Mechanical Design
11/2/14
met with group - decided on drone and need to talk to prof sullivan about specs and how the heck to make it
11/3/14
anne met with prof sullivan, got insights into design, parts and how to make it
11/10 /14
anne and arly bought drone supplies at RC warehouse
11/20/14
Upon further inspection of the items, and a reassessment of each team member's coding, solidworks and design capabilities, drastic re-scope occurred.
motorized hot air balloon steering
this removes the third dimension from calcs as a hot air balloon is neutrally buoyant already. much more manageable
11/29/14
return drone items, purchase
1. little servo motor
2. little dc motor
3. little proppeller
Size and weight are huge limiting factors balloon size increases drastically with small changes in weight.
11/30/14
program servo motor to steer propeller
/*
Controlling a servo position using a potentiometer (variable resistor)
by Michal Rinott <http://people.interaction-ivrea.it/m.rinott>
modified on 8 Nov 2013
by Scott Fitzgerald
http://arduino.cc/en/Tutorial/Knob
modified on 11/30/14
by Anne Faber
to include serial output
*/
#include <Servo.h>
Servo myservo; // create servo object to control a servo
int potpin = 0; // analog pin used to connect the potentiometer
int val; // variable to read the value from the analog pin
void setup()
{
Serial.begin (9600);
myservo.attach(9); // attaches the servo on pin 9 to the servo object
}
void loop()
{
val = analogRead(potpin); // reads the value of the potentiometer (value between 0 and 1023)
val = map(val, 0, 1023, 0, 180); // scale it to use it with the servo (value between 0 and 180)
myservo.write(val); // sets the servo position according to the scaled value
Serial.println(val);
delay(15); // waits for the servo to get there
}
12/6/14
calculate balloon size requirements based on
inputs:
mass of basket, motors and fabric (mass, m)
room temp, Tcold
hot air temp, Thot (assuming candle flame source)
cold air density, pcold - based on chart from
http://www.engineeringtoolbox.com/air-density-specific-weight-d_600.html
(phot is derived in equation, not an imput)
Then balance the forces at work.
1. Fgravity
2. Fbuoyancy cold air
3. Fbuoyancy hot air
Equation to calc balloon volume:
Vballoon = mass/ (pcold*(1-tcold/thot)
Input estimates
mass ~ 1 lb
Tcold = 70 deg F
pcold = 2.02 (from chart)
Thot = 150 def F
Vballoon = 1.7m^3
diameter balloon = ~5 ft (little larger than expected).
huge limiting factor is the heat source. need to brainstorm more ideas for that
12/11/14
Get the basket designed in solidworks and laser cut to resemble a basket weave pattern
took the printed piece and folded at all the joints to create a square basket. Held together with wood glue which firmed up the carboard.
then, attach servo motor
12/12/14
condundrum. both the dc motor and the wires available are both "male parts" so have to expose the wires on the dc motor, then solder them to the other wires. (first time doing that! whew). Success!
then, get dc motor to work (several broken potentiometers later) with code below
int pwm = 12; // assigns pin 12 to variable pwm
int pot = A0; // assigns analog input A0 to variable pot
int t1 = 0; // declares variable t1
int t2 = 0; // declares variable t2
void setup() // setup loop
{
Serial.begin(9600);
pinMode(pwm, OUTPUT); // declares pin 12 as output
pinMode(pot, INPUT); // declares pin A0 as input
}
void loop()
{
t2= analogRead(pot); // reads the voltage at A0 and saves in t2
t1= 1000-t2; // subtracts t2 from 1000 ans saves the result in t1
digitalWrite(pwm, HIGH); // sets pin 12 HIGH
delayMicroseconds(t1); // waits for t1 uS (high time)
digitalWrite(pwm, LOW); // sets pin 12 LOW
delayMicroseconds(t2); // waits for t2 uS (low time)
Serial.println(t2);
}
and we're in business!
Then, run over to Art dept for computers with photoshop, and design poster for event!
Project notes and recap:
over all, massive exposure to coding, solidworks and laser printing design for a group with total coding, building and design experience of right around 0 from the start. So proud we were able to produce a working prototype for the event and it was really cool to see other projects and get ideas of how to take this further.
Notes on where this project is going.
1. need to free the basket from wired connection to the power
2. this will increase weight drastically as batteries/power source need to be added into the basket
3. need alternative hot air, have to get the Thot to increase a lot
possible ways to increase temp
- use thermite? - burns super hot, but may be super dangerous
- get a bigger flame than a candle can provide (again, weight factor)
4. assuming we find a hot, lightweight fuel source, need to control the flame remotely as well.
Super excited to look into these possibilities. the goal is to have a fully functional (~3 ft diameter balloon) so that it can be flown inside using a remote control.
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