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« on: March 23, 2009, 09:11:46 PM »
anwar
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A typical power system for foam planes consist of a motor (we will stick to brushless ones, since they offer better power/performance), an electronic-speed-controller (ESC), a right sized prop and an appropriate Lipo battery.  Picking up the right combination of these is vital for success of whatever one is trying to achieve, whether it is slow flight, fast flight, or hovering-with-high-thrust.

What are some of the tricks and rules-of-thumb that people use to determine what combinations work ? 

Should we go for a low KV motor, or a high KV motor ?  How much Amps should the ESC support ? What size prop would a particular combination of Motor/ESC support ?
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« Reply #1 on: March 23, 2009, 09:55:36 PM »
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Hi ,
I normally go essentially by the weight and type of flying to determine the motor .
The Motor's max amp x 1.5 is normally my thumb rule for ESC .
Current Draw of the motor determines the Battery Capacity ( MAH ).
flying Charecteristics of the aircraft determines the Voltage selection .
Motors KV rating largely determines the prop size .
EG
MR MOSS Glider :
Trainer Version : 36 " wing span AUW : 250 gms  , Motor : 2204/14 , 1400 KV  Max amp 6 amp , ESC : 10 Amp , battery : 7.4V 850 MAH
Competition Version : 48 " Wing Span : AUW : 310 gms : Motor 2205 , 1400 KV : Max amp 8 , ESC 10 amp : battery : 11.1V 400 Mah  as competition required excellent climb rate for max duration 1 min hence choise of 11.1V 400 mah.
PROP in both cases GWS 8040 with prop saver

MIG 29 : depron Quick Build : AUW :  400 gms : Motor : 2212/06 KV 2400 , Max amp 22 amps , ESC : 40 amps , Battery : 11.1V 2650 mah  Prop size 6 x 4 APCE .

ONE IMPORANT FACTOR THAT HAS TO BE ALWAYS REMEBERED IS THAT MOTOR SPEED IS INVERSLY PROPORTIONAL TO TORQUE .

HENCE LOWER KV MOTORS SWING A  BIGGER PROP AND VISE VERSA .

One interesting case that could help in better understanding is the CASE of The PILOT Models Seduction  which both myself and Chan fly :
My Motor is a 3520- 6 T , 700 KV  started with  11 x 7 prop on 4 s ( 14.8 V )and used to be very sluggish till I accidently was forced on the field to fit the only prop I had a 15 x 8 APCE with a 3 S 11.1V .
In 1 flight its performance was Transformed .
I was worried about the current draw but to my surprise at full throttle it was only 46 amps .
Hence Proping up and reducing battery weight was just the right thing for this plane .
The same happened with the Pheonix tiger 60 as well on a 15 x 8 APCE .

Chan is on a 2826 Motor ON 4 s ( 14.8 V ) for the same plane am I right Chan ?
Both combinations are amazing on the same plane.

Sai

PS : The Pink Seduction is Chan's and the yellow one Mine

CHANSEDU 51.jpg
Re: Selection of motor, ESC, prop and lipo for foam planes
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« Reply #2 on: March 23, 2009, 10:03:20 PM »
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How do you normally measure the max current/amps being pulled at full throttle, or during a climb out ?
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« Reply #3 on: March 23, 2009, 10:12:01 PM »
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You can measure the MAX Current Draw at full throttle with a WATT Meter  which you connect in line between the ESC and the Battery  . It is a Static test on ground not in the air .
EG : Like this one http://cgi.ebay.in/TURNIGY-Multi-F-DC-Watt-Meter-75A-Radio-not-needed_W0QQitemZ110269842696QQihZ001QQcategoryZ2563QQcmdZViewItemQQ_trksidZp1742.m153.l1262

This does not need a radio as it has a potentiometer that simulates variable throttle inputs

sai
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« Reply #4 on: March 24, 2009, 04:15:36 PM »
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Yes uncle,
You are right.  I am flying on a Turborix 2826 with 4s 14.8V 3000 mAh Lipos!!  That works fine on a 10x7 prop for me.  Inspired by you, i tried the 3 cell route on my motor as well.  Put in a 13 x 6.5 prop and used a 2650 mAh 3s 11.1 V Lipo.  Was a big failure.  Took off, but had hardly enough power to keep it airborne.  One circuit and i brought her down.  And i also used a 11x7 on the 4s setup and did not find much of a power difference but batttery was draining faster.  So went back to the original 10x7 setup and am happy with it Smiley..

For Foamies,
I generally look at 500 gms AUW.  I would prefer a 1000kv motor on a 3s which would draw about 13 to 15 amps max.  This should work perfectly on a 10x4.7 prop.

