Project Number: P20229

Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York 14623

A SC ALE MO DEL O F A DR EADNOUGHTUS T AIL

A mrit Gautam Stefan Maczynski Computer Engineering Electrical Engineering

Ryan Kent Joseph Samuelson Electrical Engineering Mechanical Engineering

Julia Solinas Kaiya Li Mechanical Engineering Mechanical Engineering

AB STRACT While the physical remains of an ancient creature may lend a great deal of insight into the dimension and shape of the being, these remains are not enough on their own to describe the full makeup and capabilities of said creature. This may be particularly true for the ancient Dreadnoghtus, truly a giant dinosaur, and a member of the genus titanosaurian sauropod. In an attempt to answer the question as to the capabilities of the Dreadnoughtus, and more specifically the function of the ‘chevron’ on the creatures tail, a scale model was developed which would allow for an investigation into the forces and constraints at play. This model tail uses the nature of the documented remains and attempts to replicate the construction of the tail in order to achieve movement in line with the expected behavior given the hypothesized size and placement of the major muscle groups. As a tail is essentially a complex arrangement of elastically connected compound pendulums, it is understood that a purely math model would take a great deal of time to develop, and would be unverifiable on its own. Instead of building a mechanical structure based on a theoretical series of symbolic relationships, our team has begun with the construction of the mechanical model, and based on observations regarding the response of the system to input conditions have changed the inter-link connectivity and the form of the input force. In attempting to build the system such that it responds to a stimuli “true-to-life” for the musculature of the tail our team believes that we have made findings as to what may have been the construction of the Dreadnoughtus.

BA CKGROUND (O R M OTIVATION) Dreadnoughtus is an enormous, exceptionally complete sauropod dinosaur with an exceptionally long protruding neck and tail. Dr. Kenneth Lacovara, an associate professor in Drexel University, who led the discovery of the Dreadnoughtus fossils skeleton in southern Patagonia in Argentina describes Dreadnoughtus as an interesting

supermassive dinosaur species with some interesting features to study. With the inputs from Dr. Kenneth Lacovara and the goal of furthering the study of a dreadnoughtus, a working scale model of a dreadnoughtus tail must be developed. To date, a functional model does not exist, and the functionality of the chevron in the dinosaur’s tail is of undetermined use. Potentially, the chevron allowed for the muscled to impart a larger force onto the bones of the tail, allowing for a more effective defensive instrument.

The expected end result is a robotic model of the tail that is controlled through a graphical user interface, robust enough to endure hours of examination and testing, has enough sensors to understand the movement of the tail (including forces, acceleration, and flex), allows for variables tail acceleration, and accurately represents the bone and muscle structure of the dreadnoughtus’s tail. The goal is to deliver a working model, capable of accurately representing a dreadnoughtus’s tail. It will serve as a tool to expand support for future paleontological research. Deliverables include: all design documents, a technical paper, a poster, and a prototype.

DE VELOPMENT O F T HE DE SIGN

Figure 1. Prototype Figure 2. CAD (Phase 1)

The first preliminary design utilized cardboard, plastic tubing and string (Figure 1). Through feasibility testing, it was found that actuation of the strings created ample and even tail movement across its length. Nylon was considered as a robust tail structure to replace the weak plastic tubing, leading to the initial CAD design (Figure 2). However, both of these ideas do not accurately portray the Dreadnoughtus bone structure with individual links. By constructing individual links out of aluminum and limiting all but one degree of freedom, the same cable driven muscle approximation could be used. Several iterations were designed. Figure 3 shows an unique link approach, in which each link reduces in size in an attempt to closely replicate the Dreadnoughtus bone structure. However, manufacturing concerns led to the grouping of links, greatly reducing the number of unique parts (Figure 4). Through finite element analysis of stress members, various modifications were made to improve the design (Figure 5).

Figure 3. CAD (Phase 2)

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Figure 4. CAD (Phase 3)

Figure 5. CAD (Phase 4)

ME CHANICAL LI NKAGE DE SIGN Approximation of the tail structure was used to limit the tail movement to the parameters most important to the study. Given the muscle structure under scrutiny, no vertical movement is required to model the impact force of the tail. Instead, by means of pin joints, all movement is constrained horizontally. Given these restrictions, as well as material constraints and testing feasibility, a decision to construct the tail 3ft long was made. Initial testing involved using ﬂexible materials, such as rubber hose or nylon sheets, to perform tail movement. However, due to the desired mass and potential force outcomes, a structural approximation using machined aluminum vertebrae with steel shoulder bolt links was decided for the bone structure of the scaled model. Approximations of chevron shapes and link sizes were used to allow for future adjustments in muscle actuation. These approximations were derived from two Doctoral dissertations referred to us by Dr. Lacovara. Design methodology was largely based on critical approximation criteria, appropriate factors of safety, as well as ease of manufacturing. Based on available documentation, the decision to

