expressions and LookAt.3dm (62.4 KB)


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