My Nasty which weighs 630 gms has a 175W 1000kv motor (Dualsky).  And it flies on a 10 x 4.7 (slow 3d flying) and a 10 x 5 (fast sport flying) with a 1350 / 1800 3s 11.1 Lipo.

Regards,
Chan
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« Reply #5 on: April 06, 2009, 03:55:21 AM »
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We generally use the following Rule-of-Thumb while powering a EP Model Plane:Power to weight ratio.
50 watts power per pound of model weight for trainer like flying, 100 watts/pound for general Aerobatic flying and 150 or more watts for 3D and extreme wild aerobatics. But here the power is the input power and not the motor's actual output power which depends on the motors efficiency. We all know that brushless motors are more efficient than brushed motors.Also,the actual force which propel the plane is the THRUST generated by the motor and propeller combination. So if we use thrust figures to select the power systems what would be the general rule-of-thumb in terms of thrust to weight ratios for different types of flying?

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« Reply #6 on: July 31, 2011, 12:01:11 AM »
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« Reply #7 on: September 15, 2011, 08:03:32 PM »
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Sir ,

is  a 30 amp  ESC   suitable  for  a 18 amp prescribed (in the web-site)   Motor ??

and  which one  is good   

Mystery 30A BEC Brushless Speed Controller (Blue Series)
                    OR
 TURNIGY Plush 30amp Speed Controller

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« Reply #8 on: October 08, 2011, 11:12:37 PM »
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I have actually built a balsa Delta wing model and it weighs around 460~500 depending upon battery i use 800 or 1000 mAh. suggest me prop and battery voltage to use for good and smooth aerobatics.:

1. volts:11.1V prop:5*5
2. volts:11.1V prop:6*4
3. volts:7.4V prop:8*4
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« Reply #9 on: October 09, 2011, 12:36:36 AM »
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I wud recommend 6x4........its magic prop!!!!!!
Still go for recommended prop for your motor!!!!!
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« Reply #10 on: April 30, 2012, 07:45:41 AM »
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can some one give set of motors,props and battery we should have ready for mid,small plane.maybe self made scratch build or kit.i think one high power esc for all should be ok.may be one smaller for very small planes
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« Reply #11 on: August 01, 2012, 10:06:23 AM »
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Hi  Hats Off,

  I plan to use 2 motors on my model (twin-engined).
  I wanted to know that can I use 2 different ESCs (1 from EMAX and 1 from HobbyKing) to drive the 2 motors, or would there be a difference in power output from the 2 motors?

TIA  Bow,
aX
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« Reply #12 on: August 01, 2012, 01:18:12 PM »
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HI,
I am scratch building a Big beaver with projected AUW to be around 700gm. I have 1100kv motor, 40A esc and a three cell 2300mah battery. I plan to use 10x4 prop. Can you tell me whether its a right combination or not...
thanks
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« Reply #13 on: August 30, 2012, 11:29:42 PM »
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I have made one Base stand for my project and Approx.

Weight of my quadcopter is around 1300 Grams.

Which Motor Should i have to select for it ?

And Which LI-PO Battery i have to select for it ?

Which type of propelors will help me for Proper Motor ?

If I have to Bulid my controlling Board, then How can i Count the Power Consumption for each component and which controller will help me for this whole project ?

Any Suggestions are there please give me it will become helpful for me For my project.
And One Main Thing is about ECS and Which type is Tx. and RX Remote Will help me?
6 channel or 8 channel ? and From where I can Make Order for Components ?

Any indian Company or Anyy indian person is my first priority to make Placeorder for my Component Order.

If anyone has made it theen also share it for this Project. Will Glad to talk about this Project.
Any training proggramme are there then Do Reply on
swapnil5775@yahoo.com
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« Reply #14 on: August 31, 2012, 07:16:53 AM »
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I thought this was a discussion on foamies, and please use the search box  Tongue Judging from your query, you are a beginner so my advice is to first buy a FC for your quad and then try to make one Grin.
From what I have gathered from reading through many forums(especially the multirotor section of RCIndia) for a 1300gm quad(AUW??), for high performance you need to have the following specs(assuming you are on a budget like I am..) :

Atleast 650gm thrust motors : Go for lower kV motors like the dt750 or "FC 28-22 Brushless Outrunner 1200kv" from hobbyking.

ESC : F20(20A) or F30(30A) ESCs work best as they can be reflashed with a suitable firmware for quads.

Props : CW and CCW (counter rotating pairs) props (Size is determined by your choice of motors).

