Hover Engine

HE3.0 DatasheetRevision 2.0

March 3, 2016

c© 2016 Arx Pax Labs, Inc. 1

Contents

1 Introduction 3

2 Single Engine Specification 4

3 Propulsion, Braking, and Control 6

4 Simulation Data at High Translational Speeds 8

5 Design Notes 95.1 Engine Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95.2 Tube Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6 Operation at Low Pressure 116.1 Thermal Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7 Testing 137.1 Testing and Simulation Arx Pax will Complete . . . . . . . . . . . . . . . . . . . . . 137.2 Testing and Design Tasks that Teams are Expected to Complete . . . . . . . . . . . 13

8 Safety 148.1 Magnet Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148.2 HE3.0 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9 Appendices 169.1 Mounting Hole Drawing for HE3.0 Hover Engine . . . . . . . . . . . . . . . . . . . . 169.2 Pricing Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

9.2.1 Pricing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.2.2 Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

9.3 Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

c© 2016 Arx Pax Labs, Inc. 2

1 Introduction

The Arx Pax Hover EngineTM 3.0 (HE3.0TM) is designed with Arx Pax’s patented Magnetic FieldArchitecture (MFATM) technology which efficiently shapes and controls magnetic fields.

The Hover Engine works by inducing eddy currents in a conductive substrate which create a specif-ically designed, dynamic primary magnetic field. The induced eddy currents result in a secondarymagnetic field which repels the primary field to generate lift.

Each Hover Engine consists of an electric motor, a motor controller, and a StarmTM. The primarymagnetic field is produced by the Starm. The system comes with a mounting bolt pattern intendedto simplify installation; see Mounting Hole Drawing for the HE3.0 in Section 9.1.

(a) The HE3.0 Hover Engine (b) The Motor Controller

Figure 1: The Components of our Hover Engine System. The motor controller is typically poweredby a DC electric power source and sends the signals to spin the electric motor. It controls theelectric motor by a software interface that allows the user to modify parameters such as current,voltage, and timing.

The orientation of a Hover Engine relative to the conductive surface can generate thrust, i.e. forcesparallel to the subtrack. See Section 3 for more information.

Teams will be responsible for designing their own mechanical and software systems to control thelift and thrust forces of their Pod engines as well as maintain the proper conditions for Hover Engineoperation. Onboard DC power should be implemented based on Pod weight, expected runtime,additional electrical systems, and any system changes that will affect lift (tilting the engines forthrust, external forces, etc.).

c© 2016 Arx Pax Labs, Inc. 3

2 Single Engine Specification

All data are based on a single HE3.0 Hover Engine operating in a stationary position over a 0.5 inch(12.7mm) thick piece of 6101-T61 Aluminum (subtrack material as of Revision 5.0 of the SpaceXSpecification).

Hover Height: Always measured from engine bottom to subtrack top. Please see Figure 2.

Minimum Clearance for Engine Startup: 10mm

Minimum Subtrack Clearance: 4mm

Maximum Lift: 68kg (150 lbs); 6mm hover height

Nominal Lift: 55kg (121 lbs); 7.5mm hover height

Engine Weight (excluding wiring): <7kg (15lbs)

Nominal Payload: 48kg (106lbs)

Maximum Thrust: 60 N (at 2◦ tilt); 4mm hover height, Nominal Payload

Nominal Engine Speed: 2000 RPM (final engine speed values TBD)

Motor Kv: 41 RPM/V

Motor Bearing Minimum Rated Pressure: 0.125psi (862Pa)

Permanent Magnet Maximum Rated Temperature: 80◦C (motor and Starm)

Motor Maximum Rated Temperature: 100◦C (includes bearings and coils)

Motor Bearing Dimensions: 16004 (20mm ID x 42mm OD x 8mm W) and 16005 (25mm ID x47mm OD x 8mm W)

Nominal Input Voltage: 50 - 72VDC

Nominal Efficiency: 80 W/kg (final engine efficiency values TBD)

Approximate Engine Dimensions: Diameter 218mm (8.58in), Height 91.5mm (3.6in).

Current Draw: This engine is expected to operate in the range of 80W per kilogram lifted. Forexample, at 60V, the system is expected to draw 1.3A per kg (0.61A per pound) payload. Actualcurrent draw varies with payload and voltage, an example of which is noted in Figure 2.

Motor Controller Dimensions: See datasheet linked below for exact dimensions.

