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Oct / Nov 2014
Underwater robot PDF Print E-mail
Written by Andrew Lee   

Building an underwater robot

I first looked at the idea of a Remote Operated Vehicle (ROV) in 2002. I had a keen interest in shipwrecks and underwater video and had already built a tethered drop camera that could go down to a depth of 30 metres.  But I could only see straight down and didn’t have much control of what was viewed. Wouldn’t it be great if I had something that could fly underwater and go and look where I wanted it to?

I was aware of ROVs but couldn’t afford to buy one—the cheapest I could see was $US12,000. But building one would be a challenge (not that I knew it would take ten years and a lot of frustration).

There was very little info out there at that time, with no one really home-building on the internet. So I had to make it up myself. With my boatbuilding background, building the hull was not too much to deal with.

After my first version which had problems with the voltage drop over the length of the cable and a persistent leak, I decided to start a new ROV with the idea of resolving issues of the first. With a couple of months of pondering I came up with my build plan. I wanted a ROV with

  • A bigger hull, so I could add various attachments, sensors etc;
  • Variable speed control for better manoeuvering and depth control;
  • On-board battery to reduce the tether size and to eliminate the voltage drop problem;
  • On-screen display (OSD) for voltage, amp draw and compass heading;
  • Better motor control that didn’t require direct wiring to the switches;
  • Joystick instead of switches for direction control;

Detachable tether (the first ROV was hard-wired to the tether).

Read more in the latest issue of The Shed

 
Aluminium Welding PDF Print E-mail
Written by Greg Holster   

Aluminium Welding

Part 4: Basics of aluminium welding, the fourth in a series of how to weld

Aluminium alloys are used in so many different applications in our modern world, from motorbike frames and boats, big and small, to superyachts. The list is endless. So when it comes to building, manufacturing and repairs, welding is often the best solution. Most aluminium alloys are weldable, but it is important to understand the special aspects and quirks of working and welding aluminium and the welding technique.

Easily the most overlooked problem in welding aluminium is not having a clean welding preparation. So first up, cleanliness is of the utmost importance. When faced with repairs in the shed or workshop, you will find aluminium that is old, dirty, or with an oxidised surface will need to be cleaned.

TIG welding uses a non-consumable tungsten electrode surrounded by a ceramic shield which controls the flow of the protecting argon gas. Argon gas shields the molten metal from the oxygen and nitrogen in the atmosphere which would otherwise oxidise the metal and rod. The argon also acts as a carrier for the current which is the heat source.

The electrode tip in the TIG torch for steel or stainless steel is very pointed and made of thoriated tungsten. For aluminium welding, the TIG torch tungsten electrode should be blunt, the corners ground off and is made of zirconiated tungsten. The tungsten electrode has a white tip for aluminium and a red tip for steel.

Read more in the latest issue of The Shed

 
Charging station PDF Print E-mail
Written by Stuart Lees   

Make a tidy charging station

There are two sure things in modern life (and no, not death and taxes): they are technology and cables. Lots and lots of cables. Some are used for interconnecting  devices such as HID or human interface devices, a computer mouse, keyboards and the like. In many cases, wireless technology is thankfully removing the umbilical tether.

But when it comes to charging our mobile devices, the spaghetti junction is still very prevalent. Until such time as the wireless charging matures into a viable option, disguise is the next best thing. So with this project, I am making a tidy station to charge a couple of iPhones, an iPod Touch and an iPad. This project is a reasonably simple build and you can tailor its complexity (more or less) to suit your skill level.

The charging station project can also be scaled to suit the number and type of mobile devices in your household.

To start, lay each of the devices out to work out the proportions of the station needed to accommodate them all. It doesn’t matter what brand of phone or touch-surface device you are making the station for. I chose to make it out of reclaiomed timber, in this case an old favourite, jarrah, and a contrasting much whiter timber, Queensland maple.

Reclaimed timber often won’t have the same yield as virgin timber but a significant benefit of reclaimed timber comes from its age. Its moisture content is stable and it doesn’t move much (if at all) when it is cut. It is also rewarding to find such good-looking and functional timber in what most people would throw away, or burn.

