Zero TiltPreliminary Design Review

Frostburg State University

Adam Rexroad, Brett Dugan, Mayowa Ogundipe, Kaetie Combs, Michael Stevenson, Daniel Gares, Tyler Lemmert, Subhasis Ghosh,

Jared Hughes, Sean Hughes, Andrew Huntley, Derek Val-Addo

October 26, 2011

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Mission Overview

2

Mission Statement: Zero Tilt’s goal is to provide, for the first time, a stable environment throughout the flight of a Sounding Rocket via two concurrent objectives:

◦Tilt correction system

◦Despun platform system

3

Mission Overview

We plan to:◦ Counteract the platform spin◦ Orient the platform parallel to the earth’s surface at all

times◦ Confirm the altitude reading using an accelerometer on

our platform

We expect to prove that it is possible to correct spin, tilt, and determine the altitude based upon a level reference.

This could benefit any scientific experiment that requires stabilization in order to collect data.

4

Mission Overview

The underlying theory and concepts:

negative feedback control systems concepts of torque and centripetal

force Micro electromechanical systems

(MEMS) Electromagnetic field theory Real-Time Systems Theory (for

multi-tasking)

5

Mission Overview: Theory and Concepts

Drexel University’s 2011 project incorporating a despun platform. The Results have not been published but the CDR offered evidence of successful trial runs at large stress.

We plan to elaborate on Drexel’s design. Modifying and improving the despun platform design in our project.

6

Past Research

Mission Objectives: Counter the spin of the rocket during flight. Keep a level surface to earth using our conceptual

design. Prove successful by comparing the acceleration data

from our zero tilt platform with that from the plate.

Minimum success criteria Our main goals as the Zero Tilt team is to receive

results indicating that we achieved zero tilt and confirming the altitude.

7

Mission Overview: Mission Requirements

crestock.com

What we expect:

Determine whether we were successful in keeping our platform level based on data analysis. (within a 10°tolerance)

Find altitude within a reasonable tolerance again based on the data we collect.

8

Mission Overview: Expected Results

Radial Acceleration

The max rate of spin of the rocket is 5.6Hz5.6Hz(2π)= 35.18 rad/secarad =146 m/s²=16g

Theory

Roll, αo X = 0o Y = cos(α)o Z = sin(α)

Pitch, βo X = cos(β)o Y = 0o Z = sin(β)

Yaw, γo X = cos(γ)o Y = sin(γ)o Z = 0

Theory (Cont.)

Converting to Spherical Coordinates

Theory (Cont.)

Counter the rotation ◦ Speeds up 8Hz◦ Stay within +- 5% the actual speed

Zero tilt◦ Keep the plate level ◦ Stay with in +- 10% of level

General Goals◦ Meet all NASA requirements◦ Fast respond time ◦ Reliable data collection◦ Reliable circuitry

Expected Results

Zero Tilt ConOps

t ≈ 1.3 min Altitude: 75

km

t ≈ 15 min

Splash Down

t ≈ 1.7 min

Altitude: 95 km

-G switch triggered

-All systems on

-Initialize despin system

-Initialize zero tilt system based on magnetometer.

t = 0 min

t ≈ 4.0 min

Altitude: 95 kmApogee

t ≈ 2.8 min Altitude: ≈115 km

t ≈ 4.5 min

Altitude: 75 km

t ≈ 5.5 min

Chute Deploys

-use the position of the zero tilt plate as initial value for the gyroscope sensor.-switch to gyro input for zero tilt system.

Subsystems

Despun Platform

Zero-Tilt Data Motors Power

Gears Gimbal Micro-controller

DC motors Batteries

Materials Gears Memory Servo-Motors

Voltage Regulators

Slip Ring Gyroscope Accel-erometers

Motor Speed

Controller

Arming

Algorithms DAC

Despun Platform Subsystem

Subsystem Requirements

The platform will be able to keep the platform parallel to the Earth independently of the rockets orientation.