Motor Controller Maximum Current: 150A peak, 100A 1-min period, 50A Continuous

Motor Controller Maximum Voltage: 72V

Motor Controller Maximum Temperature: 60◦C

Motor Controller Datasheet: Accelerated Systems Cadmium Series BAC 2000-72-100

Motor Controller Software: BacDoor

c© 2016 Arx Pax Labs, Inc. 4

Figure 2: The relationship between load and hover height as the mass of the system or payloadincreases, at the nominal RPM. In general, total power consumption increases and hover heightdecrease with additional load.

c© 2016 Arx Pax Labs, Inc. 5

3 Propulsion, Braking, and Control

Photos, videos, and other designs that demonstrate the propulsion aspects of MFA can be foundat http://arxpax.com/hyperloop-resources/

Directional control involves mechanical and software systems that can control rotational speed, spindirection, and actuation (tilt) of the Starm relative to the hover surface. Force can be generatedwith small (< 2◦) actuation angles at the expense of hover height. The relationship between tiltingand thrust can be seen in Figure 4. For a more in depth explanation of how Hover Engines cancreate 3-axis control, please see the Hyperloop Developer Kit Datasheet.

This tilt angle can be reversed such that thrust acts in the opposite direction for braking. ArxPax recommends use of reduced engine speed, which will lower Pod hover height for eddy cur-rent braking, instead of Hover Engine tilt for braking. Due to the need for redundant safetysystems, MFA should not be the sole braking mechanism for the SpaceX Pod Competition. Podcompetition designers can generate custom actuation schemes that differentiate their system end-performance.

Figure 3: Thrust C relative to tilt A and rotation B. Thrust is a function of Engine Speed, Enginespin direction, tilt angle, and hover height.

c© 2016 Arx Pax Labs, Inc. 6

Figure 4: Thrust Per Degree Tilt at Nominal Lift and RPM. We do not recommend actuatingbeyond 2◦ because Hover Height drops below the Minimum Subtrack Clearance.

c© 2016 Arx Pax Labs, Inc. 7

4 Simulation Data at High Translational Speeds

We are currently in the process of refining our models and running simulations of the HE3.0 HoverEngine at various translational speeds. The data are not yet ready for publication but we candiscuss, qualitatively, the results thus far.

First, we know that magnetic drag decreases as the magnets in the Hover Engine move faster.However, it is important to distinguish between types of magnetic drag. When using MFA, themagnetic drag is seen as rotational drag and the motor creates torque to overcome this drag. Whenmagnets are used without rotation but just in translation, the magnetic drag is seen as translationaldrag, a force against the movement of the magnets.

When Hover Engines are used in translation, the translational magnetic drag is lower than with sta-tionary magnets because the magnets are already moving (spinning) and overcoming drag. There-fore, for the same push from an external propulsion system (ex. the SpaceX Pusher), a Pod withHover Engines will have a higher acceleration and cruise velocity relative to a Pod with non-rotatingmagnets. The exact drag numbers will be released shortly.

c© 2016 Arx Pax Labs, Inc. 8

5 Design Notes

5.1 Engine Performance

1. There is an inverse relationship between hover height and payload capacity, see Figure 2.

2. The number of required Hover Engines can be estimated by dividing the estimated Pod weightby the nominal lift per Hover Engine.

3. Pods benefit from uniformly distributed mass to facilitate reasonable attitude control (pitch,roll, yaw) and to prevent one engine from being overloaded.

4. To optimize performance, additional Hover Engines may be deployed for propulsion, controland/or stabilization of the system.

5. Engines should be installed in pairs which counter-rotate with respect to each other.

6. As a general rule, we recommend that Hover Engines are positioned at least half-a-diameterapart from each other. However in various system designs, counter-rotating engines have beenplaced as close together as 2” with some (minimal) effect on efficiency. Users can determinethe best placement for their own systems.

7. Hover Engines operate most efficiently when located directly in the center of the subtrack.Lift performance will decrease if the Starm protrudes over the edge of the subtrack.

8. The motors will not be able to spin up if the Starm is touching the subtrack. An offset (seeMinimum Clearance for Engine Startup in Section 2 is required to reduce the torque on themotor (due to magnetic drag) to allow it to reach its nominal speed. Once the Hover Engineis at speed, it can be lowered to its operating height.

9. If the engines are actuated, the lost hover height is very similar to the geometric change inheight due to tilting. See Figure 5 below:

Figure 5: Starm Tilt Angle. In the figure, θt is the tilt angle, Rs is the Starm radius, and ∆z isthe change in height due to tilting.

