Hello there fellow fieldliners,
So, its been a good two years since the blue machine ran last, it's been sitting on my garage floor ever since waiting for a place to be used again. I messed it up during transport so it will need a new pivot shaft and new sliprings but nothing that can't be fixed.
At the prodding of 'dinges' (hi Peter!) I am writing this little post scriptum on what my ideas are on the way the blue machine performed and whether I consider it a success or not.
The short answer is NO. It is not a successful design.
It's shortcomings are:
- oscilating while feathering the prop
- noisy
- no failsafe mode can be found using this feathering system
- it did not produce the design goal of 2.5 KW at 350 RPM
The good parts are:
- it survived some pretty heavy winds without coming apart
- it didn't burn up when shorted out even in very high winds
- nobody got hurt
So, why so harsh a judgement ?
First of all this machine was a prototype and a study. I had never before made a full scale windmill and I figured that the only way to learn is to build one. 18 months of very hard work by quite a few people went into that machine and I'm still surprised that it actually worked.
The bad part really is (for me) the fact that no failsafe mode can be found.
What this means to me is that any single component of the governor can fail and the machine should immediately go coarse pitch. There was one glaring omission, a damper for the spring. I figured that it wasn't going to be a big deal and boy was I wrong.
On one occasion the mill almost pulled a barrel full of concrete out of the ground when going 'coarse', not a good thing to put it mildly. Adding a damper would have taken care of that behaviour, there would have been some 'hunting' but not this crazy cycle back and forth into the wind. The stresses on the tower were quite impressive and my buddy Laurences welding work performed over and above the call of duty.
This could have been resolved by adding a (hydraulic) damper. The problem with adding a damper though is that dampers are usually not designed to be swirled around all their lives. They'll lose some oil and sooner or later you'll be running without oil and the oscilatory behaviour will return. So you can't leave this machine unattended for a long time and that was what it was intended to do.
The noise was fixable as well, the biggest shortcoming here was that the trailing edge of the blades was too blunt.
The power generated was lower than the design goal because the airgap was much larger than I had planned, again something that is 'fixable'.
The new machine that we were building when we shut down our shop would have solved many of these issues, at the expense of some complexity.
Most notably it would have solved the failure mode issues. The basic alternator would have been a 'zubbly' style conversion, because zubbly convinved me that that was better from a cost point of view than an alternator from scratch. A solenoid actuated push rod would have pushed the machine from 'coarse' to 'flat' through an electronic control mechanism. Not quite as elegant as a fully mechanical governor but it would fail completely safe.
So, for everybody interpreting the story of the blue machine as a success story, it was for me, because I learned more from building it than I ever would have from reading books, but don't go and copy that design because as far as I'm concerned it is a dead end.
Also, please note that every windmill is a variation on a theme, and that nothing stands alone. There is hardly an original thought in windmill construction and without the knowledge and contribution of scores of people that machine would never have existed.
I have tried to literally put my money where my mouth was in building that thing and I think it makes me qualified to detail the shortcomings of machines of this type and closely related to it.
The best way in my opinion to get experience in this field is to go out and build something. Too many people have a nearly religious opinion on what is good and what is not in windmill design without ever having taken the time to go out and back up their words with actions.
To all the 'armchair' windmill experts:
Go out and practice what you preach, document it, post it to fieldlines and let us all be a part of your experience. That way we all collectively contribute to the amazing body of knowledge that this board represents and we can incrementally improve the quality of the designs in a way that no single individual ever could.
And if you have not personally verified a design then state so clearly whenever you are suggesting that others follow the information you are posting. There is nothing wrong with theoretical knowledge but I think it should be clearly marked as such.
best regards,
Jacques
