Thursday, March 20, 2008


Software Management
Interviewing software developers
... A suggested approach and sample questions
Agile development ... Survey of practical problems and suggested solutions

Software - Technical
Licencing ... Licencing scheme for software applications - with source code.
Help generator ... Windows help system generator - with source code.
Viterbi algorithm demo ... Mobile phone error correction - with demo application download.

Tuesday, March 18, 2008

Cute phrases

Amusing utterances from children

Isabelle (6): Q> How was school today, A> Splendid

Friday, March 14, 2008

Oar+Some - Physics Diversion

This is a diversion into some of the physics involved in water propulsion - and how it affects Oar+Some's design. Just for fun.

Why not use a screw, or water jet, or some mechanism that more naturally fits a pedalling action - with perhaps continuous rotation?

There are two good reasons.

Firstly, these alternatives require additional mechanisms or power transmission elements (chains / belts / gears etc. ) - and these all sap power, and add overall weight.

Secondly there's some fundamental physics involved, that comes out in favour of paddling or rowing - which is what I survey below.

It's called Froude Efficiency. I believe this was named after William Froude. To honour his work, not because he discovered or formulated it.

Screws, water-jets, paddles, oars etc. all drive a boat along the same way - as far as physics is concerned. They all take some water that was sitting there perfectly still until you came along, and push it backwards - creating what is effectively a continuous, rearwards flow of water. You can't push something backwards without it pushing you back the other way - ie forwards by exactly the same amount. One "Isaac Newton" is pretty un-equivocal on this - viz. Newton's Third Law. This is what make your boat go along.

The problem
The problem is that creating thrust by setting some water in motion wastes power. There is absolutely nothing we can do about it. It is a fundamental fact of physics to do with kinetic energy. If the water was still before, and you made it move - you have given it kinetic energy. Period. And there's only one place that energy could have come from. Your legs. This kinetic energy does nothing to propell our boat. It is pure waste. We'll come back to this. One thing is sure - we need to look for ways to reduce the amount of kinetic energy we give the water!

What about the thrust?
Newton to the rescue again; this time his second law! This law when applied to liquids, says that the thrust we are going to get goes up in line with how fast we make the water flow backwards, and also with how much water we do it with. So if we turn a blind eye to our kinetic energy problem, we want to get as much water as we can, going backwards, as fast as possible.

So we're stuck then?
Oh no we're not. 'Because of a square law'. It turns out that increasing the speed of the flow has a far worse effect on kinetic energy losses than the benefit it gives to increasing thrust. This is because kinetic energy goes up with the square of the speed. What that means in practice is that we must find a mechanism that creates a flow with the maximum possible amount of water, but with only a miniscule speed of flow.

Enter the oar or paddle
Oars and paddles are not just a happy coincidental evolution. The physics is with them! When you think about it, a big oar or paddle graps a great lump of water on each stroke and pushes it backwards. In so doing it is creating a rearward flow - but a nice slow one. Theoretically the bigger the paddle the better as that gets closer to the perfect physics solution - but practical limitations come - like the ease and comfort of handling. If oars and paddlles don't 'slip' a little in the water as you pull them - it feels all wrong.

Exit the screw and water jet
These are the opposite of oars and paddles in this context. They catch only a relatively small volume of water, but create a very fast rearward flow. This makes them gravely inefficient - but then that doesn't matter if your motive power is an engine, not a pair of legs.

Oar+Some- Propulsion

This is a description of the propulsion system for Oar+Some- which is pretty much the central feature of the design.

You might want to look at the video again - to be reminded of how the paddle moves.

If you look at the picture above, you will see that the rider has finished pushing with his left leg, and consequently the right paddle blade is towards the rear, and at the end of its power stroke.

During this power stroke the right blade remained securely under water at just the right depth automatically. This is because the blade is angled a few degrees off the vertical, and therefore the reaction from the water on the blade gives it a tendency to dive, but it is then constrained to not go too deep by a kind of string arrangement. The string (or tie) is not shown, but you can see the lugs for it in this picture.

During the power stroke, the water is pressing on the rear face of the paddle blade and maintaining this submerged position, but of course the rider's pedalling action is cyclic and the blade slows down and ultimately stops at the end of the power stroke. As this begins to happen, and assuming Oar+Some has some forward momentum already, the water now is pressing on the front face of the paddle, which causes it to rise out of the water. As the right blade leaves the water, the paddle's momentum causes the left blade to enter the water, and the rider times his new forward thrust with the other leg to this point - and so begins the power stroke on the other side.

Oar+Some - Prototype story so far

The most important thing to try out is the novel (and key) propulsion idea. So the first prototype step was to make a simple timber chassis on which to mount an experimental pedal bar and oar assembly.

The first challenge ...