Tx/Rx: Any 4 to 6 channel radio will be enough(I got one from rchobbyaddict)

Battery : 3S lipo with max amp draw that is more than the max amp draw of the motor used x 4. I have purchased a turnigy 20c 3000mAh

Flight controller : kkboard (or HobbyKing Multi-Rotor Control Board V2.1)

Best of luck Wink

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« Reply #15 on: August 31, 2012, 03:51:35 PM »
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Actually  I dont have Any information About KKboard .
What is it ?
cant we bult Our Circuit to make project and control the foour motors and Flip it in Air ?

And About Motor, I was thinking that, let me Take 2200kv motor so if My use will be Definately fulfilled From that. Was i Wrong about it ?

I have make Assumptions About my Project Listed Below.

Approx. Weight -
Dimension = 15'' * 15'' [If possible then will reduce it to 12''*12'']
Battery - 175 gm
base - 325 gm If another mAterial Will use.]
Battery - 75 *4 = 300 gm [Will USE 2200kv Motor So It will aroung 2000 rpm Approx.]
ECS = 15 * 4 = 60 gm [40A Will be suitable for 2200kv Motor Each]
connectors = 50 gm
Controlling Board = 200 gm
Other Peripherels = 200 gm
________________________________________________
Approx Total Weight [[MAX.] = 1310 gm ==>Max. Weight.

Is it okay ? And for that Can you suggest me how can i do work ?
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« Reply #16 on: August 31, 2012, 09:45:00 PM »
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4 batteries of 2200kV Huh? Can you please edit your post? It is very difficult for me to understand what you are going on about.. Apologies! Tongue
Do not use 2200kV(kV is per volt rpm, so multiply it by the battery voltage to get the no load speed at full throttle). And please go through the thread titled "TUTORIAL - How to build Multirotor from scratch"
HINT: Use the "search" option Grin
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« Reply #17 on: August 31, 2012, 11:06:26 PM »
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For that, Can i build my own Circuit board ? From where can i gt source to built my own Circuit board and How to interface Motor to Controller ? Can you give some more guidance for it then let me start to do work on it.
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« Reply #18 on: August 31, 2012, 11:08:15 PM »
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Dificicult to Control 2200KV ? Really ? how ?
Can you give me a Guidance for to ut GSm Module on my Quadcopter for unlimited range to control Quad Via SMS network. is it possible?

then my Modle will become 1300 gm + 500 gm = 1800gm . Is it Okay or not ?
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« Reply #19 on: August 31, 2012, 11:34:00 PM »
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Via SMS network. is it possible?
Bang Head Bang Head Bang Head
You cannot expect to send a text to your quad reading "Flip mahnnnn!!" and expect it to flip.
If you are really interested and serious about this then you have to first read a lot. Get your basics right and then think about adding exotic control systems. If you just want this to be your college "project" and be done with it, then buy some RTF and modify.

We are hijacking this thread and should stop before we get told off by one of the moderators. If you have specific questions, create a separate thread and post there. I will be happy to help in whichever way I can.
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« Reply #20 on: February 26, 2013, 01:48:21 PM »
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hey!
you have mentioned a motor being "2204/14"
what do those numbers mean?

thanks!
aniket210696
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« Reply #21 on: February 26, 2013, 02:14:15 PM »
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http://www.rcindia.org/electric-power/electric-motor-sizes/ 
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« Reply #22 on: March 08, 2013, 06:01:14 PM »
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guys one thing you can do is use webocalc software.This software suggests motor-esc-battery combination based on input like span,wingarea and most importantly weight of the aircraft. Smiley
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« Reply #23 on: November 10, 2013, 05:20:41 PM »
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Hi everyone... just wanted to know what is the method of calculating motor specs
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« Reply #24 on: January 21, 2014, 09:45:40 PM »
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can i use my lipo(11.1v) in an rtf kit in which we were supposed to use 7.4v lipo..
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« Reply #25 on: January 21, 2014, 10:46:55 PM »
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You need to tell which RTF kit you are having as well as what are the specs of motor and ESC and the prop size if you want accurate answer.
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« Reply #26 on: August 13, 2014, 07:18:29 AM »
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I need to understand how one can select motor, esc and battery for rc plane, what all parameter we need to consider and how to derive their relation with eqch other?

As per my understand first we need to select motor based on plane weight, wingsize (i srll failed to understand how to corelate these parameter to come upnwith motor KV etc.) Then once you select motor we need to select esc and battery and props.

I have build old fogey and want to understand equations / formula / thumb rules of selecting electronics for given rc plane.

