Joint Torque Calcs

Owned by Austin Tailon Huang
Last updated: May 21, 2021 by Former user (Deleted)
2 min read

Background

Rough hand calcs were conducted to to determine the torques required at each robotic joint by Ethan Cronier and Austin Tailon Huang 

Assumptions

For the current iteration of hand calcs, the following assumptions were made:

  • 10 kg arm mass, with a uniform mass distribution (this is a rough ball park based on the Cornell's arm mass. We should change this to reflect the current mass of our arm when we can weigh it.)
  • Desired end effector linear acceleration of 1m/s^2. This acceleration was chosen willy nilly and may be overkill.
  • Each joint should be able to provide the desired end effector acceleration when all other arm components are rigid. This assumption does overestimate the required torques at each joint, but was made to simplify initial calculations and can be further refined with new arm iterations.
  • Arm is defined as a point mass. Once we have an actual arm design we can properly evaluate the moments of inertia for each linkage through SW or basic geometry calculations. 
  • No arm counter weights

Methodology

For each joint, the arm was placed in a "worst case" loading scenario - A.K.A when the weight of the arm and payload are perpendicular to the rest of the arm. Check out the PDF for diagrams of each joint loading scenario. Final motor torques were determined by finding the sum of holding and motion torques:

Holding torque refers to torque required to balance the mass load of the arm and motion torque is the torque required to actually move the arm and start it's acceleration. 

Results :

Summary of Hand calc Max Torque Findings (Rounded Up)

  • A1: 16 Nm
  • A2: 200 Nm
  • A3: 105 Nm
  • A4: 30 Nm
  • A5: 30 Nm
  • A6: 18 Nm

Hand Calculations Put in an Excel Sheet:

6DOF-Calculator.xlsx

These are joint torques with a 1x safety factor. We must increase our safety factor to an agreeable value

6DoF_Arm_Rough_Torque_Calcs_UWRT.pdf

Summary of Simulation Max Torque Findings

The simulation file must be run on Matlab R2020a

https://www.robotshop.com/community/tutorials/show/robot-arm-torque-tutorial