Title: Amp rating and motor size Post by: Sahevaan on May 21, 2009, 11:04:01 AM Hi everyone ,
I wanted to know the suitable amp rating of ESC's for their motors and what type of battery (li-po voltage , amps , no. of cells) I hope this post will help all the beginers to scratch build a EP!! happy flying , sahevaan Title: Re: Amp rating and motor size Post by: GE on May 21, 2009, 03:48:50 PM Hi, would like some help too, I constantly get confused..so..what I would like is as follows...if this is the right way to split..and for EDF planes as well..
Weight ESC Motor size Prop Lipo Fan/EDF 1.5 kgs ? ? ? ? 1 kg ? ? ? ? So, what goes where, for lets say four or five sizes...would really appreciate ! Best GE Title: Re: Amp rating and motor size Post by: Sahevaan on May 21, 2009, 09:18:47 PM yes ,
I would really appriciate if some one could make a table like GE and give the description!! thanks, sahevaan Title: Re: Amp rating and motor size Post by: mpsaju on May 22, 2009, 11:23:37 AM So how do we go about sizing the motor for a plane ?
Here goes. What drives a plane… of course the forward thrust of the prop So what are the proportions …. From experience we know that the all up weight (auw) expressed in grams has the following relationship: auw(in gms) * 0.11 = theoretical power in watts...for trainers auw(in gms) * 0.22 = theoretical power in watts...for aerobatic planes auw(in gms) * 0.33 = theoretical power in watts...for 3D aircraft (extreme aerobatic) The power above is the power required to be delivered by the prop. Assuming an efficiency of about 0.75 for the motor – propeller system, the actual motor wattage could be : theoretical power/0.75 = motor wattage Next we choose the battery min operating voltage .i.e. For a Lipo 1s lipo = 3.7v 2s lipo = 7.4v 3s lipo = 11.1v And divide the motor wattage by the chosen battery voltage to arrive at the current draw of the motor. A motor is selected by the Motor wattage, current draw and its Kv rating Kv rating is nothing but the number of rpm/volt that the motor can deliver. This then relates to the prop size Prop size: There are two parameters for the prop size: Outer Diameter in inches, which has a major bearing on the thrust force the system delivers and Pitch, inch/revolution (i.e the theoretical distance the prop would axially translate thru the air if it does not slip). This has a direct bearing on the speed of the plane. The motor and prop are to be selected together as each combination of motor and prop gives a different thrust and speed value. This combination is best selected either as a motor manufacturer’s recommendation or by motor calculators such as: MotorCalc or Power Calc or Webocalc or others Finally the capacity rating of the LIPO battery is determined by how much of flying time one needs discharging at the specific current used by the motor. (The current required for operation of the servos and the radio is a few millamps whereas the current used by the motor will be in amps). LIPO's are typically codified as follows: xSyP, current rating in mah, zC xSyP where x represents the number of cells in series and y represents the number cells in parallel thus a 3S1P cell represents one set of 3 numbers of 3.7v(safe min voltage of each lipo cell) lipo cells in series. Voltage would be 11.1v min similarily 3S2P prepresents two sets of 3 numbers of 3.7v lipo cells in series, which are then connected in parallel. (totally 6 cells) Voltage would be 11.1v current rating is typically the current draw that the batterry can support for 1 hour continuously. Unless otherwise specified this is also the maximum charging current that the battery can be safely charged at. (Be careful here, special chargers are required for charging multiple LIPO cells) zC: z multiplied by current rating represents the maximum discharge current that the battery can safely support... a 20c rating of a 2200mah battery means the battery can support a maximum discharge current of 20 multiplied by 2200/1000 amps... i.e. 44 amps for a period of 2200*60/44 minutes...i.e. 3 min. Sizing of the ESC: The ESC has to be sized such that it exceeds the maximum rating of the motor so that it can operate all load conditions of the motor. I know I have only touched on the periphery of a rather large and hotly discussed topic... but I suppose one has to start somewhere Have fun Saju Title: Re: Amp rating and motor size Post by: sahilkit on May 22, 2009, 09:27:26 PM hello saju
