Model walking body in Simulink

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Nick on 20 Sep 2015
Commented: Mohamed Elshami on 26 Dec 2018
I'm trying to create a simple model of a body which will then be later controlled. However, I am running into trouble when I'm connecting both legs to the body.
What I have done is that I have built the model starting with the left foot, attached to the world frame, and then up to the torso. I ended up duplicating one of the legs and attached it again the the world frame and the torso, effectively closing the "loop". However, I get the following error message when trying to run the simulation.
'untitled/Right Leg/Hip/Revolute Joint' has a degenerate mass distribution on its follower side.
I have a feeling this has to do with the fact that both legs are attached to the torso and to the world frame.
Here is an overview:
What would be the correct way to model this so that I can later actuate the joints?

Answers (2)

Sebastian Castro
Sebastian Castro on 21 Sep 2015
The error you included usually occurs when you establish a rigid link (between two joints) with no mass. You can check that for yourself -- see if you're missing any Solid blocks, or maybe they're connected on the wrong side of the joint.
From the top-level, the model looks fine. We'd have to look inside the other subsystems, especially since the error is pointing to untitled/Right Leg/Hip/Revolute Joint.
- Sebastian
Mohamed Elshami
Mohamed Elshami on 26 Dec 2018
I have another problem in the same model
I am just began to learn your demonstration few hours ago
and I want to define the transform of both the top and the bottom of the lower_leg_length
I did as you expalined except that I defined Length and Radius directly within the model
but I got different results
like the attached Picture no.1
However, for example the bottom cordinate is the first transform and the top cordinate as the second transform:
If I considersed the second transform with respect to the first one and changed TRANSLATION and ROTATION values with respect to it I finally got the correct representation

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sudhansu tripathy
sudhansu tripathy on 20 Aug 2018
hi Nick were you able to find the solution for the error message


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