Figure 7. Full CAD tail assembly oﬀset each link one degree upwards from the last was made to more accurately portray the structure. While requiring extensive machining work, the design allowed for a more accurate model. Machining of the ½” thick raw 6061 aluminum bar stock was done using a 3-axis CNC. Pin locations were held to a tight tolerance to ensure consistency in link movement. In order to reduce friction error, oil embedded brass bushings were installed in each vertebrae. In addition nylon thrust washers held normal forces along the tail. Two main muscle groups are responsible for the tail motion studied. . From this, it is extrapolated that an estimation of the tail movement can be made using two independent control systems. The method of energy transfer chosen for the muscles groups are steel cables. While a much stronger model could be made through individual link control, a system of controlling a range of links through one cable approximated the expected tail movement. By installing cable guides and stops throughout the tail, one cable is used to model several muscle connecting points. However, due to the limited scope of the initial problem statement, having the ability to adjust muscle connection points as well as adapt to actuation methods was a viable design strategy. Large slots were machined in each chevron to allow adjustment of muscle pull locations, and guide heights. The use of cables to control large sections of the tail forced the design of a spring back mechanism. A torsion spring in between each link allows for such a self-centering force. However, upon further testing, the force provided by the springs did not keep the tail from kinking under load. In order to increase the amount of centering force, a hollow ¼” Delrin rod is installed along 3D printed guides, providing a much more rigid structure. This helped the swinging motion of the tail to provide the expected movement and simulated tendons that could have been part of the tail structure.

Figure 8. Manufactured tail system

TE ST FI XTURE DE SIGN The general structure and scale of the tail justified the construction of a ¾” plywood base to fasten all test components. A tail mounting system that accommodates the testing of different angles and shapes of the swinging tail was constructed out of the same plywood material. Ample area on the baseboard was allotted to additional test equipment fixturing.

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A system of 8020 T-slotted aluminum rails were screwed into the plywood base plate, allowing either a one or two dimensional range of motion for components that would be attached. Test ﬁxture elements could be easily mounted, adjusted, and removed if necessary with sets of screws that can be tightened to secure various components to the rails, then loosened to be moved along the rail or removed. A rudimentary force plate was designed to take advantage of an impact sensor. A large 12” x 12” aluminum plate mounted onto an 8020 structure can be adjusted to ensure consistent contact from the tail. This plate is held by means of shoulder bolts, with a constant spring force to keep pressure on the impact sensor, limiting vibration error from the plate interacting with the sensor. This constant pressure is taken into account by zeroing the data before acquisition. The supporting structure could hold the force plate in a number of positions to accurately measure the energy of the tail swing given the user input and the tail response. A two point linear calibration is applied with the force plate assembled to mimic real testing conditions. The team adjusted the location and angle of the force plate such that the center is struck by the tail, and the force is applied normal to its surface.

Figure 10. Test ﬁxture (Front) F igure 11. Test ﬁxture (Back)

SO LENOID AP PROXIMATION O F A MU SCLE Attempting to build an electro-mechanical system which correctly mimics the nature of muscles proved to be a challenging task. The resulting design is constructed with electrical solenoids and cable networks. The solenoids provide a force which increases as the “muscle contracts” and the cable network acts as tendons, pulling

Figure 12. Tension in a Muscle During Contraction Versus Time [1]

Figure 13. Force in Modiﬁed Solenoid on the links of the tail which would be connected to the muscle. The quadratic relationship between distance and force which exists in both solenoids and muscles may be observed graphically in comparing ﬁgures 12 and 13.

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Figure 14. Controlling Solenoids

As a typical solenoid is not capable of the forces demanded of the system, requiring a custom solenoid to be constructed by retro-fitting a purchased component. By ‘re-winding’ the solenoid to reduce the coil impedance and allow current to peak to an exceptionally high value; the force from the solenoid was maximized. The solenoid must be fed by a supply capable of achieving “infinite inrush” which justified the use of a one farad electrolytic capacitor. The voltage across the capacitor may be varied to control the input force from the solenoid, though this does not allow for the duration of the input force to be modulated. In the testing of this system it was found that without a mechanical damper the instantaneous force proved to be too great for the mechanical system to survive. Further system verification and testing has found that the solenoid approximation of a muscle is sufficient to induce the expected motion. Perhaps most interestingly, rather than the modulation of force resulting in desirable movement characteristics, the modulation of the time between the actuations of the two solenoids allowed for a variation in the characteristic movement of the tail, eventually leading to a movement exceedingly similar to that of a living creature. To control the solenoids, 1 farad electrolytic capacitors are charged to the desired voltage, and then the capacitors may be selectively “dumped” into the solenoids, with a configurable delay between the two actuations. In order to guarantee that the resistive line drop is minimal, over-rated relays were used, as well as heavy gauge wire.