Using the law of sines for a 2◦ tilt of a 218mm diameter (109mm radius) Starm, the decreasein height should be 3.8mm and in practice the loss in hover height is 3.5mm.

c© 2016 Arx Pax Labs, Inc. 9

5.2 Tube Operation

It is important to avoid damaging the subtrack when hovering in place (e.g. startup).

• Each HE3.0 Hover Engine will transfer roughly 66 Watts of heat into the subtrack per kg ofPod mass.

• The approximate temperature rise of the subtrack can be estimated with the equation below.In Equation 5.2, Q̇/mp is the W/kg that is transferred to the subtrack, mp is the Pod mass,ms is the subtrack mass, and cs is the subtrack specific heat.

Q̇ = msc∆̇T

Q̇

mp=mscs∆̇T

mp

∆̇T

mp=

Q̇

mpmscs

∆̇T

mp=

66W

kg∗ 1

0.0975lb/in3 ∗ 24in ∗ 0.5in ∗ 12.5ft ∗ 12in1ft ∗ .454kg

1lb

∗ 1

895W/kgC

∆̇T

mp=

66W

kg∗ 1

79.7kg∗ 1

895J/kgC

∆̇T

mp=

0.00093C

kg − sec∗ 60sec

1min

∆̇T

mp=

0.056C

kg −min

– Equation 5.2 assumes a 24 inch wide (due to 2 separate tracks of 12 inch wide) by 12.5foot long by 0.5 inch thick piece of Aluminum 6101. This was the thinnest that SpaceXhas discussed using for the subtrack so it should be the worst case for heating. Toapproximate the temperature rise per minute for a given Pod, multiply the 0.056C/kg-min by the Pod mass (in kg). The 6101 material properties were taken from MatWeb

• Limiting the time (e.g. seconds) which teams allow their Pod to hover in the launch and stoppositions on the track can be used to control the subtrack plate temperature rise.

• Here are a few tips to limit hover time:

– Equip the Pod with retractable landing gear (e.g. wheels) to support the Pod beforeand during pre-launch functional tests and ready-to-launch checklist completion.

∗ This will also reduce torque requirements during Hover Engine spin up and reducethe risk of scratching the subtrack with a Hover Engine

– Once the Hover Engines have been spun up and are supporting the Pod mass, the landinggear should be quickly retracted so that launch can be initiated immediately.

– Near the end of the braking phase, when the Pod is at low speed, the landing gear shouldbe re-deployed to support the Pod as it comes to a stop and the Hover Engines are spundown.

c© 2016 Arx Pax Labs, Inc. 10

6 Operation at Low Pressure

Issues with electric motor operation at or near vacuum pressures are known. In particular, out-gassing of lubricants and increased motor and motor controller heating due to lack of air coolingand are of significant note, for operation in the Hyperloop. Unfortunately, vacuum rated motorsthat could also provide the torque necessary for hover are prohibitively expensive for teams. Aftertesting, research, and conversations with our suppliers, we reached the specifications detailed inSection 2. Below is our recommendation for low pressure Hover Engine operation:

1. Monitor the motor and motor controller temperature (strongly recommended).

(a) The ASI motor controller has a sensor that monitors its temperature and the value is areadable object. See page 26 of “BAC Object Dictionary”.

(b) A thermistor can be attached to the motor and connected to the motor controller. SeeSection 16.7, titled Motor Protection, of “BAC Controller Manual Rev 1.0”.

(c) Additional sensors are required to check the temperature of the motor bearings, motormagnets as well as the temperature of the Starm.

2. Design a thermal management plan to keep the motor, motor controller, and Starm belowtheir maximum rated temperatures.

(a) The change of outgassing of the bearing lubricants increases with rising temperatures.In addition, Hover Engine performance can diminish if the coils or magnets are operatedabove their maximum rated temperatures.

3. Replace the motor bearings.

(a) This option is recommended for the best performance at low pressure or if proper motorthermal regulation cannot be achieved.

4. Pressurize the Hover Engine (or just the motor) to provide enough air for cooling.

(a) It should be noted that enclosing the Starm will subtract from the hover height abovethe subtrack.

