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Update! 7.5HP Baldor 12 pole conversion rotor completed
By zubbly, Section Homebrewed Electricity Posted on Fri Jun 16, 2006 at 08:29:45 PM MST
there are 10 pictures to view (warning for anyone on slow dialup)

hey guys!
i completed my rotor for the 7.5hp Baldor conversion today. i drilled and threaded a total of 48 holes (8/32 SS screws). i then put locktite thread locker on all the threads and even a little under the mags. not sure if the locktite will stick to the epoxy coating on the mags, but they are very secure with just the screws.
about 6 months ago (maybe longer) i gave my ideas about magnets to a canadian supplier. i always wanted the 2x1x1/2 mags with 2 holes in them and then countersunk to accept tapered head machine screws. i also explained how the old #29 style curved magnet would make small conversions with a skew very useful for helping to defeat the cogging issues which have always been a problem to deal with. Kenny Dyal, the supplier on E-Bay known as "tropical_son" took my ideas to heart and had them made. they have greatly helped my efforts to develop a good motor conversion. Thanks Kenny!!
the rotor has a total of 24 mags (N40 grade). they are zinc coated and then epoxy coated. you must be careful mounting them as the epoxy coating is very tender. just my opinion, but i think they would also be great on dual rotor gennys with no need to use a resin filler around the mags.
i painted the ends of the rotor, and also the new shaft to stop any future rusting. i made a few scratches on the mags while installing them, so will also give the whole rotor a good coat of clear high heat engine enamel. for the first, i assembled a rotor and didn't get even one blood blister. LOL!
here are the pics.

the next step is to install a new set of bearings. this rotor has a 6307 bearing on the drive end and a 6206 bearing on the opposite drive end. next thing after that is to install a one turn test winding, do a lathe test to gather data to calculate the new winding.
hope you enjoyed the update! :)
zubbly

Update! 7.5HP Baldor 12 pole conversion rotor completed | 33 comments (33 topical)

Re: Update! 7.5HP Baldor 12 pole conversion (3.00 / 0) (#1)
by dinges on Fri Jun 16, 2006 at 02:43:34 PM MST

Very nice!

I definitely like the idea of bolting the magnets down with SS screws. To me it seems like a more reliable solution than just epoxy to keep them on the plate. Also for axial flux gennies, like you said. Or you could do both, epoxy and 2 screws. Belts and braces, so to speak.

Noticed that one of the bearings on your 7.5HP motor is a 6206; I have the same ones on my 3HP motor... That 6307 is a bit beefier, of course.

Very interested in the power it will output. Hope you exceed 'Zubbly's law' (150W/cubic inch). Made some quick calculations on my 3HP conversion, and no matter what I do, I can't fit more magnets in than what will deliver 580-620W. (I can get 15x8mm ones and 12.7x6mm ones; I'm going to use the last ones, but would prefer ones a bit higher, like 12.7x8mm).

Was the price of the magnets comparable to normal 2"x1"x.5"? I like them!

Peter.

Re: Update! 7.5HP Baldor 12 pole conversion (3.00 / 0) (#5)
by oztules on Fri Jun 16, 2006 at 05:18:45 PM MST

Before any dejection sets in regarding the power output, what rpm are your calculations based Peter.?

I notice that Zubbly has added a few insurance welds to the rotor/shaft interface, may be a good idea for others to pickup on if their interferance fit is a bit dodgy.

Will look forward to both your Diary and Zubblies conversion being completed and tested.

...........oztules

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion (3.00 / 0) (#6)
by dinges on Fri Jun 16, 2006 at 05:32:00 PM MST

No calculations, Oz, just applying "Zubbly's law". Have no idea at what RPM this applies. BTW, have re-designed the rotor so I should now get 930W max. Am really curious whether my real results will reflect this law and how well it complies.

Zubbly, I am faced with a big (theoretical) problem regarding skewing. Please see my diary with a question to you (post #40). VERY interested in your opinion.

Peter.

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion (3.00 / 0) (#10)
by zubbly on Sat Jun 17, 2006 at 06:25:05 AM MST

hi Oztules,

i really didn't plan on welding the rotor to the shaft, but when i had the mig out to weld the internal cooling fan back in place, i said what the hell, give it few shots there as well. like you say "insurance" :)

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion (3.00 / 0) (#9)
by zubbly on Sat Jun 17, 2006 at 06:21:49 AM MST

hi Peter,

i think the mags with the holes sell on ebay for $150 (quantity of 24). he also sells the regular 2x1x1/2 mags for the same price i think.

zubbly

[ Parent ]

RE (3.00 / 0) (#2)
by A6D9 on Fri Jun 16, 2006 at 02:56:13 PM MST

enjoy would be an understatement, congrats zubbly, and very very sexy looking,

do you ever sell your conversions? if so I would be very interested in prices. they are so well done.
Thanx Darren

Re: RE (3.00 / 0) (#3)
by wind pirate on Fri Jun 16, 2006 at 03:25:07 PM MST

Excellent Zubbly!!