All electrical components must be wired to a battery source without twisting the wires.

The assembly must be contained within the size requirements.

Subsystem Components1. Motors

1. Drive motor2. Tilt motor3. Spin motor

2. Gears1. Drive Gear2. Main Gear

3. Gimbal 4. Platform5. Slip ring6. Center shaft7. Bearings

1. Spin bearing2. Tilt bearing

Diagram

Main gear

Drive motor

Spin motor

Tilt motor

Drive gear

Gimbal

Platform

Slip ring

Center shaft

Spin bearing

Tilt bearing

Gears

http://www.daerospace.com/MechanicalSystems/GearsDesc.php

Gear 1 is the drive motor. It will be 1” in diameter. Gear two is the main gear and will be 6.5” in diameter. This will make the gear ration 6.5:1. Both gear will be made of 7075 Aluminum machined in-house.

Torque

The torque required by the drive motor was calculated through the following equation.

=

The calculated torque is 5.0152mNm based on G force 25 and 360 maximum rpm.

Gimbal

The Gimbal will support the platform and spin with the assembly. This component will be made out of 7075 Aluminum.

Platform The platform will be made of polycarbonate and will hold

the microprocessor. The microprocessor and components to control the tilt and The tilt motor will also be embedded in the platform.

The platform will have a hollow shaft which runs through it, this will allow the wires to be run of the board and onto the gimbal. The tilt motor will act as a bearing at one end, while the hollow shaft will be encased in a bearing on the other end as it enters into the gimbal.

Slip RingAeroflex CAY-1398

ELECTRICAL

1. Contacts: Gold on gold 2. Bearings: Precision ball bearings 3 Dielectric Material: High grade epoxy 4. Torque: .20 in.-oz. maximum (12

rings) 5. Speed: 1000 rpm maximum,

intermittent 6. Life: 30 x 106 revs min. @ 100 rpm 7. Rotation: Bi-directional 8. Frame: Stainless steel

MECHANIAL

1. No. of Rings: 12 maximum 2. Current: 1 amp maximum 3. Voltage: up to 150 volts 4. Dielectric Strength: 500 vrms, all

combinations 5. Contact Resistance Variation:

Less than 10 milliohms 6. Leadwire: #30 awg, teflon

insulated

Center Shaft

The center shaft will encase the slip ring. This will not only take the force off of the slip ring, but also act as a gear for the spin motor. Teeth will be machines to the outside of the shaft to allow the gear on the spin servo to adjust the yaw of the gimbal.

Bearings

There are two bearings included in this design. The first is the bearing located in the gimbal which allows the platform to rotate. This will be a very small grade 5 or 7 ball bearing.

The second bearing supports the gimbal. It is a grade 5 ball bearing.

Materials

There were four materials considered for this project.

◦Aluminum Pros - light weight Cons – low shear strength

◦Steel Pros – easy to machine Cons – high density

◦ Titanium Pros – very strong Cons – high density, expensive

◦ Polycarbonate Pros – Very high tensile strength Cons – not rigid

After considering all of the materials chosen, Aluminum and polycarbonate were chosen as our materials. The poly carbonate was chosen for the platform material because of its light weight and strength. Aircraft grade aluminum was chosen for the gears and gimbal because it has a high strength and light weight.

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Materials (cont.)

Design Changes

In the conceptual design, thrust bearing were going to be used to keep the rotating parts stable. Due to the compact size of the rotating parts, using a ball bearing should be sufficient in stabilizing these parts. By not using the thrust bearing the friction will be kept to a minimum.

