Team Rocket 2015 WSGC Collegiate

Rocket Competition Design Report

Cullen Billhartz, Alex Stange, Stephen Slattery, Mathew Holly, Sam Wolcott

Austin Jefferies, Mike Keck, Max Stange, Danny Lerner, Tashi Atruksang

Faculty Advisor: Aaron “Sonny” Nimityoungskul

April 17th, 2015

Table of Contents:

Contents Executive Summary .......................................................................................................................... 3

Design Features of Rocket ............................................................................................................... 3

Body Tubing ................................................................................................................................. 3

Dart Size and Shape ..................................................................................................................... 3

Booster Size and Shape ................................................................................................................ 3

3D Printed Boat Tail ..................................................................................................................... 3

Fiberglass Molding - Transition .................................................................................................... 4

Fiberglass Molding – Tail Cone .................................................................................................... 5

Design of Fins ............................................................................................................................... 5

Center of Pressure and Mass ....................................................................................................... 6

Design Features of Avionics ............................................................................................................. 8

Data Collection and Sensors ........................................................................................................ 8

Data Logging ................................................................................................................................ 8

Telemetry ..................................................................................................................................... 8

Prototyping .................................................................................................................................. 9

Custom Printed Circuit Board Design........................................................................................... 9

Anticipated Rocket Performance .................................................................................................. 10

Rocket Construction ....................................................................................................................... 12

Fins and Centering Rings ............................................................................................................ 12

Boat Tail ..................................................................................................................................... 12

Transition and Dart Tail Cone .................................................................................................... 12

Body Tubing ............................................................................................................................... 12

Assembly .................................................................................................................................... 13

Launch Procedures ..................................................................................................................... 13

Conclusion ...................................................................................................................................... 13

Budget ............................................................................................................................................ 16

Executive Summary The objective of the 2015 Wisconsin Space Grant Consortium Rocket

Competition was to design a rocket that achieves the maximum possible altitude with a boosted dart. Design restraints required that the rocket use a Cesaroni 475-I445-16A. Our rocket’s dart must successfully drag separate after burnout from the booster stage. Both stages are to be recovered in flyable condition in order for the launch to be deemed successful. Attitude and altitude data recording is to occur in the dart portion of the rocket.

The design process for the rocket began with the realization that, in order to maximize altitude, the size and weight of all components would need to be minimized. All subsequent decisions were made in the interest of minimizing these factors. Examples namely include printing a custom circuit board for data recording, custom molding a fiberglass transition, and 3D printing a hollow tail cone.

Design Features of Rocket

Body Tubing The rocket was constructed out of “Blue Tube.” This material was used because of its

desirable structural properties over standard cardboard. Using this material should assure that

no deformation occurs due to the elevated G-force levels that will be experienced at liftoff. Also,

the stronger body tube will allow for a faster acceptable descent rate, and thus a smaller and

lighter parachute. Carbon Fiber and other composite materials were avoided because they are

more difficult and hazardous to machine. Because wet conditions are a possibility, the body

tubing was coated with a bee’s wax to make it hydrophobic before apply spray-paint. The

combination of these surface treatments will prevent structural degradation in wet conditions.

Dart Size and Shape The dart portion of the rocket uses a 38mm blue tube. It contains two sections of body

tube of lengths 7.5” and 6.8” The lower portion (6.8”) of the dart contains the 24” elliptical

parachute. This parachute will cause a descent rate of 20 feet per second. The upper portion

(7.5”) will contain the electronics bay.

Booster Size and Shape The booster was constructed out of 76mm blue tube. The booster contains two sections

of body tube of lengths 5.5” and 5.1”, respectively. The lower portion (5.1”) of the booster

contains the inner tube and rocket motor. The upper portion contains the 30” parachute. This

parachute will also create a descent rate of 20 feet per second.

