|Dec 04, 2003, 07:11 AM|
Joined Nov 2002
> if I use larger dia. wire and fewer turns; will the current
>increase for the same applied voltage and at the same RPM?
"fewer turns" means reduce the motor rotating generative voltage.
Then, the difference voltage between the battery and motor is increased = the power line current is increased..
|Dec 04, 2003, 07:46 AM|
Joined Nov 2002
W stator CD-ROM motor
number of winds 24
wire size 0.4mm dia. Delta
magnets used 5x5x0.9 N45 (from Miki Hobby) x24
loaded voltage 5.5V
amps 3.5A, 6.6krpm
input watts about 20W
prop size 6x5 GWS, DD
ESC Jeti/Hacker Mater4-3P
|Dec 04, 2003, 08:00 AM|
I too considered using J B Weld but rejected that idea figureing that it was an epoxy too, forgetting that it is impregnated with metal and therefore should be better able to withstand the heat.
I guess that the problem I was having with the bond failing was due to " OLD EPOXY " and since has been corrected by using fresh from a new package.
That was IMO only a contributing factor as I believe that I was generating too much heat by over propping with the 1260
I have since run a 1080 @ 3600 rpm for 30 min without overheating the stator & magnets
The excess heat was causingthe motor to slow down and if I stopped it, it would not restart. It just jittered failing to start and run.
I still want to run a 1260 @ 3K so I will try some more windeing combinations, most likely a Delta wind next.
Thx to everyone, your input has been helpfull!
Roger aka GIFLYRC
|Dec 04, 2003, 10:51 PM|
Joined Nov 2003
I would like to know how you guys keep the rotor shaft from pulling out of the stator (in a pusher configuration), and rotor pushing into the stator (in a normal config) ?
Also, is there is a place in US to buy ball bearings for these motors ? Any website ?
|Dec 04, 2003, 11:11 PM|
I'm now converting my first CD-ROM motor for e-flight, so I have faced some of the same questions you have posed.
My motor uses a 3mm shaft and ball bearings from a GWS IPS motor. Both components are readily available as spare parts from many vendors. GWS 4mm shafts and bearings are also available. So if either 3mm or 4mm components will work for you, these are inexpensive solutions. Another source for bearings of many sizes (as well as countless other parts) is McMaster-Carr.
To secure the shaft, I designed the motor to use the stock e-clip. At the other end, a small washer between the bell (rotor) and the stator prevents the stator from contacting the bell.
Here are a couple of photos. I still have to replace the stock ring magnet with N45 magnets. The finished motor will weigh more than an ounce, much heavier than some. For my next attempt, I will use lighter weight materials instead of all that brass.
Here is a test assembly of the motor. A couple of washers will go on the end of the shaft, then an e-clip to hold it in place.
Here are the major components, except for the stator. I soldered a length of 9/32" OD brass tube to the original stator hub. The 1/4" OD aluminum tube slides into the brass tube and is swaged to accept the 6mm diameter ball bearing. This would have been a much easier project with metric-dimensioned tubing, but I have not been able to find it in small quantities.
Below is a photo of the ball bearings. One is CAed into the original stator hub, which has an inside diameter of 6mm, the exact diameter of the GWS ball bearing. I enlarged the end of the aluminum tube with a screwdriver to accept the other bearing.
If metric-dimensioned tubing had been available, I would not have needed the aluminum tube. The only reason for the aluminum insert is that I could not figure out a way to swage brass tubing to accept the 6mm bearing. My metalworking tools (and skills) are modest!
|Dec 05, 2003, 12:44 AM|
CD-ROM HP x 52
Now I have it on GWS B drive. Funny thing, it doesn't want to run, when ESC is powered from 3s LiPo. It just stops when I apply more than 1/3 throttle. On the other hand it works fine on 2s LiPo.
So here is my setup (the best I got):
2s 340 LiPo
GWS B drive
GWS 7x4.3 slow fly prop
Everything on the plane 24in wingspan and 240 sq in.
The airplane RTF total weights 5 3/4 oz - I love this 3.5 oz/sq ft wingloading
at 3/4 throttle at 3.5 A the thrust balances the plane (5.75oz).
at full throttle and 4.5 A the thrust is about 2 oz more. I can live with that. It should give me flight time only 5-8 min
I didn't measure RPM, but calculating power from HP calculator I guess the efficency is about 75%. Good or bad?
Still original magnetic ring.
|Dec 05, 2003, 01:02 AM|
|Dec 05, 2003, 08:45 AM|
Hi Roger, congratulation on success!
I think efficiency matters to justify the motor is good. Better efficiency will prevent heat of course.
Parameter for major APC and GWS props are measured and published in Germany and there is an online calculator available here It calculates efficiency etc from rpm, V and A. Amazing work. Very good they are!
How good CDROM motor efficiency can/should be? 70%? I read reports that archived over 80%.
Mr. Shimizu and I do not use any stopper to keep shaft from pulling off. Strong magnet will keep it in place. On pusher configuration, I put some plastic washer to keep space between stator and bell.
Very nice piece of work, Jeff. Yes, GWS spare gear box parts are good source. I remember there was a mention GWS bearing cannot sustain very high RPM (>30k?) but should be fine for our CDROM motor. I also got bearing with flange from local source and worked well. Yes, I have seen some people uses 8mm OD, 6mm ID aluminum (or copper) pipe to hold stator.
|Dec 05, 2003, 10:05 AM|
Brushless CPU fans have ball bearings that fit a G.W.S. G.b., but the O.D. is larger. Still they may be useful in a CD ROM mod, and discarded ones should be free for the asking!
There is one B.B. per motor
|Dec 05, 2003, 12:52 PM|
Thank you. I hope my motor will work as well as yours! I think I will test it with the ring magnet first, then add the 5x5x1 N45 magnets.
I have 26 turns of #26 wire (~ 4mm). What size prop will be good for a slow flyer like the GWS Tiger Moth? Battery will be either 8.4V NiMH or 7.4V li-poly.
In the USA, metric ball bearings with and without flange are available from McMaster-Carr. They are rated 50K+ RPM. But they are expensive -- $8-$14 each -- so I used the $2.50 GWS bearings.
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