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Model walking body in Simulink

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Nick
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?

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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

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Nick
Nick on 21 Sep 2015
I have uploaded my model. First run the parameters then the simulation. The way it works now is that the legs hang from the body. I want the legs to stand on the "ground" and actually have the torso be supported by the legs. The joints are not actuated so the system should collapse (or not if i aligned everything correctly).
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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