Bongo delay issue

Bongo
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1

I found bongo has this delay issue randomly with IK chain

As you can see the element is not following the position it should be.

But if I stop and wait for a sec, it will be corrected, like this:

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However, this is totally random. As I have 4 legs, with exactly the same settings. The other 3 can follow their positions perfectly.

And this is even random. That every time when I open the model, their is always 1 random leg that has this bug.

Unfortunately, when I render the scene, bongo wouldn’t wait for the model to be settled, so this bug will be displayed in the output video

Try.3dm (4.1 MB)

2

Hi Danny,

The “issue” is the due to the fact that result of the constraint of the hydraulic cylinder depends on the result of the constraint of the ‘foot’ following its Path. The order in which both chains - the leg itself and the hydraulic cylinder - are calculated is random. In your model the legs should be calculate first and then the hydraulic cylinder. Unfortunately Bongo does not allow the user to determine in which order chains have to be solved.

Reversing the chain of the hydraulic cylinder solves the issue. Hence it can be included in the basic chain of the leg. Having multiple constraints in one chain is no problem for the IK solver. That’s also the reason why the hydraulic cylinders in the arm of your machinery do not have the “issue”. All constraints are part of the one chain that begins with Object 1.

In Try 001.3dm (4.2 MB) I transformed one hydraulic cylinder (coloured golden).
2 Auxiliary point had to be added. I assume you can do the others cylinders yourself.

BTW, Interesting model. The fancy walking makes the apparatus look very cute.

If you’ll allow me, some comments…
Object 12 has a ‘empty’ Simple Constraint installed. Unharmful but unnecessary. For Objects 7, 113, 133 and 127 the IK ‘Joint and constraint’ is used. ‘Joint’ suffices.
Object 153 also has an unnecessary Simple Constraint, probably intended to control the telescopic arm. I took the liberty of adding 2 simple Position-keyframes to make the neck extend.

Have fun,
Luc

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Hi @Luc

Thanks for your explanation, it is super clear!

I was being lazy and directly uploaded the entire model. I’m very grateful that you actually took some time and looked into the model.

For object 12 & 153, yeah I was using simple constraint ‘to path’ to make them move. After that I decided to make some keyframes with transforms instead. Then forgot to remove the simple constraints, haha.

For the 4 connections at legs, that I applied ‘Joint & constraint’, they were simply joints before. Afterward I found an IK chain with 3 elements will bend into undesired shape when they are following the ‘stepping motion’. Thus, I banned the rotation of the middle one.

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Thanks for your advices, really helped me out.

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OK Danny, now I see… indeed yes a chain with 2 hinges midways is ambiguous.
AmbiguousChain

But, in order to get rid of the Rotation, you can simply release Objects 113, 119, 127 and 133 (the knee elements) from their Hinge properties, hence from all IK properties.
A uncomplicated, straight forward, ‘child’ can be part of an IK chain, as good as Hinges and Telescopes.

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Thanks again for sharing your model.
Luc

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Hi @Luc

I see, this is much more elegant, so does the backward IK chain you mentioned before.

Your suggestions really opened my mind. Thank you very much!

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