Thanks,
Niteen
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« Reply #27 on: August 13, 2014, 08:53:51 AM »
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No easy solution. I will be writing an article on this today
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« Reply #28 on: August 13, 2014, 12:00:24 PM »
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I found this

http://www.rcgroups.com/forums/showthread.php?t=1136470&highlight=noflyzone

I think this will help me to understand how it works
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« Reply #29 on: August 26, 2014, 10:49:17 AM »
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Anyone tried using Webocalc to decide on motor / prop / battery for given plane?
http://flbeagle.rchomepage.com/software/webocalc_1.7.6/html/webocalc_imperial.html
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« Reply #30 on: August 26, 2014, 11:08:09 AM »
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@niteenk
I had suggested this in this forum a year or so ago.
Webocalc is good for getting a rough idea of the type of performance likely from the airframe, motor, prop, battery used.
However if you use it for a while, you will notice that it:
1. Underestimates battery requirement
2. Overestimates duration likely
3. Overestimates field size reqmt
4. Cubic loading calculation appears incorrect.

Happy landings!
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« Reply #31 on: August 26, 2014, 11:51:17 AM »
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All these web-o-calcs and other softwares are approximate, and theoretical. There are a lot many more factors, which make purely deductive applications redundant, and demand some degree of empirical investigation.

Here is a simple apparatus I made for this:

http://s25.postimg.org/bomd3mhq7/20140808_184009.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/li3kgfjun/20140808_200722.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/4a1mozl8f/20140808_200738.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/xip0h5r9b/20140808_200812.jpg
Selection of motor, ESC, prop and lipo for foam planes
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« Reply #32 on: August 26, 2014, 11:54:33 AM »
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http://s25.postimg.org/bskrxmclb/20140810_204444.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/yg013rs5b/20140810_204551.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/t9ovsqddr/20140811_125559.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/no2goocov/20140812_171034.jpg
Selection of motor, ESC, prop and lipo for foam planes
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« Reply #33 on: August 26, 2014, 12:02:26 PM »
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@sanjayrai55 sir,
My test rig. Core is an Eent!
Motor run in reverse to avoid liftoff during thrust testing!
Regards

image.jpg
Re: Selection of motor, ESC, prop and lipo for foam planes
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« Reply #34 on: August 26, 2014, 12:06:22 PM »
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http://s25.postimg.org/hoepl0rwf/20140825_165927.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/4zp0f3b5r/20140825_165931.jpg
Selection of motor, ESC, prop and lipo for foam planes


http://s25.postimg.org/o3dqhoym7/20140825_165944.jpg
Selection of motor, ESC, prop and lipo for foam planes
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« Reply #35 on: August 26, 2014, 12:08:06 PM »
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Iyer sir, what is an Eent? An electronic diagnosis system for Ear Nose Throat diseases?  ROFL
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« Reply #36 on: August 26, 2014, 12:10:49 PM »
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With this Rig I get accurate measurements of

1. Static Thrust
2. Watts at different throttle settings
3. Volts at ""  ""  ""
4. Amps at "  "    "
5. RPM (measured with a tachometer.

So now, to come back to motor ESC prop selection. Read on......
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« Reply #37 on: August 26, 2014, 12:16:58 PM »
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I would like to clarify here that I am not an electrical man. I don't like Electric guys cause they overcharge  ROFL

Also, I have only been into electrics for a year.

But some things are basic. (No units here, I am showing proportionality. If you want exact numbers, put in the units and constants)

Power = Amps X Volts (for DC)
Power = Torque X RPM
Thrust is dependent on torque

Motors do not have linear dynamic characteristics i.e. If you keep increasing the throttle the output will not keep increasing proportionately. The peak efficiency of a motor would normally be in the 50%-75% range.
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« Reply #38 on: August 26, 2014, 12:39:04 PM »
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Iyer sir, what is an Eent? An electronic diagnosis system for Ear Nose Throat diseases?  ROFL

It is something replied to by Pathar!
And
How come your pics are big and mine are tiny?
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« Reply #39 on: August 26, 2014, 12:44:46 PM »
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Now this Pathar is intriguing  Giggle Giggle

My pics are bigger because of the Dumbledore effect
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« Reply #40 on: August 26, 2014, 12:51:16 PM »
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Respectfully, there might be some problems with your test rig as I see. I might be wrong, please correct me if I am. The things that I am assuming are that the rig is used in the configuration as seen in the pictures and the motor is not parallel to the wire under tension. The problems that I see are:
1) When the wire connecting the rig with some rigid support through the weight scale becomes taut, the entire weight of the scale is supported by the thrust of the motor.
2) If the thrust line of motor is not co-linear with the scale and the wire, you will get inaccurate readings.
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« Reply #41 on: August 26, 2014, 12:56:43 PM »
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Suppose I have a high wing trainer of airframe weight 800 grams.

