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10 years, 175 days
University of Waterloo

MaplePrimes Activity

These are answers submitted by bjdehart

Hi Bendesarts,

Provided you know your initial conditions (ICs) in relative coordinates, you can either determine the ICs in absolute coordinates or simply measure the absolute variables of interest during simulation, depending on your desired application(s).

If you setup the model using your relative ICs and force all joints (and other DOFs) to be static, you can use absolute sensing components to directly evaluate the absolute ICs. This will give you calculated absolute ICs based on the known relative ICs, which you can use to replace the relative ICs if desired.

If the goal is to simulate in absolute coordinates, without needing to know the absolute ICs directly, you can simply use your relative ICs to setup the model. Then you can easily control and measure absolute variables and motions directly using the appropriate components, without ever needing to know the ICs in absolute coordinates.


Brandon J DeHart

Answer to original question copied from comments for clarity:

"The values that you set in the Parameters area of the subsystem are the default values, which were originally set to 1 when the parameters were created. If you delete the '1' values shown in the Inspector, then the default values will appear."

Answers to follow up questions also copied from comments:

"The default value will only be used if it appears in the Inspector tab in the Schematic view. In other words, if you don't delete the '1', then the value that is used will be 1."

"Since this is a standalone subsystem, you can do one of two things to achieve your goal: either enter the values as defaults and delete the '1' values (as described above), or enter your custom values/equations directly into the Inspector tab so that the default values are ignored."

"If you're planning to use more than one copy of the subsystem, then you should convert the subsystem to a shared subsystem. For shared subsystems, the easiest way to do what you want is to define all of your default values directly in the Default Value fields in the Parameters area. If you then make a copy of the subsystem and delete the original, the copied subsystem (and any other copies you make) will automatically have all of the parameters in the Inspector tab populated with your default values."



Hi nic_rf,

If I undersand your question correctly, you have a multibody object whose position you want to modify using real-valued parameters and a custom component. This can be done using the Prescribed Translation multibody component and a set of Constant components, one for each of the parameters.

The Constant components allow you to convert the parameters into real-valued Inputs, which can be connected to your custom component. Once you've calculated the desired (x,y,z) locations in the custom component, the Outputs can be connected to a Prescribed Translation component. The Translation component's multibody frames can then be attached on one side to a Fixed Frame at the origin (0,0,0) and on the other side to your multibody object.

Hope that helps!



Hi raphrf,

The reason that running the analysis again gives you a system with 2 DOFs is because the constraints on the initial pendulum model have been removed using the 'disable/enable' function of MapleSim (looks like a red circle with a line through it at the top of the schematic view).

In order to generate the same equations as the ones that are shown in the analysis attachment, both the spherical joint S1 and the fixed frame FF4 (along with their connections) in the right side of the initial pendulum model need to be enabled. Once this is done, the analysis attachment will generate the same equations as they previously showed.

Note that enabling S1 and FF4 will cause the end of the double pendulum to have a set position. If you want the simulation to run properly again, the constraining elements (S1 and FF4) need to be disabled. This will allow the pendulums to move freely due to gravity instead of being stuck at a specific location.

Another source for information about how to generate inverse kinematics for a system can be found in the YouTube video on tracking a fixed position using a radar dish on a moving airplane:

Hope that helps!


Brandon J DeHart

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