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dondo

Creating An Ik Setup For A Mechanical Robot Arm

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  • I have a mechanical arm similar to those used in automated warehouses that build cards and such. I have a series of parents setup with some expresso sliders to animate with (I believe this is called an FK chain).

    I would however, like to animate it like an IK chain by animating the position of a target and the rest of the arm would follow along. The main thing I want to consider is constraining the different pieces of the arm to only rotate on one axis. I know only a very basic amount of rigging and I'm not sure where to start. Does anyone have any advice or can point me in the right direction?

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    You constrain the IK to only bend in one axis by adding a "Pole Vector". Just a matter of selecting the IK tag and clicking on "Add pole". You move it out a bit and move it into the hierarchy. I showed the entire process in the R10 rigging tut.

    Here's a quick scene showing this in action. Press play. Hope this helps. (11.5 version)

    3DKiwi

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    Howdy,

    Here is an example of a robot arm rig that automatically rotates the base when you move the IK goal:

    http://www.cactus3d.com/RobotArm.mov

    ... and here is the file:

    http://www.cactus3d.com/RobotArm.zip

    The file uses my CD Character plugins, which can be downloaded and used in the Runtime mode to open the file to study the setup.

    Adios,

    Cactus Dan

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  • Thanks to both of you, that is helpful. Dan was more what I was looking for with the swiveling base. I picked through both of the project files and as far as I can tell, Dan is using a null as an Up vector target to force the joint to stay upright. I tried putting a target tag with a null to straighten it on Nigel's project and then using the goal as an up vector and it works for that but now it seems the goal has the opposite effect: the joint tries to stay away from it. Any ideas?

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    Pass. You probably need to attach your scene file for us to check.

    3DKiwi

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  • It's an iteration on the file you posted.

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    Howdy,

    The Target tag can't go on the joint with the IK tag on it. The arm joints need to be parented to a base object and then the Target tag needs to be on that base object. Take a closer look at the object hierarchy in the file I posted.

    Adios,

    Cactus Dan

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  • Well I'm totally lost now. I have dissected that file and I apparently just don't get it. I tried adding some extra joints, a swivel and a base, putting a target tag on the swivel joint that points to a target null directly above with the goal as the up vector. Then I placed a target on the goal that uses that target as an up vector. I guess I just don't get it.

    What's funny is I realized that final animation won't even require having a swiveling joint, I can hide it off screen but now, I want to figure it out because I refuse to be defeated! I thought it would be as simple as constraining axes on a joint so the values stay constant but that doesn't work either.

    Hmph.

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    Maybe this tutorial can help understanding how joints & constraints work:

    http://greyscalegorilla.com/blog/2011/02/how-to-make-a-hydraulic-arm-in-cinema-4d/

    I myself tried to create a 6 axis industrial robot with a lot of suffering due to the many joints and their behaviour.

    Having two simple IK chains (like in the vid) with two goals to animate got me the best result and a really nicely animatable rig without having to worry about constraining too many parts.

    Hope this helps.

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    Howdy,

    The setup in the file I posted is basically the same setup as the mechanical bull from this tutorial:

    The only difference is that the mechanical bull doesn't have a 2 link arm using IK, but instead has a single link arm using an aim constraint.

    Adios,

    Cactus Dan

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