Overview

Raise Robotics was switching to a new tracked mobile base from the previous mecanum wheel mobile base. I was tasked with integrating the new mobile base into the existing robot assemblies and preparing the model for URDF simulation and real-world assembly and deployment. I quickly noticed a design flaw where the robot would easily tip over. I then collaborated with other engineers to develop a stability outrigger system with actuated legs. Overall, I greatly increased simulation accuracy and stability of the robot.

Tracked Mobile Base

I didn't have access to a 3D model of the tracked base at first, so I manually converted an AutoCAD file into an Inventor model, extrapolating dimensions when necessary. Later I received more detailed drawings and parts, and these were integrated into the model.

URDF Preparation

I removed the previous mobile base and replaced it with the new tracked base model I created. Next, I addressed issues with the assembly in order to increase model accuracy.

Model Mates: Many constraints were broken or didn't exist due to past exports into different software versions. I carefully reviewed all of the model mates in each assembly and made adjustments where necessary to ensure that they were accurate and properly aligned.
Geometries: I reviewed all of the geometries in each subassembly and made adjustments where necessary to ensure that they matched the real-world dimensions of each part. Multiple parts were outdated, which I replaced with newer assemblies, fixing mates when necessary.
Mass/Material Assignments: Finally, I reviewed all of the mass/material assignments of each subassembly and made adjustments where necessary to ensure that they accurately reflected reality.

Stability Simulation

Assigning materials and weights to every subassembly meant that the center of gravity was not much more accurate. I noticed that due to the track geometry and location of the center of gravity, the robot would likely be prone to tipping. Thus, I decided to run multiple dynamic simulations in order to determine how to prevent tipping. I simulated assuming the arms were rotating at max torque and an approximate friction coefficient.

I repeated the simulation with multiple counterweights, but due to the robot's already high mass, any effective counterweight would greatly impact the max load of the mobile base, and would not increase stability significantly. I repeated the simulations with accurate suspension damping, and the results were the same.

Outrigger Development

I collaborated with other engineers to design a stability outrigger system with actuated legs. I conducted FEA and further dynamic simulations to determine the optimal geometry and attachment structure. I also researched various actuation methods such as pneumatics and electric linear actuators, optimizing for system complexity, energy efficiency, precision, strength, and speed.

Construction Robot Stability Outrigger Simulation