I promised to write up some of the rocket details for a few people, so here goes…

I’ll start with some pictures of the actual launches, then talk about the technical detail.

Preparing

Ready for pressurisation

Launch

Drogue parachute deployed perfectly, but no main

Probably a good job the main parachute didn't deploy, else we'd have ended up in the trees rather than the brambles. Also learnt that if you stand around pondering for long enough there's bound to be a sillier idiot than you willing to go climbing through the brambles.

Oh, and we did have some minor mishaps too...

Launch video (which I seem unable to embed)

Rocket body pressure chambers

The failed 'Anna Chapman' rocket

After the impressive sight, but inevitable failure of the Anna Chapman last year (launch video) I fancied building something similar but hopefully more successful. Last year we did find that 500ml bottles seemed to have a lot more bang for their buck than 2L bottles but this didn’t deter me too much. I’m still not really sure why it was, but I imagine it had something to do with cross sectional area versus volume. I surmised a longer rocket might well work better.

Inspiration from a rather impressive looking Air Command rocket using asymmetrically spliced bottles.

Air Command Water Rockets is an excellent resource, with some amazing launch videos which I wanted to try and at least go some way towards replicating. After some research I followed their Asymmetric Splice #5 Tutorial to build a number of spliced double-ended bottle sections. I shan’t repeat their tutorial, but I ended up using different glue as PL Premium is all but impossible to get hold of in the UK. I used Sikaflex EBT from Screwfix to seal the splice and a 2:3 Gorilla Glue:Polyfilla mix for the sleeving (more details on this Water Rocket Forum thread with links to Flickr pictures). Needless to say my garage is now covered in Polyfilla and glue; it gets everywhere.

IMPORTANT TIP: Wear gloves when handling Gorilla Glue; and replace said gloves if they break. Even the small amount I got on my thumb through a hole in my glove took over a week to wear off. It’s evil stuff.

The benefit of making a series of pressurisable ‘units’ rather than one long one is that they can be individually static pressure tested and the failures thrown away without affecting the rest. Having said that I am tempted to try and make a three or four bottle long ‘unit’ at some point.

Connected spliced bottles ready for launch

Bottle joins

The plan was to then join three or four of these together into a longer rocket using Tornado tubes from Hawkin’s Bazaar; but at £3.50 each they do work out rather expensive and the Northampton branch doesn’t seem to stock them.

Foreground left: Joined bottle connectors with various sized holes to allow air/water through. Foreground right: Gardena nozzles made to fit bottle top. Rear: Failed bottle top connectors.

From a thread on the Water Rocket Forum I came across a bright idea that Dan Brooker from British Water Rockets had to fuse two bottle tops into a coupling. He has made a demonstration video of how to do this. Despite his lack of testing at that stage I thought it worth a go. My success rate was less than one in three and I began to run out of bottle tops, but I found that some of my attempts withstood a static pressure test to 100psi. I’m not sure how much higher they’ll go, but Dan has reported some failures since. YMMV.

Talking of failures… when carrying out static pressure tests be wary of how much water leaks and air is let in – I had an inadvertent launch at 10 o’clock at night into next door but one’s garden.

Launcher

My old Clarke cable tie based launcher

Martin's Clarke cable tie based launcher, with 21.5mm launch tube

New launcher with optional boosters (annotated)

Having read about possible options on Air Command Rockets, I decided to have a go at a Gardena (Hozelock) launch mechanism. Reasons were two-fold: a. it might seal better; b. the smaller nozzle may sustain flight longer (albeit at a lower force, but that comes in handy when using boosters). I could always revert to the old launcher if all else failed.

Safety

A safe distance from the launcher - hosepipe and string allows remote compression and launch

Oh, and being the sensible one, I elected to put a length garden hosepipe between the launcher and the pump. This reduced the risk of personal injury in the event of catastrophic failure and also kept the operator somewhat drier.

Others may not have thought ahead so much...

