Looking at the LayerOne 2013 "Near Space Exploration" (https://youtu.be/4-v-B03a1Jk ) conference, I thought it would be cool to send some electronics at lower altitude. The first solution that comes to mind is drones but they are expensive and not really accessible to everyone.
My plan is to use kites or hydrogen balloons to send some electronics at low altitude (like arduino boards or a raspberry pi with a camera) for as cheap as possible.
It's been a long time since my last log. Thank you to all the people that liked and followed the project.
Kite design is way more complicated than what I anticipated. There's a lot of ressources on the web and a decent kite usually mean a bigger budget than what I had in mind when I started this project. So I think I'll focus on the balloons for now.
I already know that I'll need multiple balloons but I still haven't determined how I'm going to produce the hydrogen. The first option is to use electrolysis.
Pros : I've done it in the past and there's a lot of documentation on it.
Cons : It's a slow process. It needs a power source so it's not portable. It means that you'll have to produce it at home first, then take it with you and I don't really like the idea of moving around a big quantity of flammable gas. Finally it's kind of power hungry so not a very cheap solution.
Second option is to use a chemical reaction. For example : when iron reacts with hydrochloric acid, hydrogen gas is produced. It's quick if the contact area is big (you can use iron powder for example). It can be done anywhere if you bring the chemicals with you. The chemicals are quite cheap and easilly available. The only problem that I can think of is to find a way to stop the reaction once you've produced enough so that you don't waste chemicals and produce more hydrogen that could cause a fire hazard.
I've already got some ideas on how I'm going to solve this problem so I think I'll go whith the second option. If you can think of any other option please comment !
I tried a few more times today. There was a lot spaced out gusts so the kite would go up quickly for about a minute then fall slowly. It flew decently high though, it just needed a more constant wind.
The conditions where not optimal but I tried to fly the kite with a 50 g load. Just to see if it would take off. Even with the strongest gusts I didn't worked. I guess it would have been too easy with such a simple kite, so now I have to find a better kite design. I don't know much about kites so if you have some suggestions feel free to comment.
I couldn't resist until Tuesday. Due to the lack of wind I only was able to fly up to 5 m without any load.
Hydrogen balloons have the advantage of not needing any wind so I made a few calculations. Since I want to make the project as cheap as possible I'm going to focus on party balloons. I measured the pressure inside an inflated balloon to see if there was any significant overpressure that I would need to take into consideration. The overpressure is very small (about 30 hPa) so I'm going to neglect it.
Using Archimedes' principle I can get a rough idea of the maximal mass that a spherical balloon can lift up :
with a radius of 15 cm that makes a mass of about 15 g. Not that much so I'll have to use multiple balloons or find a cheap alternative for a bigger balloon.
My first attempt will be with kites because they are less dangerous than hydrogen balloons and easy to build for cheap. The main question is "Can my kite lift my electronic device up ?" and it's not an easy one. The answer depends on many variables (wind speed, type of kite, ...) so I'm going to answer it empirically.
I've started by measuring the mass of a typical electronic device, that way I can use a load of the same mass for my first flights without the risk of breaking some expensive things.
Here's the results :
Arduino uno : 21 g
Raspberry Pi : 42 g
AAA Battery : 24 g
I made a small bag for the load that I can fill with rice or sand. I've planned my first test for Tuesday with a 100 g load. The kite will be made of a single A4 paper sheet and a wooden skewer.