Search found 375 matches

by Ross Miller
Mon Jan 08, 2024 7:19 am
Forum: OpenSim Moco
Topic: Stiffness optimization in the exmpleSquatToStand of MOCO matlab
Replies: 5
Views: 812

Re: Stiffness optimization in the exmpleSquatToStand of MOCO matlab

Hi Yimeng, In the solution file, are you 100% sure there is no value indicated for the stiffness? In my solution files with parameters optimized, these values are easy to miss, they will have the single parameter value in the first entry (first "timestep"), then the value at all other timesteps will...
by Ross Miller
Wed Dec 20, 2023 4:51 am
Forum: OpenSim
Topic: External Load "Body Force" Setting
Replies: 4
Views: 1057

Re: External Load "Body Force" Setting

Here is a nice post from Ton van den Bogert on Biomch-L that explains the difference between these options (point force vs. body force) for GRF well: https://biomch-l.isbweb.org/forum/biomch-l-forums/general-discussion/32938-non-planar-moving-force-plates-in-c3d#post39057 Essentially the "body force...
by Ross Miller
Wed Dec 13, 2023 2:58 pm
Forum: OpenSim Moco
Topic: Orientation Tracking Setup
Replies: 36
Views: 6275

Re: Orientation Tracking Setup

I think the header in the file probably just needs to say bodyset/pelvis

You can thank Brian, Nick, and Chris for most of the code I paste here, they indirectly wrote ~ half of it!
by Ross Miller
Wed Dec 13, 2023 11:46 am
Forum: OpenSim Moco
Topic: Orientation Tracking Setup
Replies: 36
Views: 6275

Re: Orientation Tracking Setup

My response won't be very helpful sorry, but just some background: the reason I used setStateReference instead of setRotationReference was because I could never figure out how to get setRotationReference to work. I wanted to minimize the angular motion of the torso in the global frame, but because t...
by Ross Miller
Sat Dec 02, 2023 5:33 am
Forum: OpenSim Moco
Topic: Unexpected interruption of optimization iterations
Replies: 5
Views: 1005

Re: Unexpected interruption of optimization iterations

One of my frustrations with IPOPT is that the value of "objective" printed to the screen during iteration is not exactly the value that is being targeted for minimization. Similarly, the data printed to the screen are related to the values being checked against the constraint and convergence toleran...
by Ross Miller
Fri Dec 01, 2023 10:03 am
Forum: OpenSim Moco
Topic: Explaining The Optimal Control Problem
Replies: 4
Views: 575

Re: Explaining The Optimal Control Problem

Hi Jayson, Are you referring to the optimization algorithm? Moco uses IPOPT, which is explained here: https://link.springer.com/article/10.1007/s10107-004-0559-y For more information on the direct collocation method, these papers are good. Moco doesn't use exactly the methods described in these pape...
by Ross Miller
Wed Nov 29, 2023 12:44 pm
Forum: OpenSim Moco
Topic: Moco goals for average speed in cycling model
Replies: 39
Views: 20251

Re: Moco goals for average speed in cycling model

Hi Ana, The following paper might be helpful on modeling the crank mechanics: https://www.researchgate.net/profile/Benjamin-Fregly-2/publication/12286992_Bicycle_Drive_System_Dynamics_Theory_and_Experimental_Validation/links/540787b90cf23d9765ab9d08/Bicycle-Drive-System-Dynamics-Theory-and-Experimen...
by Ross Miller
Fri Nov 24, 2023 12:26 pm
Forum: OpenSim Moco
Topic: Moco goals for average speed in cycling model
Replies: 39
Views: 20251

Re: Moco goals for average speed in cycling model

Hi Ana,

I wasn't suggested to track the pelvis motion. Assuming the crank angle is a state in the model, you can use a periodicity constraint combined with a prescribed final time to prescribe the average speed of the crank (360 degrees / Tfinal).

Ross
by Ross Miller
Fri Nov 24, 2023 4:39 am
Forum: OpenSim Moco
Topic: Moco goals for average speed in cycling model
Replies: 39
Views: 20251

Re: Moco goals for average speed in cycling model

I don't know of a way to enforce a constant speed (i.e. the instantaneous speed of some coordinate is always the same value). I think in the original Chow & Jacobson (1971) paper they prescribed the motion of the pelvis somehow, but not sure how that was done or if Moco can do a similar thing. https...
by Ross Miller
Wed Nov 15, 2023 6:02 am
Forum: OpenSim Moco
Topic: MocoFrameDistanceConstraint
Replies: 1
Views: 297

Re: MocoFrameDistanceConstraint

Hi Mohadeseh, I think the projection vector has to be specified using Vec3, and you probably also need to specify the type of projection, e.g.: distanceConstraint.setProjecVector(Vec3(1,0,0)); distanceConstraint.setProjection(string); % this string can be 'none', 'plane', or 'vector' If your goal is...