Martin getting a tad soggy. Note: Some of the photos I've used, including this one are from one of the 2010 Ballistics events

Nozzle

Air Command Water Rockets has a nice tutorial and videos about preparing a Gardena nozzle, so I shan’t dwell on that much. As they note, I had trouble finding a nozzle with a seal, so tried using some Sikaflex as a seal with mixed results. Ultimately, it was the nozzle that limited launch pressures to about 80psi, so this is where more work is needed to get a good seal between the Gardena nozzle and the bottle top.

Rather than the direct string pull I sought some mechanical advantage from a level arrangement for the launch release. In use we found that it still needed quite a tug to release and on one occasion the string snapped. Again, this needs more work.

Boosters

As if I’d not created enough trouble for myself already, I thought it would be cool to have more than one stage. Direct staging mechanisms seemed a little complex for a first go at anything more than the plain bottles we launched last year, so boosters seemed a sensible bet. Again, Air Command Water Rockets provided much of the inspiration with their Drop Away Boosters and Cluster Launcher pages.

The principle behind the boosters was pretty simple, but also very critical with a number of single points of failure (no manned versions of this bottle rocket design). The boosters were set up such that they would produce more force than the main rocket until exhausted at which point they passively drop behind the main stage. That’s the theory at least, my design wasn’t quite as sophisticated or refined as Air Command’s. The pictures below illustrate the coat hanger hook and pen cylinder receptacles making up the mechanism. They didn’t operate particularly smoothly, though maybe a neater effort would have better results – I was pushed for time.

Booster with hooks

Hook receptacles on main body bottle

Overall, the boosters didn’t work out too well. Even with PTFE tape around the booster launch tubes it was difficult to get a good, consistent seal on each of the three bottles; invariably, one let go and began to leak under pressure. And the minor mishap illustrated in the first series of pictures at the top of this post was due to one of the hooks detaching from its bottle.

As well launch efficiency, the reason for the launch tubes was to allow the compression line to remain dry/ This would allow the pressure to equalise between the boosters. However, looking at the failed launch with hindsight, we missed out a non-return valve. This meant that water from the main rocket filled the booster compression lines and prevented the pressure from equalising. I don’t think it was causal to the catastrophic failure, but it can’t have helped.

Parachute

I went a little overboard on the parachute. In the past I’ve found charity clothing bags ideal for building parachutes, but while light, they aren’t particularly resiliant and the my choice of tether line (dental floss!) got tangled easily. So I splashed out on some Ripstop Nylon from Ebay and got sewing.

Leo Singleton‘s Bottle Rocket Handbook (PDF) had a nice section on parachute design. I chose to build an elliptical design, calculated using his Elliptical Parachute Calculator (36KB ZIP)

My first parachute took the defaults from the tool and ended up a rather too large 1M diameter, still it would be a nice gentle float down. As I didn’t think I’d be able to deploy this on its own, I built a drogue of 40cm.

Drogue (40cm) and main (1m) parachutes

Parachute mechanism

Again, drawing on ideas from Air Command Rockets I built a Parachute Side Deployment Mechanism, with their elastic band release modification. I didn’t have time to acquire a Servo Timer II nor much faith in guessing the timing accurately so decided to use a 35MHz radio control receiver to control the server.

Activated parachute mechanism

Parachute mechanism atop the rocket. Upper half of the top bottle contains the drogue chute and R/C release mechanism; the lower half the main chute which failed to deploy

As the main chute was too large to fit within the elastic deployment pocket, I bargained that the drogue would lift the whole mechanism from the rocket top and deploy the main. On both parachute-recovery launches the drogue deployed perfectly, but the main chute failed. With hindsight, I should have attached the drogue directly to the main and had a hole or flap for it to deploy through.

Next time, I think I’ll build a second deployment mechansim, attach a medium sized (70cm?) parachute and trigger it shortly after apogee with an altimeter. The existing R/C drogue parachute can act as a back up.

I’ve written enough for now, feel free to ask any further questions in the comments below, or in person.