The next step will be becoming a familiar one, as it is common for most projects—dressing the timber.

Read more in the latest issue of The Shed

 
Dovetailed drawer PDF Print E-mail
Written by Sid Aksoy   

Dovetails

Basic cabinetry: Part 4, Making and fitting a dovetailed drawer

A dovetailed drawer is easier to make than most people think. Sure, a little practice on a few off-cuts is recommended before you attempt the actual drawer. But once you get a feeling for the tools and the timber at hand, you will always be ableto apply this skill to a good piece of furniture.

Dovetailed drawers are a giveaway sign of quality and a craftsman’s skill level and expertise. This little detail lets a prospective buyer know straightaway that the tradition of the craft is still alive and the product is a piece of quality, integrity, beauty and love. It is also a very sustainable approach to create long-lasting furniture. I have not seen well-made, dovetailed drawers fall apart.

To fit the front and sides, first measure the space between the sides of the carcase and the height between the rails and cut a piece of 19 mm thick timber to fit the dawer space.

I recommend that you fit the drawer front so that it goes in easily but without any gaps at this stage. Make sure that you mark the drawer-front with a triangle, as this is essential for knowing what is in and out, up and down.

Cut the drawer-front slightly tight and fit it with a hand plane. A fine-tuned block plane or even No.4 bench plane does a very good job here. I personally like wooden planes a lot and my Japanese “Miki” (Akio Uozumi) makes fitting a dream.

Read more in the latest issue of The Shed

 
Bill Blair PDF Print E-mail
Written by Nathalie Brown   

Photography: Derek Golding

Modern man, ancient craft

It's a radiant blue winter's day. The frigid wind is sifting through the match lining in Bill Blair's shed at the edge of the Oamaru Harbour while the coppice craftsman puts together a plate for his afternoon smoko. He eats half a mutton bird and two slices of sour dough bread, wipes his lips and settles down to talk.

Asked why he has spent the best part of 20 years producing garden trugs, besom brooms, bentwood log carriers, wooden pitch forks and rakes, he says he's always had an inbuilt love of wood, of trees and the desire to work with his hands.

“I was brought up on a farm in North Otago and in the Moeraki village. My parents valued things like gardening, sewing and cooking and being self-sufficient. And those values were inculcated in me. In those days woodwork was still valued as a school subject although it was an activity for what they called ‘less academically gifted’ students.

“But they still have craft colleges in Germany and France where traditional crafts are given more status and it seems pretty obvious to me that it's important that people are able to make things with their own hands.

“I think most crafts are an art in themselves. I like hand-making useful and good-looking items out of products which are locally available and might otherwise go to waste.”

Read more in the latest issue of The Shed

 
Oscilloscopes PDF Print E-mail
Written by Richard Feltham   

Oscilloscopes: seeing is believing

An oscilloscope displays a changing electrical voltage as a visual pattern. We are all familiar with these devices, thanks to the plethora of medical television programs that show the poor patient’s heart monitor flatlining in ER as the struggling staff attempt to resuscitate him. This is simply an oscilloscope doing what it does best—measuring low voltages with great precision in real time.

If you invoke Ohm’s Law you can also obtain measurements of resistance, inductance and capacitance. The digital age has made these available at modest cost, around a few hundred dollars for a basic model. If you are using electronics in your shed in anything more than a trivial way then an oscilloscope is a valuable and incredibly versatile tool.

It moves into the essential bracket if you are dealing with complex waveforms and pulse timing from digital circuits. Being able to see what your Arduino programming is actually doing is a huge help in debugging.

Spurred on by the recent Shed article on quadcopters (“A drone of your own,” Aug/Sep 2014), I spent several enjoyable weeks building my own version. With everything tested and working correctly on the ground, I launched into the maiden flight, only to have it go out of control after 20 or so seconds and crash in the most spectacular, and terminal, fashion. The various flight controls had just seemed to stop working.

I recovered the radio parts and tested them with the oscilloscope. The aileron (yellow) and elevator (blue) pulses follow each other in time at a constant rate of 48.1630 Hz. With the stick in neutral the pulse widths are about the same, around 1.20 milliseconds (mS) in duration.

Read more in the latest issue of The Shed