2D Design

2.6250

2.8750

2.50003.2500

0.2500

2.7500 2.0000

0.2500

1.0000

Risk Matrix

DP.RSK.1◦ Gear teeth shear off

DP.RSK.2◦ Main gear flexes until

it no longer makes contact with drive gear

DP.RSK.3◦ Wires snag or twist

and break DP.RSK.4

◦ Assembly becomes off balance and wobles

DP.RSK.5◦ Two points of rotation

bind

PROBABILITY

CONSEQUENCES

DP.RSK.3

DP.RSK.4

DP.RSK.1

DP.RSK.2

DP.RSK.5

Zero Tilt System

Zero Tilt Definition

System Components:

Gimbal, “Goal Post” structure now moved to underneath the despun platform.

Servo Motors One will make adjustments in spin so that the long side

of the plate is parallel with the direction of the rocket. One will correct the tilt relative to the earth’s surface.

Microprocessor and Gyroscope Gyro will send data for tilt correction (spin and tilt) to the

microprocessor. Microprocessor will forward the data it receives to the

two servo motors.

Zero Tilt Description

Servos Servo 1 attached directly to shaft to resolve spin. Servo 2 attached to side of gimbal to resolve tilt.

Zero Tilt Gear Weight should not be a concern on the tilt platform.

Therefore the torque produced in a one to one gear ratio between motor and tilt gear should be sufficient.

Fabrication Currently have a prototype of the zero tilt platfrom

made from polycarbonate. Hoping to use the same material for tilt gear. (all

manufactured in-house)

Zero Tilt Requirements

Number of Requirement

Description of requirement

1 Initially we hope to be able to rotate the platform 360°. This is to ensure it remains stable through the entire flight.

2 Microprocessor should be able to pass minimum voltage requirement of 2.4V to gyroscope.

3 Microprocessor should be able to pass minimum voltage requirement of 2.4V to gyroscope.

4 Gimbal, Platform, and components shall survive the intital shock and 25g in flight acceleration.

5 The platform will be balanced to conform to center of gravity constraints,

6 The platform will be within specified design constraints. Preliminarily < 2 inches in height and 4 inches in diameter,

7 Servo motors are adequately powered and provided with correction data in appropriate time frame.

Zero Tilt System Gyroscope StudyCharacteristic L3G4200D (digital) LPR403AL (analog)

Voltage Requirement 9 7

Current Requirement 9 7

Process speed 8 10

Angular Rate Noise Density

7 9

Self-Test Capable 7 10

Survivability( shock, g’s)

10 10

Availability 8 8

Size 10 8

Cost 8 10

Total (out of 100) 85 84

Zero Tilt selected Gyro (L3G4200D)

Three selectable full scales (250/500/2000dps)

I2C/SPI digital output interface

16 bit-rate value data output

8-bit temperature data output

Two digital output lines (interrupt and data ready)

Integrated low- and high-pass filters with user selectable bandwidth

Ultra-stable over temperature and time

Wide supply voltage: 2.4 V to 3.6 V

Low voltage-compatible IOs (1.8 V)

Gyroscope Schematic

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Zero Tilt (ZT) Risk Matrix

ZT.RSK.1◦ All of the risks associated

with the despun platform ZT.RSK.2

◦ Servo motors will not be able to keep up initially.

ZT.RSK.3◦ Vibrations will destroy

gimbal arms or ZT platform ZT.RSK.4

◦ High Gs will cause disrupted platform adjustment

ZT.RSK.5◦ Stress on joining areas

resulting in breaking.

Data Subsystem

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Data Subsystem

Accelerometer 1

Accelerometer 2

Microcontroller

Power Supply

Digital to Analog

Converter

Slip Ring

Gyroscope Microcontroller

Motor

Servo φ

Servo θ

Gyroscope Vs. Accelerometers

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• Tilt SensorGyro vs. Accel Gyroscope Accelerometer

Cost 10 10

Availability 10 10

Noise 8 2

Range 10 10

Accuracy 10 8

Power Supply 8 8

Average: 9.3 8

• The cost and availability are both 10 because they are both less then $15.