3D Printed Boat Tail In order to reduce our drag, a boat tail was designed to taper from the outer diameter

of our booster body tube to the outside of the motor retaining ring. The tail cone pictured in

Figure 1 below could have easily been manufactured out of HDPE with a CNC Lathe, however,

the resulting piece would have been completely solid and heavy. Instead, a 3D printer was used

to create the boat tail, which resulted in a hollow part with reduce weight. The orange lines in

Figure 2 show the internal cross-section. The part was printed with ABS on a Dimension Elite.

Although this object could have been fiberglass molded, we felt the tolerances needed could not

be held by fiberglass molding.

Fiberglass Molding - Transition For the transition between the booster stage and the

dart, the team identified three possible manufacturing

processes. The first process was purchasing a nose cone,

cutting off a portion, and fitting a coupler on the end. This

option would give very few choices in terms of length and

contouring, resulting in a difficult time in optimizing the

shape. The second option was using a CNC lathe to turn a

custom HDPE part. Choosing this path would have allowed us

to optimize shape and hold very tight tolerances, however it

would have created a solid part resulting in a drastically

increased weight. The last option was to fiberglass mold. This

solution is the most lightweight and the size and shape could

be easily optimized for our rocket. To verify this could be a

practical solution, a test transition was molded using

polystyrene as a male mold and Z-poxy as the finishing resin.

The test model had no obvious issues thus our team decided

to mold this portion of the rocket. As shown in Figure 3, the

transition features three slots that will constrain the fins of the dart, preventing any

rotation about the axis of the rocket. Within this transition is a pocket for the tail cone

to sit. This design will prevent the fins from being pushed down and pinched on the fin

Figure 1: Lathe Product Figure 2: 3D Printed Product

Figure 1: Transition CAD Model

slots. The shoulder of the transition will remain as polystyrene that is epoxied into the

booster.

Fiberglass Molding – Tail Cone The tail cone of the dart was also fabricated with fiberglass

molding. The reasoning was the same as for the transition - it is a light

weight and highly customizable solution. We decided not to 3D print

this part because the tolerances for this piece were very loose and the

fiberglass molding was also a more cost effective solution.

Design of Fins The fins were designed to fit around the components and create a stable rocket.

The booster fins and dart fins have a surface area of 22.2 in2 and 6.94 in2 respectively.

This fin area was used because it results in the center of pressure being correctly

positioned relative to the center of mass to create a stable rocket. Eighth inch nominal

slots were cut into the fin tab in order to fit into the fin guides as shown below in Figure

5. In order to recover our rocket with the fins undamaged, the overall fin shape was

chosen to be as sturdy as possible. The angle between the trailing edge root and the

surface of the body tube is greater than 90° to prevent the rocket from landing on a

corner and causing a large stress concentration.

Figure 2: Tail Cone CAD Model

Figure 3: Dart and Booster Fins

Figure 7: After Burn-out, No fuel mass

Center of Pressure and Mass In designing our rocket, it was important that the stability factor was within the range of

one and two. The figures below show that the full assembly from launch to burn-out, as well as

the dart after separation, hold a stability that is within the desired range. The booster stage

after separation will not be stable, which is acceptable because the apogee of the booster stage

is irrelevant and it is no longer being propelled. No safety issues exist here. All dimensions are

given from the tip of the nose cone

Figure 8: Booster Stage after Separation

Figure 6: Rocket at Launch

Figure 9: Dart after Separation

A stability versus time analysis was computed to ensure that the rocket would

remain stable throughout the duration of the flight. The graph shows the stability

margin caliber increase as the motor loses fuel and mass. The stability then begins to

fluctuate as vertical velocity decreases. The stability drops to 0.73 just seconds before

apogee is reached. This is acceptable because the rocket’s vertical velocity will be near

zero at this time. The overall graph suggests that our rocket will remain stable

throughout its flight

Figure 4: Stability Analysis

Design Features of Avionics In order to satisfy the requirement that data collection be performed using custom

hardware, the team elected to design a tailor-fit PCB which could carry out said tasks. This route, though more time consuming and complex, was chosen to ensure the most robust avionics package in the smallest form-factor. The initial design and prototyping of this board was divided into three sub-categories: data collection, data logging, and telemetry. What follows is an in-depth discussion of each aforementioned component.