The cross beams have insufficient torsional stiffness. They don't deflect downwards problematically, but they twist forwards excessively - due to the rider's weight being significantly forwards of the structure.

Of course the timber chassis bears little resemblence to the triangular crosss section in the more detailed design - but that too is unlikely to be stiff enough in torsion and a re-think is needed.

The optimum structure to bear twisting moments is a circular cross section tube. So how do we integrate this with a structure that can also cope with the vertical loading - while remaining in our space envelope and being as light as possible?

Here's my idea - see picture. This is a minature cardboard model - intended to quickly and cheaply explore the stiffness and strength of this structure. It combines an I-beam and a circular tube co-axially, with the loads being presented via flanges with annular bonding to the outside of the tube.

I've been pleasantly surprised at the performance of this model. Take a look at this picture. The minature model is only cardboard, and weighs just 3 oz = but it can cope with the considerable weight of 5 litres of oil - with no perceptible deflection.

So the next step is to make a full size prototype chassis based on this structure - which is the point I've reached - and the status quo!

Oar+Some - A fast pedal driven catamaran

Oar+Some is a boat concept and design project. The quickest way to get the idea is to view the video, or the browse the pictures. In essence it is a human powered (you pedal it), catamaran designed for speed. Think of it as a top notch, high performance touring bicycle for water.

Design goals
To aspire to the straight-line efficiency in the water of a racing kayak or rowing shell. To exploit human leg power, comfort and endurance. To provide a facing forward sitting position. To be sufficiently stable for non-experts to use. To have very low power transmission losses.

Current status
A concept is designed - including a novel propulsion system using a semi-automated oar-paddling action. This has been detailed to an extent in 3D CAD - as a communication and 'buy-in' medium. This is where the 'virtual' photos and video come from. Prototyping and validation of the key concepts has started. Early consultation with water sports experts and manufacturers has taken place.

Take it on - get involved - collaborate - help!
I have decided to turn this over to being an open and collaborative project. This act of placing the design in the public domain means that no-one can now patent it ! (Patent law). Anyone is welcome to take the idea forward in any way they want to. If like me you are chiefly interested in validating and developing the design - please get in touch, or go your own way and keep me informed. If you are an entrepreneur and think there is money making potential - by all means go for it - but I would appreciate being kept in the loop.

The propulsion system
This is the key unique feature of Oar+Some. See the dedicated page describing the propulsion system.

The story so far - prototype
See dedicated prototype page

A physics diversion
Interested in some water propulsion physics? - here's a brief discussion of Froude Efficiency.

Hobie's competitive pedal power system
The water sports product company "Hobie Cat" have a product for pedal-powering kayaks - called the Mirage Drive system. It is a stand alone kit that can be fitted to existing boats, and converts your reciprocal pedalling action into a wave like motion of fins under the hull. Very interesting. See their Mirage-Drive site here.

Thursday, March 13, 2008

Viterbi Demo

The Viterbi algorithm is used in mobile phones to remove noise from the received signal.

Demo application
The screenshot shows a demo application - written in C# / .Net as a learning exercise.

Download ... Download and run the demo application (double click on 'setup.exe' inside this zip file)
Article ... A more detailed article

Pete's Piano - Software Development

Please see the new dedicated site

Engineering and Design

Under construction

Home Life

A celebration (mostly) of family life.

Cosy Nocturnal Adventure Taking daughter to airport

Soggy Story 6 year old writing, 11 year old singing

Amusing utterances Funny things our children come out with

Macavity take 2 Feline adventure story

Cosy nocturnal adventure

3:30 am, driving my 9 year old daughter through the city to the airport. She's off to a gymnastics competion in Portugal with her club.

So many pleasures. Special companionship of just one of the three daughters alone. half asleep in the vaguely menacing night-time urban scenery. Lovely swooshy drive through the empty streets. Bright eyed enthusiasm of the other children as we gather. Paternal pride in her sporting accomplishements. Esprit de corps, and gratitude towards the coaches and judges. She rings at 0930 to say she's arrived, and that it's all sunny and warm. (Unlike here).

Soggy story

How can life with children be anything other than just brilliant? Stupid assertion that really, but I hope you know what I mean. The eleven year old daughter is practising a song for an audition. I have to make an effort to take an interest - but I'm so glad I did - the joy she's getting from the feedback and the anticipation is heart warming.

The six year old has quite suddenly latched on to writing (barely comprehensible) stories - removing sheets of paper to scribble on from the printer at a rate of about one every five minutes. She's gets rather fixated by such enthusiams (just like Dad) and quite happily writes while the breakfast "spoil" seeps up through the paper.

That's getting your priorities right. (comment from Ali (wife) - you rotten liar, it drives you up the wall really) Ok I'm torn.