• The Gyroscope filterers out Angular Rate Noise

• The Gyroscope has faster and easier calculations

Gyroscope Vs. Accelerometers

42

• Spin Sensor

Gyro vs. Accel Gyroscope Accelerometer

Cost 10 10Availability 10 10

Range 0 10Accuracy 8 8

Power Supply 10 8Average: 7.6 8

• The cost and availability are both 10 because they are both less then $15.

• The max rate of spin of the rocket is 5.6 HZ. This means the accelerometer need to read up 16 G

• The ADXL278 has a range of ±37g.

• The gyroscope will need to be able to read up to 2016 dps

Low g Accelerometer for Initializing Zero-Tilt

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• Accelerometers: ADXL203 vs. ADXL278

Accelerometer ADXL203 ADXL278

Cost 10 10Availability 10 10

Range 10 10Accuracy 10 2

Power Supply 10 8Average: 10 8

• The cost and availability are both 10 because they are both less then $15.

• The range is ok for the ADXL203 and the ADXL278. The ADXL has a range of ±1.7g which gives it more accurate low g readings. The ADXL278 has a range of ±37g which collects more accurate high g readings.

• The power supply for the ADXL203 is between 3 and 6 volts which gives a wider range of voltage than the ADXL278 which has a voltage range of 3.5 to 6.

• The ADXL203 is a better fit for initializing zero-tilt.

High g Accelerometer for Determining Angular Velocity

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• Accelerometers: ADXL203 vs. ADXL278

Accelerometer ADXL203 ADXL278

Cost 10 10Availability 10 10

Range 0 10Accuracy N/A 8

Power Supply 10 8Average: 7.5 9.2

• The cost and availability are both 10 because they are both less then $15.

• The range is better for the ADXL278 since it can collect high g readings.

• Although the ADXL203 has a better accuracy, it will not be taking readings in a high g range so accuracy it N/A. The ADXL278 is not as accurate but it will meet our requirements.

• The power supply for the ADXL203 is between 3 and 6 volts which gives a wider range of voltage than the ADXL278 which has a voltage range of 3.5 to 6.

• The ADXL278 is a better fit for determining angular velocity.

Block Diagrams

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ADXL278

ADXL203

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Our electronic system requires a conversion from Digital to Analog signals for our motors.

A Digital to Analog convertor (DAC) is needed

DS - Analog to Digital Conversion

ATMEGA32-16PU-ND: we chose this chip due to its operating temperature and its compatibility with our devices and program language.

This chip is also familiar to our team, the previous model was used in our mentors Rockon project and have been extensively researched.

Having been used in the Rockon project we know that the stresses the chip undergoes will not produce an undesirable outcome.

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Data Processing

48

DS - Risk Matrix

DS.RSK.1◦ Microcontroller Power Fails

DS.RSK.2◦ Motor Communication Fails

DS.RSK.3◦ Stationary Accelerometer

Communication Fails DS.RSK.4

◦ Motor fails in measuring own speed.

DS.RSK.5◦ Microcontroller can’t survive

launch conditions. DS.RSK.6

◦ Communication between despun and zero tilt systems fail.

PROBABILITY

CONSEQUENCES

DS.RSK.1

DS.RSK.2

DS.RSK.5

DS.RSK.3

DS.RSK.4

DS.RSK.6

Motor Subsystem

Motors

The motor subsystem is divided in to two sub systems:

Motor for de-spinning the platform

Motors for adjusting the tilt of the platform and turning the gimbal

De-spinning the platform

Requirement for motor 0 (despun motor) The rocket is estimated to spin at 5.6 Hz

(336 rpm) Requirements:

Current < .4A Voltage < 30V Torque < 5.0152mNm Max. Height < 2.75in

MS – Trade Study

Specification

System Requireme

nts

2232…BX4 S

3268...BX4 SC

3268...BX4 SCDC

RPM 12,100 rpm 5,500 rpm 4,500 rpm

Voltage < 30V 24V 24V 24V

Amperage <.4A .088A .215A .210A

Torque < 5.0152 mNm

29.4mNm 137mNm 137mNm

Height < 2.75in 1.95in 3.36in 3.36in

Cost n/a n/a $383.90 n/a

Brushed/Brushless

Brushless Brushless Brushless

MS – Selected Motor

3268...BX4 SC Brushless DC-Motor from Faulhaber.

