Big Prop II

[Timothy Barker]

This is the latest version of Big Prop which uses the Dynohub as a generator. The same blades are used as previously described but a wooden extension to the hub is now screwed onto the smallest of the two hubs (having nine holes). This then allows the blades to be more rigidly fastened to the hub extension and prevents less transverse osciallation (wobbling about) when turning. This is something to be avoided since essential energy is being lost. However, there is still some unwanted oscillation as the unit yaws (turns around) principally because the tail fin is not yet rigid enough and the upright is not tethered by lines, etc. The latter is of less concern as this is just a test rig at this stage but the tail fin design will have to be improved as it just looks way too clumsy when turning to face the wind direction. This version definitely needs to be in high winds due to the resistance on the dynohub so it does need to be quite a sturdy affair.

Placed in a prominent, high position this set-up should produce around 12 Volts it is hoped. This will be then be used to supplement a 12v solar array charging a 12v battery. Certainly the latter is proving quite inefficient at this time of the year in the UK. At this time, the skies are grey and the wind is rising! Here we can see a close-up of hub showing how the unit is bolted together. Its a good idea to be try to make the unit as easy to disassemble as possible. It eases maintenance plus means that should it need to travel, e.g. to a hill top, then it is a relatively less troublesome affair than permanently fixing pieces together. In this respect the dynohub itself is a great complement to this philosophy as it too can quite easily be dismantled - as we did - to maintain it.

And so, the experiments continue. Prototyping is a long and laborious process at times but it is also a lot of fun and, for sure, the 'end' product is always worth it. Although as to whether the methodology ever leads to and 'end' point is highly debatable!

[Timothy Barker]

Forgot to say that the new wood hub extension is the base from a 'mug tree' purchased from a charity shop for a pound. The centre hole was then widened with a couple of different sized files so that it fitted over the axle.