YariLei
Posts: 17
Joined: Tue Jun 02, 2020 12:45 pm

Mid-altitude Pi-balloon

Tue Jun 30, 2020 6:20 pm

Hi,

I have an old Canon Ixus camera which still functions. I had the idea of sending that out into the air with a helium balloon, along with a GPS tracker, so that I can retrieve the images it takes along the way. I believe the Pi could do that GPS transmission for me, with a GSM module.

The basics are these:
A store nearby sells 90cm diameter latex balloons filled with helium for about 30€. I calculated that a fully inflated balloon this big can carry approximately 500-600 grams of stuff. This balloon can reach about 10km on paper; however, if I only inflate it with half the helium gas (ie. 250L instead of 500L), there's a small chance it might fly higher before popping (I'm still working on that whether it's plausible). I might actually get two balloons filled with one's volume of helium. Obviously, I would need a permission from the local air traffic organization to release this, and make sure the winds are favourable. According to some articles, a meteorological balloon which flies as high as 35 km will travel about 200km, so if I can get to half of that or less, I should be looking at about 100km travel to get the stuff.

I've got some extra XPS insulation foam left over, so I could make a box out of it and stuff the camera and the Pi inside it. I suppose I would need to buy a clear acrylic sheet for a window. Anyone have any experience of photographing at 10+ km high through an acrylic sheet, will I get glares? The point here is that once that thing lands, it needs to float in case it splashes on water. As a parachute, I plan on using a plain old plastic bag! It can dangle behind the whole thing during ascend. Or will it freeze and break? Do I need to heat these things up at that altitude? At least the Pi won't need any heat sinks...

The camera would be set up to take a photo every 5 seconds or so. That way I should be able to fill about a 4Gb or 8Gb card within the 2-3 hours the balloon is up in the air, as long as the battery lasts (I need to check that it does...).

For the Pi, I already have an old 2000mA battery bank. I've got an Adafruit v3 GPS module with a backup battery (why does it have a backup battery if it's connected to a power Pi? It can't broadcast it's location so what does it need a battery for, unless it's able to store the GPS location data?). I need to buy a GSM module for the Pi and set it up to transmit the location data via SMS. If I can get a GSM module with 3G or faster, maybe I could even install another camera to the Pi and get it to transfer all the photos online directly to my ftp server? I've got some cheap camera for a Pi, but it's not a very high resolution one. Perhaps I should also invest in a barometric/altitude sensor module and store the flight data, just for giggles. Of course, with a limited battery bank, the less data crunch the better. I've got another battery bank of same size I could throw in there, maybe a good idea?

For weight calculation, the Canon Ixus weights about 128g with battery and card. The battery bank is about 75-100g. GPS and GSM module weight, don't know yet but shouldn't exceed 50g? A Pi board weights about 9-45g, so that's about 300g of equipment inside the foam case. The case itself... not sure how much that would weight, since I haven't carved it out yet. Wouldn't expect it to be too much? Overall, we should be within the lifting capability of the 90cm balloon, as long as it's fully inflated, or two balloons half-filled with helium.

My question to you good people at Raspberry Pi Forum is this: Which Pi should I put in? I've got a Zero, Pi1B+ and Pi2B to spare. Each cost me about 15€, so we're talking dirt cheap experiment here, as the Canon Ixus is 10 years old and has no value left. I know there's a weight difference between the boards, but that's about 10% of the whole mass. Still, less is better, right?

I suppose the total cost of the whole project comes to about 60-70€, so totally worth it. I don't want to invest too much on this, considering I might just lose it all. Has anyone ever tried this? Any tips on setting up the Pi? One thing is for sure, I need to disable HDMI, leds, pretty much everything else than what I need. Anything I've missed here, is this even possible?

Cheers!

-Yari

blimpyway
Posts: 353
Joined: Mon Mar 19, 2018 1:18 pm

Re: Mid-altitude Pi-balloon

Wed Jul 01, 2020 8:46 am

You might not want a Pi to monitor the GPS, but a more power efficient arduino that will save you a lot in battery weight.

