Tom beat me to answering and gave a better answer than I would have! (Hi, Tom) To elaborate a little -- in your example of a Weld joint vs. Weld constraint: Say we weld body A to body B. With a weld joint, A and B essentially become the same body, with B attached exactly as specified by the joint. T...

Hi, Harshal. An important thing to know is that Simbody expects inertias to be provided taken about the body origin, NOT the body mass center. I suspect your specification of the motor inertia was intended to be about the COM (0,0,.4) but Simbody interpreted it about (0,0,0) which, when shifted to (...

Of course there is a limit to how big a system can run in real time, but I don't think you're close to it yet. Take a look at "ChainExample". That's an interactive 3d example with 100 bodies connected by ball joints so 300 dofs. Depending how stiff your springs are, you might find an explicit integr...

The rule to follow is this: Imagine the system with just the bodies and joints (constraints removed). That tree-structured system defines the mass matrix and must be non-singular. So you can weld massless bodies together if they are part of the tree system (i.e. using a weld joint rather than a weld...

No, sorry Nicos. Angular velocity is not the derivative of Euler angles (except in one special case: when all three Euler angles are zero). Otherwise you have to use Euler angle derivatives for u to get N=identity. Angular velocity is in fact not the derivative of any set of q's -- there is always a...

Hi, Nicos. No, that's a very reasonable question! The answer is that FunctionBased Mobilizer is a special case of Custom Mobilizer provided for convenience. The author of that class designed it to work only for mobilizers where qdot=u (that is, N=identity). The general Custom mobilizer supports N !=...

Nice! Congratulations.

You're welcome!

Here is a plot of the three components of the angular velocity of the shaft, expressed in the shaft frame. I set the initial conditions to (10, 1000, 1000) degrees/s. The y & z velocities vary between +/- 1414.21 degrees/s. plot.png The modified code I used is here: #include "Simbody.h" #include <io...

Hi, Naushad. I found a few minor problems with your implementation: - angular velocity in Simbody is given in radians/sec, not degrees/sec - angular velocity for a body B is given and reported as w_GB_G, that is, the angular velocity of body B in Ground, expressed in Ground; what you are interested ...