Backpack model

Main Forum
1

Hi,
I have a quick question on the repository models: I read in some threads of a Backpack model; was that available in the past? I see no such model in the Demo I have downloaded. Is it available somewhere?

Thank you,

Michele

2

Hi Michele,

I think the only way to get the model would be to install an older AMS version containing an old AMMR version with the backpack model in.

Alternatively it might be on this forum in some form if you search for it.

Best regards
Søren

3

Hi Søren,

thank you for your answer, I was able to download it from the forum. I would have a question though: in the model the CoM driver constrains the CoM to be above the global ref, and when the backpack is introduced, the initial position consists in a model leaning forward; I believe it is the ankle joint flexion which is free and changes with the backpack weight, controlled by the CoM driver, right?

I though it would be more natural to have the model leaning forward as a result of spine flexion, rather then ankle flexion, and therefore I tried to drive the ankle flexion to a zero value and to comment out the PelvisThoraxExtension degree of freedom. Doing so, however, results in an “initial conditions” with flexion of the spine even when the backpack has 0 mass or it is removed, and in fact it happens also on the Demo Standing model of the current repository, which I tested for this behavior.

Could you please tell me why? Is it possible to have the CoM above the global reference system by acting on the flexion of the spine?

Thank you,

Michele

4

Hi Michele,

The CoM measure will always measure wrt to the world coordinate system so lets say you driver one direction to zero it will be wrt to the global zero. This means that it then matters where the feet are attached to the ground their position forward/backward will change the results, i am wondering if this is what you see here.

Is it possible to have the CoM above the global reference system by acting on the flexion of the spine?

I am sorry but i do not really understand this question. The CoM will always measure wrt to global ref.

Best regards
Søren