Motion using Markers with Revolut joint

Mrage

Hello,

I am trying to add a Translational motion on a simple Pendelum connected to a Revolut joint by using Markers. For that i added an additional Marker. Within the Motion i added Marker "Global Frame" as Marker 1 and "New_Marker" as Marker 2. Although Translational along axis of Marker 2 is chosen i get an rotaional movement.

Using a fixed joint instead of an Revolut Joint no issues occure. What am I doing wrong here?

Thank you!

Chris Coker_21312

A simple pendulum with a revolute joint consists of 1 rigid body, and a joint that constraints 5 degrees of freedom, leaving only the rotational degree of freedom free.  This model has 1 DOF, and that's in the rotational DOF.  Trying to add a translational constraint to this will not work.

 

 

For simple models like this you have pay careful attention to the .log file, and make sure you are not overconstraining the model.  MotionSolve will automatically remove constraints to make it solve, but you may not get the results you are looking for.

Mrage

Hi Chris,

Thanks for your quick reply. So this explaines why it worked with a fixed joint. MotionSolve probably removed the translational constraint on the x axis. i will definitly have a closer look on the log-file.

What can i do to solve my problem? I guess what i need than is a combined Revolute/Translational Joint. I could not find any information on how to combine joints. Or is there another way to add translational motion to a revolute joint?

Thank you!

Chris Coker_21312

Mrage said:

Hi Chris,

Thanks for your quick reply. So this explaines why it worked with a fixed joint. MotionSolve probably removed the translational constraint on the x axis. i will definitly have a closer look on the log-file.

What can i do to solve my problem? I guess what i need than is a combined Revolute/Translational Joint. I could not find any information on how to combine joints. Or is there another way to add translational motion to a revolute joint?

Thank you!

Combining Joints doesn't make sense, again because you are over constraining the equations.

Example:

The pendulum body has 6 DOF.  If I add a revolute joint, I take away 5 DOF, leaving 1 DOF remaining.  If I somehow combine joints and add a translational JOINT to the model, that takes away another 5 DOF, leaving me with an overconstrained model.  Then adding the motion to that takes away another DOF.

You have not stated your problem very clearly.

If you are trying to model a pendulum that can also translate, what you need are two bodies.  First the pendulum, and then the body that is supposed to translate.  The one body is attached to ground via a translational joint, the pendulum is attached to the other body via a revolute joint.  Then I apply a motion to the first body, which can translate, and the pendulum will also translate with it.

 

It seems you might be quite new to multi-body dynamics.  I would highly recommend starting with some of the introductory tutorials for MotionView, starting with MV-100.  Also, there are regularly scheduled classes that are held online, which you can sign up for at learn.altair.com

Mrage

Alright, now I got a hold of the principle. And it worked out. Indeed I am very new to this. I will definitly check out some the introductory tutorials. Thank your very much.