Why doesn't Hugh use disk brake rotors ?

[daleh007]

I was looking at the plans I got from Hugh Piggot and noticed that there are 2 12" dia 5/16" thick steel disks used to mount the magnets. They use a disk brake hub and spindle to mount these disks to and I was wondering why they don't just use the disk brake rotor itself, especially since it's already got the mounting holes drilled.

Daleh

[hiker]

when they first started out --they used the brake disk--now they use a lighter disk..

[DanB]

Actually I dont believe Hugh was ever using brake disks in his design.

His older design was a radial field unit and used a brake drum.

I think he prefers not to use brake disks... perhaps because, if you had to buy them new they would cost a bit - and often times the holes in the disks, and the holes in the hub are different sizes.  and the brake disk weighs quite a bit more than it needs to, so by cutting disks from 5/16" steel, you save some weight... and you build the whole thing from scratch.  Odds are I think, if you have the tools and resources to build the rest of the machine, you can get a couple disks cut out.

I like to use brake disks because it seems I have a nearly endless supply and it does make things easy - but there are other compromises involved.  Im not really sure if more weight in the rotors is a good... or a bad thing.  Of course, it would spin up a bit more slowly - but it would also slow down more slowly!  The added weight may also make it yaw, and furl a bit more slowly which also has it's own set of pros and cons.

[nobicus]

There is a brake disc rotor shown on this site where the holes on the hub and discs line up, as they are all Volvo.  The cost of a pair of the Volvo 850 discs in the UK, new from a company called "German and Swedish Car Parts" is $23:62 plus delivery of $8:75.  I don't know how much it would cost to have a local engineering firm cut and drill a comparable pair of discs much more I suspect.

[dconn]

That does seem very cheap - 5/8 inch disks cost me a lot more to have laser cut and holes drilled.

Are the disks 12" or smaller (740 disks are only 11") and I'm not sure if there is enough space for the 2 X 1 inch magnets (I mean 2" between the hub and the outside of the disk) - Hugh Piggots plans say 12 1/2" disks I think.

The other thing is that the cast brake disks seem to rust quickly - if you are not by the sea it may not be a problem.

Derek

[nobicus]

As a new boy who has yet to get Hugh's books I have been collecting info where I can preparatory to attempting my first windgen.  There is a great series of photos with text showing the building of the Volvo disc generator.  I merely started to cost up what a windgen is likely to cost and got the prices for discs. I presume that as standard discs they will rust as they do on the car.  Presumably the fibreglss resin that is put on over the magnets will tend to either slow or stop this.

[daleh007]

 I have seen the Volvo plans using the disk brake rotors and that's what sparked my question about the Piggot plans not using them. I also thought that the fiberglass resin would help to protect at least one side of the brake rotor and I suppose you could always paint the other side. Old rotors are cheap and/or easy to find (heck my brother has 3). So if you are using the matching hub/spindle assy. it seems like it could be much easier and potentially cheaper to just use the brake rotors. So far I see no compelling reason not to use them.

Daleh

[scoraigwind]

Just caught up with this one.  I suppose the answer is that its simpler to start from scratch.  

I designed the brakedrum machine, and thought it was really neat to re-use automotive parts, but people trying to follow my plans seemed to find it very hard to get the right brakedrum, the right laminations etc etc..  Most folk on this list would use what they can find and be adaptable but those who buy plans seem to like to follow them to the letter in many cases, and they can get very upset if they cannot find the right stuff.

So instead of using recycled stuff as I always loved to do before, I decide to try to use stuff that everyone could buy.   At first it was a hassle buying steel disks and drilling them and so forth but it gets easier and cheaper to have them laser cut as time goes by.  I have just ordered ten disks cut with holes in them and everything for ten pounds each (which is 18 dollars but doesn't usually buy as much).

Secondhand brake disks would cost less or nothing but mostly the ones I see in scrap yards here are too small and the wrong shape and do not look as if they would carry the flux anyway.

So those are the reasons why.  I don't have a problem with other people using them in fact I admire the use of recycled parts but it just didn't seem to work so well for what I was doing.

[nobicus]

As the really new boy let me explain.  At 63 years old it is some 45 years since I read up on any physics and electricity.  Not only have I got to relearn what I have forgotten but also learn new terminology (I still don't know what cogging is yet!!!).  BUT I do want to make myself a windgen - for a multiplicity of reasons.  Is is much easier to follow, almost slavishly, the plan from someone like Hugh, the world's guru on home windpower, than to learn stuff first.  I want to know how you calculate what thickness of wire to use together with how many magnets so that I can solve my own problems but I don't need to know this to follow a plan - if it says ten coils of x then that's what I'll make.  Hugh's plan shows fairly cheap magnets the Volvo rotor needs 24 circular magnets at $20 each - $480 for my first imperfect windgen would be too much to stomach.  But I am sure that there must be a way of calculating what to do to use cheaper magnets even if it produces less power (I can always build two windgens!!!) but to have to stop and learn this would put the construction of a windgen further away and probably into next year now that winter is coming.  Building to a plan allows me to do it immediately.  

[DanB]

Hi nobicus -

In qty's of 24 (which is what you need for the dual rotor machine) we sell the 2" X 1/2" disks for about $10 ea...  so they are not that expensive, althought he 1" x 2" X 1/2" magnets are much less expensive, about $6.50 ea.  I'm finding, that unless the line is very long and resistive, that the 2" diameter magnets make for an alternator which is too powerful for the 10' prop - they seem to work pretty well with an 11' diameter prop.. Im trying a 10' machine now with the 1" X 2" magnets and the rotors look exactly like those in Hughs plans.

If you want to follow plans, which are well proven.. and well sorted out and have good details about every step along the way.. I'd suggest getting Hughs plans.  What I put here on our website - are not plans, but just some documentation about my own experiments which are very much inspired by Hughs plans to begin with.  I guess my goal is to make use of available scrap parts, and build a somewhat larger version.  So far... after a bit of tune up and adjustment, most of the machines we've made here are working pretty well... with 1 big exception (Which is unfortunate) - our freind Scott, who recently upgraded his machine with a 50' tower and an 11' diameter prop had a failure last week... he was lowering his tower to reinforce it, and it broke... - the machine came crashing down.  I've not seen it yet - more to come on that!  I guess we cannot blame the machine for that - I suspect the blame lies with the rather light weight 2" pipe which he used - it was salvaged from an indoor sprinkler system, it was too small in diameter and too thin, my guess is that's where the problem arose.

[nobicus]

Thanks for that - back for the eyetest again!!!!!!

I would not want a 50 foot tower as my first foray into windgen.  I am looking to have a scaffolding pole tower of about 20 foot. Also 10 foot diameter is a bit large as a starter for someone who has never carved a prop.  I shall be posting my little cheque off to Hugh today and will order both his books. (I shall be able to impress my friends and relatives by talking about axial flux as if I understand what it all means!!!!!)

[DanB]

Excellent!  Your in for lots of fun reading ...