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Joint Torque

ECoetzee

Hi All

I haven't used ADAMS for a while and am now starting to use it again. I have come across an issue that I do not know how to solve. I have a simple pendulum with a rotation joint which the pendulum swings about. I want to create a state variable or a measure to measure the torque around this joint. When I do this the calculation produces 0 for different types of commands, either for the TZ or JOINT commands. Ultimately I want to know the different contributions to the overall torque around the joint. For instance, I would like to the contribution from the inertial effects, the torque from an applied torque etc. I can get the overall torque if I multiply the angular acceleration with the Izz inertia around the joint, but I assumed there is an easier way than this. Any pointers would be helpful because I seem to be missing something very obvious.

Regards

Etienne

  • 0

    Hey Etienne,

    When creating measures in Adams you should keep these two things in mind; 

    1 - You may always create a measure for any marker to measure kinematics (position, velocity, acceleration)

    2 - If you wish to measure force, or torque, through a joint, you must create a measure specifically across the I- and J-markers of the desired joint

    If you do not make the measure across the I-J-markers, then you will always get a zero resultant. Easiest way to figure what the I-J-markers are that you need to make the measure for is to right-click on the joint in the model browser, and click "info". In the information window that appears, you will see the I- and J-marker numbers in the rows of info about the joint. That's it! Good luck Slight smile

    Best, James

  • 0 in reply to James Parkus

    Thanks James

    I have implemented a measure referring to the I and J markers from the joint, but I am afraid that I still get the same result. I will try some other combinations.

    Thanks for the suggestions.

    Regards, Etienne

  • 0

    Hi Etienne. Yes, it has been a long time since your name showed up in my flow. Welcome back.

    So you are trying to measure the torque in a joint in a direction that is not constrained. Yes, that will always be zero. Applied torques around this direction, you have to measure separately.
    The TZ() function used to be very useful (View 8.2 and earlier) where the user created every marker by hand and then applied elements between markers. Then you could use the same markers for the joint as for an applied torque. And then TZ() would return what you where after. But as View today creates new marker for each element you create, that pretty much rendered TZ() and it's "sum-of-all-forces-at point" siblings meaningless.

    So how to do this? One possibility: Break the pendulum in two parts. One top part connected with your revolute joint and taking all applied torques. Can be massless and zero dimensions. Then connect the pendulum to this first part with a fixed joint. Now you can measure anything you want in that fixed joint. 

  • 0 in reply to Jesper Slattengren

    Hi Jesper

    It's been a while! Thanks for the explanation. It is very helpful. I will give it a try. 

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