Data Acquisition The InvenSense MPU6050 6-axis accelerometer/gyro and Xtrinsic MPL3115A2 altimeter

were chosen to accurately measure the Euler angles of the rocket in flight as well as its vertical altitude. The MPU6050 reads raw accelerometer and gyro values then utilizes an onboard digital motion processor to fuse the sets of data to calculate the yaw, pitch, and roll of the rocket. This method yields a far more accurate determination of attitude by allowing the accelerometer and gyroscope data to complement one another. Issues seen in systems which implement only gyroscopes, such as drift and the need for frequent zeroing, are eliminated. The MPL3115A2 contains both pressure and temperature sensors, the latter of which is used to compensate for drift in the former. Pressure data is easily converted into altitude given the inherent quasi-linear relation of these values at low (sub-10000 ft) altitudes.

Data Logging In the interest of simplicity and ease of data retrieval, a microSD card was chosen to

implement logging capabilities. This device communicates on an SPI bus which allows for straightforward prototyping and connection to most microprocessors, and is favorably sized with a footprint of just over 150 mm2. The SPI bus system is excellent for communicating with peripheral devices quickly at short distances – which is exactly the case when writing data from on-board sensors to an SD card – and can operate at a sufficiently high clock frequency. Accessing the data is as simple as removing the card from its socket and connecting it to a laptop via a built-in adapter.

Telemetry It was determined that the ability to transmit data between the flight vehicle and

ground, though not required, would be advantageous for a number of reasons. Foremost among these justifications is that it provides redundant data logging; the flight vehicle transmits at 100 Hz a copy of all data written to the SD card. This data is received by a ground-based antenna connected to an identical transceiver, which then passes the data to a laptop computer where it is logged and graphically displayed. Telemetry also allows for commands to be sent to the rocket which, although not necessary during an ideal flight, can be used to deploy the parachute or safe the deployment charge. Lastly, this endeavor serves as a proof-of-concept for future vehicles which may have a more explicit need for in-flight communication with the ground. To expedite the prototyping and integration process, two 900 MHz Xbee’s were chosen – one for the vehicle and one for the ground station. These devices can perform reliable point-to-point

serial communication at distances over 1 mile and are easily configured. On the ground, a laptop processes and displays the attitude data in 3D using a custom LabVIEW program.

Prototyping The goal of the first phase of development was to verify that the

components worked as expected, that the code libraries were functional and easily modified, and that the devices would all work in conjunction. Breakout boards, one of which can be seen in Figure 1, and Arduino UNO’s were purchased to facilitate this prototyping. The Arduino UNO’s Atmega328P processor is capable of SPI and I2C communication and is easily programmed using the Arduino IDE. Code libraries for the MPU6050, MPL3115A2, and SD card were implemented to further ease the initial development. This initial

phase encountered no significant issues and was completed in less than a month.

Custom Printed Circuit Board Design Design of the custom PCB was done using Eagle software over

a period of two weeks. The two-layer board, measuring 1.25” by 3”, was dimensioned to fit within the 38mm diameter dart. A surface-mount version of the Arduino’s processor, the Atmega328P, was chosen to allow for straightforward porting of existing code. The board implements SPI and I2C data buses to communicate with the SD card and sensors respectively, and communicates with the Xbee using transistor-to-transistor (TTL) logic. A MOSFET was selected to serve as the trigger for the parachute deployment charge. The board’s power supply is a 7.4 V LiPo battery, chosen for its ability to drive high currents for short periods of time – necessary for triggering the deployment charge – as well as its inherent reusability. The board components themselves are powered through a 3.3 V regulator. This results in a slight overclock of the processor, which runs at 16 MHz, but removes any need for level-shifting of data lines. The board, “Avios,” is fully designed and is currently being manufactured by OSH Park.

