Morphological Animal Design App: Parameterized Quadrupedal Anatomy and Locomotion

A small project of the Computational Robotics Lab at ETH Zurich

Table of Contents

• About the Project
• Getting Started
  • Blender
  • Base Application
  • Install Dependencies
  • Install Add-on
• Usage
  • How to Create an Animal
    • Load an Existing Animal
    • Interactive Modeling
    • Morphing
    • Store an Animal
  • Run the Principle Component Analysis
  • Create the Walk Animation
    • Reference Animal
    • Store the Parameters
  • Quick Blender Tips and Tricks

About The Project

This project provides a tool inside the 3D software Blender, to quickly prototype quadrupedal anatomies and their respective walk motion. The repository contains the source code for the Blender add-on and the Blender file with the animation skeleton. Please follow the instructions below to get started and how to use the tool. Read the report for detailed information and design decisions.

We present a general animation skeleton parameterized by the location and size of its joints (in red below):

Furthermore, we present a parameterization of the walk locomotion relative to the configuration of the animation skeleton. A visually viable walk motion is constructed from an existing reference motion assuming dynamic similarity.

(a) African Elephant, (b) Horse, (c) Stag, (d) Lion, (e) Cheetah, (f) Wolf

Getting Started

Blender

The application runs inside the open-source 3D software Blender.

• Download Blender here

Blender 2.82 or higher is required

Base Application

• Download the BaseApplication.blend file.

The file contains the animation skeleton and a Blender environment setup for the application.

Install Dependencies

Blender runs inside its own python environment. To install the external dependencies, a script is ready inside BaseApplication.blend.

• Open BaseApplication.blend
• Switch to InstallDependencies tab (top of screen)
• Press Run script (top right corner of screen)

Try to run Blender as administrator should the script fail.

Install Add-on

• Download morph_animal and zip the folder
• Open BaseApplication.blend
• Navigate to Edit -> Preferences -> Add-ons
• Click Install... and select morph_animal.zip
• Enable the installed Morphological Design Animal App

Usage

How To Create An Animal

Load An Existing Animal

There are 15 predefined animals. Select one from the Animal Library and press Load "NameOfSelected".

Interactive Modeling

• Use Blender's 3D View to move and scale the joints manually. Quick Blender Tips and Tricks
• Update the underlying animation rig by pressing Update Skeleton.
• Adjust Pole Knee/Elbow to fix the orientation of the limbs
• Classify the animal as Unguligrade or Digitigrade

Create a pose that is consistent among all animals. Typically, the MTP joint (between the toe tip and ankle) lies directly under the hip joint.

Morphing

Requires that the Principle Component Analysis has been done.

• Adjust the weights of the Principle Components to create a new animal
• OR morph between two entries from the Animal Library.

Store An Animal

• Enter a Name for your configuration
• Press Store Anatomy "TheNameYouGave" to add the configuration to the Animal Library
• Save the Blender file

Run The Principle Component Analysis

The Principle Component Analysis (PCA) calculates a low dimensional vector representation of the skeleton configuration based on the entries in the Animal Library. This unlocks morphing and is used to internally compare two configurations. It must be recalculated every time the application is started:

• Activate the Create Animal tool
• Press Perform PCA - Initialize

Create The Walk Animation

The walk animation is generated by switching to Tweak Gait. Press Play to start the animation.

Reference Animal

The values of the walk parameters are determined based on the stored parameters of a reference animal. Default reference is the Horse. When the Principle Component Analysis has been performed, two configurations are compared based on the squared distance of their weight vector. Among all animals that have stored walk parameters, the one with minimal distance is chosen as reference.

The application comes with walk parameters stored for Wolf, Cheetah, Lion, Horse, Rhinoceros and African Elephant.

Store The Parameters

• You can interactively tweak the parameters. For further information, a tooltip appears when hovering over any parameter field.
• Press Save Gait "NameOfAnimal".
• Save the Blender file

You can only store the walk parameters for entries in the Animal Library

Quick Blender Tips And Tricks

• Mutate selected joint

  Left Click - Select
  G - Move
  S - Scale
  

• Change Viewport

  Numpad 1 - Front View
  Numpad 3 - Right View (Default)
  Numpad 7 - Top View
  Numpad 5 - Toggle Perspective / Orthographic View
  
  Scroll - Zoom in and out
  Hold Middle Mouse - Rotate in 3D 
  Shift + Hold Middle Mouse - Move Viewport
  
  Useful on laptop: Enable Edit -> Preferences -> Input -> Emulate Numpad
  

• Tool disappeared?

  T - Toggle sidebar
  

• The virtual armature must be selected and in 'Pose Mode' otherwise the tool disappears. To fix this:

  Select the virtual armature
  Hold Tab and select 'Pose Mode' from the pie menu.