Three years ago, during my last year at school back when neodymium magnets were actually affordable, I made a 3m diameter wind turbine incorporating active pitch control. At the time there didn't seem to be much on forums discussing these things, so I never got round to posting it and had difficulty researching. I'd pretty much forgotten about it as I've not got space to use the wind turbine at home, it's just lurking under my CNC router (
) which I will one day use to make the blades. I recently happened to notice the thread here about someone having made one with active pitch control, so I thought it was about time I posted my version.
This is how far I got with it:
I machined every part on the wind turbine using manual lathes/milling machines, except for the gears and the magnet rotors and stator bracket which I got laser cut.
Here's a video showing the construction of the PMG and me testing it as a motor (well why not...) using the ESC and transmitter from my model car, with a few pictures of the start of the blade hub:
It's the standard 2x1x0.5" magnets...cutin speed is about 130rpm (13Hz). Used Femm to aid the design, but it wasn't really required. I did couple it to a bridgeport milling machine with two 92Ah 12V batteries and a rectifier, wired in star, to test the PMG. My readings were OK up to around 800W where the coupling started slipping, hence the anomalous result in the graph below. I did get it up to 1.2kW but couldn't get reliable RPM readings at that speed, but that's not a big deal as clearly the thermal conductivity of the stator is too low for it to run at this speed for more than a few minutes. I'm not intending to use such a crude system when I actually use the wind turbine. Hopefully one day I can do a better test:
Anway, here's the blade hub, early stages:
Later on:
As you can see I used a stepper motor in the hub to drive the blades via a worm gear, so the motor current could be reduced when the pitch is fixed and bevel gears to link all the blades. Each blade will be mounted on the stainless steel shafts which pass through 3 deep group bearings and a thrust bearing. I'll make the blades from fibreglass using a mould I will make on my CNC Router, which I made about 2 years ago and still haven't got round to using for the blades! Might use it to make some nice blades from wood one day, who knows...I did make some 700mm blades from fibreglass using a mould I cut on the router. They seemed very effective.
Drawings (disregard the blades, they are out of date):
Plan was to have some sort of slip ring or rotary transformer to transfer the power from the generator to supply the motor and electronics in the hub, with a battery in the hub for obvious reasons. I designed a board which uses a PIC to do the control based on measuring the frequency of rotation via an accelerometer or zero-crossing detector.
I made a paramaterised model of the blades in Solid Edge linked to a spreadsheel. Subsequently I put it in Matlab and finally VB ... unfortunately I can't find the latest drawing, but my smaller wind turbine has fiberglass blades I made using this process:
http://www.youtube.com/watch?v=FJ1yrMSFPQI&feature=plcpThat was for a smaller wind turbine, I put a video of it on YouTube.
Looking back, although I did calculate the required sizes for some parts to obtain sufficient strength, I realise now I should have made some bits a bit more substantial for this size turbine - in particular the worm gear I made is a bit small. I'm not sure why at the time I decided not to use the method with a linear actuator as that's bound to be easier than my method. Maybe I should make a smaller one so I can actually use it, since unless my mum moves house I'm not likely to be able to test it! I'll post some drawings of the concept here first if I do, but I would base it around using a ballscrew to make a linear actuator as that would be compact, provide plenty of force with negligible play and require very little power to drive.
I think that's enough, if anyone's interested I can post more pictures and drawings or whatever really. Please note not all of the images I have posted are up to date.
