


Re: Re: Re: Re: Re: Re: Re: Re: Brushless mystery uncovered  part two
Quote:
http://www.rcgroups.com/forums/showt...hreadid=179305 RysiuM 





FEMM Modelling
Quote:
http://www.engconcepts.net/Magnets/P...x_Magnets.html I was going to see if the 2mm thick magnets were an improvement, but then the bell has to be bigger so its not really a fair comparison. I think I'll try some FEMM modelling. Anyone else try this and any comments on its usefulness (or should I start a new thread)? http://femm.fostermiller.net/ Rick. 




Re: CDROM motor RC Prop. torque meter
Quote:
Power = Torque x rpm Torque = Force x pivot arm Force = indicated mass x gravity So in SI units: Power [W] = indicated mass [kg] * 9.81 [m/s2] * pivot arm [m] * 2pi * rpm [1/s] for units more common: Power [W] = indicated mass [g] / 1000 *9.81[m/s2] * pivot arm [mm] /1000 * 2pi * rpm / 60[/min] so Power = Mass x Arm x RPM x Factor where: Power in [W] Mass in [g] Arm in [mm] RPM in [rpm] Factor = 1.03 * 10^6 Is it right? RysiuM 



Tokyo, Japan
Joined Nov 2002
943 Posts

Re: Re: Re: Re: Re: Re: Re: Brushless mystery uncovered  part two
mmormota,
>This extremely simple sensing part is really enough for the firmware? It is full runnig on may test bench without Rx interface power control software(I need a time to write the software). Takao 


Tokyo, Japan
Joined Nov 2002
943 Posts

Re: Re: CDROM motor RC Prop. torque meter
rysium,
Power = Torque x rpm Power in [W] torque in [g/cm] Takao 



Re: Re: Re: CDROM motor RC Prop. torque meter
Quote:
W (Watt) is unit of measure for power in SI, and = kg*m2/s3 Unit of measure for torque is Force times Distance. In SI it is N.m (Newton times metre) = kg*m2/s2. The measured weight (the force of the pivot on the scale) is in kg which is equal to the force of 9.81 Newtons. Rpm is measured in 'revolutions per minute'. In SI the unit is [1/s] (one per second), so the conversion factor is 1/60 It's not as simple as you wrote. It's easy to get lost in that. What i'm trying to find out is, when you build a torque meter out of the postal scale (like you did) how to calculate the results. I just run into website for torque calculation: http://hem.passagen.se/suntool/utils/p2t_en.html When I enter 0.001028 kW and 1 rpm I got the torque = 9.81 Nm that the force of 1kg weight (in earth gravity). So I guess the factor of 1.03 is OK, right? And when the weight is in grams and distance is in cm then the factor must be divided by 10^5. If the pivot arm = 1cm, and proppeler spinning at 1000 rpm gives 100g on the scale, then the power is 1.03 W Correct me if my calculations are off. I even confused myself. RysiuM 




Torque meter
I'm sorry to get the whole discussion about this torque to power calculations started. But it's not out of the topic at all.
I need to know that because my new CDROM motor (that one with new magnets) gives me very poor results on the bench. When I calculated the PowerIn (U x I) and PowerOut (using HP calculator) I got 50% efficiency. I need to build such torque mettering stand to know exactly, what is going on. RysiuM 



Re: Re: Re: Re: Re: Re: Re: Re: Brushless mystery uncovered  part two
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According to the schematics, using small smd parts, it could be as light as 2g without wires! 




Re: Torque meter
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The usual CDRom motor efficiency is rather low, I compared my cdrom motors to a PJS300SF and found that the PJS is much better (the PJS efficiency itself is not very high). 




Re: CDROM motor RC Prop. torque meter
Quote:
I'm going to build my own torque meter just to see how are these brushless motors doing in example compared to razor 300. It is important to me, because I want to use BL motor on my 75% Depron Edge 540 Profile, and saving 20g on motor and another 20 on battery makes a big difference (compared to Razor 300) on 24 in wingspan 3D plane. But if there is no way, I can get enough power out of CDROM, then I'm in big trouble. I didn't see any other 20g BL motor that will pull 10oz static thrust with 2 or 3 340 LipPo. RysiuM 




mmormoto said
Quote:
Is it prehaps because that stator length is too short? Would love to know reason for this. 



Tokyo, Japan
Joined Nov 2002
943 Posts

Re: Re: CDROM motor RC Prop. torque meter
I have checked the balance of mass and wiring torque mistake.
Number of winds 39 Wire size 0.32mm, Delta Magnets used 5x5x0.9 N45 (from Miki Hobby) Loaded voltage 6.95V. 2s etec 700 Amps 5.7A, 9720rpm at full charge Input watts 39.6W prop size 5.5x4.5 APC, DD RPM:9720rpm Torque:189g*cm:1.9N*cm Output Power:18.0W Effciency:45.4% ESC JES 043P Static thrust:135g(APC 5.5x4.5),173g(GWS 6050) 


QLD, Australia
Joined Sep 2003
1,572 Posts

Takao,
your torque results asume you have no prop losses !!!! From what i have read , the best prop is only about 72% efficient , smaller props are less so . I beleive the motor is getting much better than you are measureing with your setup . Stewart 



Quote:
The PJS motors are very similar to a CDRom motor. While the PJS efficiency is not the best compared to other outrunners, much better then the CDRom motor. Differences (possible reasons):  stator length longer, as you wrote (maybe it is important, PJS moved from the short&big diameter 500 to the longer 550)  extremely small airgap, smaller then possible with 12 stock magnets (machined magnets) 

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