6.1 Thermal Management

As discussed in Section 5.2, approximately 66 of the 80W/kg go into subtrack heating. Theremaining power heats up the motor and the controller and the approximate values are below:

1. Motor Heating: 10W/kg

2. Motor Controller Heating: 4W/kg

By multiplying by Pod mass, the heating rates can be calculated to inform the necessary level ofcooling. Proper cooling is imperative to maintain engine performance. See Figure 6 for tempera-ture rise of an unloaded motor with no Starm at 1psi.

c© 2016 Arx Pax Labs, Inc. 11

Figure 6: Heating Rate of an Unloaded Hover Engine Motor at 1psi. The temperature rise willincrease with increasing load or decreasing pressure, due to the loss of convective cooling.

c© 2016 Arx Pax Labs, Inc. 12

7 Testing

We strive for complete transparency in order to set teams up for success. Therefore, we want tomake it clear what additional testing we plan on completing (as fast as possible) and what we areleaving to the teams.

7.1 Testing and Simulation Arx Pax will Complete

1. Simulation of lift (Fz), drag/thrust (Fx), lateral forces (Fy), and torque (τz) for incrementalinitial translational velocities between 0-200mph

(a) 2000 RPM, level (non-tilted) Hover Engine

(b) 2000 RPM, tilted Hover Engine

(c) 0 RPM, level (non-tilted) Hover Engine

(d) 0 RPM, tilted Hover Engine

2. Simulation of a Hover Engine over a seam (gap in between subtrack plates) at various speeds

3. Testing of static hover height and thrust forces for 2000 RPM, tilted Hover Engine for nominal(55kg) engine load. Completed. See Figure 4.

4. Testing of engine power efficiencies for loads from 15-75kg

5. Further vacuum testing for heating and outgassing

6. Basic EMI testing

7.2 Testing and Design Tasks that Teams are Expected to Complete

1. Hover Engine actuation systems (e.g. mechanism, actuators, control system)

2. All control algorithms and models of their system

3. Motor, Starm, and motor controller temperature management

4. Some mechanism to separate the Hover Engine 10mm from the subtrack to allow it to spinup. Once at nominal RPM, the Hover Engine can be lowered and operate normally.

5. Teams are expected to design their Pods taking into account the recommendations outlinedin this datasheet

c© 2016 Arx Pax Labs, Inc. 13

8 Safety

8.1 Magnet Safety

The neodymium magnets in our Hover Engines and associated components are extremely strong.They must be handled with care to avoid personal injury or damage to the magnets. Precautionshould be used when using ferromagnetic parts, (steel, iron, nickel, etc.) including control hardware,support components and tools. Likewise, parts made from conductive materials may heat up if theyare in close proximity (less than 10 cm) below the Hover Engine during operation.

NEVER GET CLOSE TO THE HOVER ENGINES IF YOU HAVE A PACEMAKEROR SIMILAR DEVICE. THE STRONG MAGNETIC FIELDS NEAR THE MAG-NETS CAN AFFECT PACEMAKERS, ICDS AND OTHER IMPLANTED MEDI-CAL DEVICES. MANY OF THESE DEVICES ARE MADE WITH A FEATURETHAT DEACTIVATES IT WITH A MAGNETIC FIELD. THEREFORE, CAREMUST BE TAKEN TO AVOID INADVERTENTLY DEACTIVATING SUCH DE-VICES.

Powerful attraction forces can cause serious injury.Neodymium magnets are more powerful than other kinds of magnets. The incredibly powerful forcebetween magnets can often be surprising to those unfamiliar with their strength. Fingers and otherbody parts can be pinched between two magnets. With larger magnets, injuries of this type canbe severe.

Magnets can affect magnetic media.The strong magnetic fields near neodymium magnets can damage magnetic media such as floppydisks, credit cards, magnetic I.D. cards, cassette tapes, video tapes or other such devices. They canalso damage televisions, VCRs, computer monitors and CRT displays. Avoid placing neodymiummagnets near electronic appliances.

Neodymium magnets can become demagnetized at high temperatures.While operating temperatures are often listed as 80◦C (175◦F), the actual maximum operatingtemperature of a magnet can vary depend on the grade, magnet shape and how it is used.

Neodymium magnet powder or dust is flammable.Avoid drilling or machining neodymium magnets. When ground into a dust or powder, this materialis highly flammable.

