Weather Balloon 2016

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This article follows on from the attempt to fly a tethered weather balloon in July 2015, see the blog here.

An opportunity arose early in 2016 to fund another flight of our Helium filled Weather Balloon. This time it was to be used to observe the Isle of Wight Festival. The school I work at is used each year, along with other parkland, for this large music festival. As part of a community involvement by the organisers, the school is given a number of tickets for the event and these are given to students in return for them becoming involved in various projects. This year the Geography Department wanted to look at the environmental impact that the festival has on our community, in particular the problems of litter and the waste generated by the festival.

I was approached to see if the weather balloon could be used to photograph the festival site and the quest for funding started. I had several short meetings with the Geography teacher running this project, but it was not until funding was confirmed in April/May 2016 that planning began in earnest. The price of Helium had increased since 2015, but I managed to track down a supplier who sold us five 0.42 cubic metre balloon gas cans for just over £120. These cans are supposed to fill 50 x 9 inch balloons and from experience will provide about 250 gms of lift.

From our experience the biggest problem was to stop the electronics package from spinning and the original idea was to suspend the package from the balloon, then attach the kite string to the bottom of the package. However, I was concerned about the package surviving the forces involved and went for attaching it as we had done last year (see the blog here). A suggestion was made that we use a wind sock to stop the package from spinning, but as with everything else involved in this project we had nothing to guide us. Eventually we settled on a wind sock about fourteen inches long with the mouth about four inches in diameter (see the photograph below). Four pieces of cord were used to attach the windsock to the end of the package.

We were limited to one of four days, 4th to 7th June as the festival started on the 8th June. The long term weather forecast at first did not look too promising  but by the week before it seemed that Tuesday 5th looked our best bet. It was forecast to be overcast with only a small chance of rain, but more importantly the wind speed was forecast to be about 2km/hr. When the day arrived it was warm and sunny with partial cloud cover, and almost no wind.

It took about an hour to fill the balloon and we used four and a half tins to fill the balloon and provide about 1200 gms of lift. The balloon was then walked to the geography department where the electronics package was started, set to record video then attached to the balloon. The wind sock was fitted to the end of the package and we walked the balloon down to the field alongside the festival.  Weather conditions were perfect and the balloon rose easily to about 100 feet, but the wind sock was too heavy and simply hung below the package, blocking the camera. We brought the balloon back down and stuffed the wind sock onto the top of the package and sent the balloon up several hundred feet.

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showing the windsock mounted in the best position

Lady Luck was certainly on our side because the wind blew the wind sock off the package in such a way that it was supported on the top of the package. At this point it did exactly what it was designed to do and kept the electronics package perfectly still! Over the next two hours we sent the balloon up to various heights and it was not until the end of the day that increasing winds started to move the balloon horizontally. On the last time we brought the balloon down we pulled it down, laying the kite string on the ground, with out winding it onto the reel and this allowed us to measure the height that it reached.

At the end of the day we decided to burst the balloon rather than try to store it overnight, much to the delight of several classes of students who had come out to watch the balloon.

Conclusion:

We achieved all our aims with this flight as far as the balloon was concerned, we were able to control it with ease and confirmed that each container of Helium gave about 220 to 250gms of lift. However,  the electronics package did not perform as expected. I had been testing it for almost a year, running it on battery power for up to eight hours at a time, and it performed perfectly. As I wanted to control it using the LPRS radios I would start the python program using VNC or ServerAuditor on my iPad. However, when the iPad went into screen saver mode it shut down the python program. The solution is to start the python program using  WiFi, then to turn off the router.  VNC or ServerAuditor can be switched off and the python program will continue to run, I have no idea why the python program stops when the header less  control program is shut down, it just does!

The day before the launch, the control of the Raspberry Pi became erratic (it later turned out to be one of the small heat sinks plugged onto the back of the USB sockets that had fallen off and was rolling across the Pi, shorting out connections as it went). As I seal the package with cable ties and wanted to make sure we were filming I set the video to run for 30 minutes. It performed perfectly, it just took 20 minutes of video of the ground as we fitted it to the balloon then walked it to the launch site. For the remaining 10 minutes it filmed the wind sock as it flapped about in front of the camera. As a result we recorded almost no useful video.

The students took plenty of video and still pictures of the event and I am sure the report they write will justify their festival tickets. The students were fascinated by the balloon and followed us wherever we went. Teachers brought their classes out to watch and I am sure the students appreciated the chance to lie on the grass in the sun rather than be stuck in a classroom.

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bursting the balloon at the end of the day. The white substance is the French Talc in the balloon.

I would like to thank Ann and Toby for their help and suggestions and to Caroline for coming up with a project that allowed us to fly the balloon again.