I reckon total weight of about 1.1 Kg with motor esc and battery

So I need (very approximately) 2.2*1.1*75 Watts OUTPUT from motor

Assuming an efficiency of 75%, I need 242 Watts.

Next, look at motors of 240 watts or thereabouts. Also, how will I be flying? As it is a trainer, I would be flying it easily generally.

I want ground take-off capability too, as I don't want to risk a hand launch (which cannot be aborted easily)

So I want thrust about 75% AUW at least. And I don't want too high an airspeed
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« Reply #42 on: August 26, 2014, 12:59:12 PM »
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Respectfully, there might be some problems with your test rig as I see. I might be wrong, please correct me if I am. The things that I am assuming are that the rig is used in the configuration as seen in the pictures and the motor is not parallel to the wire under tension. The problems that I see are:
1) When the wire connecting the rig with some rigid support through the weight scale becomes taut, the entire weight of the scale is supported by the thrust of the motor.
2) If the thrust line of motor is not co-linear with the scale and the wire, you will get inaccurate readings.

Of course, the vector projection along the wire only would be measured. However, they actually are all parallel. Maybe the photo doesn't show it clearly. When the motor runs, the wire tautens, and the wire, scale and motor axis are parallel an horizontal
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« Reply #43 on: August 26, 2014, 01:06:00 PM »
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And about the first point?
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That form ever follows function. This is the law.
 

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« Reply #44 on: August 26, 2014, 01:09:54 PM »
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@lastrites
When i tried measuring by attaching the scale to the tailwheel of my taildragger, she rotated on the main gear just enough to hit the floor with the prop... Grin
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« Reply #45 on: August 26, 2014, 01:12:26 PM »
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To continue:

Let's look at this motor:

Avionic C2836 KV1120 brushless motor

with this manufacturer's data

Specification:
RPM / V - 1120 rpm
Weight: 76 gms

Combination of usage:
PROP 9x4.7E
● Get 450gms Thrust
Lipo 2cell 7.4V
Operating Voltage 7.3V
Amp draw at load 10.7 amp
ESC - 20 amp
Power 75W

PROP 10x7E
● Get 600gms Thrust
Lipo 2cell 7.4V
Operating Voltage 7.3V
Amp draw at load 11.2 amp
ESC - 20 amp
Power 78.5W

PROP 11x5.5E
● Get 700gms Thrust
Lipo 2cell 7.4V
Operating Voltage 7.2V
Amp draw at load 11.7 amp
ESC - 20 amp
Power 79W

PROP 9x4.7E
● Get 1100gms Thrust
Lipo 3cell 11.1V
Operating Voltage 10.6V
Amp draw at load 21.7 amp
ESC - 30 amp
Power 217W

PROP 10x7E
● Get 1200gms Thrust
Lipo 3cell 11.1V
Operating Voltage 10.5V
Amp draw at load 25 amp
ESC - 30 amp
Power 247W

PROP 11x5.5E
● Get 1400gms Thrust
Lipo 3cell 11.1V
Operating Voltage 10.5V
Amp draw at load 26.5 amp
ESC - 30 amp
Power 265W

PROP 9x4.7E
● Get 1500gms Thrust
Lipo 4cell 14.8V
Operating Voltage 13.9V
Amp draw at load 31.5 amp
ESC - 40 amp
Power 441W

Now, I only own 3S Lipos. In fact, I only own 1800 mAh LiPos! (Assumption)

So, I select the 3S (11.1 V) option.

All 3 prop sizes given here will fly my plane. Differently.

The 9X4.7 will give me least ampere draw, so longest flights, but slow (4.7" pitch) and less thrust (9")
The 10 X 7 will give me maximum power and maximum speed, having the highest pitch (7")
The 11 X 5.5 will give me maximum thrust, and an in-between speed.
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« Reply #46 on: August 26, 2014, 01:14:55 PM »
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Lastrites, the scale weighs < 50 grams. If that is your concern, it is a non issue.
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« Reply #47 on: August 26, 2014, 01:20:34 PM »
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Another frequent question is how long will the battery last?

Say the 10*7 is being used, which draws max. 25 A at full throttle. The Lipo is 1800 mah = 1.8 Ah = 1.8 * 60 = 108 Ampere-minutes

@ 25 A, we get 4.32 minutes.

Of course we never fly continuous full throttle. In typical trainer flying can expect 6-8 minutes.