NortHACKton member, Charlie Webb, recently completed this project based around an arduino and a keyboard. Fed up with the way Windows forced him to switch between his different keyboard layouts (qwerty to Dvorak) he decided to take the process entirely out of windows hands. He modified an old keyboard, inserting an avr microcontroller between the keyboard and the PC. At the flick of a switch the MCU performs the entire keyboard remapping between the two different layouts.

The microcontroller in the keyboard also allowed him to add some extra features at the same time. The big red button on the front of the keyboard generates a whole stream of text to be inserted into whatever you’re working on. Knowing Charlie I suspect this is currently being put to extremely good use harassing the noobs on some First Person Shooter somewhere (“OMG, WTF, I Iz Leet” etc, or maybe minecraft as that’s what the cool kids seem to be doing atm)

More photos and some diagrams of the project can be found in on picasa

And he has been kind enough to supply us with the arduino code for the job too.

After discussions with the Maker Faire people last week it appears it’s going to be a bit tricky to take the whole spider along to Newcastle. We can erect it outside the stadium but we need to be able to prove that it isn’t going to blow away which is apparently a little more than just looking at the vast weights in the feet and saying ‘That looks heavy enough’. So we struck a compromise deal which suits us pretty nicely. We’ll only take the front half of the spider and we’ll prop it up against a wall inside the venue. then we can set up stall underneath it. Suits us in many ways because the front half is already made and it will be easier to transport.

I realise it’s not overly worthy of an update post but I spent 20 minutes this afternoon doing a quick framework test. I screwed some of the longer pieces together to test my plans for the joint. It’s pretty strong but would benefit from a matching plank on the other side of the joint, so I shall head back to Wickes tomorrow to buy the rest of the wood and something suitable for the job. Hopefully I’ll have more to show by the other end of the weekend.

(and yes I realise that first image shows it resting on a window ledge but that does simulate the additional leg joint that will be going down there)

I was inspired the other day when I meandered round the internet and I saw a lot of Computer controlled etch a sketches, but not a single etch a sketch controller computer. So I put aside my other projects for a night or two and set about actually making one of these things. I’m quite pleased with the results, but you can take it for a test drive yourself, when NortHACKton go to the UK Maker Faire next month.

The basic construction is an MDF frame, mounted over an LCD monitor. Two water bottle caps act as the knobs for the etch a sketch and the guts of an old roller ball USB mouse have been re purposed to control the PC.

An old mouse already has two sets of rollers, one for left-right and one for up-down. These normally press against the ball to detect the mouse movement. A slotted disk on the roller spins between an LED and opto sensor pair to detect the rotation of the knob. I have extracted these roller and sensor arrangements and put them on the left and right of the screen. The left and right clicks have also been extended and put behind each knob.

I extended the cables from the PCB in the mouse, it’s quick and dirty, I didn’t even common up the ground wires. It works and that’s good enough for a hack right? The tricky bit was aligning the LED with the sensor correctly and was achieved with lots of careful adjustments before glueing each knob section together. Finally a little bit of friction prevent the mouse unclicking, so I wedged a small section of foam into the gap to help it return to the off position.

Higher res photos can be found here and a small sample video should appear below.

NortHACKton met this evening at our new NSME facilities (http://www.nsme.co.uk/). The club house was pretty much perfect for what we needed, we made good use of the projector and it was nice to have tea and coffee on demand. As most of us drive and don’t drink anyway it seems to suit us well. From now on we will probably meet there twice a month, once for a project night and once for a lecture night, after the lecture we can probably retire down to the Malt shovel anyway.

Back to this evening anyway. The idea was to build a loop to drive the remote control car around. This is a precursor to any potential wipeout track we want to build for the Maker Faire. We previously had a 3D model for a loop made in paper so this evening was about scaling it up to a useable size. This was also a key factor that we needed to test in order to make the large spider bot. We used a projector to shine the pattern onto sheets of cardboard so we could draw round it and cut them out at the appropriate sizes. A team of cutters and some people drawing and we had all the bits we needed cut out and ready for sticking. More team work ensued with one man on the hot glue gun, one folding and holding tabs till the glue dried and a third pair of hands to feed the card in and we were done.

