Acknowledgements

Quadruped RobotCarly Beardall, Matt Johnson, Bryson Murray, Zach Walker, Eddie Yazzie

Advisor Dr. Sanford Meek

ChallengesControl System ComplicationsThe control system for the quadruped uses a controller made by dSPACE. While this controller is sufficient, it came with a steep learning curve. dSPACE uses its own dedicated program, Control Desk, to interface a Simulink model with the controller. The Control Desk program was not intuitive, therefore a lot of time was spent learning the program. In addition to this, our team had to learn to use a Roboteq amplifier that can also be used as a controller on its own. There were many options and settings available we did not need and had to work around. The combination of learning dSPACE, Control Desk, Simulink, and the amplifier all at once resulted in a significant challenge.

Unanticipated Redesigns and ModificationsThe integration of a control system for the existing robot, which was designed and fabricated by previous teams, proved to be more difficult than was originally anticipated. Redesigns of mechanical components were necessary in order to accommodate electrical components such as optical encoders, servo motors, and all of the required wiring. Modifications to the following components were necessary for the success of the project:

• Motor mount plate – to accommodate encoders• Servo guide plates – to route Spectra cables to the feet• Interchangeable feet – requested by customer• Hip joint datums – to keep legs parallel• Mounting screws – for the servo cables• Upper thigh cantilever springs – to lower stiffness• Hip drive shafts – machined to fit D-collars• Drive motor keyways – made longer for better grip• Keyless bushings – for precise leg alignment• Hip Joints – redesigned to withstand torque

There were flaws in the original design that had to be re-engineered in order to get the robot to trot. For example, the original design of the hip joints used a friction joint to couple the legs to the drive system. These joints slipped under the torque required for motion and had to be redesigned. The new design uses a D-shaft and D-collar to couple the shaft to the leg using a mounting screw that fastens the D-collar to the side of the leg.

The main goal was to engineer a control system that enabled the quadruped to perform its intended function, which is to trot. The necessary sensors and component modifications were designed, and the hardware was installed. The electrical components were configured and connected such that the necessary inputs and feedback from the robot would be possible. A complex Simulink model was designed to command all of the necessary motions of the robot using feedback from the installed sensors. In addition, a testing platform that protects the robot and uses an actively controlled treadmill to aid in testing was designed and manufactured. There were many challenges along the way, but overall the project was successful.

Sponsored in part by the National Robotics Initiative 1427422

Model of testing structure and robot

Simulink model of control system

Transfer Function Curve Fit

Root Locus Plot

Testing PlatformTesting StructureThe structure suspends the quadruped from linear bearings, allowing the robot to trot freely, while preventing it from fallingand incurring damage. The structure also allows the quadruped to pitch up or down, providing a more realistic trotting gait.

TreadmillA treadmill with active velocity control, via an Arduino microcontroller, maintains the robot’s position. This allows continuous testing and observation of the robot’s motion.

The main objective of this project is to design and implement a control system to enable the existing quadruped robot to trot. Trotting is defined as the synchronized movement of alternating diagonal pairs of legs in four-legged animals.

IntroductionRobots have many modern-day applications, ranging from industrial to domestic. Quadruped robots, specifically, have many potential uses, such as search and rescue, long distance travel, and exploration of inhospitable environments. However, our team’s quadruped robot will be used for research in animal dynamics.

An Inherited Project

In order to achieve this objective, our team focused on two designs:

• Control System – The control system includes multi-faceted code, a Simulink model, and a power system which work together to control the two encoders, two drive motors, and four servo motors. This system not only synchronizes the legs to produce a trotting motion, but also lifts the feet so the robot will not trip over itself.

• Testing Platform – The testing platform includes a structure to support and allow the robot to trot freely, but safely, as well as a treadmill with active velocity control to allow the robot to stay in place.

A skeleton of a tiger, an example of a quadruped animal(http://www.joelmongeon.com/Rigging.html)

Original design from past teams

What the Robot Will Be Used For

Studies have shown that three separate evolutionary paths led to a “knees-in” leg configuration, which the vast majority of quadruped animals now exhibit. Our robot will be used for research in quadruped animal dynamics.

Past teams designed and manufactured the structure and mechanical components of the robot, although, at the time our team took on the project, the quadruped’s movements had only been simulated.

The legs of the quadruped were designed to be directionally compliant, so the force on each leg is directed to the center of the robot’s body. The legs are also intended to be passively stable and under-actuated in order to minimize the amount of mechanical components on the robot.

Directionally compliant, passively stable, under-actuated leg design

Project Description

3-D model of current design

Determination of System Gains• Root Locus Techniques• Simulink and Sisotool

Transfer Function

Model Transfer Function

ControllerSimulink software and a dSPACE controller board provide the quadruped with velocity control. Through the use of Control Desk software, variables from the Simulink block diagram can actively be adjusted to change various aspects of the quadruped’s motion.

Hip Joint Redesign

Conclusions

Control System