The smart thing is do the first flight for say 3 minutes, and measure the battery voltage. That will tell you at what Duty Cycle you are flying. Then you can judge reasonably accurately.
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« Reply #48 on: August 26, 2014, 01:35:30 PM »
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Which brings us back to the test rig. Why do we need it at all?

Because, the manufacturer's test data is not always accurate, and/or under lab conditions. Also, at times for a particular application you might want a prop which is not listed. Or you might want to experiment with different props to optimize between thrust, rpm and thus power.

For example, I have recently got a Multiplex Tucano, and want to use a NTM 3548-900 KV motor on it. Which prop?

Weight of model: 1.85 Kg AUW. Type: Low wing aerobatic speed/sport. I need about 450 W. I have 3S batteries only.

Specs: (from the HK Product Page)
Model: NTM Prop Drive Series 3548 900kv
Kv: 900rpm/v
Poles: 3
Motor Wind: 7T
Max current: 55A
Max Power: 570W @ 12v (3S) / 815W @ 15v (4S)
Shaft: 5mm
Weight: 171g
ESC: 60A
Cell count: 3s~4s Lipoly
Bolt holes: 18.9mm & 25mm
Bolt thread: M3
Connection: 3.5mm Bullet-connector
Prop Tests:
Data available soon!


I tried a 11*7. Flop! 290 W!

13*6.5 - better. 390 Watts.

14*7 - Bingo! 500 Watts
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« Reply #49 on: August 26, 2014, 01:44:42 PM »
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On a 4S battery, I will of course get the desired wattage and thrust on a 11*7

And now, the ESC selection, and the elusive "C" Factor.

I will be drawing about 48 A max.

So, I will go with a 60 A ESC with a built in BEC. I am using 4 Servos 17 gram, one Servo 19 gram. 3A on the BEC is enough here.

@ 48 A, if I use a (say) 2200 mAh 20 C Lipo, I can only draw a maximum of 44 A theoretically (2.2 X 20). In practice, this LIPO if used continuously @ 40 Amps will pack up very, very soon.

Say I used a 3000 mAh 20 C Lipo. This will give a maximum rating of (3 X20) 60 Amps. So it will be safe.

If I had to use a 2200 mAh, it would be OK at a 30 C rating (66A)

In actuality I will be using a 3300 mAh 25-50C in the fond hope I will get some decent battery life  Giggle
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« Reply #50 on: August 26, 2014, 04:51:23 PM »
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Can you explain little about "Gear Ratio" and is it mandatory to be 1 while selecting motor and prop for given model? what will happen if I have Gear Ratio slightly great than 1 i.e. 1.05-1.1 or lower i.e. 0.95 - 0.99 etc
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« Reply #51 on: August 26, 2014, 05:27:50 PM »
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The only time I have come across the term Gear Ratio is in relation to Brushed motors, wherein a gear box is used to reduce RPM without sacrificing torque and power. Unfortunately I have not encountered this term in Brushless Motors. Could you explain your question in more detail, with specific reference to the context?
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« Reply #52 on: August 26, 2014, 05:50:34 PM »
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@niteenk
Where did you see such gear ratios? In Webocalc?

In Webocalc a gear ratio of 2 means that for the selected prop to produce the predicted result with the given motor kv, motor efficiency and cell count, the prop shaft needs to be geared down by a factor of 2 as compared to the motor shaft. Ie, prop to turn at 50% of motor rpm.

Ratios of close to 1 simply means the match between motor, cells and prop is slightly off.

Don't bother too much about webocalc. The built in assumptions and scope for variation in input data are such that you can only get a broad idea. Don't think the results will be like 99% or 101%. Use it only to get a rough estimate.

I've not come across ratios like you mention anywhere else.

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« Reply #53 on: August 26, 2014, 06:36:04 PM »
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Re:

Thanks Sanjay sir andIyer sir for information. I have built rc plane of weight 700 gm with wing span of 38" and trying to figure out which motor (baded on required thrust etc) choose for it. Getting confused day by day with lots of info available on web. Sad
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« Reply #54 on: August 26, 2014, 07:51:02 PM »
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Respectfully, there might be some problems with your test rig as I see. I might be wrong, please correct me if I am. The things that I am assuming are that the rig is used in the configuration as seen in the pictures and the motor is not parallel to the wire under tension. The problems that I see are:
1) When the wire connecting the rig with some rigid support through the weight scale becomes taut, the entire weight of the scale is supported by the thrust of the motor.
2) If the thrust line of motor is not co-linear with the scale and the wire, you will get inaccurate readings.
With all due respect....
I feel the 1st point stands true
The thrust line in the apparatus is parallel but not in line with the weighing scale used for measurement of the static thrust..

