These tend not to be the electronics but from not understanding the balloons and how they work. So, the first part of this presentation is to build awareness of what the mistakes might be. If you release a balloon and you had an error is how you prepared and planned the launch, the balloon will probably be lost.
If you recall your high school chemistry, you studied the gas laws and promptly forgot them. They are important. The gases we use, hydrogen or helium, and the atmosphere are basically ideal gases. So lets talk about them without using any math.
An ideal gas means the atoms and molecules are moving around as if they are the only ones there. They are not attracted or repelled by their neighbors. The kinetic energy (speed) determines their temperature. The number of them in a volume determines their pressure.
A convient amount of particles for chemists is the mole. (A mole of electrons is 1 Farady Constant of charge.) At sea level on a regular day, that many particles occupies 22.4 liters, no matter which gas it is. That is a cube on the order of 11 inches per edge. If it is a mole of air, it weighs about 29 grams. If it is a mole of hydrogen, it weighs about 2 grams. That much hydrogen in a balloon displaces that much air so the bouyancy is 27 grams. As the balloon rises, the temperature and pressure change and they expand the same and so the lift is the same. That means the lift on the ground will be the lift until the balloon bursts or reaches float.
Lets go over the two types of balloons
Burster: This balloon has a stretchy latex balloon and as the balloon rises, the gas expands causing the balloon to stretch. It will continue to stretch until the latex fails. This balloon can carry payloads of 5 pounds or more so complex packages can be launched. The flight lasts a few hours and reaches altitudes over 100,000 feet. If you are lucky, you can find it and use it again.
Superpressure: This balloon has a plastic envelope. When launched, the envelope is not filled and as the balloon rises, the gas expands and eventually fills the balloon. Once full, the plastic cannot expand and so it’s density the lift decreases until it reaches float. It now has a pressure greater than the air, this is superpressure. This type of balloon can stay aloft for months, if you are both good at it and lucky. It carries a payload of around 15 grams and is solar powered. The are very rarely recovered but a few have been. It can circumnavigate the world. They float in the range of 40,000 feet. They are generally smaller, and will travel with the winds.
Most flights use two sources of balloons. Regular party balloons will not do much for you. The volume and the weight is too low to perform well. The commonly used ones are the SBS-13 made by Scientific Balloon Solutions and the clear 36” balloons made in China through AliExpress.
The SBS-13 balloons cost in the range of $165, are high quality and will float a little higher than the clear Chinese balloons. Follow the instructions given by them and you are in pretty good shape. The volume is around .5 cubic meters and they weigh about 105 grams. The instructions tell how to fill, seal and assemble the flight. Experience points to a “free lift” of about 6.5 grams as a sweet spot.
The Chinese balloons cost around $1.50 each in lots of 10, two are required for a normal payload and the quality control is poor so you must do some prestretching and testing for pinholes, film quality, and weak seals. They stretch to a volume of around .17 cubic meters and weigh about 35 grams. Because of the weight to volume ratio of these, they float a little lower but high enough to circumavigate the earth multiple times.
Qualatex also makes a 36” balloons that works but is less commonly flown.
They both SBS and clear chinese balloons comfortably carry around 15 grams of payload.
It is very common to fail with either of these choices. The best and lightest electronics are useless if the balloons fails so don’t overlook this part of the hobby. The common failure mode can be from too much gas, leaks causing gas loss, insufficient altitude to clear weather, floating into clouds during ascent, a launch that never clears the power lines and so on.
Clear chinese balloons are the most cost effective but require the most skill.
The first step is that of doing the prestrech and pressure testing. The balloons can burst between .5 psi to maybe .65 psi. They need to be pressurized to at least .5 psi to pretretch the balloon. They need to be held at pressure for a while to allow pinholes to appear if they are going to and to allow the plastic to stabilize so it does not contract much.
The equipment needed is an aquarium air pump, tubing, and fittings, a pressure gauge and a water column of some sort for pressure regulation.
(insert photo of test setup)
The aquarium pump provides all the air pressure needed, the balloons can be taped to either the tubing or a stiff tubing of some sort. The pressure regulation is done by a water column and adjusting the depth of the tube in the water. A leak is noticed when the bubbles stop and closing lines off one at a time will find it rather easily.
To prepare for launch, remove the air. One of the air pumps can be turned into a cheap vacuum pump and used or you can just roll up the plastic or put it under a blanket to slowly press the air out.
To prepare for a launch you need a hydrogen supply. The simplest way is to just get a cylinder from a welding supply store and buy a hydrogen regulator. A few have generated their own hydrogen. I am a chemical engineer and I looked into that. You should never start a chemical reaction you cannot stop and it is not a simple as you would think from the idiots on YouTube. Doing it well is expensive and difficult. I have only seen that done once but you can buy a hydrogen generator and do it with electrolysis.
Next you need a small scale to measure in grams. Put hydrogen into the balloon until is begins to rise. At this point, the gas has carried the bag and the extra lift will carry the payload and provide the extra lift called “free lift” The free lift is the critical number. Too little and the balloon will rise slowly and be vulnerable to gusts, moisture, etc. Too much and it will burst. Experience will teach you how much free lift but something like 5 grams per balloon seems to be good. So, zero the scale with a weight and a clip as the tare. Clip the balloon to the scale and read the lift as a negative number. The room should be free of drafts. When you reach your chosen amount, roll the neck and clip it.
You must know how much gas to seal inside the balloon. That is where the gas laws and lots of math comes in. Fortunately, the whole job has been written as a spreadsheet so you only need to know the inputs and outputs. The spreadsheet has the name float1g. The most current version can be obtained from (england website)
(show float1g and mention the inputs and outputs.)
Hydrogen will diffuse through the plastic film. In a day, a chinese balloon will lose in the range of .5 grams of lift. You can seal the balloon once it is filled or wait to just before launch and adjust the gas prior to sealing. Gas diffusion at float is not a problem as the pressure and temperature are much lower. The SBS balloons have something like 1/6 the diffusion loss so they can be sealed upon filling for launch the next morning. Sealing is done with a simple band sealer. Two or three seals are a good idea.
Once sealed, the balloons can be placed in a garbage bag for transport, wrapped in a sheet or towel and put in the back of your car. The whole package is assembled at the launch location. It is itmportant to have low wind and to not launch into clouds.