Calculating Required Torque for a Mobile Robot Flipper

Omniverse Isaac Sim
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Isaac Sim Version

4.5.0
4.2.0
4.1.0
4.0.0
4.5.0
2023.1.1
2023.1.0-hotfix.1
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GPU Information

  • Model: RTX4090
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Topic Description

How to get Flipper’s torque?

Detailed Description

Hello,

I’m trying to determine the required torque for a flipper mechanism that will be mounted on a mobile base via a joint. The flipper itself weighs 6kg. My goal is to calculate the torque needed for the flipper to lift itself from a horizontal position (0 degrees) upwards by 30 degrees.

I’ve looked into some official documents and user examples regarding torque calculation but haven’t fully grasped the methods. I understand that for dynamic movements, factors like acceleration and inertia are crucial. However, for this initial stage, I’m primarily interested in the static torque required to hold the position or lift it very slowly.

Could you offer some guidance or ideas on how to approach this calculation? Specifically:

  1. What information about the flipper’s geometry is essential (e.g., its overall length, and critically, the location of its center of mass relative to the pivot point)?
  2. Are there standard formulas for this kind of static torque calculation?

Furthermore, I’m considering how to model this in a simulator like Isaac Sim to eventually verify or refine these calculations:

  • If I only have a visual mesh of the flipper in Isaac Sim, can I derive or accurately approximate the necessary physical properties (like the center of mass and moments of inertia) required for torque estimation?
  • Or is it generally essential to create a separate URDF file for the flipper, meticulously defining its inertial properties (mass, center of mass, inertia tensor) and joint parameters, to get a reliable torque assessment, even for static or quasi-static scenarios?

I’m eager to understand the correct approach to both the theoretical calculation and the practical simulation setup. Any success stories, common pitfalls, or insights you could share would be greatly appreciated.

Thank you.

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3

Hi @Kinesis19, thank you for posting your question. I am still trying to understand what you are trying to achieve.

The typical way to get an articulated object to a specific joint position is to user a controller, like a Proportional Derivative controller. This is what is currently already implemented in Articulation objects if you turn your prims into an Articulation.

If you are trying to figure out what is the feed-forward force to get the links to hold a position (given that it is currently already at that configuration) then, you will need to analytically figure out what the torque at the joint will be given:

  1. Vector of support arm (Vector from joint position to Center of mass of the flipper).
  2. Gravity vector.

You want the moment/torque to be zero so you want to output a torque equal an opposite to what
cross_product(support_arm_vector, gravity_vector) returns.

4

Hello!

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