Criteria Selection: possible PWM controllability. Ease of use.

Technology 4 pole brushless motorHas an integrated speed controller. Pre-configured to a continuous current. integrated feedback system.

MS – Risk Matrix MS.RSK.1

◦ Required Torque exceeds stall torque

MS.RSK.2◦ Motor-Battery

Communication Failure MS.RSK.3

◦ Motor gear head and platform may lose contact under 25G

MS.RSK.4◦ Battery unable to sustain

variable rpm requirements MS.RSK.5

◦ Motor may not respond to the micro-controller signals correctly.

Consequence

MS.RSK.5 MS.RSK.3 MS.RSK.2

MS.RSK.1 MS.RSK.4

Possibility

Adjusting the platform tilt

Requirement for motor 1 (tilt motor) We estimate no more than 20 degrees/sec. Requirements:

Current < .3A Voltage = 5-6V Torque approximately 400mNm Max. Height < 3in

MS – Trade StudySpecificatio

nSystem

Requirements

HS-5245MG AM2224-R3

Series 3056(Stepper Motor)

RPM 360 83.33 rpm 5,500 rpm 8790 rpm

Voltage 5-6V 4.8-6.0 Volts 1.4V 12V

Amperage <.3A .18A 1 A .168A

Torque 400 mNm 567mNm 22 mNm 95mNm

Height < 3in 1.54in 1.98in 2.64in

Cost n/a $70.00 n/a n/a

Control PWM Separate Encoder

Separate Motor Controller

MS – Selected Motor

HS-5245MG Digital Mini Motor from ServoCity.

Criteria Selection: High standing torque PWM controllability Ease of use.

TechnologyHas an integrated speed controller. 360 degree continuous rotation.

MS – Risk Matrix MS.RSK.1

◦ Required Torque exceeds stall torque

MS.RSK.2◦ Motor-Battery

Communication Failure MS.RSK.3

◦ Motor gear head and platform may lose contact under 25G

MS.RSK.4◦ Battery unable to sustain

variable rpm requirements MS.RSK.5

◦ Motor may not respond to the micro-controller signals correctly.

Consequence

MS.RSK.5 MS.RSK.3 MS.RSK.2

MS.RSK.1 MS.RSK.4

Possibility

Adjusting the platform turn

Requirement for motor 2 (turn motor) Requirements:

Current < .3A Voltage = 5-6V Torque approximately 400mNm Max. Height < 3in

MS – Trade Study

Specification

System Requireme

nts

HSR-1425CR

AM2224-R3

Series 3056(Stepper Motor)

RPM N/A 52 rpm 5,500 rpm

8790 rpm

Voltage 5-6V 6 Volts 1.4V 12V

Amperage <.3A .12A 1 A .168A

Torque 400 mNm 330mNm 22 mNm 95mNm

Height < 3in 1.59in 1.98in 2.64in

Cost n/a $0.00 n/a n/a

Control PWM Separate Encoder

Separate Motor Controller

MS – Selected Motor

HSR-1425CR Robotic servomotor. Criteria Selection:

High standing torque PWM controllability Ease of use.

TechnologyHas an integrated speed controller. 360 degree continuous rotation.

MS – Risk Matrix MS.RSK.1

◦ Required Torque exceeds stall torque

MS.RSK.2◦ Motor-Battery

Communication Failure MS.RSK.3

◦ Motor gear head and platform may lose contact under 25G

MS.RSK.4◦ Battery unable to sustain

variable rpm requirements MS.RSK.5

◦ Motor may not respond to the micro-controller signals correctly.

