Acknowledgements

GoldMiner Fundraising

Kathy Allen, Jon Beegle, Tracy  Bowers, Eugene Carter, Martin Carter, William Carter, Michael Dale, Nila Fenton, Richard Fenton, David Flint, Ashley Flynn, David  Gibson, Ira Green, Marc Grundfor, Doobie Househer, Terri Murphy, Marcia Nation, David O’connell, Andrew Pearce, Marian Reagan, Mary Sheldon, Donna Tellschow, Julie  Thomas, Lynette Thomas, Dana Tomlinson, Art & Pat Turek and Frank Turek

Technical Advisors

Braking Technical Advisor – Dr. Steve Geer – ME Faculty 

Controls Technical Advisor – Darren McSweeney – EE Lab Manager

Power Technical Advisor – Dr. Robert Kee –  ME Faculty 

Propulsion Technical Advisor – Tyler Evans – CSM Graduate Student 

Stability Technical Advisor  –  Greg Vanderbeek – ME Faculty

Selected Contributors

Karl, a former team member, was crucial to the propulsion subsystem fixing the motor coolant system and answering lingering questions about the system as a whole.  

Tyler, the propulsion technical adviser, offered insight on the previous team’s design decisions as well as crucial advice for machining and fabrication. 

Clayton, a former project lead, was extremely helpful explaining the overall current design and was always available to help when problems arose.

K2 Energy’s engineering team and donations.

Dr. Kristine Csavina, Diggerloop’s PA, for her guidance, direction, and motivation.

Arizona State University for allowing access to their test track.

Video

Elevator Pitch

Diggerloop 2020 inherited a partially completed pod from the previous year and began immediate fabrication to conduct full systems testing on the 1/4 mile ASU test track.  All subsystems made significant progress in attaining that goal, however closures due to COVID-19 prevented the team from conducting full system testing.  Please see the video that highlights much of the team’s progress during the fall and spring semesters. 

Design Approach

Design Solution

Braking :

Braking Alignment 

The 2020 Hyperloop Team braking design consists of two sets of brakes. These are  mounted on either side of the pod, for evenly distributed braking force onto the SpaceX I-beam rail. Using a lever-arm design, linear force generated from a pneumatic actuator is multiplied to the final brake pad assembly. The pads are contained within rotating boots, to allow for parallel contact to the rail. The diagram to the left shows the clamping method this design uses. Below is the free body diagram model of the input, actuator force, and the output, brake pad force.

  Braking Free Body Diagram

Finite element analysis of the braking system demonstrates the structural safety designed into the system. FEA results are tabulated below. One of the simulations from the FEA is shown under the table.

Braking FEA Analysis

Testing at 100 psi of pressure, fed from the pressure vessel, produces successful clamping action. The two system states, clamped and unclamped, are shown above in the Design Approach. The actuators remain in the braked configuration even after pressure has equalized through the pneumatics.

Controls:

Control System Schematic

The Controls Subsystem was designed to be as quick and reliable as possible. To achieve this, a National Instruments CompactRIO is used as the electronics behind the subsystem. This module preconfigures its computing logic so that, while the pod is operating, it can respond extremely fast without computer delays. This module controls the pneumatic brakes, the motor controller, and receives accelerometer data to determine speed. The low voltage batteries that power the subsystem were chosen for their high safety factor. 

Much of the subsystem’s work this year was focused on learning how previous teams had designed the subsystem and adding necessary components/ optimizing the existing components. New coolant pumps were added to the system to keep the motor controller and motor cool, relays were added to power the braking solenoids, a new accelerometer was integrated to provide more accurate velocity data, and an RS-232 data line was added to allow the motor controller to communicate to a laptop. These new additions allow the controls box to more efficiently integrate with other subsystems and gives the team better control over the pod’s actions. 