can you point me to a more detailed explanation ?? and from where did you get these figures (your own??) Quote auw(in gms) * 0.11 = theoretical power in watts...for trainers auw(in gms) * 0.22 = theoretical power in watts...for aerobatic planes auw(in gms) * 0.33 = theoretical power in watts...for 3D aircraft (extreme aerobatic) I'm building a simple 2 channel RC plane and expecting the AUW to be under 300grams, this is the power setup I'm using GWS EP350C/BB-D(6.6:1) with GWS EP/DD 1060 prop n Hyperion LVX 7.4volt@400amh 2S pack, according to the specs this motor/prop setup should produce 256grams of thrugt at 7.4volt n 4.8 amp draw! which equate to near .853:1 power to weight ratio (taking 300grams as all AUW). your comments on my setup?? thanks looking forward to your reply sahil Title: Re: Amp rating and motor size Post by: mpsaju on May 28, 2009, 02:19:18 PM Sahil
Lets start at the very beginning... The rule of thumb that I have quoted is just the experiences of a number of writeups by more experienced fliers with the conversion from glow to electric. Let me quote from a very reliable guide "Shaw's guide to e-flight" as follows: "If you don't always just want to be flying around level and want some aerobatic performance - roll, loops, etc., these mild aerobatic maneuvers need 50 to 60 watts per pound. If you want good aerobatics - pattern capabilities - you need 70 watts per lb. for outside maneuvers, knife edge, etc. Pylon racers are up over 100 watts per lb. Multiply the performance level you want in watts per lb. times the weight of the airplane to establish the required power." Suffice to say that these old timers were quoting in watts/ lb which when converted yields the figures I have given earlier. i.e 50watts /lb =0.11 watts/gram 100watts/lb = 0.22 watts/gram 150watts/lb (3D flight requires high acceleration capabilities) = 0.33 watts/gram Quoting from another more recent writeup "Magic numbers for modellers" "Buy your watts by the kilo (or Pound) The first magical number tells you how much watts you need to fly your plane. Of course, it works only for decently matched systems. A GWS parkflyer won't fly with a 300gr motor, however powerful it is... Foamie, motorglider, Piper Cub: 100watt per kilogram (2lbs) Trainer: 150 watts per kilo Warbird, 'sport' aerobat: 200 watts per kilo Racer, 3D: 300 watts per kilo EDF Jet: 400 watts per kilo Examples: a 3kg (6lbs) 150cm (60") Hurricane will fly on a 600watts setup. A 2.5kg Calmato will require 375 watts, etc." That settled let us now talk about your set-up Motor: EPS350C/BB-D(6.6:1) Prop: GWS EP/DD 1060 GW/EPS-350C-DS PROPELLER Volts Amps Thrust Power (w) Efficiency (V) (A) (g)/(oz) (g/w) (oz/kw) EP1047 7.2 5.7 314/10.99 41.04/7.65 268 EP1047 8.4 6.2 350/12.25 52.08/6.72 235 EP1047 9.6 9.3 510/17.85 89.28/5.71 200 EP1060 7.2 4.3 252/8.82 30.96/8.14 285 EP1060 8.4 5.5 318/11.13 46.2/6.88 241 EP1060 9.6 7 403/14.11 67.2/6 210 EP1060 10.8 8.2 455/15.93 88.56/5.14 180 EP1080 7.2 7.1 293/10.26 51.12/5.73 201 EP1080 8.4 8.8 347/12.15 73.92 /4.69 164 EP1080 9.6 10.9 402/14.07 104.64/3.84 134 Battery used: Hyperion LVX 7.4volt@400mah 2S pack.... 20C safely i.e burst current of 8 amps Max voltage to motor at full charge = 4.2*2 = 8.4v This means the max thrust available as per chart above is 318gms at a current draw of 5.5 amps (chart is from GWS website) Max capacity of battery = 0.4*60 amp minutes = 24 amp minutes When drawing at 5.5amps, the approx. time of flight at full power = 24/5.5 = 4.3 min You need a larger capacity battery!! AUW = 300gms ... for a trainer one would require 0.11*300 watts = 33 watts You have a max safe burst power of 5.5*8.4 = 46.2 watts. Your flights will between a trainer and a moderately aerobatic model. Hope I am clear... if not dont hesitate to ask Saju Title: Re: Amp rating and motor size Post by: chanvivek on May 28, 2009, 03:30:09 PM Very detailed explanation! {:)} {:)}
