Another good question, thanks Kaiwen. I had to think about this one for a while since it has been a long time! This comes from Simbody's definition of the position constraint matrix P, based on the intended use in computation. You can see the definition in Doxygen here (scroll down to "Theory discus...

Thanks for this great question, Kaiwen. Here is our thinking behind this constraint: Simbody constraints always model some physically-possible system, always assuming that the position and velocity constraints can't be exactly satisfied (they never are in practice). It is easiest to think of this by...

Hi, Harshal. Simbody is not doing anything. The user applied an angular velocity to one body in the assembly of two bodies (a cylinder and a brick). Every point of both bodies that is not aligned with the angular velocity vector will have a translational velocity also (think of a spinning propeller ...

You're welcome!

3. From the example "ExampleMotorWithSpeedControl": MyTorqueLimitedMotor (const MobilizedBody& mobod, MobilizerUIndex whichU, Real gain, Real torqueLimit) What is the use of MobilizeUIndex. According to my understanding U stand for generalized speed, which contains 6 elements ( 3 angular and 3 linea...

In DzhanibekovEffect, you were surprised that changing the angular velocity from (10, 0, 1e-10) to (10, 10, 1e-10) caused translation to occur. That's because the angular velocity value you chose gave the system center of mass a non-zero translational velocity. You can see that by adding the followi...

These are great questions, thanks Amit. I'll answer one per post: I want to provide Initial angular velocity to the whole body , not one body. is function "setUToFitAngularVelocity" (https://simbody.github.io/3.5.0/classSi ... de27544411), but this function only provide the angular velocity between ...

I think you wanted: so that you are working with the actual MobilizedBody in your system rather than a copy.

I'm not familiar with OpenSim's IK interface so this is just Thanksgiving speculation in case no one else is available: - assuming there is a way to loosen the tolerance, you may find you can solve the problem using joints and constraints with a little more slop allowed - you may have a problem with...

This diagram may help (scroll down to "Mobilizer Terminology and Notation") -- notice that a mobilizer is a relationship between two frames. One (F) is on the parent (inboard) body and the other (M) is on the child (outboard) body. A Pin mobilizer aligns the Z axes of those two frames. Each frame c...