This document summarizes work on physically-based modelling and simulation of a robotic explorer called the SCORPION. Key points: - The SCORPION robot is modelled in detail and simulated in a physics engine to test navigation controls inspired by biological vestibular systems. - The simulation integrates 3D models created in tools like 3D Studio Max, a physics engine, and controller scripts to emulate the robot's real-world behavior. - Tests examine how accurately the simulation replicates the real robot's walking patterns and ability to stabilize its view using sensor feedback. Future work aims to improve the model detail and simulation flexibility.

1. PHYSICALLY-BASED MODELLING OF ROBOTIC
EXPLORERS EMPLOYING THE EARBOT
NAVIGATIONAL CONTROL
Darin Rajan, Purdue University, IN/ Education Associates Program
Craig Slyfield, UC Berkley, CA/ Education Associates Program
Alexander Twombly (IC), USRS-RIACS, BioVIS Center, Moffett Field, CA
Jeffrey Smith (SLR), NASA-Ames Research Center, BioVIS Center, Moffett Field, CA
Richard Boyle (SLR), NASA-Ames Research Center, BioVIS Center, Moffett Field, CA

2. Introduction
• EarBot is a biologically-inspired vestibular system that is
to be applied to the underlying control mechanisms of
navigation, balance, and motor control found in robotic
explorers, namely the SCORPION.
• The testing and development of these systems are done
in simulation, where the walking SCORPION is in a
physically emulated, true-to-life environment.
• This simulation is used to measure performance
benchmarks by providing an overall integration platform
of robotic systems, control strategies, and an assortment
of terrain. Such benchmarks include:
– Gyro and acceleration feedback
– Omni-directional motion control feedback

3. Overview
• The SCORPION is an eight-legged walking robot. The legs are
controlled by a basic motion pattern (BMP) generator to
achieve walking behaviors and styles1
.
• Simulating the SCORPION, and its control mechanisms, is
done by the combination of two systems working jointly-
together. First at the core of the simulation is NRG, a graphics
wrapper simulation which interfaces a dynamic, physics-based
engine created by Arachi, Inc. Second is 3D StudioMax, a 3D
modeling tool created by Discreet, Inc.
• NRG is in charge of all the physics, viewing, and control in the
simulation. Each system (both static and dynamic) that appears
in the simulated environment is specified in a modeling system
such as 3D Studio Max. Through NRG’s built-in plug-in to 3D
StudioMax, models can be exported to a .XML format (.3ML)
for viewing. The xml exporter is able to make most of the
information available in the .max file description, including
geometry, color, texture, hierarchy, cameras and lights. The
models exported via the xml exporter may be used for either
static display, kinematic animation, or dynamic interaction.
Dynamic models require some additional information that is not
normally associated with graphic models. This information
include, link joints, object mass/inertia, friction properties,
collision models used, sensors and control information.
• Finally, using a scripting language called Python, Arachi loads
the system of models into the NRG viewer
1
Klaassen B., Linnemann R., Spenneberg D., Kirchner F. (2002) Biomimetic walking robot SCORPION:
Control and modeling. Robotics and Autonomous Systems 41: 69-70
Spenneberg D. & Kirchner F. (2001) An Approach Towards Autonomous Outdoor Walking Robots,
Proceedings of 10th International Conference on Advanced Robotics (ICAR 2001), Budapest, Hungary.

4. SCORPION Simulation
SCORPION Simulation
NRG Executable Static and Dynamic Models
Arachi Physics Engine
Graphics Viewer Real World Physics
Controller
3D StudioMax
PolyTrans
SolidWorks
Python Script

5. SCORPION Anatomy
strut
motorB
motorC forearm
elbow
lowerarm
main
Vestibular
Each section of every leg is
connected to a parent section. At
the top of the hierarchy is the
‘main’ body. After physical
properties have been added to the
sections of the leg, a controller is
interfaced through the physics
engine via a Python script that is
loaded at run-time of the
simulation.
main
--strut
----motorB
------forearm
--------elbow
----------lowerarm
------motorC
--Vestibular Camera
SCORPION Hierarchy

6. SCORPION Navigation
• A series of “Basic Motion Patterns” were
added to the SCORPION’s walking
behavior. BMPs include fundamental
walking algorithms, such as forwards,
backwards, and sideways motion. Through
a combination of keyboard and mouse
callbacks the end user of the SCORPION
simulation is able to navigate through the
simulation.
• Each of these behaviors are added to the
SCORPION at different levels of priority,
depending on the frequency of the desired
callback. That is if both forward and
sideways BMPs are active and if sideways
motion has a higher precedence, the
SCORPION will walk more to the side than
it does straight.
• The Vestibular camera allows the
SCORPION to stabilize its view and create
a fixation point. The camera is then
interfaced with a Neural Network, where it
will be able to gather information on any
point in the simulation, focus on it, and
finally accurately stabilize the camera’s
view. A simple demo program, pictured,
demonstrates this

7. Method of Simulation
1. Create individual models of parts making up articulating objects
The first step in modeling a robotic explorer so that a simulation
can be created is to develop a 3D model using SolidWorks. The CAD
model contains the basic defining mesh for the rigid body structure.

8. 2. Assembly of parts to create model
3. Conversion of assembly into file type readable by 3D StudioMax

9. 4. Grouping and hierarchy
The SCORPION model
is an exact replica of
the original robot,
assembled in 3D
StudioMax. The entire
model is divided into
separate sub-objects
that consist of struts,
motors, joints, and
legs. These objects fall
into an ordered
hierarchy of nodes and
links.

10. 5. Textures and lighting
Textures and lighting are needed to add realism to the simulation.
It brings the digital, simulated world to life. This digitization is achieved
by wrapping images around the geometries of the rover mesh.

11. 6. Creating Terrains
Vertex translation of
polygon mesh to create
a crater.
Mars Texture
Brick Texture
Asphalt Texture
Using 3D StudioMax,
meshes can be
modeled around real
life terrain features,
which can test the
rover’s agility and
maneuverability in
unique situations.

12. Model Comparisons
K9  214,384 polygons
SCORPION  550,298 polygons
MER  320,454 polygons

13. Direct Comparison of Model Data for Hip Joint
Simulated Model
Theoretical Model
Real Model

14. Current Status
• The SCORPION model has been updated completely with the
a new high-res model and does not require the old model to
be a ‘ghost’ or backbone to it.
• The controller is now able to guide the SCORPION to walk in
all directions, and can be interfaced with the neural network to
provide for Vestibular Camera stabilization.
• Many different types of terrains have been designed to
challenge the rover and test the simulated movement
produced, providing an initial test bed for the accurateness of
robotic simulations.
• The walking pattern of the simulated SCORPION robot
matches that of the original robot and allows for the sensors
to be rea

15. Future Work
• Update the current high-res model with a
higher resolution, more precise model to
allow for a higher degree of accurateness.
• Update the user interface to allow for
models to be loaded and terrains to be
changed while the simulation is running.
• Upgrade the existing system to future
versions of the Arachi Physics Engine.