Figure 5, MPU-6050 breakout

Figure 6, Avios PCB layout

Figure 7: Dart Flight Path

Anticipated Rocket Performance Open Rocket was the primary tool used to predict the rockets performance. In the figures

below, the velocity, acceleration, and altitude are plotted against time. The dart is projected to

reach a total altitude of 5100 ft, with a max velocity of 700 ft/s and a max acceleration of 800

ft/s2.

Figure 8: Booster Flight Path

The booster is projected to reach an altitude of 1,100 ft, however this number is

constructed with low confidence. Because of the booster’s instability after separation, and the

inlet that will allow airflow through the booster, the simulation is very complicated and is

difficult to model properly using Open Rocket. The max velocity of the booster is projected as

700 ft/s and the max acceleration as 800 ft/s2.

The difference between apogees of the dart and the booster is thus expected to be

4000ft. The max acceleration of the entire rocket is experienced at liftoff and is estimated to be

800 ft/s2.

Rocket Construction

Fins and Centering Rings Once the 1/8th and 1/4 inch plywood was received, an Epilog Mini 18 Laser Cutter was

used to laser cut out the fins, centering rings, bulk heads, and electronic bay components. All

parts were given 0.01” extra on dimensions so that the charring could be removed without

under sizing the part.

Boat Tail The boat tail was 3D printed on a Dimension Elite 3D printer using ABS plastic. Once

received, the shoulder was sanded to the inner diameter of the body tube to ensure a tight fit.

Transition and Dart Tail Cone Both the transition and the dart tail cone were constructed using fiberglass molding. For

both these parts, a male plug was used instead of a female mold. The advantage of the male

plug is that it was easier to manufacture and shoulders could be molded with the transition. In

retrospect, the female mold would have provided a superior external surface finish which would

increase aerodynamic properties. A revision for future competitions will be to better explore

female mold fabrication via CNC milling.

To make the male plug, polystyrene was formed using a hot wire cutter. Cardboard

cutouts were used as guides as they cannot be cut by the wire cutter. Each section of the

transition was cut then glued together. The entire piece was put on our drill-lathe to be sanded

and given the correct contour. Z-poxy molding resin was mixed with the fiberglass and laid over

the male plug. Multiple layers of fiberglass cloth were added at the same time. The mold was

left to dry over a 48 hour period and was then sanded and spray painted. The fin slots for the

transition were cut with a Dremel tool over a down draft table. Proper safety protection such as

gloves and a dust mask were worn.

Body Tubing The body tubing was cut to length on a horizontal band saw and then squared on a

lathe. In order to make the fin slots, a 3/32” in-end mill was used on an Eisen Milling machine. A

super indexing spacer was used to ensure that the fins were exactly 120° from each other. The

inner tube had 0.005” removed from the inner diameter by using a boring tool on a lathe. This

was done per request of WSGC Safety Judges to ensure a good fit for the motor in the blue tube.

Assembly Once all of the parts were manufactured, a dry-fit was done to ensure that all parts

would fit as intended. Following this prcess, the assembly procedure listed below was executed:

Booster Assembly

o Epoxy centering rings and bulk heads to motor inner tube

o Epoxy motor tube assembly to inside of booster lower body tube

o Insert fins and epoxy to channels in centering rings and fin slots in body tube.

o Apply JB weld to motor retaining ring and inner tube and let sit for 24 hours

o Epoxy parachute mount ring to booster lower body tube

o Epoxy booster coupler to booster lower body tube

o Drill holes in coupler and booster upper body tube for shear pins

o Epoxy parachute mount ring to booster upper body tube.