Consequence

MS.RSK.5 MS.RSK.3 MS.RSK.2

MS.RSK.1 MS.RSK.4

Possibility

Power

Battery

9 Volt Lithium

Voltage Regulators

• 5V • 3.3V

Who are you sharing with?◦ Harting

Plan for collaboration◦ Communicated through email◦ We shall share designs and

ideas through email We are still working on the

structural interface with them but have decided upon position in the cannister. Harting will be above us below. (plate in between)

66

Sharing Logistics

grandpmr.com

Project Management Plan

67

68

Organizational Chart

Project ManagerKaetie Combs

MentorsAdam RexroadBrett Dugan

Faculty AdvisorDr. Mohammed Eltayeb

Despun PlatformDaniel Gares

Tyler LemmertKaetie Combs

Zero Tilt PlatformMichael Stevenson

Daniel GaresAndrew Huntley

SensorsKaetie CombsTyler Lemmert

Andrew HuntleyMichael Stevenson

Data SystemJared HughesSean Hughes

Mayowa OgundipeDerek Val-Addo

Breakdown of Sub-Systems

69

Despun Platform

Zero Tilt Platform

Data Systems

Sensors

Design:

Daniel GaresKaetie CombsTyler Lemmert

Gears:

Tyler Lemmert

Design:

Daniel GaresMike Stevenson Andrew Huntley

Everybody will be involved with programming.

Processors: Jared HughesSean Hughes

Motors:

Mayowa OgundipeVal-AddoSubhasis Ghosh

Accelerometers: Kaetie CombsTyler Lemmert

Gyroscope:

Mike StevensonAndrew Huntley

Schedule

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Tentative Schedule

• Finalize Design

• Beginning of November: Start ordering parts

• Now until end of semester: Start testing electric components, test gyroscope output, test accelerometer outputs, test servo response, make sure we are able to supply necessary power, and complete despun subsystem.

• Next semester

• End of February: Zero Tilt platform completed• For the rest of the semester we will continue testing and

correcting problems to prepare for the launch in June.

Budget

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Item Part Number

Manufacturer

Vendor

Quantity

Price (each)

Total

Dual Axis High-G Accelerometer

AD22284 Analog Devices Analog Devices

2 12 24

Dual AxisLow-GAccelerometer

AD220372 Analog Devices Analog Devices

1 10 10

Microprocessor ATMEGA32-16PU Atmel Digikey 2 8.28 14.56

Slip Ring CAY-1398 Aeroflex Aeroflex 1 As of yet unknown

~300

Gyroscope L3G4200D ST Microsystems Arrow 3 15 45

DC Despin Motor 3268BX4SC FaulHaber Micromo 1 383.90 383.90

Tilt Servo motor HS-5245MG Hitec Servocity 1 70 70

Spin Servo HSR-1425CR Hitec In house 2 In house 0

Flash Memory AT26DF161A Atmel Digi-key 2 4 8

Components still under research

Raw materials

Total Ceiling 1500

Breakdown of Sub-Systems

72

Despun Platform

Zero Tilt Platform

Data Systems

Sensors

Design:

Daniel GaresKaetie CombsTyler Lemmert

Gears:

Tyler Lemmert

Design:

Daniel GaresMike Stevenson Andrew Huntley

Everybody will be involved with programming.

Processors: Jared HughesSean Hughes

Motors:

Mayowa OgundipeVal-AddoSubhasis Ghosh

Accelerometers: Kaetie CombsTyler Lemmert

Gyroscope:

Mike StevensonAndrew Huntley

We hope to order 90% of the materials required and begin fabrication of the gears.

We need to solidify our power requirements as well as our electric circuitry.

We must test our materials for weight and decide if our current materials will handle the stresses of rocket flight.

We intend to finalize our budget and remain within our $1500 ceiling.

Determine how fast the rocket changes angle with respect to starting position.

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Conclusion