Power: 

In order to test the system,  theoretical analysis was required to reduce the possibility of a dangerous failure. Arcing calculations were conducted to find the minimum distance between terminals for arcing. The results show no threat of any battery terminal arcing and shorting.  Also, a heat transfer analysis to find if the casing would possibly fail at elevated temperatures was conducted in MATLab. At the expected power output, the casing would be perfectly safe from failure. After these calculations, we were confident enough to turn the system on and were excited to see the BMS was properly identifying and monitoring the batteries. Due to COVID-19 we were unable to test the system to find the offset voltage to turn the motor, and establish a relationship between voltage and velocity.

Arc Calculations

Heat Transfer Analysis

Propulsion: 

Motor Oil System

As previously mentioned the propulsion system is being modified and there were no large design changes. The biggest modifications came in the motor coolant system as it was the limiting factor for motor testing for the majority of the time. Modifications of this system included lowering the coolant pump to ensure it was lower than the lowest point in the motor’s fluid reservoir and would not create cavitation in the pump. The other major modification was to the piping for the motor coolant as well, where a clear tube was added to the outlet of the motor which created a visual cue to indicate when the motor was full of the coolant as well as if the pump was properly circulating coolant. Both of these modifications can be seen in the figure below. 

In addition to the changes above the propulsion, the team has been providing maintenance on the chain tensioner, wheel, and pneumatic clamping system and fabricated the pre-designed motor controller coolant system. 

Stability: 

 Hammer Arm FEA
 Min FOS = 3.5

Several FEA analyses were carried out on critical components of the stability system. These analyses were carried out for gross yielding, Factor of Safety, and deformation. A mesh with default refinement and curvature-based meshing was used, with mesh control employed about the holes in the part. Only the FOS plots of the most critical parts are shown here.

After running the FEA for the critical axles and hammer arms, the stability team feels confident in the system’s ability to withstand the forces that it will encounter on the track, as all factors of safety were well above 2. However, just to be safe and double check the FEA, hand calculations were done to validate  FEA results.

The hand calcs were conducted using the following assumptions:

 Ground Guide Axle
 Min FOS = 67.

•   All 100 lbf is transferred from the wheel to the acoustic foam.  However this is a conservative analysis because some of the force will transfer to the axle on the handle of the hammer arm.
•   The buckling analysis was conducted using an average value of Second Moment of Inertia (I) due to the varying cross sectional area.
•   Half of the 100 lbf is transferred to each hammer arm due to symmetry. 
•   The pin connection is in a state of double shear. 

While this data shows that the stability system will not fail due to static loading; sensors must be placed on the system and force data recorded so cyclic loading failure analysis can be conducted.   

Isolation Theory

    Isolation Theory Equations

In isolation design, the tuned variable is the natural frequency. The natural frequency is a system property associated with the frequency at which a system oscillates given a single input ─ either impulse or displacement ─ and no energy sink; it is a function of the material spring constant ‘k’ and the oscillating mass ‘m’ (see eq.1). Damping is the system’s energy sink frequently denoted ‘C’(see eq. 2). The damping ratio, ‘ζ’, is the ratio of the applied damping over the critical damping value (see eq. 3). Transmissibility ratio, ‘TR’, is the designed quantity and refers to the system output as a ratio of the input. In layman’s terms, this is a transfer function that, when multiplied by the input, produces the output (see eq.4). It is​ important to understand that the transmissibility ratio equation is the same for both transmitted force and transmitted displacement. ​ For the purposes of this design, displacement was used as the​ actual force of the impulse is not known. The variable ‘r’ is the frequency ratio and refers to the ratio of​ the input frequency over the natural frequency (see eq. 5), for the purposes of this design the input frequency is the impulse frequency of the step.  

Isolation System Design

Farrat Vibration Dampening    Foam

The design of the isolation system focused on manipulating the system natural frequency (ω n ). To this end Farrat provides performance curves for each of its products. These curves are industry standard and other companies that produce similar products also post charts showing this information. 

 The system’s natural frequency is a function of the pressure applied to the foam pad which produces two tunable parameters: Applied load, and application area. For the Ground Guide system, the applied load is fairly fixed and is a function of the pod’s mass and the total number of systems. Given an applied load, the application area can be easily adjusted to produce the desired natural frequency. The tuning parameters for both pads are shown in the design table below. 

