Monday, 25 July 2011

Battle Blimp PCB

One of the projects I'm involved in running is the University of Canterbury Aerospace Club.  Our big event this year is Battle Blimps :)

The plan is for people to battle their blimps until the other blimp is no longer capable of flight.  The simple version of the rules is as follows:

100 gram weight limit. (including envelope)
No flame weapons.
No untethered projectile weapons (Unless you are prepared to demo its safety int he usual fashion)
No intentional jamming of opponents controls.

Other than that people can do what they like.   I designed a pair of battle blimp boards, a micro board and a battle blimps motor board.  The micro board is based strongly off the tested mini rocket flight computer board ( but with better separation between the analog and digital sections.   The motor/high power board is a pair of TB6612FNG dual H bridges and 4 30 amp NFets as low side switches.  It also has a RMF12B transceiver with a  library based on the JeeLabs JeeNode code:

Obviously the traces will horribly explode if someone tries to draw 30 amps though the board but we have a work around for that.  Not that I can think of a battle blimps need for 30amps but people can then use the boards to drive little robots etc.

The design will be licenced as open hardware.

The Microcontroller board with ARM cortex M3

The Battle Blimps high power/motor shield with the RMF12B transceiver

Microprize flight micro/altimeter.

We have been having some pretty good success with the flight computers we have been building.   They are based on the excellent leaflabs maple.
The Front of the board.  This shows the72MHz ARM Cortex M3 (STM32F103RB) with 20k ram and 128k flash.  It also shows the currently unpopulated voltage regulator.

The back of the board with the SD card socket, 200 g accelerometer (unpopulated in the pic) , BMP085 pressure sensor and two dual channel N-fets for ejection charges (4 channels total)

The board is only 18mm wide and as such will serve as a development board with the larger flight computer.  The larger flight computer has more sensors and a set of lower g accelerometers for dead reckoning in case the gps fails.

The GPS we are using is the venus module from sparkfun.  The breakout board just fits on the top of the board using header pins.  I considered using the module without the breakout board but I'm not that confident that I can design the high frequency bits of the circuit well (you have to make sure your antenna feed traces are 50 Ohm impedance etc)  Basically I decided to trust sparkfun on this one.  Plus it gave us one less thing to debug.

Obviously the 200 g accelerometer is pretty overkill and doesn't have much resolution in the range even rockets work in.  In fact the noise in its signal is about +-0.3 g  (one standard deviation) with a fair degree of oversampling and simple digital filtering.    This isn't too far from the chips stated RMS noise of 0.28g so I'm pretty happy with that.    The main reason for this is to test some launch techniques and to estimate shock loads.  (parachute openings etc.)

Saturday, 9 July 2011

Robot that balances on a ball

This robot uses 3 sets of omniwheels to balance on a ball.  Kinda like a 2 axis segway.  It's quite impressive.

"Singularity Drive System"

This is a pretty neat video of I guess you could call it a continuously geared wheel drive. Its simple and seems to work really well.

Friday, 8 July 2011

Drilling small holes on the lathe by "catching the centre"

Nice technique for making small centered holes with the lathe. I'll have to give it a try when I next make up some some injectors.  Every time I've tried to drill .5mm holes on the lathe I've just broken the drill.

Tuesday, 5 July 2011

100k foot Microprize

There is currently a prize on offer on the Arocket mailing list for USD10k (ish) for the next team to launch a rocket 100 000 feet above its launch altitude. Its being offered primarily by John Carmak of Armadillo Aerospace and Doom fame.

The team 9.99 special project division currently intends to do this by launching a scratch built rocket with an off the shelf solid rocket motor from a balloon. Little rockets hate drag, being at ~30km at launch means the rocket can go much high than it can in the lower atmosphere.   This little rocket is going to be a fair bit larger than the D-motor rocket we tried to launch from a balloon last year :P

Proceeds of the prize will go toward a little celebratory beer and building bigger rockets :P  But realistically we are just having fun with this project.