Search found 800 matches
- Thu Nov 16, 2023 9:53 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Get internal forces for a MobilizedBody
- Replies: 14
- Views: 2098
Re: Get internal forces for a MobilizedBody
Hi, Simone. I don't think there is a pre-existing function that would provide exactly the quantity you want. That might be a nice addition! However I can think of a few ways to get it: - thinking of a free-body diagram, use F=MA to obtain the net spatial force F from the body's spatial inertia M and...
- Tue Oct 31, 2023 7:40 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Modal Analysis
- Replies: 3
- Views: 651
Re: Modal Analysis
:facepalm: yes of course you're right. You want partial(acceleration)/partial(state). Simbody can provide acceleration(state) (fast) but you would have to differentiate that numerically to get the matrix. That's easy to do by hand or using Simbody's Differentiator class.
Sherm
Sherm
- Mon Oct 30, 2023 7:48 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Modal Analysis
- Replies: 3
- Views: 651
Re: Modal Analysis
You can obtain the system Jacobian using
SimbodyMatterSubsystem::calcSystemJacobian(). I believe the manual is referring to the eigenvalues of this matrix as the system modes.
Sherm
SimbodyMatterSubsystem::calcSystemJacobian(). I believe the manual is referring to the eigenvalues of this matrix as the system modes.
Sherm
- Sat Oct 14, 2023 4:11 pm
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Rotation Matrix notaion
- Replies: 2
- Views: 376
Re: Rotation Matrix notaion
Hi, Amit. Good question! Terminology for transforms and rotation matrices is tricky, because they serve as both "verb" and "noun" depending on your point of view. As a verb, we have v_B=R_BG * v_G, mapping G to B (as long as you multiply from the left!). The notation ensures you get that correct bec...
- Tue Sep 05, 2023 8:07 am
- Forum: OpenSim
- Topic: Rolling on Surface Constraint Usage
- Replies: 3
- Views: 467
Re: Rolling on Surface Constraint Usage
According to the OpenSim documentation here it uses a Simbody PointInPlane constraint for the normal contact. That is described here . I'm not sure why it wasn't implemented by a Simbody SphereOnPlaneContact constraint, but I believe it produces a similar result. Ajay Seth might have further insight...
- Mon Sep 04, 2023 8:52 pm
- Forum: OpenSim
- Topic: Rolling on Surface Constraint Usage
- Replies: 3
- Views: 467
Re: Rolling on Surface Constraint Usage
The constraint is applied at the point of contact.
- Sherm
- Sherm
- Tue Aug 15, 2023 8:37 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Unstable equilibria
- Replies: 3
- Views: 337
Re: Unstable equilibria
Thanks for your kind remarks -- I'm glad you're finding Simbody useful. Yes, minimizing PE only finds stable equilibria. You should be able to find everything you need in SimbodyMatterSubsystem . For example you can calculate accelerations udot directly with calcAccelerations() and you can convert t...
- Sun May 28, 2023 10:20 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Drone
- Replies: 1
- Views: 373
Re: Drone
Yes, a Free (6dof) joint for the body and Pin (1dof revolute) joints for the propellers.
- Thu Apr 20, 2023 10:39 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Ragdolls
- Replies: 2
- Views: 316
Re: Ragdolls
Hi, Nat. There is one ragdoll among the Simbody examples that I know of. It's called "Gazebo2Simbody" and is mostly about reading .sdf files. But the .sdf it reads by default is a ragdoll -- you can run it and see the ragdoll fall down.
Regards,
Sherm
Regards,
Sherm
- Fri Feb 24, 2023 11:53 am
- Forum: Simbody: SimTK multibody dynamics API
- Topic: Running Simbody on Apple Silicon
- Replies: 3
- Views: 532
Re: Running Simbody on Apple Silicon
Definitely possible since we don't currently build Simbody on arm64 Macs in CI. If you have access to one and are able to find the problem we would welcome a pull request so others can benefit!