DA TA AC QUISITION TH ROUGH SE NSORS The acceleration of the prototype’s tail, the amount that the tail bends, and the force that the prototype asserts on an object were all necessary parameters to measure for the Robo-Dreadnoughtus. Between the tail’s acceleration, motion, and force imparted on an object, a paleontologist would have ample information in order to determine the use of the dinosaur's tail. First, a microcontroller was chosen that would meet the needs of the controls circuitry and the sensor circuitry. Assuming a worst case scenario situation, containing up to two solenoids, five accelerometers, eight current sensors, six flex sensors, and four load cells, the microcontroller must have at least 24 digital GPIO pins, 5 analog GPIO pins, and at least one I2C bus. In order to account for additional sensors to be added, the minimum number of present pins were double, meaning, at least 48 digital GPIO pins, 10 analog GPIO pins, and at least 2 I2C busses. The Arduino Due microcontroller was selected as it met all of our desired specifications as well as having a large open source community. In order to minimize the number of ports used on the microcontroller, I2C was considered the most desirable communication protocol as only two pins on the microcontroller are used to communicate to any number of sensors. The first sensor chosen was a nine-degree of freedom sensor (which can be used as an accelerometer), the LSM9DS1 from STMicroelectronics, on a breakout board produced from Sparkfun. An Arduino library was provided in order to communicate with the microcontroller being used. The device has a programmable range of plus or minus 2g, 4g, 8g, or 16g. Being able to set the range allows the sensor to obtain a higher resolution at lower accelerations (with the downside of having less range). After analyzing the expected movement of the tail, it was

decided that five nine-degree of freedom sensors would be able to acquire data from the locations on the tail with the highest range of motion. However, each sensor has a fixed I2C address. Therefore, an I2C multiplexer was needed in order to use multiple nine-degree of freedom sensors on the same line. The TCA9548A I2C multiplexer from Texas Instruments (and packaged on a breakout board by Adafruit) was selected as the device allows up to 8 followers to have the same I2C address on a single line without issues. Between the two parts, all five accelerometers could be used. After extensive research, no flex sensors were found that communicated through I2C. Therefore, an analog reading circuitry was designed to be read by the analog pins on the Arduino. As the flex sensor is a potentiometer that varies from 60 kilo ohms to 110 kilo ohms, a voltage divider was designed in order to see the change in voltage over the resistance change in the sensor. Five volts from the Arduino was divided into 2.5 V using a voltage divider consisting of two one-kilo ohm resistors. One terminal of the flex sensor was connected to the node at 2.5V, while the other terminal was connected to an 82 kilo-ohm resistor tied to ground and the positive terminal of a voltage follower operational amplifier. The output of the operational amplifier was attached to an analog pin of the Arduino, and the design was repeated four times (once for each flex sensor). The range of the output voltage is between 1.1V and 2.2V; safe operating voltages for the Arduino being used. Lastly, the analog load cell uses a I2C interface board in order to communicate with the Arduino. An overview of the complete sensor circuitry can be found in Figure 1 4.

Figure 15. An Overview of the Sensor Schematic Circuitry

GUI - SO FTWARE DE SIGN The Robotic model of the tail and data acquisition is controlled through a graphical user interface, or GUI. The GUI is built with Processing, an IDE for Arduino GUI development, and displays the input from the user and interprets signals from Processing to the Arduino using USB serial communication. The GUI recives data using asynchronous serial communication from arduino sensors to a Processing sketch on a personal computer that will then graph the sensor’s value on screen using the same baud signal.The GUI has functionalities to start and stop tail swing, voltage control, data acquisition if data is available through arduino and an option to generate .csv file in a local directory for easier data reading. The start and stop of tail swing can be controlled from the user's computer using a keyboard. Left arrow can be used to start the tail swing and the right arrow can be used to stop the swing.

SU PPORTING FE ASIBILITY EV IDENCE The ﬁnished prototype is a mechanical dinosaur tail. Both major muscle groups present in the dreadnoughtus were modeled by the use of two solenoids. The delay of the two solenoids can be programmed

