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Old Jan 28, 2004, 06:23 PM
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rysium,

This one is a small motor with even smaller place for windings. I was not satisfied with it's efficiency, thats why I tried the lower airgap. (Rm represents all of the current-dependent losses in the motor, it is not equal to the dc resistance of the coil: that is 0,7 ohm in this motor.)
The reason I wrote about it that I haven't seen so far numerical results on airgap size.


I have a little bit bigger motor, 24 mm stator, it has much lower resistance: Rm:0,36 at Kv:1329. Actually these parameters are similar to the bigger PJS300SF. This motor "cogs" so much it is hard to turn the shaft by hand. The motor has low airgap too, and very big magnets: 5*10*2. I like to try it with 5*5*1,5, but it needs some more work. I like to measure the difference on iron vs. alu ring too.
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Old Jan 28, 2004, 08:53 PM
Lawn darts, anyone?
Long Island, NY U.S.A.
Joined Oct 2003
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mmormota-
I have been thinking about making an aluminium bell to substitute
for the iron bell of CDROM BL on my workbench. In your opinion, would non-ferrous metal bell reduce flux density and result in less
than optimum performance?
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Old Jan 28, 2004, 09:14 PM
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mmormota's Avatar
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Quote:
Originally posted by jbatch
mmormota-
I have been thinking about making an aluminium bell to substitute
for the iron bell of CDROM BL on my workbench. In your opinion, would non-ferrous metal bell reduce flux density and result in less
than optimum performance?
I am sure it will reduce the performance, but really curious how much.
The bell of the popular PJS motors is plastic. It is light as well despite of the 4mm shaft - i doubt if there is too much iron fluxring inside the plastic...
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Old Jan 28, 2004, 09:27 PM
Lawn darts, anyone?
Long Island, NY U.S.A.
Joined Oct 2003
647 Posts
Being easier to shape quickly and accurately and being very much
lighter than iron, Aluminium has obvious advantages. If magnetic
flux is not reduced significantly, it will be a good choice. I will give
it a trial.
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Old Jan 28, 2004, 09:58 PM
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Dunlap, Illinois, United States
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jbatch,

You may want to look into this thread. http://www.rcgroups.com/forums/showt...=aluminum+bell
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Old Jan 28, 2004, 10:32 PM
Lawn darts, anyone?
Long Island, NY U.S.A.
Joined Oct 2003
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JRW21, looks like the shavings will be Fe, not Al...thanks for
the reference. Too bad there aren't iron/aluminium alloys.
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Old Jan 29, 2004, 10:16 AM
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USA, IL, DeKalb
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Okay, finally time for me to throw my hat into the ring. This beast began its life as a Toshiba XM-5701B. Stator measures 24 mm in dia. by 5 mm thick. Center bore through stator is a little over 3/8's of an inch. Two 3x6mm bearings were in the stock motor. I made the bearing tube from a 1 inch long piece of 3/8's aluminum rod. Chucked the rod up in a hand drill, and held the bit with visegrips(can't justify a new lathe at this time ). Bored entire length slightly less than 6mm, then bored ends at 6mm to set the bearings. Attached the stator with JB Weld. Removed the stock black/brown magnet and replaced with 24 6x3x1.5 mm N45's aranged NN SS NN.... Air gap I'm guessing is between 1/4 and 1/2 mm. Replaced short shaft with laser unit carrier shaft from same drive. For the prop saver I cut a short length of the 3/8's aluminum, bored at 3mm and cross drilled and taped for 4x40 socket head cap screws.
Motor is wound with 31 turns of 26 gauge(RadioShack green mag wire) wired wye (or star). Speed controller is CC PH10, I think its a micro but don't know how to tell. For initial testing, and low expense, I have been using a partially drained 12v gell cell from my gasser flight box. (I know....watch the amps!!!! ).
Initial testing with GWS 9x4.7 shows 5.5 A 11.3 V. I'm waiting for a tach and scale from my brother. My first observation is that this might be a little high on the watts. If the motor is run at WOT for about 10 seconds, the stator gets pretty warm, a little short of the threshold of better let go before it burns .

What do you guys think, should I leave it at 56 watts with a little heat at WOT and utilize throttle control, or should I make it a little milder?

Also, FWIW, I tried the 24 magnets NSNSNS.... would only run up to about half throttle(was looking for more torque)

Hopefully I will have more test info and better pictures this weekend.

