Structurally Smart Animatronic Figure
Structurally Smart Animatronic Figure (SSAF)
MAE156B SP 19
Allysa Penamora
Zachary Pierson
Selina Wade
Robert Zarick
Background
ATA Engineering, Inc. specializes in the design, analysis, and testing of structures in dynamic environments. They use advanced, computer-aided engineering software to solve problems for their customers in mechanical, structural, and aerospace industries. Their consultation services extend to structures in the themed entertainment industry, such as animatronics and theme park attractions. To improve their analysis, ATA requires a modular animatronic figure with multiple degrees of freedom to physically test and validate their software's theoretical results. Upon completion of the project, they wish to present this figure to their customers to showcase their accurate analysis and consultation capabilities.
Purpose
There are a variety of commercially available animatronic arms. There is also analysis on stress resulting from dynamic loading and the effects of stiffness on an animatronic arm's dynamic behavior. However, there is not a commercially existing model that can be used to demonstrate these principles. ATA Engineering would like an animatronic figure that has linkages they can physically alter in order to observe the changes in its dynamic behavior, and compare it to the results from their software. Our design takes inspiration from current models of animatronic arms, and incorporates the ability to test the behavior of the animatronic arms to compare with existing stress and dynamic 3 DOF arm analysis.
Objective
To assess and improve the accuracy of ATA’s analytical models, our goal is to design and build a simple, animatronic arm structure with multiple articulated degrees of freedom that can be physically correlated and tested. The reference coordinate system is shown below.
This will be done by completing the following:
Provide motion in three degrees of freedom.
One torso will be required that rotates in the RZ-axis
Two upper arm links of different structural resonances.
Stiff in all planes
Stiff in RY-axis, flexible in RZ-axis
Two forearm links of different structural resonances.
Stiff in all axes
Stiff in RZ-axis, flexible in RY-axis
A mechanism so that the arm links will be interchangeable to allow operation with varying structural dynamic configurations.
A single-board-computer control system to move the three articulated joints through prescribed motion profiles.
Figure 1: Orientation of Figure
Design
The design is inspired by the human upper body and consists of the arm and the torso. The arm consists of three motorized joints, two links, and a "hand." The joints are motors that act as the shoulder, elbow, and wrist of the arm,and the linkages are the upper arm and forearm. Through the motors, the arm is able to move its hand up and down, and forward and backward. The torso rotates the arm via a pulley-bearing system along the RZ-axis, allowing the hand to move left to right. In addition, the torso supports the arm, with a shoulder counterweight to balance the load of the arm.
Figure 2: a) Full Assembly; b) Pulley-Bearing System
Figure 3: a) Stiff Linkage Design b) Flexible Linkage Design
An interesting feature of the arm is its linkage designs. There are two link designs that can be interchanged to alter the stiffness of the linkage: the stiff link design that restricts movement in the RY-axis and RZ-axis, and the flexible link design that restricts movement in the RY-axis or RZ-axis.
Figure 4: Example of 3 DOF Motion
To test the dynamic behavior of the arm, a motion profile was designed to imitate moving a cup from place to place. Each linkage and the torso were given a range of motion, similar to that of a human arm. Using the ArbotiX-M Robocontroller and UartSBee FTDI, the motion profile was coded using Arduino and code provided by the distributor, Trossen Robotics. When the code was uploaded to SSAF, the motors would actuate so that the figure moved through the motion profile.
Results
When testing the SSAF, the figure was able to perform the motion profile twice until the ArbotiX-M Robocontroller burned out. After disassembling the figure, the five motors were retested to see if the burned-out board affected the motors' performance. Unattached to the arm, the motors performed the motion profile as expected. After ensuring the motors were not affected, it was speculated that that the ArbotiX-M Robocontroller burned out due to the increased current the motors drew in order to support the weight of the arm during the motion profile.
After meeting with our sponsors, ATA Engineering, we were able to diagnose and resolve the issue with a new hardware configuration: instead of supplying power directly to the board, the power was supplied to the motors via a 6 Port AX/MX Power hub, and a 1-Amp fuse was utilized to limit current to the ArbotiX-M Robocontroller. Doing so allowed the SSAF to run through the motion profile smoothly.
Figure 5: New Hardware Configuration with Power Hub and 1-Amp Fuse
Click here for the Executive Summary.