Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
1
FFuullllyy AAuuttoommaatteedd PPaarraacchhuuttee DDeessiiggnn
Team -“T-Wolf”
Colorado State University - Pueblo
Senay T. Imam, Berry William, Scott Kennymore, Diego Ramirez Cesti,
Richard J. Chartarro Junior
Advisers: Dr. Huseiyn Sarper
Date 4/7/2008
2
Table of Content
1. Introduction:
2. Design Approach
Mechanical design
Electrical Design
3. Landing Estimation
Analytical analysis
Program Output
4. Conclusion and recommendation
Annex 1
Annex 2
Reference
3
1. Introduction:
Background
The T-Wolf Parachute Lander is a Colorado state university – Pueblo project design
sponsored by Colorado Space Grant Consortium in collaboration with CSU-Pueblo. The
entire purpose of the project is to build a completely autonomous rover that can
simulate an autonomous robot mission on Mars and a completely automated
parachute Lander that holds this rover. This report, therefore, presents the concepts
considered and the process used to make our design decisions for the parachute
lander.
Objective:
The T-Wolf parachute Lander team designed a balanced and aerodynamically stable
parachute probe that would maintain structural, aerodynamic, and survive impact
upon landing.
The probe was designed to be launched with a balloon and caries it to about 1500 ft.
At this altitude a microcontroller triggers a release mechanism to detach the parachute
from the balloon. Once the release mechanism is triggered, information is sent to the
ground that notifies the beginning of the descending process. The probe makes a free
fall for a specific period of time (≈6 to 10 seconds), until the parachute adjusts is itself.
After the probe is adjusted, it starts to descend at an acceptable terminal velocity until
it reaches to a level of 2.5 ft from the ground. Once the microcontroller detects a
surface, it triggers another release mechanism to detach the probe from the parachute
(canopy). Once the release mechanism is triggered, the probe makes a free falling to
the ground. This is basically designed to clear a path for the rover when it exits the
probe.
4
Project Schedule:
January 18th: First Group Meeting
January 28th: Allocating of tasks to each team member
February 5th – 8th: Researches, Literature review, design proposal, brain storming ideas
February 12th – 22nd: Analyzing the mechanical and electrical conceptual design
March 26th: Ordering of Materials
March 11th- April 31st: Beginning construction of the probe
April 1st – April 4th – Testing different mechanism of the probe including the parachute
2. Project Approach
The project were split into two sections, design concept and location prediction. To
utilize time and specialties of team members, the design concept was further split into
two subsections, mechanical and electrical.
2.1 Design concepts
2.1.1 Mechanical concept
The mechanical design concepts are categorized into
a. Mechanics of Ascent
b. Probe shape
c. Release Mechanisms
d. Parachute specification
f. Material selection
a. Mechanics of Ascent
The probe is attached to 8in diameter high altitude helium balloon which delivers it to
the specified height (1500 ft) for release.
5
b. Probe Shape
The shape and geometrical features of the probe is selected after careful consideration
of the weight limit, its ability to settle down on its desirable position and withstand sock
during the process of crash landing. The probe has a shape of geometrical pyramid
made up of aluminum sheet, imbedded inside a semispherical shaped aluminum tubes.
c. Release Mechanisms
The release mechanism is based on the process of gun trap. In this design, Nichrome is
used to trigger the gun trap. Nichrome is a nonmagnetic ally of nickel and chromium
with a very high melting point of around 1400oC.1The gun trap is designed to be
triggered on three different stages: releases the balloon from parachute, the parachute
from the probe and finally opens the doors of the probe.
d. Parachute specification
Based on the information collected from different literature reviews the parachute was
decided to be a round parachute.
e. material selection
The material selection system for the entire project is based on weight, strength and
price. The materials used in construction of the probe are aluminum sheet, large
aluminum tubes, foam padding, a manner of attachment, such as bolts or rivets,
microcontroller and gun trap assemblies.
The pyramid-shaped probe is fabricated from sheet aluminum stock, and the “cage”
assembles from the long aluminum tubes. Small booster cables are used to open the
1 Wikipedia – Nichrome
6
bay doors upon trap detonation. The probe doors will be attached via two spring-
loaded hinges.
