Questions about Revolute Joint in Simscape Multi Body.

I have question regarding the revolute joint in simscape multibody .

1. What are the the input units when inputing position? (my guess is rads)
2. What is the units for the output?
3. How can I set an initial positon for my simulation that is independent of a controller? I have tried editing "State Targets/ Specify Position Target" with no luck.

Answer 1

[Amanpreetsingh Arora]

Following are the answers to your queries on Revolute Joint block:

1. What are the the input units when inputing position?

The input unit is inherited from the input physical signal itself. If there is no unit, radians is assumed.

2. What is the units for the output?

Radians by default. However, it can be converted to other units using "PS-Simulink Converter".

3. How can I set an initial positon for my simulation that is independent of a controller?

"State Targets/ Specify Position Target" is the correct parameter for this purpose. Can you share your model where modifying this parameter does not work? There might be some other part of your model that is enforcing an initial condition on the joint. Did you try setting "State Targets/ Specify Position Target/Priority" to "High (desired)"?

[fmo2641]

I shared two simulink files, my more complex simulation("PT_TF_Sim_RL2") and a simpler simulation ("simple"). "Master.m" should initialize everything to run the complex simulation.

I was able to succesfully use "State Targets/ Specify Position Target" in the simple simulation to set the initial conditions. But when it comes to my more complex simulation it seems to initialize at 0 eventhough there is a non-zero input in "State Targets/ Specify Position Target".

I have also tried with a high priority.

I imported my model from a CAD file using smimport , I am not sure if that caused a problem. I also think that the model data file might contain reduncancies.

[Amanpreetsingh Arora]

In case of model "PT_TF_Sim_RL2", you are providing a motion input to the joints and therefore during simulation it is obtaining the initial condition from the input profile. You can check in Mechanics Explorer that values from "State Targets" are used only when the diagram is updated (using Ctrl-D) but during simulation the values are obtained from the input profile.

In this case, you will have to specify the initial condition at the motion input using the "IC" block. Refer to the following documentation for information on "IC" block.

https://in.mathworks.com/help/simulink/slref/ic.html

[fmo2641]

Will using IC allow me to remove the conditions remove state targets ?

Answer 2

[Mario Castro]

When using a torque input, which are the units the Revolute Joint expect the signal to be? N*m?