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projects:parafoil:two

Mission: Two - Tethered Ballon Drop Tests

Aims

Components

  • Payload from Mission One
  • Gumstix 400xm
  • Audiostix II
  • 3 degree accelerometer
  • Rate Gyro
  • Jupiter Rockwell GPS
  • Servo Snooper
  • Aerocomm 868Mhz Radio
  • Cutdown device

Construction

GPS

GPS is a cheap Jupiter Rockwell GPS unit that was bought off ebay for £10, its relatively large for a gps unit but out puts at TTL so can easily be wired up to the gumstix's TTL serial ports. Information about the pinouts etc can be found here. As a warning the rockwell jupiter has annoyingly spaced pins which require a special socket so instead of that hassle using a soldering iron i removed the pins and directly soldered wires to the holes that the pins sat in originally :-D. Also this hack reduces the height of the gps making it easier to intergrate.

The GPS requires an antenna which attaches with a mcx connector - I also got one of these off ebay (you can also get them from maplins) - the cable was far to long so i shortened it by cutting a section out and resoldering the two ends being careful to keep the different bits of the coax cable seperate. I used an active antenna so added a power line from the gumstix. One thing i've noticed is when the gps is powered on and the gumstix is off the nmea pulses seem sufficient to cause the gumstix light to flash in time. Doesn't seem to effect the gumstix but will require some more investigation (perhaps something to do with the common ground). eeeek - I suspect you will find that this the gumstix being partly powered via the input pin protection diodes - the gps output will be higher than the gumstix Vdd - hence the protection diode will try to pull the Vdd up - generally not good for the GPIO port :-( - to stop this happening either power on the gumstix first or wire both the gumstix and the GPS behind a common power switch. Alternativlty a small resistor (about 270ohm should provide some protection) - rocketboy

On the software side the gps is connected to BTUART and therefore ttyS1 - A perl script is used to read the gps and log to /gps.log - exactly as is done with the Pegasus missions.

Accelerometers and Gyro

Servo Snooper

Cutdown Device

Aerocomm Radio Modems

Had the development kit for these lying around so thought they would be an appropriate system. The great thing about them is that in their default state they work as just serial port extenders. Amazingly they have the same stupid pinout size as the GPS which makes finding a connector that fits nearly impossible so using random connectors I managed to get enough wires to the right pins (Tx, Rx, GND and Power (3.3v)). The radio modem is connected up to the ttyS0 serial port and runs at 57600baud. While data can be sent directly from the console using the echo “data” >/dev/ttyS0 command instead data is sent from a c program that reads the accelerometers and gyro and gps and formats them into a single string, opens the ttyS0 serial port and sends the data down.

The radio modem on the ground side is still on the development board and is powered and communicated with via usb (with a usb→serial convertor embedded). On Mac OS X data is either read by kermit on the console or by a graphical interface written in RubyCocoa which displays the data, logs it and also has some call little bars that move depending on the reading from the adcs.

R/C Gear

  • Exactly the same as in Mission One however the Servo Snooper is now interfaced to monitor the PWM signal.

Power Supplies

projects/parafoil/two.txt · Last modified: 2008/07/19 23:33 (external edit)