2.1.2 Mechanical Design
Design: Autodesk Autocad and Autodesk 3DS Max software are used in developing the
probe design in a 2D and 3D design respectively.
Figure 1.1 2D Probe design
Construction: The probe will have a square base, and will resemble a pyramid shape;
with the help the foam, this will house the rover tightly to avoid any damage incurred
by landing. The means of having the rover land upright consistently will be through
three 30” diameter circular tubes forming a spherical shape around the rover bay unit.
This will allow the center of gravity caused by the weight of the rover to settle on the
base, no matter at what angle of impact. The bay doors will be operated via a
pressure-fit gun trap, allowing the doors to open upon receiving signals from the
onboard microcontroller. Two doors are employed in this system, in case one door
cannot function due to an external force or obstruction.
7
Systems: The parachute lander will employ a number of assemblies and systems to carry
out its function. The entire vehicle will be fitted with an onboard microcontroller; its
function is to properly engage various circuits and processes designated by speed and
height. It will send impulses to the gun traps, as well as transmit its position to a land-
based computer system through a streaming connection or constant beacon.
Another system is that of the gun traps. Their purpose is to provide a constant link or
connection via a silver-soldered cable, until a predetermined time. The gun trap is
designed to have a pressure fit holding the assembly, and a small powder charge held
in place by a cotton ball will separate the respective sides. After testing, the correct
powder charge used in the assembly is 6.1 grains of IMR4831 smokeless gunpowder.
Assembly: Preliminary assembly of the rover entry vehicle started with fabricating the
pyramid-shaped housing out of sheets of .032” 6061 aluminum sheet. All edges are
lapped and pressed, to increase rigidity of the unit. The rover bay is assembled on an
18.5” square, with approximately 10” of height. The rover itself is 8” tall, so protective
padding will keep the unit in place during ascent and descent. A small box fabricated
with 6061 aluminum sheet is used to shield the microcontroller on top of the pyramid
bay. Spring-loaded hinges are attached to the top of the pyramid bay, to assist
opening the bay doors. The initial design plan was to use the spring loaded hinges as
the primary opening mechanism for the system, but upon actual assembly they were
found to be insufficient at opening the doors effectively. To overcome this problem,
two small bungee cables attached to the “cage” will be more than sufficient to fix the
problem, at little cost to weight limit. Next, a small gun trap tunnel is also fabricated out
of aluminum sheet, to shield the rover from the internal gun trap detonation. The gun
traps were the next to be fabricated; using spent and deprimed .44 Remington
8
Magnum cartridges and a piece of aluminum tubing stock at .45” diameter. A lathe
was used to machine holes for the primer exit from the assembly, and threads and a
shoulder were cut into the assembly to support and seal the system. Wire was silver-
soldered to the plugs on either end, to allow attachment to different mechanisms.
Assembling the traps themselves required model rocket fuses to be shielded with rubber
shrink tubing. The fuses were then inserted into a drilled out primer hole in the cartridge,
until approx. 1.5” of total primer is exposed. It was then held in place by modeling clay,
and .6CC’s of clear epoxy was injected into the cartridge to seal the primer hole and
retain the fuse. After the epoxy hardened, the clay was removed and 6.1gr of
smokeless powder was added to the cartridge, which is held next to the fuse by a small
piece of cotton ball. The plug was machined to .425”, which allows a tight press-fit that
can hold double the amount of actual weight of 15 pounds. The plug is inserted into
the cartridge and the gun trap is ready to be installed onto the entry vehicle. One of
the last stages of frame construction is bending 8ft 1” aluminum tubing into a 30”
diameter, which is approximately 95 inches. A homemade bender was employed to fit
the 3 tubes around a 30” diameter round metal disc to retain most of its bent qualities.
Next, the 3 tubes were placed in a conduit bender to achieve the exact 30” diameter.
