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I have been following the Back Shed site with great interest for some time now and am very impressed with the enormous effort and expertise shown, great job. I am now excited about my own project, thanks to Geoff for sending me a F&P motor to myself here in Canada (it took nearly 4 months), I am ready to start assembly. Today its now -30C outside, great time for a project.
I am making a few deviations from Glenns plan, partially due to the imperial measurements used in the materials here and partially because of the materials at hand. I do not think this is a concern as long as I keep this in mind for the calculations for furling. However I have found a couple of problems with my calculations. It appears to me that the numbers in the furling section must refer to the earlier kit since the inputs for the formulas do not fit my design. My values come out quite different and I believe they are not correct because the tail pivot offset is greater then the turbine offset. For example; I think if the tail pivot offset is twice the measurement of the turbine offset as measured from the mast axis, then due to leverage, the force required to lift the tail from the stop would be half the force indicated the furling formulae page. Does this sound reasonable? Also 20 Kg seems like a lot of wieght on the tail, I would like to get it closer to 10 or 15 KG.
My calculations came up with;
- Turbine Offset=0.0625m
- Tail to mast axis offset=0.095m
- 55.8 kg Turbine Thrust
- 3.488kg Turbine moment
- 2.418kg Furl Resistance
= 1.44m tail with a wieght of 10kg
I am excited about Glenn's new design for staged loading using varied number of coils. I think it has promise to make the output greater with the lower wind conditions that we normally get at our lake(in a forest). I will not use a dual rotor design due to the cost of shipping another motor here, however I thought a 3 stage design might work for a single rotor.
-First stage - one 3 phase Y configuration with 4 coils for light winds.
-Second stage - three 3 phase Y configurations with the normal 2 coils and
-Third stage - 2 delta configurations with 2 coils for heavey winds.
I will be using PVC blades simular to Glenns only made from 20.5mm pipe and my length will only be 94mm (I made a mistake of only getting 3 feet of pipe). I was going to make 3 blades however I noticed that Glenn used a 6 blade configuration for his new turbine. I beleive this will provide greater low wind torque but sacrifice higher RPMs. Any advice?
John
brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548
Posted: 08:09pm 20 Jan 2008
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Hi John ,welcome to the dreaded hobby of building wind-gennies !!.
I think you may have told us the wrong dimensions and length of your blades.. My abs plastic blades are approx 4 feet 6 inches long ,making a dia of nearly 9 feet. These were cut out of 15 inch dia pipe. I'd suggest you make your blades around this size,as the F&P seems to need and perform best with "largish" blades..
The 3 stage stator windings seem to sound good ,,I've not tried any of them yet,,just the straight forward re-configuration of the coils.
I've noticed the power output is better if you convert the rotor into a Neo magnet rotor--but thats another story.
Best of luck in your adventures,
BruceBushboy
wind-pirate Senior Member Joined: 01/02/2007 Location: CanadaPosts: 101
Posted: 03:53am 21 Jan 2008
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Hi John
I noticed your tempature is -30. You must be from Sask too. If your not to far from me, I would like to see how your F&p works.
THE Pirate.
stealing wind & solar energy is fun
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669
Posted: 04:56am 21 Jan 2008
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G'day CanTinker2,
Welcome to the forum.
With reference to,
I can see your uncertainty over the figures and I have to agree they do not seem right. I have recently done some furl testing using these figures and the tail weight seems awfully high to me. I have been through the figures many many times and in greater detail than the simplified version presented on the Furl Page and the only area I have difficulty with is the calculation of the force on the prop. I have researched this part of the formula and cannot find one that I would hang my hat on. In fact the one Glenn uses is the least understandable with no apparent relation to the accepted formula.
A common formula for prop loading is for construction calculation of tower and guy wire loadings where it is acceptable to consider the prop as a solid disc. This produces a far greater loading than reality, and, whilst suitable for that purpose, produces a huge tail weight when used in furling calculations. I do wonder if that is the case here but as I have said, I cannot find one that I would rely on and at best it could only be a guide as props vary in design so much in spite a matching diameter.
The tail offset you refer to has little bearing on tail weight as the resisting moment is from tail to yaw bearing times it's horizontal force, and any offset even if twice the prop offset makes so little a change to the tail moment that for simplicity is not included. I think you may need to study the forces and relationships a little more, but you are right in that the tail weight calc is too heavy.
With my furling adjustments I ended up putting the calculations aside and completed modifications using road tests.Edited by Gill 2008-01-22was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
Thanks Bruce
Before purchasing my pipe for a guide, I was using;
1. The Back Shed site, the wood blade plans for F&P generator are 1m long, and
2. In the forum Glenns design had 6 PVC blades 1.1m long for his dual motor generator.
I did think my blades would be just a little short, but yours are much longer. Its my understanding that the longer the blade the lower the RPM. Do they still get the RPMs up for good output?
Wind Pirate
I live in Winnipeg Manitoba, so we are fairly close depending on where you are in Sask, however I plan on using at our place at a lake north of Lake of the Woods. Please email me, my address is listed in my profile. I am also interested in your wind plans, I might come take a look if its not too far. Have you any experience with PVC in the cold? My wind generator is still in the construction stage however I am enjoying the challange and opening books that I havn't looked at for a long time.
Thanks Gill
I was worried I had made an error. I think I will take your advice, research a little more. I am starting to get anxious though, so I don;t have too much luck I will build it and then fine (or course) tune the furling later.
As I mentioned, I got the F&P motor from Geoff and he has been a lot of help. He had mentioed he built his generator from the Back Shed design and his tail was much lighter as well.
As for the staged cut in design I mentioned, I am having second thoughts about the third delta 2 coil. My calulations show it may not start charging a 24 v system until the winds are very strong and probably not a good choice in the long run. Has anyone tried a delta 3 coil design? My system is currently 12 VDC however I would like to test it on a friends 24 Volt system as well.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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