Wednesday 12 October 2011

Battle Blimp Boards. Motor Drivers

Last Sunday  we ran the second part of the aerospace club board building workshop.  Again it went pretty well, I was rather pleased at the turn out given how busy everyone is at this time of year.   We finished up most of the megamini boards and made good progress on the Battle Blimps Shield.  (We really need to crystallize on some consistent names for these things)

This afternoon I wrote a partial port of the Adafruit motor driver library.  Once it compiled, it worked first time!  That never actually happens in real life.

From Battle Blimps Boards.
See, it can even drive a motor backwards and forwards.

I'll try  add some photos to the album over the next few days but sadly it looks like we all worked hard on Sunday and didn't actually take any pictures of the build :P

Monday 3 October 2011

Building the MegaMini

On Sunday the canterbury aerospace club populated the first of 2 PCB's for the battle blimps competition.  Hanna took some great photos and video of the build day.

It went reasonably well and we got the maple bootloader onto a few of the boards.  Next week we will run the second half of the workshop where we build the battle blimps shield which we will be using for communications and motor driving on the blimps.   We will also finish up the few boards incomplete megamini boards

It was great fun to use the pick and place machine and looking at solder paste under a microscope is amazing.  It looks like a pile of ball bearings, I strongly suggest you try it some time :)

Quite a number of the group had never even soldered before and I think throwing them in the deep end and starting with surface mount has been quite good.  There seems to be a perception that surface mount is really hard when actually it isn't that bad. 

Friday 2 September 2011

Rockoon Flight, CAA preliminary approval.

Me and Hanna went up to Wellington last week to try and convince CAA to let us fly the microprize rocket from a balloon without a transponder.   Looks like they are going to let us do it :)   There are some provisions we have to meet, but I anticipate no big problem with them.

We were planning to fly in the Canterbury plains but due to all the controlled airspace there we are going to have to move the flight to Southland.  At the moment I'm roughing out flight predictions centered around a small town called Tinkertown, which seems appropriate :)    We will also have to start the flight at night to avoid as much air traffic as possible and there are a lot of flight zones we must keep out of at all times (such as around Queenstown).  This should all be doable and with the rocket launching at or just before dawn should make for some spectacular photos from the top.  

Battle Blimp Boards, PCBs

The PCBs for the battle blimps boards have finally arrived.  We got them on the Dorkbot PCB group order and they have taken ages to arrive.  I think they got lost in the postal system as the PCBs from dorkbot have always arrived much faster than this.

The battle blimp boards are based on the Leaflabs Maple.  The PCBs on the left are the microboards with the ARM cortex chip, the ones ont he right are the motor/radio shield.  In all we got 18 PCB's of each made up.

We will have one spare which we can use to test the current handling of the motor driver chips and the high power Fets.   As the traces are only 1ounce per square inch they won't handle that much current before exploding so we will investigate roughly what that point is.  We have a work around for people who want to sink heaps of current with the fets.

I'll order the parts from Digikey this evening and then we will run the SMT assembly workshops once they arrive :)

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.