You've evolved motor conversion to a functional art form like Dan has with dual rotors. Great job and very sexy.

I would be interested if you were to sell any of these conversions as well.

Thanks for all the great info.

Wind Pirate

[ Parent ]

Re: RE (3.00 / 0) (#11)
by zubbly on Sat Jun 17, 2006 at 06:28:09 AM MST

i have sold a few gennys in the past.

i do have extra baldor motors which are very similar to this one. if this one proves out good, i may make up a few other units for sale. i have no idea on what the price would be at this time.

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion roto (3.00 / 0) (#4)
by WXYZCIENCE on Fri Jun 16, 2006 at 05:11:14 PM MST

Zubbly, did you machine a new rotor for the conversion? Joe.

Re: Update! 7.5HP Baldor 12 pole conversion roto (3.00 / 0) (#12)
by zubbly on Sat Jun 17, 2006 at 06:32:18 AM MST

hi Joe,

i did make a solid rotor from cold rolled steel and then machined the flats on it.
the shaft is made with high tensile strength material.

just eyeballing the original rotor, i am sure i would have ended up under the depth of the aluminum bars in the original rotor. so i decided to go with a solid rotor from there.

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole (3.00 / 0) (#7)
by willib on Fri Jun 16, 2006 at 05:42:45 PM MST

Mr Zubbly it looks very sweet , i for one can't wait for the test coil .
what will it look like?
how many turns are you gonna use?

Carpe Ventum (seize the wind)

Re: Update! 7.5HP Baldor 12 pole (3.00 / 0) (#13)
by zubbly on Sat Jun 17, 2006 at 07:28:51 AM MST

hi Willib,

i never use just one coil for the test winding to calculate the full winding. that method does work well, but i alwyas like to have the full reaction of the complete rotor and stator to base my calcs.

i simply install a complete winding with one turn. basically a wave winding. this way there is no interconnections in the phase. i then join the 3 beginnings from the phases as star and take my readings from the 3 ends of the phases.

wave winding is very simple for a test winding. start in slot 1 and go back in slot 4, go back up slot 7 and come back in slot 10. once phase A is done, start phase B in slot 3 and continue to slot 6 and so on. start phase C in slot 5 and continue to slot 8.
its that simple. total wire used will be much less than using one full coil and calculating from that.

thats kind of a quicky crude diagram for the test winding. but its that simple.

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole (3.00 / 0) (#30)
by willib on Sun Jun 18, 2006 at 10:17:33 PM MST

huh , that was clear , thanks
any results? i know it was fathers day , but where are your priorities man . :)

Carpe Ventum (seize the wind)
[ Parent ]

Re: Update! 7.5HP Baldor 12 pole (3.00 / 0) (#33)
by vawtman on Sun Jun 25, 2006 at 07:15:31 AM MST

Hello Zubbly
Ive got some no. 14 on hand could i use it for the test and then go 2 inhand no. 17 for the final?

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion roto (3.00 / 0) (#8)
by wdyasq on Fri Jun 16, 2006 at 06:06:07 PM MST

I'll fly over and take a look.

Ron
Adventure is just bad planning." -- Roald Amundsen

Re: Update! 7.5HP Baldor 12 pole conversion roto (3.00 / 0) (#24)
by RP on Sat Jun 17, 2006 at 11:34:45 PM MST

Good one Ron.

That's just how I pictured you! :-)

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#14)
by Ungrounded Lightning Rod on Sat Jun 17, 2006 at 11:55:23 AM MST

Great!

And thanks for talking the guy into making magnets with countersunk mounting holes.

(Are the holes countersunk on both ends or are there distinct N and S magnets?)

Is there room for a flat and a lockwasher under the head, without filing on the screw? (I don't like the idea of counting on a screw to stay put long-term without a lockwasher or glue, and don't like the idea of a lockwasher working directly against the magnet or its coating. I suppose the thing to do would be epoxy or locktite the screws in for the final assembly, though.)

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#15)
by dinges on Sat Jun 17, 2006 at 12:13:11 PM MST

I was assuming he had the screws locktited in place. If not... It's not a matter of if but when they come loose.

Peter.