Flying the weather balloon

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The day finally arrived to fly the balloon. From what I could find on the internet each cubic foot of helium will lift 28gms and although it was difficult to confirm, it seemed that the party balloon gas contained about 14 cubic feet of Helium. I needed about 1 kg of lift, so I would need three to four containers of gas. These gas containers were supposed to fill around 50 x 9 inch balloons.

I used a 5kg spring balance to measure the lift and discovered that each container of Helium gave about 250gms of lift and not the calculated 440 gms. I filled the balloon with six containers of gas giving 1.3kg of lift, which as it turned out was a little too much! I purchased a kite winder from Amazon and two spools of a lightweight kite string. This string had a breaking strain of 3 to 4 kg and 300 feet weighed 83 gms. The total weight of balloon, string and electronics package was 733 gms.

The balloon took about 45 minutes to fill and was just under five feet in diameter. The filling  tube was a thicker material than the main balloon and just over an inch in diameter. I used a large rubber bung with a hole in it and attached 2 metres of rubber tube. I connected the rubber tube to the valve on the container directly and did not use the balloon filling valve that is normally used to fill party balloons.

By the time the first container was empty the balloon had started to rise, I tethered it to a table. I measured the lift after each container had emptied by tying a loop in the tether string and a 5kg spring balance was hooked onto this. Pulling the spring balance down and the reading on the balance gave the lift. After five containers of gas had been used the lift was just over 1 kg, but adding in the weight of the balloon this gives 1200 gms, or 240 gms of lift per container of gas. This would have been more than enough to lift my payload, but I decided to add one more container of gas to give a lift of 1300 gms (total 1500 gms with the balloon weight).  The filling tube was folded over and cable ties used to seal it. Kite string was passed through the loop formed and the electronics payload suspended from this loop.

It was surprising how hard it was to pull the ballon down by the string and obvious that for safety sake thick protective glove should be worn to avoid injury from the kite string pulling through the fingers. The electronics package was attached. The wind speed had increased from 2km/hour to about 14km/hour by the time I was ready to fly the balloon and it was extremely difficult to handle. The payload was spinning wildly around the balloon kite string and a completely different means of hanging from the balloon will be needed next time.

The balloon was allowed to rise slowly by controlling the kite string reel, but this needed some effort. The balloon was stopped at about 50 feet to take photographs, but the payload was spinning wildly around the balloon string. Allowing the balloon to rise to about 100 feet had to be stopped as the strong wind was carrying the balloon horizontally as well as upwards. It was decided that it was not safe to continue and the balloon was brought back down to the ground.

The balloon probably had too much lift and probably should have been left at about 1 kg lift. Next time I would not attempt to fly a balloon if the wind speed was above 5km/ hour. To stop the payload spinning wildly I think it should be suspended so that the kite string went through the centre of the payload.

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The electronics package hanging from the ballon.

What about the performance of the payload? The electronics consisted of a Raspberry Pi model B+ fitted with. BMP 180 pressure sensor, a DHT11 humidity sensor (temperature could be read from either of theses two). Plugged into the USB sockets was a WiFi dongle, an 8gb memory stick for pictures, a LPRS 900mhz radio and a FTDI adaptor. A UBLOX Neo 6 GPS connected to a logic level converter was connected to the FTDI adaptor. A Raspberry Pi camera was used to take pictures.

A python script was used to collect data from the sensors and send and receive data from the ground station using the LRPS radio. WiFi could be used to control the camera up to about 100 feet which allowed an Android phone (using raspiCAM Remote) to take pictures or BerryCam on an iPad. However, the main control was over the LRPS radio using a VB6 program on a Windows laptop. This program was described in an earlier blog.

One of the planned activities was to measure the height of the balloon using GPS, atmospheric pressure and from the ground by measuring a distance of about 50 feet from the point where the ballon was tethered, the measuring the angle from the ground to the balloon. Trigonometry was used to calculate the height of the balloon. All three methods gave different results!

Photographic results: The spinning of the payload gave some interesting still images. Straight lines were strongly curved and the image blurred as the camera moved. The best result was from video, the camera faced straight down and the violent spinning made watching the video a little uncomfortable. However, some good still frames were extracted and next time I will shoot video at 90 frames per second ( so it can be slowed down to reduce the effects of spinning) and extract stills rather than trying to take still images.

The cost: I purchased the Helium from Amazon at £25 per container and the weather balloons at £3 each, so to launch the balloon costs £153. However, I felt that only five Helium containers were needed reducing the cost to £128. The kite reel, kite string and electronics package are all reusable and cost around £70.

Further thoughts: Wait for still weather, the original plan was to let the balloon rise to 300 or more feet, but with any wind the balloon could travel some way horizontally and become impossible to control. The balloon could be used over several days, if somewhere safe to store it overnight could be found. Some modification of the software is needed, the ability to use 90 GPS for video needs to be added. Using VNC to talk to the Raspberry Pi caused the Python script to close when the Pi lost the WiFi, but experiments have shown that running the Python using SSH may prevent this happening.