29th August 2010!
That’s when the Racecourse Park will echo to the bizarre sounds of our tennis-ball lofting machines. Meet at 2.30pm, and we’ll start cooking at 4pm. There will also be chemical and water rockets again, with material for those wanting to build water rockets.
There’s no specific plan for specific categories of launch. If anyone requires this, leave a comment here, and one will be written.
As well as the standard pub meet this month (Tuesday 17th August) NortHACKton is holding TWO other events. The dates for these events are up for selection by doodle poll until the 27th July where I shall pick the highest-voted days out of a hat of some kind, moderated by any mitigating factors that become apparent (site availability etc). Vote now!
Hack Evening Workshop
Our first workshop will be a series of short informal talks. These will not be held in the public area of a pub, but either a back-room or a community centre. Contact the mailing list or me directly if you’d like to give a talk. There will be time for questions and networking after each talk, and a projector for those with slides.
Ballistics Day
The previous rocketry day was a success. So we’re going to repeat it, but with the addition of trebuchets, or other catapults or methods of propulsion. Bring tennis balls, and then show how far you can propel them. Again, there will be a barbecue, and some raw materials for hacking on the day.
Flickr pictures are tagged with northacktonrocketryday1.
YouTube links
With the success of the (probably annual) NortHACKton rocketry day just behind us and the ever likely possiblility that there will be another day shortly to launch the chemical rockets; I thought I would take the opportunity to write up my two little rocket launcher designs so that other people can copy and expand upon should they wish. Alternately it’s only 363 days till the next rocketry day so get going now and consider that to be tinkering time.
Cork and Valve Launcher
I wanted to start with something so simple that anyone could make their own and then go play with it. You will need:
The reason I think this simple launcher was so effective is that it takes time for the cork to slide out of the neck. If you pump quickly then you can get a suprising amount of pressure into the bottle before it launches. Mine were often getting to 80 PSI. If the cork becomes too loose in the bottle then just wrap another layer of tape around the cork.
Cable Tie Release Launcher
The cable tie release mechanism is a rather elegant solution to the problem of holding the bottle onto the launcher. This design is a very much minimalist version of the system but was employed with great effect on the rocket day. All the fizzy drink bottles have a little lip of solid plastic just below the cap. This launcher makes use of that lip by gripping it with the cable ties, holding the bottle down until it is ready for release.
You will need:
Feeling the need to create something needlessly complicated to short a battery across the ignitor of the chemical rocket motor I turned to my Arduino Mega.
I already have a dot matrix display for my Arduino and have been using it to scroll the word ‘NortHACKTon’ when we go to the NortHACKton pub meets so that those people looking for geeks in a pub know who we are ”(cos we would’t stand out enough without it 
)”. I figured the dot matrix could be used to provide a visual countdown and the Arduino could activate a relay which connects the 9V supply directly to the rocket and then whoosh off it goes.
Schematic
It’s a very simple little board, consisting of a driver chip and a relay and the connection to the dot matrix display. I chose to use the ULN2003 to switch the relay primarily because the package already contains a freewheeling diode and can be directly driven from the arduino and secondly because I have 3 tubes of them in the shed already due to a misorder on a previous project. The dot matrix was also used on the same project. It is the 0832 from sure electronics and can be brought pretty cheaply on ebay, for only £7 inc P&P.
Arduino Program
Being an arduino most of the code is already written in other projects, (that is after all why we use arduinos isn’t it?). The program needs to read in the input from the micro switch to determine when the countdown should be running, it should only count down while the switch is depressed. When the countdown reaches zero the arduino should trigger the relay should be activated. Both of these functions are standard IO type code using digitalRead and digitalWrite. The DotMatrix is driven by the “Matrix Display” Library. The display is initialised when the program starts and images displayed by turning single pixels on and off.
I modified the Font.h file slightly to incorporate more of the ascii characters so I have included my version of the Matrix display library in the source code attachment. If someone were to be really keen I would suggest moving the character mapping function into the header too and creating the rest of the ASCII characters for the display. It’s on my list of things to do along with a variable width font, but that list is already pretty large so this won’t be done for some time.
The scrolling display displaying the NortHACKton url is created using the drawString functions provided as part of the library. The rocket and abort animations are defined as byte arrays at the top of the code and drawImage function simply calculates the visible part of the array and writes that data to the display.
Steve setting up the rocket
The arduino rocket launcher ready for action
Demo Video
More photos of the rocketry day can be found here
On a cloudy Independence Day, over 30 people gathered on the Racecourse Park to make and launch water bottle rockets. This is our largest group event by an order of magnitude, and thanks to everyone who came. We’re currently waiting what look to be an excellent crop of pictures from @alanjames. There’s a few pics on the @northackton feed at the moment as well. When new sources of pics turn up they’ll be linked from here. The wiki page will also be updated.
To summarise the day then; we started setting up at just after 2pm, to a rain-free but very windy day (22mph according to the BBC). The first rocket was launched at about half two, and rockets were launched frequently until 4pm when the barbecues were started, which proved to be deliciously distracting. A number of families turned up, and bottles, card, and cardboard were used, under careful supervision, to make rockets for the kids, which were also launched. The wind proved to be a bit troublesome, as rocket fins would get caught by the wind and blow the rocket off course quickly. 
Disappointingly the height competition did not go well as the theodolite I constructed couldn’t be used quickly enough to measure apogee well. It also may have moved when used for measurement as the angles it read seems surprisingly low. Martyn’s alternate device appeared to work more successfully, if it was in pre-war units!
After the barbecue the few remaining expressed their disappointment that it was too windy to launch chemical rockets. And then we launched some anyway! The first rocket had been launched before on a D class rocket engine. Unfortunately the C class used this time did not give it sufficient altitude, and the wind pushed the fins so that the rocket flew horizontally, and then landed before the parachute ejected. As it landed on its nosecone, this ejection charge merely blew the rocket apart, quite satisfyingly. The second rocket was much more successful. So successful in fact, that we don’t know where it landed, it was still afloat on its parachute when it left the park! So now we know, if it’s so windy the launchpad blows over, it’s too windy to launch. Everyone seemed to have a great time, and were all keen that we run another, so perhaps before September, maybe we shall run this again.
The poll is now closed, and the most popular date is the 4th of July. Football fans will be relieved to hear there is no World Cup match on this day. The start time will be 2pm. It’s a bit difficult to say exactly where we will set up as it will depend on who’s playing sports or sunbathing when we arrive, but I suggest that arrivals aim for the racecourse sculpture-thing which is opposite the main entrance of the Avenue campus of Northampton University. It’s about half-way down St George’s Avenue. We’ll have a gazebo in case of rain, so that should be visible, and if not, look for rockets.
We’ll start the barbeque towards 4pm. In order to minimise food wastage I’d suggest bringing your own food, as otherwise we’ll either run out or have too much. There’s no shops within staggering distance.
Suggested things to bring:
See (or edit) the wiki page for further information. I’ll keep an eye on the weather, and I suggest the backup day is the 10th if the weather threatens to be horrible.