- Chan Title: Re: Amp rating and motor size Post by: sahilkit on May 30, 2009, 01:08:52 PM thanks saju, i think my model is going to be a floater ;D
nice reference was every helpful :) sahil Title: Re: Amp rating and motor size Post by: mpsaju on June 01, 2009, 01:43:25 PM Sahil
You owe me and this forum a little more than that.... Atleast the result with photos of the plane and a little flight report... confirming or otherwise the data and results. Saju Title: Re: Amp rating and motor size Post by: sahilkit on June 03, 2009, 10:30:05 AM hi saju
i have already started a build log here (see link) will update it once my ESC is done! http://www.rcindia.org/electric-planes/scratch-built-rc-traniner-plane-2-channel-build-log-!/ (http://www.rcindia.org/electric-planes/scratch-built-rc-trainer-plane-2-channel-build-log-!/) sahil URL Fixed Title: Re: Amp rating and motor size Post by: vaibhav on January 16, 2011, 01:45:34 AM hii..everyone..!! i need some help with ESC of RF electric car with its electrical connections with 12 volt brushed motor ,battery and receiver..
m using 6 channel radio system. pls someone help me out...with it...thnks in advance Title: Re: Amp rating and motor size Post by: anwar on January 16, 2011, 07:55:26 AM Hi Vaibhav - Welcome to RC India :)
Please use the search option... for example, I got the link below by searching for "connection diagram" ! http://www.rcindia.org/electric-power/my-esc-and-motor-burnt/msg14549/#msg14549 The setup is same for brushed... you will have only 2 wires between motor and ESC (brushless will have 3 wires). Title: Re: Amp rating and motor size Post by: vijeeshkumar on May 06, 2011, 05:30:11 PM Seems like a helpfull thread for beginners
http://www.rcgroups.com/forums/showthread.php?t=739069 Title: Re: Amp rating and motor size Post by: kartikmadhira on May 26, 2011, 12:26:37 PM Indeed a very useful post by mpsaju....but m confused about maximum discharge thing..not able to understand it ...can ne1 please help??????????
Title: Re: Amp rating and motor size Post by: kartikmadhira on May 26, 2011, 12:30:32 PM deed a very useful post by mpsaju....but m confused about maximum discharge thing..not able to understand it ...can ne1 please help?
Title: Re: Amp rating and motor size Post by: adijoshi11 on October 29, 2011, 10:42:08 PM Thank you saju sir ;D very helpful info!
-aditya. Title: Re: Amp rating and motor size Post by: prashant_rc on January 25, 2012, 11:21:47 PM some i know and correct me if i am wrong
let us assume with three things 1. Motor, if ur motor draw continuous current of 20 amps, then go for 15% to 20% higher rating ESC ( like 25 amps or 30 amps), but do NOT exceed recommended prop size on ur motor, because that would draw more than continuous current and motor gets hot and burn off so motor continuous rate, always go for 15% to 20% 2. ESC, as mentioned above, go for setup which is slightly more amp rated than ur motor, so that ur ESC is so hot after flight time. 3. Battery ratings, u can know a battery can provide continuous current by mah x C rating on battery/1000 gives u the continuous current a battery can provide. So higher mah batteries can provide longer flight time, but they always carry a weight, so just decide with motor power and AUW Regards Title: Re: Amp rating and motor size Post by: anwar on January 25, 2012, 11:51:27 PM Changed item [1] in above post to read "do NOT exceed" (it was "do exceed").
Every beginner should spend some time understanding how motor, esc and battery are related to each other, and how it all relates to the AUW of the plane (and the type of the plane to some large extent). Title: Re: Amp rating and motor size Post by: prashant_rc on January 26, 2012, 10:35:49 PM thanks for correction Anwar sir
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