Isolation Pad Design Parameters

Performance

The figure below, shows the performance curves associated with both VR2725 (blue) VR2750 (red). These curves are functions of the transmissibility ratio rather than the transmissibility ratio itself. Recalling that the transmissibility ratio is defined as the output over the input, the displacement (Y-axis) was derived by multiplying the transmissibility ratio by the known, input displacement, 0.04 in.

Resonance Peak Velocities

Transmitted Displacement as a Function of Pod  Velocity

The performance shown above translates to the isolation envelopes shown below. The image was taken from Brakes’ velocity vs distance calculations and the isolation zone approximated based on the range of operating velocities. It is worth noting that the resonance condition occurs twice; once during acceleration and once during deceleration. The expectation of this design is that the pod passes both resonance points very quickly such that it spends very little time at resonance with the vast majority of the run spent in the isolation zone.

Next Steps

The next iteration of Diggerloop needs to conduct a full system test in AZ and the proceed with redesigns based on SpaceX’s expanded competition rules and lesson’s learned from the system test.

Braking:

Braking will build and validate pod-ready eddy current braking systems to supplement the friction brakes. With both sets of brakes validated, a competition-ready design can be developed. Furthermore, the braking system will implement changes to the friction brake system to comply with Hyperloop Competition rulesets. For instance, no quick-detach fittings. Of high importance is to also perform further testing, including under pod locomotion on a test track. These tests will lead to further iteration and improvement pending results.

Controls:

To improve the function of the Control subsystem, the most important next step is to implement the CAN bus and interfaces. This technology will allow for the collection and organization of key datasets such as battery temperature, motor temperature, motor controller status, and pressure. Another important task would be to troubleshoot the motor controller function with the RS232 software and USB connector. At the conclusion of work this semester, the batteries and control system are both hooked up to the motor controller but it is unclear if the unit was receiving power. More testing needs to be done to determine where the problem lies. A final key step to get the Control subsystem operational is to implement the telemetry equipment and software to track position and velocity in a different way. This is currently done with an onboard accelerometer, but the telemetry would be useful as well.

Power:

The next team should focus on implementing the motor and finishing the current design of the system. Also, in order for the Power system to follow SpaceX’s rules, LEDs must be implemented to provide status and alert the user when the pod is safe to approach. These LEDs should be implemented on a panel that is attached to the outside of the chassis. The LED’s will need to purvey information from the BMS and cRIO, it is up to the future team to decide how to implement this. Additionally as mentioned previously, future teams should work with K2 Energy to get all of the design documentation, so that they will not have to wait for K2 to be available to help. K2 Energy has expressed interest in the past for sharing all of the documentation they have, if our team would be willing to sign an NDA.

Propulsion:

The propulsion team recommends that the current system be scrapped in favor of a new design. There are multiple components on the propulsion subsystem that break the guidelines set by SpaceX for the competition. If there is any desire to compete with the Diggerloop team, serious changes must be made in order to become compliant with competition rules. 

The future design that is recommended is the design created by the Diggerloop 4 propulsion team. There are copious amounts of verifications on the future design which indicates that the new system will be sufficient mechanically. 

This design is theoretical and has been created for past SpaceX rulesets. Moving forward, it is essential that the next propulsion team considers the ruleset at every turn. It is likely that the ruleset will change and as a result, the design will need to change as well. A great way to ensure smooth proceedings, the team should lay out their path forward and check off essential specifications set in the rules. As seen below in the Figure  below, the system has various subsystems that will most likely require alterations in their dimensions like the individual stability system.

Renduring of Future Propulsion System

Stability:

The entire stability system needs a redesign to reduce the complexity for ease of manufacturing, reduction in manufacturing time, and increase is precision.  Key components need to be kept and adapted to the new chassis design.

Chassis:

The current chassis design is two parallel I-beams.  This was a simple design that provided lightweighting but mainiting stiffness along the long axis.  However, this design proved to be difficult to interface with, and an entire chassis redesign needs to be made.  This redesign needs to be conducted with each subsystem in mind, and provide a specific location and strong interface for each component.

Meet the Team