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Treadmill Motor PVC Blades | 49 comments (49 topical, 0 editorial)

Re: Treadmill Motor PVC Blades (3.00 / 0) (#15)
by packman1234 on Wed Aug 6th, 2008 at 04:12:39 AM MST
(User Info) packman1234

So much info here..

I guess my question is this- Should I try making a mark 2 inches in from the root on the leading edge and draw a line on the existing blades to shorten them to 24inches? If so- How wide should the tips be?

Or...
Should I start over with 4inch pvc and make them shorter than 24inches? Would I just cut the 4inch in half and use the halfs to make quarters? If so-where would I draw the line to narrow them?

It all comes down to this...The wind speed here averages 9mph. I need something that would be useful in slower winds and still be able to charge a battery or two- Can I do this or is this a waste of time with this motor?

I also have a woodshop in my basement and have not ruled out making wooden blades out of laminated hardwood...what are your thoughts on all of this???

Thanks for all the great info!

Bob

[ Parent ]

Re: Treadmill Motor PVC Blades (3.00 / 0) (#17)
by roadranger (Road Ranger at G Mail dot com) on Wed Aug 6th, 2008 at 11:28:05 AM MST
(User Info)

The amount of power in the wind rises at the cube of its speed. A 30mph wind has 64 times the power as a 7.5 mph wind. To get 100w at 7.5mph would need a windmill with maybe a 24 foot rotor and 6+ blades and a 32:1 gearbox. Below 10mph solar would be a better solution.

Oh, and most folks say wooden blades are way better (2x ?) than pvc - but I don't know of any comparison using a properly calculated PVC rotor. A properly carved blade will always outperform any "pipe blade" but I don't know by how much?

Cutting a PVC blade that "looks good enough" as the how-tos show and expecting optimum results seems a bit silly to me. If you are interested in seeing the most annoying presentation of the proper design of a pvc blade you are likely ever to see check this out:
http://www.youtube.com/watch?v=BawUfbDDvtA
I calculated mine in a similar fashion but i think I compensated for a couple issues he overlooked. For instance, how you sharpen the trailing edge has a large effect on the blade angle, especially out near the tip which can be going 160mph in a 20mph wind!

[ Parent ]

Re: Treadmill Motor PVC Blades (3.00 / 0) (#18)
by packman1234 on Wed Aug 6th, 2008 at 04:59:47 PM MST
(User Info) packman1234

Roadranger

That video turned me off!

In your opinion, should I scrap this idea(Thats all I really wanted to know)
I would like to try something with it and was hoping for a more doable solution with the 4inch or cutting the existing blades shorter and narrower.. Could I try that and see what happens..
if you had this---what would you try to at least get it to spin in a 10mph wind.

Thanks for your opinion

Bob

[ Parent ]

Re: Treadmill Motor PVC Blades (3.00 / 0) (#21)
by roadranger (Road Ranger at G Mail dot com) on Wed Aug 6th, 2008 at 07:56:44 PM MST
(User Info)

It really should at least spin as-is in a 10 mph wind. I'd first try to balance it better using a piece of shafting and a couple ball bearings. Some have taken their motor apart and just used the armature with it's bearings to balance with but you'd have to convince yourself that you know how to get it apart and together without messing up the brushes. Then with this motor I'd try the 3' version of my rotor first. Then if you are up to carving wooden blades I'd search around a bit for the measurments and go for a 3' rotor designed for a TSR of 8. I don't think a 4' rotor can ever be fast enough to work well under 15mph.

Where did you get your motor? The eBay 130V "windmill" motors are all 6750rpm which is completely unuseable!

[ Parent ]

Re: Treadmill Motor PVC Blades (3.00 / 0) (#23)
by packman1234 on Wed Aug 6th, 2008 at 08:06:40 PM MST
(User Info) packman1234

I got the motor out of a Sears treadmill that my sister had.
I took it apart a few times to replace the two bracket mounting screws and see what it was all about..No biggie playing with this-Very strong magnet and sucks the case end in super hard and tight!

Bob

[ Parent ]

Re: Treadmill Motor PVC Blades (3.00 / 0) (#25)
by roadranger (Road Ranger at G Mail dot com) on Wed Aug 6th, 2008 at 08:16:06 PM MST
(User Info)

Just for reference this is the "originally spec'd" motor:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=220008972818

[ Parent ]

Re: Treadmill Motor PVC Blades (3.00 / 0) (#28)
by packman1234 on Wed Aug 6th, 2008 at 08:39:05 PM MST
(User Info) packman1234

Thats not even close to the one I have,,,specs are but hub is bigger and not threaded.
Mine is 2.5hp at 130v at 3200 rpm

[ Parent ]

Treadmill Motor PVC Blades | 49 comments (49 topical, 0 editorial)

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