Two of the aluminum tubes were now cut in half, and cut with an approx. 20” base, so
the bottom could be fastened to the probe bay. The center tube spanning the unit
horizontally has the other tubes welded to it, making a sufficient mounting point for the
parachute and upper gun trap. The tubes had to be heat treated during welding, to
avoid cracking the thin tubing. At this point, the foam insulation was cut and fitted to
the inside of the bay, which is adhered to the siding by using commercial spray
adhesive. The last piece of sheet metal fabrication involved the round parachute-
9
mounting disc. A disc with approximately 6” had 16 notches cut into it at 22.5 degrees,
to evenly distribute the parachute cords. A hole was cut into the center of it to allow
for the mounting of the gun trap. The ends were slightly folded over, so commercial
tape could be wrapped around the perimeter so the parachute cords were retained in
the assembly. The last stage of assembly is attaching the parachute to the balloon. A
wire rill be run from the microcontroller to the upper gun trap, and the trap will be
fastened to the balloon and a small hole in the top of the balloon will allow for one side
of the trap to be placed through it, and retained by a piece of aluminum sheet and
cardboard. These pieces will drop out once the unit is separated.
Operation: The entry vehicle assembly will be attached to its descent mechanism from
the top of the “cage”. The descent mechanism used in this case is a 96” parachute
designed for a fifteen-pound payload. The parachute will be fully deployed for the
current challenge, since an ascent mechanism is required to reach its proper altitude of
1500 feet. A large weather balloon attached to the top of the parachute will cause
the unit to ascend. A positioned gun trap will cause the balloon to separate, and the
parachute will fully deploy. Upon detection of the proper altitude (via an onboard
altimeter/accelerometer), another gun trap mechanism will disengage the parachute
from the rover bay at a designated height; in order to clear the landing area of a
possible hazard caused by the parachute. At this point, the bay’s geometry will allow
the unit to land upright on any surface at any angle of approach. After a designated
time or sequence a gun trap, utilizing a cable with attached machine screws, will
activate and cause the doors to open, thus allowing the rover to exit.
10
2.1.3 Electrical Concept
2.1.4 Electrical Design
Materials used:
For the main system:
- Arduino micro controller board w/ atmega 168 chip
- PC with arduino programming software/drivers
- Parrallax ultrasonic sensor
- 433MHz wireless transciver.
- Battery pack/connection.
For balloon Release Timer: (schematic included)
- .01 uF Ceramic Disc Capacitor
- 4700 uF Electrolytic Capacitor
- 1N914 Silicone Switching Diode
- 555 Timer Integrated Circuit
- 10Kohm carbon film resistor
- 47 K ohm PCB Mount Micro Potentiometer
- General Purpose PC Board
- 9 Volt Battery Clip
11
Figure 2 Overall electrical system Layout
Figure 3: Time Mechanism
12
Operations
1. Initiate launch
2. Time assent to determine altitude
3. Release balloon at appropriate altitude to begin descent
4. Detect proximity to ground to release parachute to avoid entanglement
5. Detect or time landing to open doors and release payload
Control systems:
Electrical work has been done primarily off of the Amtel Atmega based arduino platform.
The complications of running a wire from the microcontroller up to the top of the parachute to release
the balloon have made it impractical. There fore so a more simple device using a standard 555 ic timer
circuit to delay for a certain rise time is used and this at a designated time release the balloon from the
craft and allow it to return to the surface. This device will delay a predetermined time and then initiate a
small powder charge ejecting an interferance-fit coupling, effectively releasing the landing craft.
A microcontroller/board is used as a central controlling system. It is programmed in the C programming
language and written to the eeprom using software and usb drivers available on the internet. The probe
uses an ultrasonic range-finder device to test proximity to the landing site in order to effectively release
the parachute prior to landing to reduce the risk of the payload becoming entangled in the chords.
It was initially hoped that a wireless link could be created between the landing craft and a notebook
computer on the ground that would relay data about the stages of the operation on the probe and the
state of the processor; however, due to time restraints and a mistake made during ordering, it is
excluded from this project. Despite such mistakes, the wireless link on the craft will be constructed;
however the uplink on the ground will be missing.
The ultrasonic device produces an analog output relative to the distance it detects which is read by the
13
microcontroller which can make logical decisions based on its input.
