Connected my GPS up this evening to the Ublox U-center to confirm that everything was in working order. Changed the baud rate to 57600. (maybe someone can confirm if this is wise or not?) and yipee everything seems to be functioning.
I’ve read a a number of forums regarding the Ublox GPS and they advise to set the GPS into flight mode, of which I have done. I found this site useful to connect the GPS with U-center. Ublox GPS – U-center
Found some Arduino code on Git Hub for an RTTY based tracker based on Habduino, called Flextrack . It sounds as though it may work for my purpose if I want to use RTTY for the 2nd tracker. However I’m still awaiting the delivery of my UHF transmitter so only have the GPS working via the code so far.
Connected it all up to my Arduino Nano and I;m already getting the Flextrack GPS debug messages. So far so good..
The Ublox 7M seems to be working much better than the GPS in my primary tracker which is only a 6. Much faster in acquiring a fix.
Really need the transmitter to arrive so I can really start to get into the fun stuff.
There are many photo’s and videos around the internet showing the beauty and awe of near space. The sheer contrast of the earth below with a dark black emptiness of space above.
Being my first launch, I want to ensure that I too get to celebrate a successful mission. Nothing helps show others what can be achieved then some great photo’s or video.
However I certainly don’t want to place super expensive camera equipment with the risk of never recovering it into my first launch. So I have attempted to keep it relatively inexpensive but still with some good quality.
I have seen a lot of success with Go pros and also moded Canon camera’s. So I have gone down that path.
First up take a look at the CHDK Wiki who list several models of camera that can be modified to function to your requirements. They also provide all the instruction needed to complete the mod.
I purchased a cheap Canon IXY digital camera and just had to place some software on an SD card that when loaded by the camera allowed it to automatically start taking a sill shot every few seconds. The CHDK code allows for many other features as well.
I also acquired a SJCam SJ4000 as it looked like a cheap Go Pro alternative. It supports HD video and will also can take a still every 5 – 10 seconds. I haven’t decided yet, but may use this as the main still taking camera.
With the amount of Go Pros
heading into near space, I thought I may as well go the distance and risk it for some decent video footage. So I stalked Ebay for a 2nd hand Go Pro
Hero 2. This will be used to shoot constant video for the flight.
There are many things to consider to ensure I get some great photo’s and one of them is to ensure I have enough storage for the flight, so I have picked up a 32 GB SD card as this is supposedly the maximum for this camera.
I need to ensure I set the camera for a good quality shot, but I must not fill the card to quickly. I estimate I need to shoot for at least 2 hours. This also indicates that the battery must last the duration of the flight, so some battery expansion will be required.
Deciding on a parachute seemed a little harder than I first thought. It needs to be big enough to slow the payload decent so it can be recovered intact. At the same time if its to big the payload will drift a lot further on its decent and potentially take much longer to reach the ground.
To assist with the parachute decision most manufacturers provide a guide to the decent rate based on the weight of the payload. Some parachutes aim for a decent rate of around 5m/sec. Spherachutes lists it chutes based on the payload weight and other websites provide similar info.
For my project I went for a 48″ or 1.2 metre chute from Spherachutes.
This seemed to fit the estimated weight of my payload of which was still under construction so I hadn’t determined the final weight. Spherachutes charged a small additional fee to sew some straps at the top of the chute for the balloon to attach to.
The air temperature at higher altitudes tends to be below freezing, thus there is a risk that the batteries in the payload won’t operate effectively. Batteries in cold climates are know to have a higher resistance and will usually become flat very quickly.
I don’t want to risk the chance of my payload loosing power, as it will certainly result in a lost payload.
One solution is to choose batteries that function better in cold climates. According to battery university all batteries are impacted by the cold, however some handle it better than others. Certain NiCad and Lithium Ion Batteries can still operate at -40 Degrees C but at a reduced discharge.
So to attempt to keep the payload at a warmer battery friendly temperature, I am considering some air activated toe warmers, the type you place in your ski boots when in the snow.
These toe warmers can reach 40 Degrees C, so a couple of them should keep the payload warm when its -40 outside.
I still need to test this functionality to ensure it actually works, and that camera lenses won’t fog, but I;m feeling confident.
One of the problems I am going to face when it comes to launch time, is exactly how much helium do I need to get the required lift. To much and the balloon will burst early and not reach a high altitude. Not enough and the balloon could just float aimlessly without ever bursting, and very likely land in the ocean.
You can use various calculators around the internet to get a rough idea, such as the habitat burst calculator. You enter the type of balloon and the altitude your attempting to reach and it will provide a ‘Neck Lift’. This is the weight the balloon should be able to left in order to take the payload to the aimed altitude.
When filling the balloon with helium you need to check how much force it is lifting, by either using some luggage scales , or attaching a weight such as a water filled bottle that is at the predetermined weight.
I purchased a small digital scale to assist with filling helium into the balloon.
I chose this particular model as it has a fairly secure handle that I could attach a rope into. Other models had a hand grip which would have been harder to tie down. I just need to be careful of the hook to ensure it doesn’t penetrate the balloon cutting my mission short.
I most probably will have some pre-filled bottles that are at the required weight as a backup, as its the first launch I don’t know how accurate the scale reading will be.
Reading several blogs about High Altitude Balloon launches in Australia, it appears I may need a way to cut the payload free from the balloon mid flight.
This will ensure that the payload doesn’t travel into a unrecoverable location such as the ocean or dense scrub, but more importantly it can be terminated if the payload looks like it may land into a densely populated area.
I plan to build a cut down circuit and control it via a 2nd Arduino. I’m hoping to be able to transmit a tone such as DTMF to the Arduino and have it trigger a current through some nichrome wire.
I’ve found a cut down circuit on Bovine Aerospace and have built a trial system.
I have tested some AA’s in parallel to get approx 6v’s with a higher current, which seemed to be enough to heat the wire. However the current was over 2 Amperes and I only had a small relay capable of 2 Amperes and it became damaged. I have since upgraded to a relay that supports more Amperes and everything seems to be working again.
The first test I ran was using some baler twine with a milk bottle on the end. The milk bottle was approx 3 Kg for this test. I’m still yet to confirm if the AA’s are the best batteries for the job, maybe I need something more compact or more current to get the wire glowing red hot.
This is already being activated by the Arduino using a digital output but I am still yet to implement a receiver based activation. I also still need to determine the best way to trigger it.