Thus there is a moment arm being created causing two vectors at the point where the weighing scale is attached... One in the line of thrust and one in a vertical direction trying to lift the tail of the apparatus.  So the static thrust reading would be actually less then the realistic value.
Please correct me if am wrong.
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« Reply #55 on: August 26, 2014, 09:01:05 PM »
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@niteenk
Not only too much info on web, also oldies like me trying to give too much so called gyan.
To avoid confusing you further, i will stop with this last post. Pm me if you need more.

A models ability to fly and its flight performance depend (to a large extent) on two factors, and their combination
1. Wing loading
2. Power loading
3. Combination of wing loading and power loading

Restricting ourselves to a typical high wing trainer of 36"-48" span:
   wing loading.          Power loading.               Performance
1. 6-7oz/sqft                  50watts per pound.         Light wind slow flyer for new pilot
2. 7-9oz/sqft                  75watts per pound.         Reasonably slow. Can handle 5-10kmph wind
3. 10-11oz/sqft.              100 watts per pound.      Can do loops and rolls, handle 10-15kh wind
4. 10-12oz/sqft               150 watts per pound.      Aerobatic. Too much for beginner.
5. Over 12oz/sqft.            Whatever the power.      Will fly like a bomb or a brick. Too much for a beginner!

(Note for experts: I am only talking here about small planes less than 4' span)

I guess your 38" span is about 6" chord or say 228sqin or 1.6sqft.
And weight of 700gms or 24oz is including motor, prop, esc, rx, servos, battery
So you will be in 15oz/sqft range.

With low power you have a brick, with high power you have a bomb!

Would you like to post a pic, give dimensions of wing area, and clarify whether 700gms is bare airframe without electronics, power, battery or all up?

If you are interested, i can post links to videos of how some of my trainer models fly. The links are already there somewhere on this forum, but i can find them for you.

Best wishes. Bye.


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« Reply #56 on: August 26, 2014, 10:25:34 PM »
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Doc Nayeem:

In no picture is the wire of the Scale taut. Therefore I fail to understand why the supposition.

The wire and scale are parallel (to the eye) under operation.

I fail to understand the nit-picking. This is an idea - please do improve on it! I will be delighted, and the loudest applause will come from my side. Clap Grin Grin

The point is there is an inexpensive and reliable method of judging the motor characteristics under different prop conditions, without shooting in the dark Cheesy
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« Reply #57 on: August 26, 2014, 10:26:57 PM »
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Iyer sir... this is lovely!

What about motor rpm and prop selection?
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« Reply #58 on: August 26, 2014, 10:42:46 PM »
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@sanjayrai55

Mai chup rahoongi
Kyonki
Mere test rig ki koi tareef naheen hui
No vector, no twisting moment...

Perhaps many newbies fall between two stools.
Neither badhais nor aerodynamicists.

So in my posts i try to stop just before i get carried away completely.
(Even though i often cross the line suggested by you)

About rpm and prop selection, better than giving my gyan, i could give links to posts of certain other members / master coroplasters, as i've been doing in the past...
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« Reply #59 on: August 26, 2014, 10:50:17 PM »
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@sanjayrai55
Sir,
Niteenk is worried about, of all things,
An Old Fogey that he built.
(I expect an Old Fogey could fly like my Indore Bipe, ie, backwards if necessary...)
Have referred him to devashish, who built one last week and may test fly coming sunday

BTW, did you see my post on Nagar to FAI?
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« Reply #60 on: August 26, 2014, 10:55:51 PM »
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Iyer sir

Your test rig was simple and effective  Bow Bow Bow

VK Nagar is a friend, and a wonderful human being. Always wish the best for him Cheesy
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« Reply #61 on: August 26, 2014, 11:21:26 PM »
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Rai saheb
You are too kind as usual
Always feared waking a tiger...
But if you are awake, or tomorrow, pl see my last posts on Basic aerodynamics thread
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« Reply #62 on: August 27, 2014, 09:29:01 AM »
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@rai sir
Am still a bit confused
Hope this picture dipcts my query

tapatalk_1409111466688.jpg
Re: Selection of motor, ESC, prop and lipo for foam planes
* tapatalk_1409111466688.jpg (63.48 KB, 800x600 - viewed 833 times.)
This post has 1 more images(s)/attachment(s). Please login or register to view them.
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« Reply #63 on: August 27, 2014, 09:37:32 AM »
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Doc, the test rig is on smooth wheels. When the motor runs, the rig moves forward. The rig is anchored via the Scale by a thin steel wire

When the rig moves forward, the wire is under tension and tautens. In the tautened state, it (the wire) is horizontal, and parallel to the motor axis.