3. Landing Estimation
A communication signal is attached to the parachute that sends a signal when the
parachute is released from the balloon and starts descending, however this signal does
not provide any direction of descending or location of landing. What’s more adding
GPS to the parachute was beyond the budget allocated for the project. Therefore the
team decided to write a program using Matlab that inputs all the governing factors
and predicts the velocity and direction of descending and the possible landing
location of the parachute. Although the program was tested to see its reliability of
estimation for the velocity, the reliability of the direction and the estimation of the
landing location haven’t been tasted yet. However, the results obtained from various
tests have proven to have similar output to the results obtained from the program.
Methodology:
Using the inputs, the program computes the ascending and descending velocity, location of possible
landing location and its range from the launching site. It also uses a Mont Carlo simulation system to
determine the mean direction and speed of the wind. Furthermore, the program is designed to function
using two basic unit system, English and Metric system.
3.1 Analytical analysis
Following are the analytical analysis used in determining velocity, location and range landing of the
probe:
1. ascending velocity:
Lift force = Buoyant – Weight of the probe + Weight of the balloon
Ascending velocity = square root (8*Lift/ (Coefficient of lift* density of air *Pi*Diameter of balloon^2))
2. Descending velocity
14
Total Weight = Drag force
Total Weight = weight of the probe + weight of the parachute
Deriving the descending velocity from the weight
Descending velocity = square root (8*Total weight/ (Coefficient of drag* density of air *Pi*Diameter of
parachtue^2))
3. Range
Range = average wind speed *(ascending time + descending time);
Program output
------------Location Estimator---------------
----English System -----
Lift (lbs) = 120.282725
Ascending ---->Velocity (m/sec) = 10.870617
Ascending-----> time (sec) = 138.798933
Descending----> velocity (ft/sec) = 16.504768 Time (sec) = 90.882829
WIND ---> Mean (ft/sec) = 8.334849 Stdev = 1.435354
Range (ft) = 1914.362899
ANGLE ---> Mean (degree) = 165.006475 Stdev = 6.130701
Direction of wind ---> SOUTH EAST
Programming code is attached at on Annex 2.
3. Conclusion and recommendation
The main purpose of the project is to build a robust parachute lander with a reasonable
or affordable price. Having been able to achieve this target, the next level of the
project should aim on upgrading the mechanical system, minimizing the size, weight,
15
and the electrical assembly system and also adding more navigation analysis to make
the system more robust.
The team recommends that, materials such as GPS, Telemetry system, and more
sophisticated balloon release system, which were need but not being able to be used
due to budget and time constrain, should be available to enhance much more
research, as the direction and the goal achieved so far are promising.
We recommend that the project be continued next year in much more detailed
design. Building upon our future experience, the future team could improve in by
implementing
1. More sensors such as infra-red devices, speed of sound sensor, and aim to test the
project in a very high altitude.
