This was a school flight, where they built the payload and did the launch, I supplied a self-contained radio tracker, and a 3rd party supplied 2 rugged mobile phones to take video during the flight. It gave me a chance to test a live streaming setup that I intend to use on all of my flights from my launch site.

Since the school’s payload weight was already about right for the parachute size, I decided to use a lightweight tracker in a small foam egg. Based on a small AVR, it doesn’t include landing prediction but is a reliable basic LoRa tracker. I set it to mode 1 with a packet sent every 5 seconds, and I enabled calling mode so that receivers could be set to the calling channel.

Live Streaming

I’ve streamed video from the launch site before, but that has been either directly from a Raspberry Pi with a camera (using ffmpeg to stream to YouTube) or with a camcorder connected to a video capture device connected to a laptop.

For this flight I tested a new, more flexible setup. I used the popular and free OBS (Open Broadcaster Software) which is an incredibly capable program for combining various video and other sources into a single video screen which it can record locally and/or stream to various online services, including YouTube.

The basis of my stream was an IP camera in my garden, looking over the area I use for filling the balloon. All that needed to be done was to find the URL for the camera video stream, and enter that as a video source in OBS.

Next I wanted to add telemetry from my tracker. I now run my own internet server which runs a program that collects balloon telemetry from various sources, including my LoRa receivers at home. So I needed a way of displaying this telemetry as a text overlay on top of the IP camera video. One of the OBS options is to feed the contents of any program window into the output video stream, so I wrote a small program to collect the telemetry from my server, write that as text on a green background, add this program as a video source into OBS, and finally add a ChromaKey filter within OBS that removes the green background.

I also wanted to add data from my weather station. That station automatically uploads to various services every few seconds, including Wunderground which has an API for getting the current data from any station. So I added some code to my internet server that polls Wunderground for this data every few seconds, and then sends it my overlay program. This is how the ChromaKey works:


Finally, I added the school’s logo as a fixed transparent bitmap, and set OBS to stream to my YouTube channel. Here’s the resulting stream, just before launch:

The Launch

Predictions for the flight were fairly stable, with the landing position moving steadily SE during the day. The launch was a bit later than planned so it did land further SE than planned, but more on that later.


The day itself was very hot, during a week-long UK heatwave with daily temperatures up to 30 degrees C. So hot in fact that the mobile phones used for flight overheated when still on the ground! They were cooled prior to launch by dipping them in a tub of water (I told you they were rugged!).

Here are the team, posing with probably the largest helium balloon they’ve ever seen!

Launch was easy enough, though the excited schoolkids launched the balloon before I’d had a chance to get my drone ready to record the launch; I’m hoping to record or possibly stream drone footage on my next flight. So here instead is the launch captured by my field time-lapse camera:

The Flight

The flight proceeded pretty much as expected, however a combination of factors meant that it landed further south than planned, which could have been unfortunate as that took it into the Forest of Dean. Why are balloons magnetically attracted to trees?? Those factors were that after the initial ascent rate being the planned 5-5.5m/s, the ascent slowed once it entered the stratosphere, resulting in it spending longer in a south-westerly direction.

Later, heading west, it ascended almost 3km above the prediction, bringing it further west. So the net shift was a shift south-west from the planned landing near Longhope:

Note the large expanse of green in that map. And note the high density of (very tall) trees that it successfully managed to avoid by landing in a clearing!


We were about 2 miles away in out chase car when it landed, without a radio signal from the tracker due to a hill in the way. After stopping to check the landing position and the route, we approached along that road you can see near the landing spot, turned into the drive and called the other chase cars. At that time I spotted the parachute in the field (see arrow at the right of the image):

Once permission was obtained from the landowner, the team walked across the field to recover their precious payload!

And here they are, checking the footage that they got from their 2 phones – one with a regular camera and the other with an infra-red camera:

Finally, if you want to watch any of the launch stream, it’s here:

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