Strong magnetic fields can interfere with compasses and navigation.IATA (International Air Transport Association) and US Federal rules and regulations cover shippingmagnets by air and ground delivery. Magnetic fields can influence compasses or magnetometers usedin air transport. They can also affect internal compasses of smartphone and GPS devices.

c© 2016 Arx Pax Labs, Inc. 14

8.2 HE3.0 Safety

NEVER TOUCH THE HOVER ENGINES WHILE THEY ARE IN OPERATION.THE HOVER ENGINES HAVE A SPINNING COMPONENT CALLED THE “STARM”,WHICH SPINS AT HIGH VELOCITIES AND CAN CAUSE SEVERE INJURY IFTOUCHED WHILE ITS OPERATING.

As stated earlier, our Hover Engines are comprised of motors, various other components, and a high-velocity spinning armature that is called the “Starm”. Among other things, the Starm containsthe magnets that are being rotated.

Before and after use always inspect the bottom of the Hover Engines and Starms for anythingthat might have gotten attracted to magnetic field and stuck to the Starm (washers, screws,Allen wrenches, etc. can unknowingly get stuck to the engines and then fly off during enginestartup).

Take special care not to allow spinning Starms to contact anything (especially the conductivesurface) as this may cause the Starm to break apart.

Keep fingers clear of the bottom of the Hover Engines and Starms.

The strength of the Starms can surprise even those experienced in working with Hover Engines andmay snap together pinching hands, fingers, or other body parts.

The Hover Engines operate in a high current range (especially if loaded) so proper safety cutoffsshould be established for testing and operation.

c© 2016 Arx Pax Labs, Inc. 15

9 Appendices

See Appendix 1 for Hover Engine mounting hole pattern

See Appendix 2 for pricing and commercial/technical support information

9.1 Mounting Hole Drawing for HE3.0 Hover Engine

Figure 7: Mounting Holes of the Stator

c© 2016 Arx Pax Labs, Inc. 16

9.2 Pricing Information

9.2.1 Pricing

Please note that the minimum order size is four (4) Hover Engines. Additional Hover Enginescan be ordered in groups of two (2). Some Pod configurations may require more Hover Enginesdepending on overall mass, and other Pod-specific design parameters. All competition participantscan purchase Arx Pax Hover Engine technology, which includes a license for use solely in thePod competition and for their ongoing research. Participants will be restricted from using thetechnology for commercial purposes. We are offering specially discounted pricing for universitiesand nonprofits. The costs are as follows:

1. Basic 2 Pack, HE3.0 Hover Engines: $9700

2. Hyperloop Developer Kit (HDK): $1289

9.2.2 Technical Support

Arx Pax wants all participants to succeed in bringing their vision to fruition. In order to facilitatethe incorporation of Arx Pax technology and products into their designs, Arx Pax will provideand maintain a FAQ list and technical support information available at http://arxpax.com/

frequently-asked-questions-hyperloop/

c© 2016 Arx Pax Labs, Inc. 17

9.3 Change Log

1. Rev 1.0 (February 22, 2016)

(a) Removed draft designation

(b) Section 1

i. Added pictures of the Hover Engine components

(c) Section 2

i. Added thrust at 2◦

ii. Added motor Kv

iii. Added Nominal Input Voltage

iv. Updated Nominal Efficiency

v. Added Motor Controller Maximum Temperature

vi. Added Motor Controller Software

vii. Added Hover Height vs Load graph

(d) Section 3

i. Added braking information

(e) Section 5

i. Changed the design recommendation from choosing a hover height to using thenominal lift value

ii. Added a note about offsetting the Hover Engines for startup

iii. Added a diagram about tilt angle

iv. Added information on subtrack heating

(f) Created Section 6, Operation at Low Pressure

2. Rev2.0 (March 3, 2015)

(a) Section 2

i. Added Minimum Clearance for Engine Startup

ii. Added Minimum Subtrack Clearance

iii. Added Motor Bearing Minimum Rated Pressure

iv. Added Permanent Magnet Maximum Rated Temperature

v. Added Motor Maximum Rated Temperature

vi. Added Motor Bearing Dimensions

c© 2016 Arx Pax Labs, Inc. 18

(b) Section 3

i. Added Thrust per Degree Tilt graph

(c) Added Section 4, Simulation Data at High Translational Speeds

(d) Section 5.2

i. Updated subtrack heating equation to 24 in width

(e) Section 6

i. Revised introduction

ii. Revised recommendation

(f) Added Section 6.1, Thermal Management

(g) Added Section 7, Testing

(h) Divided Section 8 into two subsections and added additional safety information.

c© 2016 Arx Pax Labs, Inc. 19