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#16)
by zubbly on Sat Jun 17, 2006 at 12:57:49 PM MST

hi ungrounded lightning rod,

the mags have a taper on one sode only. they come with 1/2 of the mags N facing up and the other half S facing up.

the magnets have a 3/16 hole with a 82 degree taper to perfectly match the tapered heads on machine screws. there is enough clearance that you can use flat or oval head tapered screws.

do not use a lockwasher under the head of the screw. the taper of the screw and mag are not made to work with it. simply apply some thread locker to the threads of the screw. they will not work loose. one or 2 drops is more than sufficient to lock the screw from loosening.

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#17)
by dinges on Sat Jun 17, 2006 at 01:42:23 PM MST

Zubbly,

Off-topic but still; have just finished some calculations on the bearings in my 3HP conversion (6206). They have VERY LIMITED axial load capacity; about 1000N (though there's some margin due to safety factors). With a 3m prop this means maximum allowable airspeed of 15m/s; with a 4m prop maximum 11m/s airspeed before the bearing is overloaded.

I will be replacing the front one with a 7206; exactly the same physical size, but it can handle an axial load (in one direction) that's three times as large.

I understood that your bearings are a bit larger (6307, IIRC), but you have double the horsepower too. I think it may be interesting for you to see whether an axial contact bearing replacement is available (I'm guessing at a 7307).

Just an idea.

Peter.

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#18)
by zubbly on Sat Jun 17, 2006 at 02:44:03 PM MST

hey Peter,

you can take my word for it or leave it. a 6206 bearing will take a 10 foot prop no problem at all.

the standard 6200 and 6300 bearings will take very large axial loads.

from what i have seen them take from abuse in factories, aggregate sites, and just plain abuse, they are awsome.

simple step. call a local bearing supplier. ask them to look up the maximum allowable axial thrust load on the bearing size you want. they have all that info.

my 1.5hp conversion has a 6205 bearing in the drive end. i use it for experimenting. i had an 11 foot prop on it for quite a while. it has also seen a 9 foot 2 blader, and an 8 footer. bearing is as smooth as the day it went in. about 2 1/2 years on it now.

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#19)
by dinges on Sat Jun 17, 2006 at 04:53:21 PM MST

No worries, I'll take your word for it. Good to hear that those bearings stand that kind of use. Maybe I just worry too much...

But I'm VERY interested in your opinion on the matter of skewing the magnets, see the drawing at the very bottom:

http://www.fieldlines.com/story/2006/6/15/19126/8190

I notice you skew your magnets much more than the 'official' 360deg/#slots. You take this angle and project it on a different surface.

I wonder what I should do: simply follow you, i.e. skew a lot, like 10degrees (30 degrees in reality) (with some cancellation in the stator), or apply the same skewangle as is on the original rotor (3degrees; which equals a rotation of 10deg. of the rotor).

I'm not sure if I manage to explain the problem properly. I'd really like to discuss/hear your expert opinion on the matter.

Peter.

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#22)
by zubbly on Sat Jun 17, 2006 at 10:16:07 PM MST

peter,
in 99% of my conversions, i skew by 10 degrees (thats 1 stator tooth out of 36)

in a 24 slot, you skew by 15 degrees (thats 1 stator tooth out of 24)

in a 48 slot, you skew by 7.5 degrees (thats 1 stator tooth out of 48)

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#23)
by dinges on Sat Jun 17, 2006 at 11:01:30 PM MST

Zubbly,

Thanks for the reply. But I think we are misunderstanding eachother or talking past eachother. Please check my two diaries, esp. the last one. You'll see that the magnets are skewed ONE slot exactly, yet the angle is 3.5 deg (in one plane) and 10 deg (360/36slots) in another plane.

Sorry to keep going on about this, I don't want to annoy you.

Peter.

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#25)
by oztules on Sun Jun 18, 2006 at 01:51:06 AM MST

Peter

The confusion may well evaporate if you keep to a single frame of reference.

Providing you stay with the reference that 1 slot =10 deg of radius (36 slot stator), then the start and finish points of the skew will be 10 radial degrees apart. If you swap reference points in order to draw the skew angle on the rotor, then yes, the degree number changes in more ways than one. The line being drawn then is not coplaner as it moves across a curved surface , and it all gets messy to describe in two dimensions and so i feel that it adds more confusion than is useful in general discussion. (see I'm confused already)

Thus far people have fully understood Zubblies skew description.... and in fact degrees are not required to convey the skew concept he is promulgating....even better for the mathematically challenged slobs like me. Zubbly says to skew by 1 slot... nice and simple....so perhaps it is not useful to muddy the otherwise relatively clear waters.

