[ODE] How to measure the joint torque correctly

[mango juice]

Hello!

I am a beginner of ODE. I would appreciate if you could show me
how to obtain the joint torque correctly.

As a simple test, I applied a force to one side of a link.
The other side is attached to a joint. I would like to
measure the torque at this joint. In my program, I have:

dJointFeedback* feedback = dJointGetFeedback(joint);

To obtain the magnitude of the torque, I tried two methods:
1. fabs(feedback->t1[0]-feedback->t2[0])
2. fabs(feedback->t1[0])

As I increased the applying force, the torque at the joint should
be increased monotonically. However, I got values such as:
... 2.8, 2.6, 2.6, 2.3, 15, 2.3, 4, 6.7, 6.3, 3.1, 5.4, 2.8, 4.2,...

Am I doing something wrong? Is this a bug of ODE?

Thank you.

Jimmy

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