Steve
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Old Jan 29, 2004, 10:18 AM
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and the back
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Old Jan 29, 2004, 10:19 AM
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sorry, forgot. The AUW with prop and 3 pin deans micro connector is 1.3 oz.

Steve
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Old Jan 29, 2004, 10:23 AM
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i don't think this is the case...

but check for a short. it's really easy to develop them either from winding or the bell rubbing against the wires.

i noticed last night that one of mine had the bell touching the wires as they tried to exit on top of the motor mount. i am going to try to drill some holes tonight and have them leave under the bell so they don't have any chance of touching the bell.
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Old Jan 29, 2004, 10:34 AM
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chimchim how did you get the ...

magnets to fit? did you have to grind the stator or did the magnets fit without any modifications?

good work, i like what you did with simple tools.

jeff
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Old Jan 29, 2004, 11:01 AM
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Ohio, USA
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Steve-

Nice job!

I'm particularly impressed with how you bored out the aluminum rod. How were you able to keep the bit square and centered? Seems like that would be a challenge even with a drill press, much less a handheld bit.

Your motor is similar in construction to mine. However, I used brass tubing and soldered it to the original brass hub. So my motor is probably heavier than yours. It never occurred to me to try boring out a piece of aluminum rod!

- Jeff
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Old Jan 29, 2004, 12:53 PM
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USA, IL, DeKalb
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Jeff(s),
Thank you.
First off, the 6x3x1.5 magnets fit in stock (no modification), tricky little buggers, much harder to put them in NN SS NN, the ones you want together ie, NN, just want to repel each other. I used strips of business card to space them around the bell. Then glued everything together with Ca, the paper acts like filler and helps bond the mags together on the edges, just trim off the excess with a sharp number 11 blade.
As for boring the rod. I was a little off center, but that doesn't matter to much as the construction will detail.
1. Chuck the rod in the hand drill
2. Use an automatic center punch to find the center while the drill is running.
3. Bore a pilot hole in about 1/4 inch then bore with bit one size smaller than 6mm. The bit will always try to center itself, just try to keep things straight. Worked for me on the first try, maybe just lucky .
4. Counter bore for the bearings using the same method.
5. With the N45 magnets glued into the bell, wrap the stator with celophane tape one layer at a time without overlaping at the joint(this would leave a high spot after several layers) until the stator will fit snuggly into the bell.
6. With the stator now centered you can mount it to the bearing tube. <optional> This is where you can correct for the of center bore. With the tube in the drill, use a small file to reduce the outer diameter until the tube will slide into the stator (with new shaft and bearings in place).
7. Use a moto tool, or just a pair of plyers to score the tube lengthwise where the stator will sit. Will help give the JB Weld something to grip.
8. Mix up a small batch of JB Weld and glue the stator to the bearing tube, go sparingly with the glue because you wont be able to clean any excess between the front of the stator and the bell.
9. Resist the temptation to fondle and look at your creation. Let stand for at least 10 hours. Then pull the stator and tube out and remove the cellophane tape.
10. Put back together and spin and oogle to your hearts content.

You may also want to drill lighting holes in the bell prior to installing magnets to avoid stuck filings.

Total cost about $2 and 1.55 of that was the Deans plug!

sorry for the long post, but maybe step by step instructions with hand tools may help somebody with one of these little jems.

Steve
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Old Jan 29, 2004, 01:11 PM
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Steve-

Your description is excellent. I don't think you can ever provide too much detail -- the more, the merrier.

I'm going to have to try your method for boring out the aluminum -- basically a poor man's lathe. I have a small drill press. I'm thinking I could chuck the aluminum rod in the press and press it down on a stationary drill bit -- same idea that you used.

Also, I probably have room for 24 6x3x1.5mm magnets, as opposed to the 12 5x5x1 I am using now. That would fill the bell more completely and also reduce the gap between the magnets and the stator. I think I have an extra 0.5mm available around the perimeter. See the photo below.

- Jeff
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Old Jan 29, 2004, 01:45 PM
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Jeff,

Just make sure that the bit has the ability to move around a little so it can center. My method also put the boring force on the bit, but that probably doesn't matter. You may want to try holding the bit in visegrips and pushing up into the stationary drill press. Let us know which way works better

You will be supprised how much magnet depth you gain going from 12 to 24. Looks like you should have plenty of room. My motor runs fine with an air gap equal to 4 layers of cellophane tape.

Steve
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