How to change size of simscape multibody models

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Ting
Ting 2024-9-30
评论： Ting 2024-10-9
When I changed the size of the Stewart Platform model to 10 times the default size, the model fell apart and failed as the figure shows. What other model paprameters do I need to modify after changing the size?
The attachment is the original model.
Thank you for your help!
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Ting
Ting 2024-10-1
Hi@Sandeep Mishra
Thank you for your attention!
I already upload the original Stewart platform model.I'll very appreciate it if you could give me some guidance.
Yifeng Tang
Yifeng Tang 2024-10-4
Hi @Ting,
The model you uploaded seems to be the original one from Simscape Multibody documentation. Could you please let the community know what parameters you attempted to change and ran into error? Some screenshots and explanation will be helpful.

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Yifeng Tang
Yifeng Tang 2024-10-4
Hi @Ting,
I just multiplied most of the dimensions in the subsystem mask by 10, and the model seems to assemble OK. See below. Are you able to reproduce this?
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Yifeng Tang
Yifeng Tang 2024-10-8
When the dimensions are now 1.5x of what it was, the control reference/target probably needs to be different as well. Did you scale that up? In this particular case, the dz reference needs to be scaled up. This seems to give me nearly identical looking results as before.
Then, you can start tuning the controller gain. When I tried to scale by 2.5, the original control gains are no longer sufficient. Using reasonably higher values will stablize the platform. Repeat the steps and I was able to bring it to 10x larger. I attached the model and the script with scale values and sample control gains. You can uncomment part of the param_scale.mlx script to see the progression towards 10x larger.
% scale = 1.0;
% Kp = 300;
% Ki = 20;
% Kd = 5;
% scale = 1.5;
% Kp = 300;
% Ki = 20;
% Kd = 5;
% scale = 2.5;
% Kp = 1000;
% Ki = 100;
% Kd = 20;
% scale = 5.0;
% Kp = 4000;
% Ki = 400;
% Kd = 100;
scale = 10;
Kp = 20000;
Ki = 2000;
Kd = 500;
BTW: crazily high control gains almost always lead to unstable system. Take small steps and happy modeling.
Ting
Ting 2024-10-9
Thanks a lot!@Yifeng Tang
Following your instructions, I was able to implement it successfully. These parameters do need to be changed uniformly, which I had overlooked before. Thank you very much for your continued guidance.Wish you all the best.

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