Output torque calculation of two geartrain mechanism

I tried simulating in simscape and I'm not able to get the output actuator torque. Can someone help? right now I'm getting zero torque

Answer 1

[Umar]

Hi @ Khyati,

Based on the MathWorks documentation for Simscape Multibody Revolute Joints https://www.mathworks.com/help/sm/ref/revolutejoint.html,here are the most common causes of zero actuator torque output:

Actuator Torque Sensing Not Enabled

First verify that you've enabled the actuator torque output port on your Revolute Joint:

Double click the Revolute Joint block

Under Z Revolute Primitive (Rz) > Sensing, check the box for Actuator Torque

This should expose a port labeled t that outputs the actuator torque

Joint Actuation Mode

Check how the joint is being actuated. According to the documentation https://www.mathworks.com/help/sm/ug/joint-actuation.html

Under Z Revolute Primitive (Rz) > Actuation, you need to set:

Torque to Provided by Input if you're providing torque input

OR Motion to Provided by Input with Torque set to Automatically Computed if you want inverse dynamics

If you're using motion input but torque is set to "None" or zero, the actuator torque output will be zero.

Input Signal Conversion

I see you have a constant value "3" - ensure it's properly converted:

Simulink signals must be converted using a Simulink-PS Converter block before connecting to Simscape physical signal ports

In the Simulink-PS Converter, verify the correct units are specified (e.g., N*m for torque or rad for angle)

System Load/Inertia

From the documentation on torque sensors https://www.mathworks.com/matlabcentral/answers/2085543, the system needs inertia or load:

Ensure your mechanical system has inertia blocks or loads connected

Without any load, there may be no torque generated

Mechanical Reference (Ground)

All Simscape mechanical rotational networks require a Mechanical Rotational Reference block https://www.mathworks.com/help/simscape/ref/mechanicalrotationalreference.html.

However, note that Simscape Multibody uses its own World Frame and doesn't typically require this for Multibody joints - but if you're interfacing with regular Simscape blocks, you need it.

Could you clarify

What actuation mode is the Revolute Joint set to (Torque or Motion)?

Is the actuator torque sensing port enabled?

Are you providing torque input or motion input?

What units did you specify in the Simulink-PS Converter?

This will help me give you more specific guidance without making assumptions.

Reference

Revolute Joint documentation: https://www.mathworks.com/help/sm/ref/revolutejoint.html

Joint Actuation guide: https://www.mathworks.com/help/sm/ug/joint-actuation.html

Force/Torque Sensing: https://www.mathworks.com/help/physmod/sm/ug/sense-forces-and-torques-at-joints.html

[Khyati]

Hi sir, thank you for the response, I will look into my model. About the questions that you have asked, the actuation mode is set to torque, yes the actuator torque sensing port is enabled, I'm providing a motion input, Units that i specified are rad/s for the input and N-m for the output.

Thank you