Proceedings of the Multi-Disciplinary Senior Design Conference Page 9 through the use of an Arduino Due, as well as the serial communication present in the Arduino IDE. The user can program the delay by sending any value that is not a two or a one to the device (the delay is in milliseconds). In order to swing the tail, the user sends a ‘1’ to the Arduino. To disable the device, the user sends a ‘2’ to the Arduino. While sensors were implemented on the tail to measure the force, acceleration, and overall movement of the device, the sensors could not be polled while the GPIO pins were toggled (due to the limitations of the Arduino Due microcontoller being used). Nonetheless, some engineering requirements were able to be measured and verified without the use of such sensors. The engineering requirements that were met is that the tail resembles a dreadnoughtus, the length of the tail is scaled proportionally to the dinosaur’s original size (with a 1/10th scale), the tail force would not break a bone within the tail while swinging, the number of controls is small enough for the project to be easily used, the project is safe, and the project remains within the given budget. In order to determine that the tail force would not break a bone within the tail while swinging, hand calculations were performed to determine that a force of 1501 lbs would be required to break a bone within the tail. As that force would also break a bone in our hand, we had the tail hit a team-mates hand. As the swing did not hurt their hand, the specification was determined to be met (the original plan was to measure the force exerted on the force sensor, however, the force sensor could not be polled while the solenoids were being actuated). It is currently unclear if the tail acceleration is proportional to that of a dreadnoughtus as the accelerometers could not be polled while the tail swings. Therefore, this specification is left as undetermined. Finally, the specifications not met were that of an accurately sized tail mass and an accurately sized tail height. When designing the parts, the team decided that if the tail components were to be sized correctly, they would be almost impossible to machine. Therefore, the accurately sized tail height was not considered in the design. Because the tail height has 300% error, the tail mass also had error (as 300% more material is present than should be), leading to those two engineering requirements to not be met.

RE SULTS, C ONCLUSION, A ND R ECOMMENDATIONS The tail model we constructed resembled the dreadnoughtus, and was able to swing, however we were not able to get a high enough desired force output. Some factors to this were the weight of the tail, and how fast we were able to pull the cable. If the tail had been lighter, it would have been able to swing much faster. The test fixture was sturdy enough to support the weight of the moving tail and impact of the tail swinging. However one issue we ran into was when we were trying to construct our own force plate out of parallel aluminum plates and a load cell, we had difficulties keeping the plates parallel to each other, which was solved by constraining them with springs to keep a constant force on the load cell to minimize movement of the top plate. The sliding rails to mount the force plate were sufficient, however sometimes it was difficult to adjust the force plate, which may have been due to them not being lined up properly. Electrically, the Arduino Due was not capable of reading data from the sensors and toggling GPIO pins at the same time. This is due to the incredibly large delay that it takes for an Arduino to write to one of its digital pins. As the delay to write to the pin takes over the processor, it creates incorrect readings for the sensors as clock cycles and baud rates become changes while the processor is occupied writing to a digital pin. However, separately, reading the sensors and toggling GPIO pins worked. Modeling the dinosaur’s muscles through the use of solenoids created an accurate twitching ability, similar to a muscle. The control of the two solenoids through the arduino worked perfectly in order for the user to select their own delay and choose when to start the actuation of the device. If the project could be redone, the team would not use an Arduino Due, or any Arduino device. While the devices have very fast development time, they have limited functionality (such as quickly toggling GPIO pins). Ultimately, the issue where the device could not read from the sensors and toggle the GPIO pins at the same time was down to the microcontroller choice, as this was not a well documented issue that the team was aware of. Furthermore, the team would not use the “Processing” IDE in order to create the GUI, as similar to the Arduino, while it had fast development time, it had very limited functionality (such as being able to send more than single digit numbers over UART). Recommendations for future work would be to make the tail out of a lighter material. Different rails could have also been purchased with locking sliders, however due to high cost, the 8020 aluminum was an acceptable low cost substitute. Creating a system where the tail gets less rigid the farther down the tail would also create a more accurate model (as opposed to the consistent delrin rod currently being used). Furthermore, the project should be moved to using either a different microcontroller or two Arduinos (however, two arduinos would complicate the system much

more than just using one more competent microcontroller). Finally, a body of the dinosaur should be created in order to model and study the stance of the dinosaur while the tail swings.

RE FERENCES – U SE S TYLE “RE FERENCES C LAUSE T ITLE”

[1] Choi, C. (2010, February 03). Brute Force: Humans Can Sure Take a Punch. Retrieved November 25, 2020, from https://www.livescience.com/6040-brute-force-humans-punch.html

[2] Lucio M. Ibiricu, Matthew C. Lamanna & Kenneth J. Lacovara (2014) The influence of caudofemoral musculature on the titanosaurian (Saurischia: Sauropoda) tail skeleton: morphological and phylogenetic implications, Historical Biology, 26:4,454-471, DOI: 1 0.1080/08912963.2013.787069

[3] Lacovara, K.J. et al. A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina. Sci. Rep. 4, 6196; DOI:10.1038/srep06196 (2014).

AC KNOWLEDGMENTS We would like to thank Lockheed Martin, the sponsor of our project, as well as Dr. Kathleen Lamkin-Kennard, our customer. Our guide, Jim Whritenor, for offering excellent advice on how to meet guidelines, facilitate discussions, and offer an experienced engineering perspective. Finally, Brian Tyson and Eric Wagner significantly helped the team by offering their engineering expertise in design reviews, being directly involved in significant design changes and decisions.