I appreciate that the engineer in you is busting to get out and describe the angular anomolies with more alacrity, but in reality, technospeak only generates enthusiasm in a small minority of people, and I think Zubbly is trying to talk to everyone from any walk of life who wants to convert motors successfully.

It may be that most people will mark the start and end points and draw a line between them and go from there. A few will have indexers on their milling machines, and then they will require your analysis of the change in reference points.....and a whole lot more.

angularly dislexic...........oztules

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#27)
by dinges on Sun Jun 18, 2006 at 10:23:21 AM MST

Hihi,

angularly dYslexis ;)

Yeah, maybe I was complicating things too much. Still, glad we've got this sorted out. Maybe I was the only one who misunderstood Zubbly. His prevalent rule (Zubbly's 2nd law?) is to skew ONE stator slot. The exact angle could be calculated following that, but can NOT be simply transferred to a piece of paper. Then again, if you did, the genny would probably still work ok, with perhaps a little less output. I'll stop beating this dead horse.

Enough of this angle-discussion. Time for action!

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#26)
by zubbly on Sun Jun 18, 2006 at 08:48:31 AM MST

hi Peter!

no annoyance taken.

i don't sometimes have the best way with words to cover the whole scope and different ways of looking at it. simply put, one stator slot (out of a 36 slot stator) is 10 degrees. so once you have it skewed, a good test to do is stand the stator on end, put a heavy weight on a string, and hold the string in the centre of a stator tooth. the string on the bottom end should be in the centre of the next tooth over.

oztules gave a rather good explanation concerning this. and yes he is correct, i try to explain it so that anyone with any background can understand what i mean.

zubbly

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#28)
by dinges on Sun Jun 18, 2006 at 10:43:26 AM MST

"i try to explain it so that anyone with any background can understand what i mean."

Yeah yeah, rub it in... ;)

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#29)
by drdongle on Sun Jun 18, 2006 at 12:34:46 PM MST

Just to stick my oar in the water and muddy it further isn't it really one slot and one tooth? and with a 36 tooth/slot stator (thats 36 teeth, and 36 slots all together) wouldn't each tooth and each slot actually be 5 degrees? now I'm not questioning the 10 degree rule for a 36 slot stator (it make perfect sense to me)just the physical facts, with 72 artifacts ( slots and teeth) divided into 360 degrees thats 5 degrees per artifact, but we really need to look at then in pairs one slot and one tooth as a pair.
Carpe Vigor, Dr.D
[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#20)
by WXYZCIENCE on Sat Jun 17, 2006 at 09:06:58 PM MST

Peter, I understand that you had to change the bearing because it was grinding. What is the cost difference in the 7206 vs the 6206. Might still be worth while going to the 7206. Joe

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion... (3.00 / 0) (#21)
by dinges on Sat Jun 17, 2006 at 09:21:27 PM MST

One of the bearings made a grinding sound, the other was ok. Nevertheless even if both bearings didn't make a sound they would still be replaced as part of the major overhaul. A little effort & expense now could save a lot of problems & rework later when it's on the tower.

Don't know about difference in price yet. Expect the 7206 to be more expensive. So be it.

Peter.

[ Parent ]

Re: Update! 7.5HP Baldor 12 pole conversion (3.00 / 0) (#31)
by dinges on Sun Jun 18, 2006 at 10:26:33 PM MST

Zubbly,

One small question: is it possible that the magnets in a motorconversion are TOO STRONG? Was thinking about this (for my 3HP conversion). If the magnets are too strong the core might get saturated. If it does, will it start developing a lot of heat?

I notice that you use lots & big (strong) magnets.

Maybe I'm worrying again without good reason? Still interested in your opinion on core saturation (and the winding scheme in my 3HP, which is not 12-10-8 but has 5?! instead of 6 slots inside a coil).

Peter.

(PS: can you recommend any good websites that go into detail on winding schemes for motors? I really want to brush up on my knowledge, am getting sick of having to guess and begging you for help. Prefer to help myself, so to speak.)

Re: Update! 7.5HP Baldor 12 pole conversion.. (3.00 / 0) (#32)
by nunyabeezwax on Tue Jun 20, 2006 at 11:30:38 AM MST

zubbly and all,

The magnets with holes for mounting with screws is a great idea, however I have a small issue with the choice of a counter sink vs. a counter bore. I think and have seen counter sinks on brittle materials cause issues with cracking during installation and service life of the product.

NunYa

Update! 7.5HP Baldor 12 pole conversion rotor completed | 33 comments (33 topical)

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