So, we have now officially started on machine #2 ! This project will probably occupy us during the next weeks / months, and I would like to invite you all to comment on it as it goes along.
A few decisions about this new machine have been made, but plenty of stuff is still up for grabs.
We have learned a lot from our previous experience, and we'd like to put those lessons into practice somehow and get a grip on a more complicated machine in order to help us to learn faster (we'd learn nothing by repeating the same thing over and over again).
Here are the things we are sure about:
- this will also be a 16 ' machine
- we will again aim for 2400 watts at maximum rotor speed (before feathering kicks in)
- it will be a 3 blader
- it will be an upwind machine
- it will have a frame rather than a tubular housing
- low wind and high wind performance should be maximized (#1 will do the one or the ohter but not with the same configuration)
- it should operate totally safe unattended
- it will have active pitch control
- it will - eventually, not at first - be a tailless machine
- it will be a 'zubbly' style conversion machine at heart
The reasoning behind the various choices is not always driven by 'keep it simple' here, that much is obvious, we want to learn as much as we can and what we're trying to do here is to make a scale model of a 'large' utility type windmill.
These machines are usually in the 1...2 megawat range, and obviously we will not be able to get that much power out of a 16' rotor, but we do believe that it is possible to make a fully functional model of a machine like that.
The biggest advantages compared to the 'current' machine are that the active pitch control will allow you total control over the pitch of the blades at any given RPM, it will even allow dynamic adjustment of the pitch from the ground as the machine is turning.
This will also allow you to start up 'coarse' and then to move to finer pitch as the rotor speeds up and gets more efficient.
To start this project we decided to go and look for a suitable motor to convert, and then to make a new shaft (much thicker than the original) and rotor for that motor.
After talking to Zubbly he suggested we look for a 215 T nema frame, and while shopping around we found one just like that in the local motor rewinding shop (a 215 TC actually) with burned out windings that we could take home for free. It has an aluminum housing which should facilitate cooling, and a 'through' shaft, which will make it easier to attache the pitch control unit to the back of the shaft.
We spent a day and a half to remove the old burned out windings and clean it up, and in parallel to that we have started the fabrication of one half of the rotor.
The rotor is going to be a 12 pole job, with 1x2x.5" magnets on them in two sets of 12, for 24 magnets in total.
The rotor will have 13 flat sections (drawing is here), the 13th is a half section to reduce cogging.
The rotor is split into two parts to allow us to rotate the halves with respect to each other to pick the least cogging configuration.
The first half is now ready to be milled on our newly acquired little indexing table, which we hope to get to tomorow.
pictures follow:
The industrial motor (10 HP, 4 pole, Lincoln Electric 440/220)
The front side bell
The rotor (fan & end bell still attached) notice the fire damage on the back side!
The burned out guts:
Stripping out the wiring (we couldn't put it over a fire because it's aluminum!)
Now how did that pile come out of those little slots ??
machining the inside bore for the shaft in the new rotor: (to 50 mm)
Cleaning up the outside:
The finished rotor blank, ready for milling (sitting on the index table, but not yet attached to it, I still need to drill some holes for that):
