

Dec 20, 2003, 08:09 PM  
Tokyo, Japan
Joined Nov 2002
858 Posts

Remeasured the copper loss
I had used my DC power supply source meter.
The measureing current is 0.5A. The copper wire resinstance at one phase wing is 0.3056 ohm. The copper loss is 5.7^2 * 0.3=9.75W at APC 5.5x4.5, 10kRPM Direct Drive, 2s Etec. Also, We have to consider the loss on ESC MOSFET, It is about 15mill. ohm. Obviously, 3s system is better by this result. 
Dec 21, 2003, 05:35 PM  

Gentlemen:
This thread is fascinating. I couldn't wait to get home and give it a try so forgive me for asking stupid questions and being behind the 8 ball. Here is what I got so far. I took the cdrom apart and split the motor in 2 pieces. I think next referring to the original post, I must de solder and rewire into a delta position? Is that absolutely necessary or will the motor work without all that rework? 
Dec 21, 2003, 08:30 PM  

The motor should work "as is". The Kv of the motor (rpm/V) is usually too low, it is working, but at 68 cells the maximum rpm and power is too low.
If you reconnect it to delta, the result is 1,7 times higher Kv. Similar result, if you rewind it with a thicker wire and 1,7 times lower turn number. If your magnet ring is black, then the motor can't give really good power and efficiency unless you replace the ring to 12 pcs of neodym magnets. The grey ring is much better then a black one... 
Dec 21, 2003, 08:54 PM  

RCflyer and mrmota:
Thanks for your input. To remove the stator? Sorry for my ignorance, what is a stator? Never mind. The one on the left is the entire stator then if I desolder it and rewind it with thicker wire and 17 turns in a delta config I should get more kv? Question I have, the stator has 3 wires soldered to the plate, if I desolder them, looking at the original diagram from thread 1 I see 3 separate wires and three spliced wires, but mine only has 3 separate wires (ie. green red and blue in the original diagram). So (WAIT i THINK I GET IT). I rewire it completely different with the new wire? That seems to make sense. Please let me know, and what gauge copper wire should I use? It seems mrmota recommends 17 turns, is that correct? How many turns would you recommend? Thanks, this is my first time, but it's awesome, I feel like a kid! Thanks again. Henry. 
Dec 22, 2003, 12:23 AM  

Mitsumi model CRMCFX001D
This is something I've seen the first time. This CDROM has very unusual motor. I would say Coreless
Obviously I can't rewind it (not at home) does anyone have an idea how to connect it to be able to run it? I'm just very curious how it will behave. The rotor is a flat plate with flat magnetic ring. So it's not a bell, but ring running in front of the coils. As you see on the picture it has 6 poles (3 are small and 3 are bigger) and the rotor has 8 poles (quite strong magnet). The motor weights about 20g but can be shaved a little. The coils are 1.3mm high, and the thickness of the whole motor is 7mm. Any suggestions? RysiuM 
Dec 22, 2003, 01:15 AM  

rysium
Looking at your efficiency values, I did a quick calc. and come out at a very different value. The efficiency formula I use is Prop dia to power of 4  multiplied by pitch  multiplied by rpm to power of 3  multiplied by prop factor K.  typical 1.11 (found via a link somewhere here) All measurements in feet and RPM in thousands. Thus Diameter = 9 inch = 9/12 y/x of 4 = 0,316 Pitch = 4.7 = 4.7/12 = 0.3916 RPM = 4620 = 4.620 y/x of 3 = 98.61 Therefore efficiency = 0,316 x 0,3916 x 98.61 = 12.20 Watts to prop K factor included (depending on prop) = 13.5 Watts to prop. Efficiency therefore = 35% Now have I got something wrong? If I have got it wrong, then my motor is looking awfully good for a CDrom. So somebody please give me the real formula. 
Dec 22, 2003, 02:17 AM  

Quote:
I checke alse the site : http://www.andersonparkflyers.org/flightcalc.htm And when I put yopur data through ThrustHP calculator (ver 2.0d) I got HP = 0.022 (16.4W) and static thrust = 0.44lb = 7.4oz I don't know why they are off, but maybe different prop data were used. I just printed formulas from ThrustHP calculator: Formulas from AMA mag Oct 86 Load = Prop Diameter^4 * Pitch Speed = Pitch * rpm * 0.000947 Horse Power = Load * rpm^3 / 1.4 * 10^17 Static Thrust = 0.00000000000283 * rpm^2 * Prop Diameter^4 * Air Density/29.92 * CF value Prop data is in [inch], horse power = [745W], Static thrust is in [lb] I hope this helps, RysiuM 

Dec 22, 2003, 02:35 AM  

Re: Mitsumi model CRMCFX001D
Quote:
It should run as standard 3 phase DC BL motor. Of cource you should be able to connect coils to delta to have some more power. It reminds me the motor built in MicroFlight article. http://www.rcmicroflight.com/library/motor1.asp Satoru 

Dec 22, 2003, 03:03 AM  

Thanx for your feedback rysium
Not sure exactly what you are saying, but using a K factor of 1.11, I still get the figure listed. Not sure how you get your 17 Watts. Ether way though, it a long way off the 26 Watt and 70% efficiency you had listed before. The rest of the formula listed is certainly interesting though. 
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