How can I edit SimMechanics block parameters programmatically?

I am writing a script to generate a SimMechanics model programmatically and need some help.

bdclose('all')          % close all Simulink models
new_system('K')         % start a new model called K
open_system('K')        % open the new model called K
load_system('mylib')    % loads my custom library of SimMechanics blocks (these are just the basic blocks: body, ground, revolute, prismatic, etc.)

For a block like ground, I can add it to the model and change parameters as follows:

add_block('mylib/Ground','K/Ground',...
      'CoordPosition','[# # #]',...
      'ShowEnvPort','on'); % where [# # #] is an arbitrary location

I can also add the machine environment block and modify it:

add_block('mylib/Machine Environment','K/Machine Environment',...
  'Gravity','[0 0 0]');%,...
  'Dimensionality','2D Only',...
  'AnalysisType','Kinematics',...
  'VisualizeMachine','off')

Here is the problem: I cannot seem to properly modify some the Body block parameters

add_block('mylib/Body','K/Body',...
  'Mass','0',...
  'Inertia','zeros(3)',...
  'CGPos','[# # #]',...
  'CS1Pos','[# # #]',...
  'CS2Pos','[# # #]');

Obviously, replace the '#' with actual numbers. When I run the code, the CS positions are not altered when I double-click on the block in the model. I found that I can change the CG line as follows:

CGstr = ['Left$CG$[# # #]'$WORLD$WORLD$m$[0 0 0]$Euler X-Y-Z$deg$WORLD$false$none'];

and replace...

'CGPos','[# # #]'

in the previous 'add_block' code with

'CG',CGstr

and it works. But I can't do it for the CS1, CS2, etc...Any suggestions?

[Kaustubha Govind]

What about if you use SET_PARAM after calling add_block('mylib/Body','K/Body')?

[Matthew Eicholtz]

I tried using SET_PARAM as you suggest, but it seemed to produce strange results.

When I selected View->Block Data Tip Options->Parameter Names and Values and hovered over the object, it looked like the changes took effect, but it didn't show up when I double-clicked on the block itself.

Answer 1

[Ryan G]

It looks like you found that string in the model file. There is a similar string for 'WorkingFrames'

'Left$CS1$[0 0 0]$CG$CG$m$[0 0 0]$Euler X-Y-Z$deg$WORLD$true$none#Right$CS2$[0 0 0]$CG$CG$m$[0 0 0]$Euler X-Y-Z$deg$WORLD$true$none'

So I can set

x = 'Left$CS1$[0 0 0]$CG$CG$m$[0 0 0]$Euler X-Y-Z$deg$WORLD$true$none#Right$CS2$[0 0 0]$CG$CG$m$[0 0 0]$Euler X-Y-Z$deg$WORLD$true$none';

and do this

add_block('mblibv1/Bodies/Body','K/Body',... 'Mass','0',... 'Inertia','zeros(3)',... 'CGPos','[0 0 0]',... 'WorkingFrames',x);

but you need to set all your frames in that one big string.

[Matthew Eicholtz]

Thanks Ryan! Your suggestion worked.

Answer 2

[Falk]

There is a another way to change CS-values within a body-block via code.

First, you have to build a subsystem around the body-block. You have to build a mask for the subsystem. In the mask you can define parameters. These parameters you can use as variables in the CS- or CG-positions within the body-block-mask.

At this point, everything was stupidyclicki...

But the mask-parameters you can set via code, e.g.

set_param('myModel/SubsystemName','maskparameter',num2str(value))

Each occurence of 'maskparameter' within the underlying body-block will copy its value from the subsystem (one level above) to the variable in the body-block.

[Ryan G]

This is a very good point in general, but remember he is building the model programatically!

Answer 3

[Parham Sagharichi ha]

i wanna change number of ports for joint revloute , what should i do ?

[Szymon Maczka]

Good question... I am trying to do the same with 'Spring and Damper Force' for changing stiffness parameter during simulation #2018b