# How to sense the torque with the revolute joint?

2 views (last 30 days)
Nayla on 5 Jun 2023
Answered: Nathan Hardenberg on 12 Jun 2023
Hello there,
based on the following simscape multibody example, I would like to measure the torque at the joint (see attached file). Is there a way to sense the values automatically? When setting "automatically computed" in "Actuation" there is an error message appearing.
How can i sense the torque instead?
Nayla on 8 Jun 2023
By sensing the velocity instead and then multiply it by the damping coefficient I can also get the Torque. Is this also a correct way to determine the torque?
Nathan Hardenberg on 11 Jun 2023
The name of the Block ist "Constant". In the Constant I use the deg2rad()-function to indicate that the input of the joint is in radians.
Regarding your other comment: What you describe does not calculate the torque. One example to prove my point is when your damping coefficient is 0. Your toque then should not be 0. I'm not into this topic at the moment that's why I can not tell/know how to calculate it.

Nathan Hardenberg on 12 Jun 2023
I tought about it a bit more: The torque is just dependent on the deviation to the natual position. The damper creates a torque in the opposite direction which slows down the movement, but the current toqure on the joint is just depentant on spring stiffness. Since the movement is not the problem here (it gets simulated with the multibody) the spring-torque T can easily be calculated:
with
• K : spring constant
• : diffence to equilibrium
Obvioulsly the values in the Revolute-Joint and the values in the calculation have to be the same

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