Friday, December 28, 2012

Project UberTutu

This project came about partly due to a slight obsession with things which emit many photons.
I had a string of digitally addressable LEDs from Adafruit bought because well... They were shiny! Enter Circillumina: An invite only rave dance party kind of thing... The perfect opportunity to play with glowwy lights.

Jez spinning his rather epic LED creation, the Mitochondrion

While throwing ideas around with Jillian and Rachel we decided that construction of some slightly out there costumes would be in order. Jillian is a stilt performer as one of her many many talents, she agreed to put on a bit of a stilt show at Circillumina 2 so a costume had to be created.
Rachel had a tutu in her collection of dress ups and I had the lights... Time to do something cool.

Rachel and Jillian started off by sewing the string of LEDs into the tutu whilst I ignored my nagging thoughts about how on earth this thing was going to be powered... The LEDs draw around 5W, not a small amount of power for something that has to run on batteries for several hours.

The LEDs are controlled by an Arduino which I soldered a JST connector directly to.

First test of UberTutu modeled by Rachel, Running Adafruit code.

As things were starting to come together, I turned attention back to power. I considered a number of different battery chemistries:
I have access to some pretty huge LiPo electric flight batteries, however I decided against this... The thought of strapping a battery which without warning can turn into an incendiary device to my friend did not appeal.

I have a Pag C6 video light: This has a 6V 8Ah NiCad battery pack with internal fusing. It's big, heavy, ugly and in a form factor that's not very sympathetic to being fitted to the female form. It is however safe. I used two silicon diodes in series with the battery to reduce the voltage a bit as the LEDs are designed to run from 5V.

I set about making a belt to house the battery that was comfortable and not too obtrusive.  I purchased a couple of metres of a while parka nylon from Global Fabrics in Wellington much to the amusement of the staff there.
After ten minutes with a pencil and paper I came up with a pattern. I cut the fabric out with a soldering iron in order to avoid the need to hem or fray stop the edges.

Unfortunately there aren't any more photos of the battery belt being made up as time was running short.

Jillian showing off the battery belt
Some flashier code was written and everything came together just in time for the night...

Thursday, December 27, 2012

Water Rocket Launch System

During my tenure at VUW I was in a role responsible for promoting the engineering school to potential students who were in their senior years of secondary school.

As an engineer I'm not much of a conventional marketing person, powerpoint slides and laser cut trinkets don't cut it for me. I also started playing with such toys as water rockets at a very early age... Enter the idea of running a challenge where engineering and school students are pitched against each other. Several emails later and my manager was convinced to go with the idea.

Now in it's simplest form a water rocket is nothing more than a bicycle tyre pump, a rubber stopper with a valve stem through it and a softdrink bottle. You fill the bottle say half with water insert the rubber stopper and pump in air.

Partially due to being prone to building silly contraptions that run on air and also due to restrictions imposed by the health and safety department. The idea of a joint pNuke and VUW branded water rocket launch system was conceived.

It had to be pneumatic as we already have a supply of air (the tyre pump) and so there would be no electrics to get wet.
It had to be black... In all seriousness, I build theatre and movie props... Anything not intended to be seen by the audience is matte black.

In the pneumatics stash I have a couple of HiRotor pneumatic actuators... Ridiculously oversized for this job but hey there's no chance of them breaking.

The actuators are sandwiched between two laser cut plywood plates to give the base sufficient rigidity.

Attached to the actuator shafts are plywood arms which support the two bottle retaining collars.

All the plywood components are soaked in watered down polyurethane, allowed to dry before a coat of flat black and a final coat of flat polyurethane.
The two collars lock onto the neck of the PET softdrink bottle above the flange on the neck, this ensures that the bottle is held in place very securely indeed.

The actuators are connected to the tyre pump after the bottle is pumped up. One firm pump is all that's required to pop them open.


Getting the air into the bottle proved more than a five minute task...
As the arms hold the neck of the bottle a good 100mm from the top plate, the bung had to be mounted on some form of standoff. Adding to the complexity is that the bottle is filled with air through the bung.
The final solution involved PVC pipe as a standoff, with a bit of trickery....
I set about creating what was in effect a hollow "bolt" with a 1/8th BSP fitting on one end to accept the air inlet.

This was made up from a modified tail fitting which I drilled to the inner diameter of the copper tubing. The hole was then counterbored to suit the outer diameter of the copper tube for a snug fit.
Pipe soldered into place
Drilled to suit the pipe i.d.