2. Improve the probe design and make it more impact resistor.
3. create more redundant devices that ensures the operation of the system
4. Pressurize the probe.
Annex 1
Team Picture
16
Picture 1
Picture 2
17
Picture 3
Picture 4
18
Annex 2 : Programming Code
function uplifting Cls = 0.5; %for spherical objects Cdp = 1.5; % for round parachtute %global lift_force drag_force disp('---Menu---'); disp('1. Meteric System'); disp('2. English system'); disp('Choose the Unit System'); choose= input(' '); fid=fopen('Test_result.txt','wt'); fprintf(fid,'------------Location Estimator---------------\n'); if choose ==1 fprintf(fid,'----Metric System -----\n'); else fprintf(fid,'----English System -----\n'); end switch 1 case choose==1 Dia =input('Enter Diameter of the balloon: '); while Dia<=0 Dia =input('Enter Diameter of the balloon: '); end D_air =input('Density of air: '); while D_air<=0 D_air=input('Density of air: '); end D_He=input('Desnity of Helium: '); while D_He<=0 D_He=input('Desnity of Helium: '); end Mass_Probe=input('Probe Mass: '); while Mass_Probe <=0 Mass_Probe=input('Probe Mass: '); end H=input('Max height of release: '); while H<=0 H=input('Max height of release: '); end gravity=9.81; %meter/second^2 case choose==2 Dia =input('Enter Diameter of the balloon: '); D_air =input('Density of air: '); D_He=input('Desnity of Helium: '); Mass_Probe=input('Probe Mass: '); H=input('Max height of release: '); gravity=32.17; %feet/second^2 otherwise end % inorder for lift to take place "force up = force down" % and the enternal pressure has to be lighter than the outside/atmospheric % pressure % force up --> lift % force down ---> drag % lift = Bouyant force upward - gravitational force
19
% Bouyant force = weight of balloon and probe plus the weight of helium gas % To find the mass of the empty balloon volume = pi*(Dia^3)/6; Mass_Bal=D_He*volume; Bouyant= D_air*volume*gravity; %to compute for the vertical lift velocity %Lift = cross sectional area of the ballon times density times %velocity times the coefficient of drag Lift = Bouyant - ((Mass_Probe + Mass_Bal)*gravity); if choose ==1 fprintf('\n\nLift (N) = %f\n', Lift); fprintf(fid,'\n\nLift (N) = %f\n', Lift); else fprintf('\n\nLift (lbs) = %f\n', Lift); fprintf(fid,'\n\nLift (lbs) = %f\n', Lift); end Velo_y = (8*Lift/(Cls*D_air*pi*Dia^2))^(1/2); if choose==1 fprintf('Velocity (m/sec) = %f\n', Velo_y); fprintf(fid,'Velocity (m/sec) = %f\n', Velo_y); else fprintf('ascending --->Velocity (fts/sec) = %f\n', Velo_y); fprintf(fid,'ascending ---->Velocity (m/sec) = %f\n', Velo_y); end acc_up = Lift/(Mass_Probe + Mass_Bal); %fprintf('Upward acc until the terminal velocity ---> (ft/sec^2)=
%f\n\n',acc_up); time_up1 = Velo_y/acc_up; Y = 0.5*acc_up*time_up1^2; time_up2 = (H-Y)/Velo_y; time_up = time_up1+time_up2; if time_up>0 fprintf('ascending----> time (sec) = %f\n\n', time_up); fprintf(fid,'ascending-----> time (sec) = %f\n\n', time_up); else disp('Error'); end % the free fall of the aprachute which is equal to gravity*time = the % terminal velocity will give us the time and lenght the parachute covers % to stablize it self. in this case since the parachute is open in air the % distance come out to be about 5 feet and the time was about 0.6 seconds % and therefore it is ignored from the computation
% Weight W implies to the weight of the parachute and probe Dia_par = input('Diameter of the parachute: '); V_par = Dia_par^3*pi/12; W_pra = V_par*D_air*gravity; W = W_pra + Mass_Probe*gravity; vel_par = sqrt(2*W/(Cdp*(pi*Dia_par^2/4)*D_air)); %Terminal velocity time_down= H/vel_par; if choose ==1 fprintf('Decending----> velocity (m/sec) = %f\t Time (sec) =