The whole project was a testament to teamwork. Many hands managed to get the whole pattern cut and assembled in 3 just hours.  The only real disappointment is that the loop was too big and the poor little car couldn’t actually complete a full loop. Time was drawing short so we bundled up the loop and stuck it in the back of the car. I will modify the loop making it smaller and we can try it again. Anyway the evening was a still a great night, and despite the lack of success I’d definitely do it again. All my photos from the evening can be found here. http://picasaweb.google.com/msraynsford/NortHACKtonLoopTheLoop

As a testiment to actually making things from our own little hackerspace I thought I’d post about this

The idea for a paper version of a lithophane was inspired by a conversation with one of the other NortHACKton members, Max. By building up several layers of paper it is possible to create different shades of colour when they are held up to the light. Cutting away regions within a layer you can create entire pictures using this method. I wrote a quick hack of an app that converts an image to greyscale and allows you to set the thresholds for each layer. You can then save each layer as a seperate image ready for printing.

Full details and more images are available through the instructable I wrote about it, http://www.instructables.com/id/How-to-Make-a-Paper-Lithophane/

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:

• A cork (I bought Youngs wine corks from Wilkinson)
• A schraeder valve (Just ask at your local tyre garage)
• Some selotape

1. Cut one of the corks in half
2. Drill a hole through the cork a little smaller than the neck of the schraeder valve
3. Insert the valve into the cork
4. Wrap the cork in one or two layers of selotapec
5. Fill the rocket with water and then insert the cork into the neck of the bottle

• To Launch turn the rocket upside down and fill with water, wedge the launcher into the neck of the bottle and then prop the bottle into a vertical position, I did this using some metal camping pegs. Start pumping, when the pressure inside the bottle is sufficient it will force the cork out of the bottle and the rocket will take off.

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:

• 21.5mm outer diameter pipe (this is tricky to get hold of and I resorted to the internet)
• 40mm diameter waste pipe (available from B&Q etc and the 40mm I believe is the inner diameter)
• 20-30 cable ties (these need to fit around the edge of the bottle but inside the waste pipe)
• A schraeder valve (might as well get several from the tyre place, they’re handy)
• Hot Glue
• Selotape

1. Place the 21.5mm pipe into the neck of a bottle, I used a 250ml coke bottle as it’s easier to wave around at this construction stage.
2. Loosely pull the black cable ties together and place them around the pipe, these will be used to hold the white cable ties in place. (It’s only black and white so your know what I’m talking about)
3. Add white cable ties around the pipe making sure they all line up with the lip around the bottle neck. My design used 15 cable ties and I found it much easier to space them by using an extra cable tie between every third tie.
5. Pull the black ties tight, this will hold all the other cable ties down. There should be roughly 50mm between the first outer tie and the top of the horrizontal ties. Then carefully remove the spacer cable ties, try not to move the other ties at this point.
6. Trim the cable ties to the desired length and apply a liberal coating of hot glue to the pipe and the ties. Make sure to get the glue right down into the gaps where the spacers were and also into the end of the outer ties to prevent any possibly loosening.
7. Cut a length of waste pipe to go over the cable ties, locking the bottle into place. I pulled mine manually so I kept mine long to grip it, but it could be as little at 20-30mm for other methods as long as it covers all the cable ties.
8. Finally hot glue the schraeder into the bottom of the pipe. A better design would be to pack the valve with a cork to make it fit the gap better/tighter but hot glue will do the job adequately.
9. Add a few layers of tape to the make the pipe fit the neck of the bottle snuggly, this will allow you to build up the pressure inside the bottle before release.

• To launch the rocket, fill the bottle with water and connect the launcher to it while it’s upside down. Slide the waste pipe down over the neck of the bottle and the cable ties securing it in place.  Turn the rocket the right way up and prop it in a vertical position (again with the tent pegs). Pressurise the bottle and then when you are ready to launch simply pull the waste pipe down from around the neck.