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

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

yes ,
I would really appriciate if some one could make a table like GE and give the description!!
thanks,
sahevaan

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

hello saju

can you point me to a more detailed explanation ?? and from where did you get these figures (your own??)

 
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

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

Very detailed explanation!   

- Chan

thanks saju, i think my model is going to be a floater 

nice reference was every helpful 

sahil

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

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-!/

sahil