Few questions about Building Block tutorial in the anybody website

Hi, my name is Sungwoo Park. I’m a graduate student in Seoul National
University, South Korea. I’m studying biomechanics and using AnyBody
as an analyzing tool for motion data. I almost just started to use
AnyBody, so I’m studying by myself with the tutorial in
www.anybodytech.com, especially, building block tutorial. In that
tutorial, the main purpose is to modify the existing HandPump model
to connect hands with a pedal and make it rotate. The tutorial
explains that “You may find a glove segment as well as a hand. The
glove is a remedy for the fact that we have a rigid hand in the
model. Rigid segments are infinitely strong, and when you attach
something very strong to the environment you can sometimes get
unreasonable results. So we have added an extra glove segment to the
hand.”.
I will be very appreciated if you could explain why glove segments
are needed to get reasonable results in this model. What would happen
if I just use hand segment without glove segment?

Also, then do I need to make shoe segment(or something like that) if
I want to connect foot with other stuffs which will be attached to
the foot such as bike pedal?

Thank you.

Sincerely, Sungwoo Park

Hi Sungwoo

The glove segment can be used to ensure that the connection between the hand
and the environment will not be unrealistically strong. If the hand is
rigidly connect to the environment the model will automatically try to
“exploit” the available boundary conditions in order to lower the
activations in the muscles. By introducing this extra segment which is
connect to the hand using a spherical joint with moment generating muscles
of limited strength, it is possible to control the amount of force
transmitted through the boundary conditions. So the glove is not of any use
if you have just applied force in the hand, but it can be use if the hand in
reality holds around some object, in this case the glove is a crude estimate
of the strength of the hand.

I think for the particular model there would not be much difference since
the hands are connect using a spherical joint as far as I remember, and not
with a more rigid joint.

The glove model was introduced into the models before we had the pushing
elements available that made it possible to model unilateral support forces
with friction, please see the PedalDemoConditional for an example of this.
Today usually this kind of support would be used also in cases such as pedal
foot contact.

Please write again if you have further questions.

Best regards

Søren, AnyBody Support


From: anyscript@yahoogroups.com [mailto:anyscript@yahoogroups.com] On Behalf
Of cizofu11
Sent: 02 October 2008 09:24
To: anyscript@yahoogroups.com
Subject: [AnyScript] Few questions about Building Block tutorial in the
anybody website

Hi, my name is Sungwoo Park. I’m a graduate student in Seoul National
University, South Korea. I’m studying biomechanics and using AnyBody
as an analyzing tool for motion data. I almost just started to use
AnyBody, so I’m studying by myself with the tutorial in
www.anybodytech.com, especially, building block tutorial. In that
tutorial, the main purpose is to modify the existing HandPump model
to connect hands with a pedal and make it rotate. The tutorial
explains that “You may find a glove segment as well as a hand. The
glove is a remedy for the fact that we have a rigid hand in the
model. Rigid segments are infinitely strong, and when you attach
something very strong to the environment you can sometimes get
unreasonable results. So we have added an extra glove segment to the
hand.”.
I will be very appreciated if you could explain why glove segments
are needed to get reasonable results in this model. What would happen
if I just use hand segment without glove segment?

Also, then do I need to make shoe segment(or something like that) if
I want to connect foot with other stuffs which will be attached to
the foot such as bike pedal?

Thank you.

Sincerely, Sungwoo Park

[Non-text portions of this message have been removed]