Choosing a radio band & a long range modem

We live in France.

We only have two choice, basically :

868Mhz or 433Mhz

433Mhz is jammed.. stays 868 with 500mW limitation, which should be enough

I found a 868Mhz modem long range :

http://www.y-lynx.com/index.php?option=com_content&view=article&catid=39:archives&id=82:y-lynx-releases-their-trm8053-500-868mhz-band-500mw-long-range-radio-modem&Itemid=78



It might be interesting to investigate a bit more in that direction..

Why is the choice of the GPS module so important?

Most of the GPS are compliant with what is called “COCOM Limits”. Here is the issue! 

Indeed, it refers to a limit placed to GPS tracking devices that should disable tracking when the device realizes itself to be moving faster than 1 200mph (1 900 km/h) at an altitude higher than 60,000 feet (18,000 m). In such situation, the GPS receiver continuously resets until the situation is cleared. 

The objective of such limitation was to avoid the use of GPS in intercontinental ballistic missile-like. applications. 

Some manufacturers apply this limit literally and disable the GPS tracking when both limits are reached when other manufacturers disable tracking only when one of the limit is reached (higher than 60 000 feet OR moving faster than 1 200mph). 

High-altitude balloons are released into the stratosphere, generally reaching between 60,000 to 120,000 feet (18 to 37 km). For such application, 1 200 mph speed limitation is not an issue but the altitude limit is one! 

Therefore, if you want to be able to track your balloon as we would like, you have to choose a GPS using an OR statement that would continue to function above 60 000 feet. 

This is the case of the uBlox MAX-6 we have chosen. Order placed this last weekend on HAB supplies website. 

Max altitude: 164 041 feet (50 km) 

Support temperatures down to –40°C. 

The case / payload.. getting to it, at last !!

After a great long time without working on the project (holidays, back to work and so on), I finally found some time to go on with the next steps. 

I've been working a bit more on the "case". As a matter of fact, I hadn't worked on the mechanism that would enable the case to rotate on itself. The electronic part is getting ready, but I had to find a way to garantee that once the gyroscope sends a message to the motor gear, it may rotate the case. 

So here we are. The case looks like this : 

As we can see, the "eye" is made in plexiglass, and there is a "plate" on top of the box. This is the surface to which we will be attaching the parachute. This plate is attached to the case using a lazy susan, a bit like the one below

Here we see clearly the gap between the plate and the case.

On that example, we see how the lazy susan and the motorized part are linked together

We can see that the lazy susan is attached both to the blue and the green plate

Also, there is an axis that goes throught the lazy susan, and that is attached below the blue plate.

Through the green plate, there is a ball bearing, (below in red) so that the axis turns freely.

Below, there is a structure that holds the gear motor and the two gears, as can be seen below.

We can also see a bearing, in blue, below one of the gear. Thanks to this mecanism, the axis can rotate firmly and yet freely. 

I didn't put the engine right below the axis so that it doesn't take the load directly. 

Also, there is no reduction factor because the gear motor was choosen to rotate at a maximum speed of 90rpm. I didn't want the engine to run slower for the rotationnal speed I expected. 

Also, the V sliders were thought as a plug that would fit in an identical structure attached to the case itself. It's a way to make the engine structure more rigid.

A big thanks to my brother in law Guillaume for the Catia making.

We'll be adding the electronic part & camera to the box in the next steps