The only reason I would pick a Pi zero instead is to use it with its small, light native camera and leave the 125g canon down. That should cut your payload weight in half

PS
- a single 50g 18650 li-ion is sufficient for powering several hours a Pi Zero. You can strip a power bank of its case, keep only battery and voltage booster.
- Pi Zero is the least power hungry of your boards. And probably lighter.
- You can also consider LoRa modules for data link. GSM data link with flying things might be restricted, check your local regulations. These also are very power efficient.
LoRa uses a few milliwatts and the world record for range is >700km, also with a balloon.
- for pressure/temperature can use BMP180 or BMP280 modules, they are fingernail sized.

The radio, GPS and a BMP modules together should not be heavier than the zero. GSM too can't be too big.

YariLei
Posts: 17
Joined: Tue Jun 02, 2020 12:45 pm

Re: Mid-altitude Pi-balloon

Wed Jul 01, 2020 9:15 am

blimpyway wrote:
Wed Jul 01, 2020 8:46 am
You might not want a Pi to monitor the GPS, but a more power efficient arduino that will save you a lot in battery weight.

The only reason I would pick a Pi zero instead is to use it with its small, light native camera and leave the 125g canon down. That should cut your payload weight in half
Hmm, I'm not too experienced with Arduino boards; can I have it track the GPS and transmit the signal via SMS semi-easily? There's an Arduino Uno on sale for 12€ at the moment, but not sure if it's up for the task and how hard would it be to code it to do this?

A V2 camera for the Pi is an additional 25€. The one I have is not very good quality, some old one, which is why I though to toss it in as a secondary camera just in case. I have to think about it... The cost of the balloons remains the same regardless of whether I take a fully inflated one or two half-inflated, so there should be enough lift even with the Canon on board, although it will take the ascend longer and therefore the travel time longer too.

I'm also concerned with the SD card corruption. If I set the Canon to take pictures every 5 seconds, if it crashes while saving, it won't corrupt the already-taken pictures, as long as the SD card is intact (only the last image is corrupted). What will happen with the Zero if it suddenly powers down while saving a picture on the SD card? Will it make the SD card unreadable or can I salvage the pictures?

Cheers!

-Yari

YariLei
Posts: 17
Joined: Tue Jun 02, 2020 12:45 pm

Re: Mid-altitude Pi-balloon

Wed Jul 01, 2020 12:52 pm

I actually made a small lift calculation error in this. A jumbo latex balloon itself weights about 45g. A fully inflated balloon takes about 424 liters of helium, which can lift 455g of weight. With the weight of one balloon, that's 410g payload and with two balloons that's down to 365g. The companies might not even fully inflate the balloons, which can take the payload of a single balloon down to 340g. I'll just need to make sure they put in the full load.

Regarding the maximum altitude, I did some approximate calculations. The main reason why balloons expand and pop at max 10km seems to be that the air density and pressure drops drastically after 9000m. As the balloon ascends, it’s size slowly increases. At 5000m the balloon would be around 1,5x the original size. At 7500m, the balloon is about 2x the original size. At 9k, it’s 2,5x. At 10km, it’s over 3x. At 12km, it’s over 4x and 14km it’s over 5x the original size. 15km, nearly 7x. With a half-inflated balloon, in theory, we should get some leeway into it, so if the maximum a toy balloon can withstand without bursting is about 3x the normal size, if we inflate it only half-full, we should be allowing it to expand 6x. That would put the maximum height of a half-inflated latex balloon to roughly 14,5km. That's a theoretical maximum, so in reality we would be around 12km, which puts us into stratosphere!

Also, one thing to keep in mind is temperature. The temperature slowly decreases as we go higher, settling in about -57 Celsius at 10km and keeping it at that until 20km. So, if the balloon can withstand the temperature at 10km, it will have no effect as we go past that. If a party balloon can typically pass 9000m, which is about -49 Celsius, another 8 degrees shouldn’t make much of a difference, right?

The balloon companies also use special treatment on very large latex balloons, to make them last longer, so at least in theory this should add up? The payload is a real concern here, so I really need to go as bare-bone on this as possible. Perhaps the best way forward would be with a Pi Zero, attached to a BMP280, a GPS module and either the LoRa or GSM modules. Unless a mini Arduino can accomplish all that? And I really need to think about ditching that Canon and paying the extra 20 for the camera mod...

