Hello
Ive been working on getting Kinematics of a ballet dancer in anybody. I have done most of the necessary changes required to get the motion running. I happen to get my parameter optimization to converge and complete. Also the updated parameters are being used in the marker tracking and thus running the inverse dynamics.
In chart window
I got the foot to strike the force pad at the right time as in my c3d file.
the in contact muscle and No contact muscle switch on and off at the time i wanted.
From my previous discussion at the forum, I had some problems with the ankle flexion being too much or the muscle couldnt hold the kinematics of the left foot ankle. So i was suggested to add a few measures to support the kinematics which helped and completed the kinematics.
Now that i know the Human model in Anybody is supported at the pelvic region when not in contact with the Force plates or when freely hanging in space. Once the model walks and steps on the force plate this any reaction force needed to support the model should go away and we will need the reaction force from the force plate to balance the body.
my problem in the model is
the human ground residual is not going to zero after contact with the force plate.
I also checked the Force from the force plate, it seems to be very high. the reason i say this is the dancer weights 62 kg *10 (620N) and the reaction force from the force plate is -1327 N. and when i cross checked this value with the c3d file its almost the same (-1327N). I think while calibrating the force plates something might have gone wrong. I was not present when the readings were taken so i dont know what is gone wrong. If possible is there a way i can scale these reaction force values from the fore plates in anybody ?
The residuals will only be present if there is lack of balance in the system. As far as I remember these residual actuators are weak and should not activate if joints and muscles can do the job. Which could be a problem of kinematics or force plate readings.
The ground reaction forces from the force plate may be higher than weight of the body if the person is moving. F = m*(a+g)
If the model is not moving, but reading are still large - you can typically change your c3d file using, say, Mokka.
but if the residuals are actually doing the job, they should become come close to zero on contact with force plate since we want the entire weight of the body to rest on the force plate for reaction forces to be observed. In my case it is going negative which means there are some extra reaction forces still extisting right ? i think. but i am not sure.
I think you have strong residuals that are allowed to take a lot force. Ideally they should have nothing (or body weight if hanging in the air). You could try switching the residuals to this:
#define MOCAP_HUMAN_GROUND_RESIDUALS "PelvisWeak"
But it might be just okay. I suspect that the residual that you see is the difference between weight and reading of the force plate. It is close to 600 N.
Means residual muscles are too weak and cannot provide balance for an unbalanced system. We are back to square 1. Could you somehow verify your ground reaction forces? Are there any calibrations trials? A few frames where person is not moving and just standing? You could see if there is an error in force plate measurements.
the z-axis is the vertical direction. it looks fine to me the only thing i was concerned was the reaction forces being high but as you said it could the the body accelerating so we could get high forces.
Even then i have this in mind the dancer seems to be moving very slow and hardly any acceleration, I suspect the forces are a bit too high for this movement. and stepping on the force plate the dancer is trying to balance on toe tip without sudden movements, I would say shes almost static . So we should have almost the weight of her body at this instance right ?. (refer fig 2) having 62 Kg has her body weight it should be almost 620N.
Yes, you clearly have a problem there. It should be closer to 620N. I guess you would need to adjust this file unless you can have another recording. Mokka has a function to scale data - see the screenshot. I suspect this would also make residual forces eventually smaller.
Thank you so much
I scaled it to the necessary reaction force and imported the scaled c3d file into my main any body code.
it works how i wanted it, Its a relief for now.
Fig 1 :