Thus the tension in the wire (which is measured) has no component in the Y Axis.
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« Reply #64 on: August 27, 2014, 09:42:38 AM »
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In the pictures, the motor is not running, so the wire is slack. Since I need my hands for taking pictures, and am alone, I can not run the motor while taking these pics.

I trust it is clear now, but please ask if not, or phone me. My number is on my profile
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« Reply #65 on: August 27, 2014, 09:48:52 AM »
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Re:

@rai sir... 
Its a good discussion going on...
The apparatus moves forward...  Until the wire is taut and then it stops...  So at this point we are measuring the static thrust...
Though the point where the thrust applied and the point where we are calculating the thrust are parallel but not in line that is there is a vertical distance of 4 to 5 inches this is creating a moment arm and trying to rotate the vertical arm rather then pull it and hence the resulting vectors will not be unidirectional....
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« Reply #66 on: August 27, 2014, 10:24:02 AM »
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AAha! I finally get your point - moment arm.

Will not create anything in Y direction significant as the Tension (also a vector) is in X direction.

The effect of the couple (formed by the Static Thrust and Tension) will indeed be to rotate the assembly so it tends to fall on it's nose (prop side)

But if the weight is enough to keep the wheels on the ground, there will be no Y axis forces. This is the case
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« Reply #67 on: August 27, 2014, 10:26:02 AM »
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Keep in mind the basic funda of a Chain being only as strong as it's weakest link.

The error in the reading of the Scale is less than the compounded errors in the assembly not being square, friction in the wheels etc etc
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« Reply #68 on: August 27, 2014, 05:08:41 PM »
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Subscribed.
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« Reply #69 on: August 27, 2014, 06:48:59 PM »
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« Reply #70 on: August 27, 2014, 06:49:26 PM »
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Re:

@rai sir...
The moment arm causing the rotation of the vertical arm which you have mentioned which you say is counteracted by the weight is the same force (created by the motors thrust) that won't b quantified on the measuring scale
I still feel we would get a more accurate measurement if the scale was attached right behind the motor ...
Kindly pardon me if am wrong
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« Reply #71 on: August 27, 2014, 06:57:18 PM »
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Make one and let us know Doc. It will be most useful. Keep the readings and info in the public domain
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« Reply #72 on: August 27, 2014, 06:58:39 PM »
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I personally am satisfied. And I am sure all agree on the concept for a multi-parameter tester. So, any improvements are a part of normal development
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« Reply #73 on: August 27, 2014, 07:50:51 PM »
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Re:

Hats off sir...
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« Reply #74 on: August 31, 2014, 08:55:25 PM »
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Just a small update. I'm getting sold on lower KV motors  Wink.

I used the NTM 3548-900KV on my MPX Tucan. I selected a prop of 14*7 based on testing, getting 530 W maximum. Using a 3600 mAh 40C battery, I am getting great mileage: a 6 minute flight still leaves me with 70% battery!!

Similarly, on my FunCub, I was earlier using a TGY 3536-1250KV, with a 10*7 prop. Shifted to a 3536-910 KV with a 13*6.5 prop, getting 20% longer flight times (ie 20% less power consumption)

I guess I was underestimating the importance of thrust. Low RPMs + Bigger props => better thrust, but not proportionately higher Amps.

Noticed something similar on a 2836-1100 KV when I moved from a 9*6 to an 11*5.5

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« Reply #75 on: September 02, 2014, 10:11:14 AM »
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Re:

Sanjay sir...
I too have a similar experience...  But I feel low Kv motor with large props actually consume more current... 
The increase in flying time I feel can be attributed to reduced throttle...  We tend to fly at lower throttle getting enough thrust because of larger props...
Please correct me if am wrong
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« Reply #76 on: April 02, 2015, 07:39:20 AM »
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Which electronics would you suggest for flying a 1metrr length wingspan trainer plane and body length of 30 inch
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« Reply #77 on: June 02, 2015, 10:29:41 PM »
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Hello Sir,

how to chose prop and motor combo, is there any theory or it is all abut experience.
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« Reply #78 on: June 02, 2015, 11:09:41 PM »
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Above post merged into existing topic. Please do some searching and reading here... as this topic is covered in detail in this and other threads.  If you have specific doubts even after reading, please feel free to ask.

If every newcomer asks the same questions already answered, it would lead to a lot of duplication of content, as you can imagine.  But any clarification on existing content would add value to the forum discussions.

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