%f\n\n',vel_par,time_down); fprintf(fid,'Decending----> velocity (m/sec) = %f\t Time (sec) =
%f\n\n',vel_par,time_down); else
20
fprintf('Decending----> velocity (ft/sec) = %f\t Time (sec) =
%f\n\n',vel_par,time_down); fprintf(fid,'Decending----> velocity (ft/sec) = %f\t Time (sec) =
%f\n\n',vel_par,time_down); end %Horizontal speed of the %input the upper wind speed, lower wind speed, and the mode U_Wind = input('The upper wind Speed: '); L_Wind = input('The lower wind Speed: '); M_Wind = input ('The mode wind Speed: ' ); disp('wind direction angles in DEGREE'); disp('North ---> 0 or 360'); disp('South ---> 180'); disp('East ---> 90'); disp('West ---> 270'); %the user can input any range within this values U_Ang = input('The Upper wind direction angle: '); L_Ang = input('The Lower wind direction angle: '); M_Ang = input('The Mode wind direction angle: '); mean_w= (U_Wind+L_Wind+M_Wind)/3; stdev_w=sqrt((U_Wind^2 + L_Wind^2 + M_Wind^2 - U_Wind*L_Wind - U_Wind*M_Wind
- M_Wind*L_Wind)/18); %fprintf('WIND ---> mean = %f\t standard deviation = %f\n\n',
mean_w,stdev_w); mean_a= (U_Ang+L_Ang+M_Ang)/3; stdev_a=sqrt((U_Ang^2 + L_Ang^2 + M_Ang^2 - U_Ang*L_Ang - U_Ang*M_Ang -
M_Ang*L_Ang)/18); %fprintf('ANGLE----> mean = %f\t standard deviation = %f\n\n',
mean_a,stdev_a); % Number of iteration for the simulation of the wind speed N=input('Number of iteration: '); wind=zeros(N,2); for ii=1:N Z=randn; wind(ii,1)=stdev_w*Z+mean_w; wind(ii,2)=stdev_a*Z+mean_a; end %average wind speed within a given duration Totalspeed=wind(:,1); %disp(Totalspeed); Total_wind=sum(Totalspeed); W_MEAN=Total_wind/N; Sum_std_w=0; for ii=1:N Sum_std_w=Sum_std_w + Totalspeed(ii,1)^2; end W_STDEV=sqrt((N*Sum_std_w - Total_wind^2)/(N*(N-1))); fprintf('WIND ---> Mean = %f\t Stdev = %f\n',W_MEAN,W_STDEV); fprintf(fid,'WIND ---> Mean = %f\t Stdev = %f\n',W_MEAN,W_STDEV); %FINDING RANGE Range = W_MEAN*(time_up+time_down); if choose==1 fprintf('\tRange (m) = %f\n\n',Range); fprintf(fid,'\tRange (m) = %f\n\n',Range); else fprintf('\tRange (ft) = %f\n\n',Range); fprintf(fid,'\tRange (ft) = %f\n\n',Range);
21
end %average wind direction angle within a given duraiton Total_angle=wind(:,2); %disp(Total_angle); Angle_sum=sum(Total_angle); A_MEAN=Angle_sum/N; Ang_std=0; for ii=1:N Ang_std=Ang_std + Total_angle(ii,1)^2; end A_STDEV=sqrt((N*Ang_std - Angle_sum^2)/(N*(N-1))); fprintf('ANGLE ---> Mean = %f\t Stdev = %f\n\n',A_MEAN,A_STDEV); fprintf(fid,'ANGLE ---> Mean = %f\t Stdev = %f\n\n',A_MEAN,A_STDEV); switch 1 case A_MEAN==0|A_MEAN==360 fprintf('direction ---> NORTH\n'); fprintf(fid,'direction ---> NORTH\n'); case A_MEAN>0&A_MEAN<90 fprintf('direction ---> NORTH EAST\n'); fprintf(fid,'direction ---> NORTH EAST\n'); case A_MEAN<360&A_MEAN>270 fprintf('direction---> NORTH WEST\n'); fprintf(fid,'direction---> NORTH WEST\n'); case A_MEAN==90 fprintf('direction ---> EAST\n'); fprintf(fid,'direction ---> EAST\n'); case A_MEAN>90&A_MEAN<180 fprintf('direction ---> SOUTH EAST\n'); fprintf(fid,'direction ---> SOUTH EAST\n'); case A_MEAN>180&A_MEAN<270 fprintf('direction ---> SOUTH WEST\n'); fprintf(fid,'direction ---> SOUTH WEST\n'); case A_MEAN == 180 fprintf('direction ---> SOUTH\n'); fprintf(fid,'direction ---> SOUTH\n'); case A_MEAN == 270 fprintf('direction ---> WEST\n'); fprintf(fid,'direction ---> WEST\n'); otherwise end
Reference:
1. Wikipedia, the free encyclopedia, “ Nichrome” 2. Opening Shock and Shape of the Drag-vs-Time Curve, Jean Potvin, Physics Department, Saint Louis University, St. Louis MO
3. Hemisphere Parachute Design (for parafauna) http://www.stwikipedia.org/~anthony/kites/parafauna/chute_design/
4. Balloon lift calculations with different gases... http://www.madsci.org/posts/archives/1998-08/900965216.Ph.q.html