First class-C launches with Arduino telemetry payload

As a first step to building a more fully-featured payload package for class G and larger rockets, LN member Jonathan Oxer has been working on building a telemetry payload small and light enough to launch in a class C rocket. Because class C rockets can't lift much of a payload he had to keep the mass of the electronics as small as possible. You can get a sense of scale from this photo which shows a small white bundle in the bottom of the nosecone. Inside that bundle is an Arduino Pro Mini 5V/16Mhz, a 433Mhz transmitter module, and a Lilypad 3-axis accelerometer:



The Arduino runs code that reads the accelerometer values, pokes them out the transmitter using the VirtualWire library and waits for the message to go out, then loops back to the start. The result is a stream of values that is pretty much rate-limited by the 2Kbps transmission rate.

On the ground Jonathan had his laptop connected to an Arduino Duemilanove with a 433MHz receiver module:



Running on the laptop was a little piece of code that read values coming from the USB port and displayed them on screen while also writing them to a logfile. This shot shows the values scrolling on the screen while Jonathan holds the rocket and gives it a bit of a shake:



The launches worked really well, but the accelerometer data was truncated so didn't capture the whole flight. The values came out looking like this:

562047|326|328|395
562204|322|330|393
562361|327|327|397
562516|317|335|604
562673|325|331|590
562830|328|330|514
562985|328|331|506
563142|328|331|500
563298|328|329|501

where the columns are:

1: Time in milliseconds since the Arduino booted
2: X force
3: Y force
4: Z force

That data segment is from around the time of the second launch with the Z value stable at around 394 while the rocket was stationary then jumping to 604 and falling to 500 over the next 800ms. Comms failed right at that point, less than 1 second after launch: the cheap 433MHz modules just didn't manage to do the job. Future tests will instead use a pair of 60mW XBee modules supplied by SparkFun that are a lot bigger than the 433MHz modules but should be good for 1Km+ range.

The moment of launch: