## Search found 165 matches

Tue Sep 03, 2024 7:43 am
Forum: OpenSim
Topic: Moment arm calculation of OpenSim
Replies: 4
Views: 265

### Re: Moment arm calculation of OpenSim

The paper cited by Mohammadreza is very good, but there is one error in the paper that I would like to point out (in case it causes confusion). When a model has moving muscle points, the paper says that equation (1) should be used instead of equation (3). This is, however, not correct. Equation (3) ...
Fri Jan 12, 2024 1:15 pm
Forum: OpenSim
Topic: error in inverse dynamics
Replies: 9
Views: 2483

### Re: error in inverse dynamics

The spatial registration between raw motion capture data and force plate is correct, the center of pressure is exactly were it is expected and not 0.4 meters off. I plotted the horizontal position of COP and a few markers in the lower right leg and foot. Untitled.png The next thing to check would be...
Fri Jan 12, 2024 9:00 am
Forum: OpenSim
Topic: error in inverse dynamics
Replies: 9
Views: 2483

### Re: error in inverse dynamics

I plotted your data. Untitled.png The joint moment is close to 400 Nm at the peak, which is far too large indeed. The GRF at that time is 1000 N (which is normal), so this means that the center of pressure is about 0.4 meters from the ankle joint. Unless your subject is wearing skis, that is not pos...
Tue Jan 09, 2024 11:07 am
Forum: OpenSim
Topic: GCVSplineSet errorVariance
Replies: 7
Views: 1358

### Re: GCVSplineSet errorVariance

Mohammadreza, You probably meant to say "the GCV mode can be implemented ... if I set the errorVariance to a negative value". If you know the variance, you can specify it as a positive value. And the larger that value, the more difference the spline allows between smoothed and raw data. So more smoo...
Mon Jan 08, 2024 12:41 pm
Forum: OpenSim
Topic: Simulate accelerometer on tibia
Replies: 2
Views: 727

### Re: Simulate accelerometer on tibia

Just be aware that an accelerometer does not measure acceleration. The marker acceleration is the acceleration expressed in the global reference frame. An accelerometer measures global acceleration but expresses it in a local reference frame (the sensor axes). And there is an effect of gravity. The ...
Mon Jan 08, 2024 12:30 pm
Forum: OpenSim
Topic: GCVSplineSet errorVariance
Replies: 7
Views: 1358

### Re: GCVSplineSet errorVariance

I have a lot of experience with the GCV spline code (received it in 1985 on a 9-track tape!). The Fortran source code is still available on Netlib at https://www.netlib.org/gcv/gcvspl. After the first page or two, look at the "SUBROUTINE GCVSPL" with good technical information. There is an accompany...
Tue Nov 21, 2023 3:12 pm
Forum: SCONE
Topic: GaitMeasure calculation
Replies: 6
Views: 1528

### Re: GaitMeasure calculation

That seems to work! The step velocity value is now consistent with the horizontal speed of the pelvis. Result = 0.667518 CompositeMeasure = 0.667518 Gait = 0 <- 100 * (0.0162636 > 0.05) step_velocity = 1.06426 step_count = 72 Effort = 0.618483 <- 0.1 * 6.18483 effort = 16107.5 distance = 34.943 DofL...
Tue Nov 21, 2023 1:44 pm
Forum: SCONE
Topic: GaitMeasure calculation
Replies: 6
Views: 1528

### Re: GaitMeasure calculation

Thomas, Thanks, that is amazing that you were able to fix that so quickly. I will test it immediately if you give me install instructions. I agree that the GaitMeasure should become zero during the optimization so that in the end only the effort is minimized. About the font, yes, it's on Windows. My...
Mon Nov 20, 2023 9:12 am
Forum: OpenSim
Topic: Knee joint definition issues in gait model
Replies: 2
Views: 701

### Re: Knee joint definition issues in gait model

Johannes, The knee is a little different in this model, because the axis of rotation translates relative to the femur. This translation is coupled to the rotation (i.e. a function of knee_angle) and you can find this in translation1 (x) and translation2 (y). Translation y varies from -0.39 to -0.42 ...
Mon Nov 13, 2023 2:30 pm
Forum: SCONE
Topic: GaitMeasure calculation
Replies: 6
Views: 1528

### GaitMeasure calculation

I am running a scenario where the simulation ends after a specified number of gait cycles (unless it falls sooner). It's about 34 seconds. When using MeasureGait10GRF15.scone from the examples, the gait measure component becomes quite large, which makes the effort measure less important. Here is the...