o Install parachute deployment electronics above parachute mount ring

o Use 4-40 screws to attach the transition to the booster upper body tube

o Use 4-40 screws to attach boat tail to booster lower body tube

Dart Assembly

o Epoxy centering rings to dart lower body tube

o Epoxy motor tube assembly to inside of dart lower body tube

o Use 4-40 screws to attach the tail cone to the dart lower body tube

o Epoxy parachute mount ring to dart lower body tube

o Epoxy dart coupler to dart lower body tube

o Drill holes in coupler and dart upper body tube for shear pins

o Use 4-40 screws to install the Electronics bay

o Epoxy the dart nose cone to the dart upper body tube

Launch Procedures Prior to launch, we will check to ensure that all of the electronic systems are function.

Using the telemetry from our electronics bay, we can verify that the altitude is being properly

measured and systems are functional. All epoxy joints will be visually inspected to ensure that

the adhesive is still structural. Once ready, the ejection charges and motor will be loaded into

the rocket and launch will occur.

Once the rocket is recovered, it will be visually inspected for any damaged parts and

that ejection charges will be checked for successful ignition. The electronics bay will be removed

and the data will be extracted.

Conclusion The rocket described in this design report excels in its minimization and use of proper

manufacturing processes and materials. By using fiberglass molding, 3D printing, laser cutting,

and precision milling machines, we constructed a rocket at that maximized structural integrity

with minimal weight. Based on the simulations and experiences, the rocket is expected to have a

successful launch and recovery.

Figure 13: Laser Cutting Fins and Centering Rings

Figure 14: Dry Fit of the Rocket

Figure 15: Milling Fin Slots

Figure 16: Booster Centering Ring and Fin Assembly

Figure 17: 3-D Printed Boat Cone

Figure 18: Example of Insulation Foam Plug Figure 19: After Fiberglass Layup Figure 20: After Insulation Foam

Removal

Figure 21: Laser Cut Fins and Centering Rings

Budget QTY Description Vendor Subsystem Total

1 Nose Cone Apogee Rockets Structure $25.71

1 Body Tubing (75mm ID x 48in) Apogee Rockets Structure $29.95

1 Body Tubing (38 mm ID x 48in) Apogee Rockets Structure $16.49

1 Body Tubing (54 mm ID x 48in) Apogee Rockets Structure $23.95

1 Fins (birch wood) Hobbylobby Structure $37.64

1 Polystyrene for Fiberglass mold Home Depot Structure $11.56

3 Hanger 9 fiberglass cloth Amazon Structure $20.43

1 Epoxy for Fiberglass Pacer Z-Poxy Structure $20.00

1 Parachute (Dart) Fruity Chutes Recovery $66.62

1 Parachute (Booster) Apogee Rockets Recovery $66.82

1 Parachute Padding Apogee Rockets Recovery $12.31

1 Coupler (75mm) Apogee Rockets Structure $9.95

1 Coupler (38mm) Apogee Rockets Structure $17.95

11 Shock Cord Apogee Rockets Recovery $5.39

1 Parachute Ejection System Apogee Rockets Recovery $10.00

1 Motor Retaining Ring Apogee Rockets Structure $37.00

1 Tailcone 3D Hubs Structure $47.93

1 16GB MicroSD Card Best Buy Avionics $13.00

3 Shear Pins Apogee Rockets Structure $12.00

1 170-point breadboard w/ cables Amazon Avionics $5.99

1 XBee manual Amazon Avionics $22.02

1 SD Card breakout module Amazon Avionics $5.50

1 Arduino UNO R3 Amazon Avionics $26.15

1 PCA9306 TTL level converter SparkFun Avionics $6.95

1 SanDisk 4GB SD card Amazon Avionics $4.95

1 MPL3115A2 pressure sensor SparkFun Avionics $14.95

1 GY-521 MPU-6050 IMU Amazon Avionics $5.85

1 Bluetooth Tx Module Amazon Avionics $8.48

1 Custom Avionics Board

Avionics $100.00

Shipping Charges

Misc. $75.00