Rough calculation on the insulation foam shell, a Canon Ixus camera is about 114 cubic centimeters, so if I carve a box which has 3x that as an interior space and 2 cm thickness, and considering that XPS foam weights about 0,05 grams per cubic cm, the box would be about 1000 cubic cm, which equals to 50g weight. With a battery, Pi Zero + modules, Canon and the box plus a couple of plastic bags, we should be looking at around 280-290g of payload. That is a bit close to the maximum...

-Yari

blimpyway
Posts: 353
Joined: Mon Mar 19, 2018 1:18 pm

Re: Mid-altitude Pi-balloon

Sat Jul 04, 2020 8:33 pm

I don't think you need to over do the insulation.
If the Pi/batteries/camera are exposed to sun in a thin transparent bag you might have problems with overheating not excessive cold.
Even at ground level you can raise temperature 30 centigrade above ambient in a simple transparent bag.
With increasing altitudes thermal conductivity approaches vacuum's so it will get hotter.

EDIT - the arduino, yes uno is fine, but nano or pro mini (same uC, smaller form factor) is even better.

What I doubt is the canon camera batteries would last that long. Can you trigger its shutter externally?

YariLei
Posts: 17
Joined: Tue Jun 02, 2020 12:45 pm

Re: Mid-altitude Pi-balloon

Mon Jul 06, 2020 12:02 pm

blimpyway wrote:
Sat Jul 04, 2020 8:33 pm
I don't think you need to over do the insulation.
If the Pi/batteries/camera are exposed to sun in a thin transparent bag you might have problems with overheating not excessive cold.
Even at ground level you can raise temperature 30 centigrade above ambient in a simple transparent bag.
With increasing altitudes thermal conductivity approaches vacuum's so it will get hotter.

EDIT - the arduino, yes uno is fine, but nano or pro mini (same uC, smaller form factor) is even better.

What I doubt is the canon camera batteries would last that long. Can you trigger its shutter externally?
Well, they typically pack hand-warmers to the payload, since temperature above 10km will sit at -57 celsius until above 20km, which is beyond my reach. I don't think the Pi can produce enough heat to keep the camera warm enough, especially if I swap it to an arduino.

The flight takes about 2-3 hours and there are custom firmware built for canon cameras (called Canon Hack Development Kit) with which you can set any Canon pocket camera to run a pre-written script. In that script, I can set the camera to take a photo every 5 or 10 seconds, with all other functions off (such as the backscreen etc.) and even set it to automatically shut down if battery is nearly empty or the SD card full. It should last for the duration of the flight, but I'll double-check it beforehand that it does.

Best regards,

Yari

K Research
Posts: 56
Joined: Wed Jun 19, 2019 12:45 am

Re: Mid-altitude Pi-balloon

Mon Jul 13, 2020 2:42 am

Paul McWhorter has some great info on high altitude ballooning
https://www.youtube.com/watch?v=thlqMWy ... 31xZLQwp0k

He has a bunch of info https://www.youtube.com/c/mcwhorpj/playlists

Good luck
Enjoy
Share your results please.

pidd
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Re: Mid-altitude Pi-balloon

Mon Jul 13, 2020 3:33 am

I doubt you can transfer a picture every five seconds on LORA at any sort of range, I doubt you'll get much from GSM over 5km either, the ground antennas don't transmit upwards.

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DougieLawson
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Re: Mid-altitude Pi-balloon

Mon Jul 13, 2020 9:20 am

pidd wrote:
Mon Jul 13, 2020 3:33 am
I doubt you can transfer a picture every five seconds on LORA at any sort of range, I doubt you'll get much from GSM over 5km either, the ground antennas don't transmit upwards.
I don't think Dave Akerman (the expert on this stuff http://www.pi-in-the-sky.com/) has ever considered sending real-time photos from 40K ft. I think it's hard enough to send the essential telemetry needed to track the balloon for a safe retrieval of the payload on landing.
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