The other end of the copper tube has a short length of hollow M6 bolt silver soldered onto the end of it. The threads allow the bung, spacers and PVC pipe to all be clamped into place by one M6 Nyloc nut and washer.

In testing I realised that the arms don't always open together which can sometimes result in interesting launches... One arm releases the before the other, resulting in the bottle flying off at an odd angle. A temporary fix involving a pneumatic flow restrictor connected to the faster actuator was tried with some success. This will be properly remedied in a future version by use of a timing belt or gears between the two shafts.

A number of students, staff, teachers and friends all descended on Izard park in Wadestown to try out the platform and shoot rocket videos.

Kent from Onslow college was kind enough to bring their Casio 1200FPS camera along. Slow motion rocket take off video FTW!!

A really high speed (1200FPS) close up shot of the launch platform:

Last but not least: Some proof that perhaps pigs can fly... Megan's "Pigtoria" on her maiden flight. Trajectory is a little off due to the bottle falling foul of a hair dryer during construction.

Build photos for The rocket Launcher.
Some launch Freeze frames

Sunday, December 2, 2012

Industrial Pneumatic and Vacuum Plumbing 101

This little tutorial will take you through some of the methods used for pneumatic and vacuum plumbing in an industrial environment.

We will just be dealing with flexible tubing systems as used in most smaller industrial machines, large scale compressed air and vacuum distribution will not be discussed here.

The stuff that gets your moles of air from point A to point B. The most common materials are Polyurethane (PU), Nylon and Polyethylene (PE) My favourite is polyurethane as it is very flexible making it easy to fit into tight places.


All tubing that is manufactured in europe is metric with standard outside diameters being defined. Please for the sake of my sanity use metric components in your creations as much as possible. No, 6mm tube is NOT 1/4" There is a difference and the fittings are not interchangeable.

The most common "hobbyist sizes" are 4mm and 6mm. 4mm being suitable for control lines and smaller slow moving actuators while 6mm is more suited to supply lines or for bigger faster and scarier actuators.
Festo Pneumatic Tubing
SMC Pneumatic Tubing

Tubing can also be purchased pre formed into spirals to allow for movement.


If you are building something that requires multiple lines to one component but don't want to use cable ties it is possible to get multiway tubing. That is more than one tube is fused together.
SMC Flat Tubing

Dual tubing
It's all very well having tubes to do a plastic spaghetti impression with but how does one actually connect everything together?

One of the more common type of tubing connector is the pushfit, these seal the air in using an O-Ring and mechanically hold the tubing with a stainless steel collet. Pushing on the collet cap will retract the collet and allow the tubing to be released.

Now these fittings make assembling a circuit very quick and easy, the fact that connections can be made and changed so quickly allows one to "play" and generally mess about with valves, actuators and other components.
Festo QS Pneumatic Fittings
SMC Pneumatic Fittings

There are a heap of different fittings (way too many to list here) but to name a few.
T Connectors: Used to connect three tubes together,

 T Connectors are also available as a reducer, this allows a smaller diameter tube to be connected to a large tube very neatly.

All manner of threaded fittings are available too. Most are made of brass with the threads being treated with some kind of PTFE compound or tape to prevent leakage.

A 1/4 Inch Thread, 6mm tube fitting
A 1/8th Inch Thread 4mm tube fitting

The most common threaded fittings are British Standard Pipe or BSP
Now earlier it was mentioned that mixing imperial and metric tube and fittings was a bad idea... Well things may get a little confusing here as BSP threads are imperial. The most common sizes you are likely to encounter are 1/8" 1/4" and 3/8" taper threads.

Fittings are also available with Metric threads however these most often used for smaller sized connections (M5 and M6 being common sizes) Metric fittings are parallel threaded with a sealing gasket.

An M5 thread 4mm tube fitting

Reducing fittings allow one to change the diameter of tubing in some way, Say for example a very long air line is run in a larger diameter to reduce flow restriction. The tube size then can be reduced at the supply point to allow for flexibility or if the fitting size is limited.

A 6mm to 4mm reducer fitted to a 6mm T fitting

A valve fitted with a 6mm supply line
due to space constraints.
The lines to the ram are 10mm
A spaghetti of tubing and fittings
attached to control valves and rams.

A water rocket launch pad I built at VUW.

Where to get the stuff? Here in Wellington your best bets are:
Autoline Industrial in Petone: +64 4 570 0164
SMC Pneumatics in Petone
Norgren in Seaview