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Motor Selection Beginner First-time

#1
Hello everybody,
I with my friend have decided to make a foam RC plane, we have decided to make it from scratch and not by copying any plan from the internet. I want to make it with two engines, I mean two brushless motors, The problem I am facing is choosing the right motors. I want it to be as fast as possible, So I was thinking of higher KV rated motors like in the range of 2500-3500KV, or should I go with the 1100KV ones? And also with propellers with higher pitch like around 5 inch. I want the plane to have small propellers, like around 5 inches.And is it necessary that the two motors should rotate in the same direction? I was thinking of rotating them in different directions. To maintain symmetry!:cool:
And I have another question, what do you all think about the Avionic brushless motors, are they good?
Thanks in advance.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#2
So I get that you want to build a plane without plans -- Daring and I wish you luck -- and that you want it to be a twin and fast . . .

. . . but do you have any more detail than that? Without having a grasp of how big and heavy the airframe will be, you can't estimate the prop size you'll need, which sizes the power and RPM requirements (kV*voltage will tell you RPM, but not power), which is used to size your motor/ESC/battery.


That being said . . . have you ever flown before? Building an airframe is a daunting task even with plans, and if you can't fly, you can't tell what you've done right or wrong after you've crashed -- was it my piloting skill or my design? If you build a proven design or fly an already trimmed airframe, you can learn the skills needed. Otherwise, you're building a fancy powerful static model awaiting destruction :eek:
 
#3
I am a very knew pilot, you need to think slow and stable. Top dihedral wing with elevator and rudder. All electronics can be used again when the first one is destroyed (unless you pound the motor hard into something). Build skills and move to the next thing. Foam, glue and tape are cheap.

My $.02 worth.
 
#4
Approximations and Informations

Thanks @craftydan,
Yes, this will be my first ever plane, before this I have only seen flite test and other videos on youtube. No it is not that I do not have a plan, I have made it myself.
https://drive.google.com/file/d/0B78G2W_OS-qjdUpidkhpSHdPYzg/view?usp=sharing

I want to make the plane as small as possible and so the dimensions will depend on the size of the props.
And to calculate the approximate weight,
I want to use one of these types motors of avionic
http://www.rcbazaar.com/product.aspx?productid=4086 weight 16gm
http://www.rcbazaar.com/product.aspx?productid=4088 weight 22gm
http://www.rcbazaar.com/product.aspx?productid=2396 weight 11gm

So for the time being I am considering the one with the highest weight, i.e. 22gmX2= 44gm

Most of them will be ok with 12A ESC.
So I will use like one of these
http://www.rcbazaar.com/product.aspx?productid=2443 weight 26gmX2= 52gm

For battery, ones with 25C will be OK I think, like these
http://www.rcbazaar.com/product.aspx?productid=1739 weight 100gm
http://www.rcbazaar.com/product.aspx?productid=1746 weight 104gm
http://www.rcbazaar.com/product.aspx?productid=4487 weight 163gm

I may use 2 of them, one for each motor for a longer flight time.
So with the maximum weight we get, 163gmX2=326gm

There will be 4 9gm servo motors, so approximately 40gm

And I am considering a maximum of 100gm for the foam board body, connecting wires and the reciever.
So in total I would have have plane of weight 562gm
Again I am saying, that all these are approximate and will change according to the suggestions you will make.

And yes @Ross I am also thinking like you, if it does not work, I will only have to change the foam board structure, all the electronics will be reusable.

Thank you.
 

CrashRecovery

I'm a care bear...Really?
Mentor
#5
I wish you luck with that design. Few things I have learned so far. I doubt the rudders will do anything as they will fight the other verticals you have on the edges. Also getting the center of gravity right on a design like this will not be easy. If you are dead set on going this route I suggest you look up this design and see how others have done it.
Here is a design that is close to yours. This is just a quick search and I am sure if I took more time I would find one even closer.
http://aerofred.com/details.php?image_id=80362
Yes this is a nitro/gas powered plane but that can be changed.
So please take some time and heed our advise. I hate to see you give up on r/c flight after your first attempt. If you are looking to learn to fly I would suggest the FT Flyer. From there I would go with the FT Delta.
Other wise I wish you luck.
 
#6
Thank you @CrashRecovery,
Yeah you are right about those two verticals on the edges, never came to my mind. So as you have pointed out, then I will make them extremely small.
I got the idea for this plan from this TED talk video on youtube
www.youtube.com/watch?v=RCXGpEmFbOw
Though it does not have the rudders, but I thought I will have a greater control over it if I add them. But I don't have the plan for it.
 

CrashRecovery

I'm a care bear...Really?
Mentor
#7
The thing with the verticals is that they are needed for it to track in a straight line. If you are dead set on that design I would honestly stick with the motors off the front. it will help with the CG immensely.
 
#8
Thank you @CrashRecovery,
Yeah you are right about those two verticals on the edges, never came to my mind. So as you have pointed out, then I will make them extremely small.
I got the idea for this plan from this TED talk video on youtube
www.youtube.com/watch?v=RCXGpEmFbOw
Though it does not have the rudders, but I thought I will have a greater control over it if I add them. But I don't have the plan for it.
Awesome video right there. Good stuff
 
#9
Thank you again,
I will try to deal with the structure and CG, but before that please help me with the problem I am facing in the first place, the selection of the props and the motor with the right KV rating.
 
#10
Here's some food for thought:

I'm a pretty experienced RC builder and pilot (~16 years). I had a friend who bought a Quadshot, and wanted me to maiden it for him. It was very challenging to fly, and difficult to transition to forward flight, and that was a commercial product which (presumably) went through a lot of design and testing.

All that said, to state it bluntly, what you're doing will not work. If you do manage to get it in the air, you will crash it in about 2 seconds. This is not meant in any insulting way, it's just the nature of learning to fly RC airplanes. Babies don't immediately start running, new drivers don't learn on Ferarri's, and new pilots don't learn to fly on fighter aircraft. Designing and flying RC aircraft is not an intuitive skill, it must be learned gradually.

Follow the advice on here, and get started with a trainer like the FT Flyer. You don't have to abandon your project, just put it on hold until your skills more closely match it's demands. It's not fun when the first time you try something, it ends in failure instead of success....You're much more likely to be turned off by it then (as the many people who have tried RC with advanced airplanes have discovered before you).
 
#11
Ohhh K!! :(

Hmm,
as you all are suggesting me to go against it, for me being a first timer, then let's keep that plan aside for the time being.
Will copy a plan from the flite test for my first time.
Thank you very much.
 
#12
Please follow others advice. Download a FT tried and true plan and build it, fly it and crash it. Learn how to build a plane first with the ft plans and instructional videos then take that knowledge and apply it to your own builds.
 
#13
I tried to do what you did with by designing my own trainer plane, and I can confidently say that it isn't worth trying, especially given how cheap and easy to fly the FT flyer is. I still want to design my own planes, but I am going to get a couple more of the FT planes done and then have another go
 

Jugsy

New member
#16
I love your enthusiasm, nothing wrong with reaching for the stars!

I understand the desire to make something entirely on your own, but even people who've been doing this for years struggle with that. If you have a LOT of excess money, time and patience you could have some success here, but I'm going to echo everyone else here, there's a lot of strange things about this build. And I'd forget all the parts you've picked so far.

My suggestion would be rather than trying to jump into a crazy experimental build with no experience, start with the basics and evolve the design along with your skills and knowledge to the point where this'll be successful. Start by working out the basic essence of your design. It's a flying wing. It's plank shaped. Now build that! Forget your twin motor set up and vertical takeoff and rudders, just build a 3 channel rectangle wing. Now you can start working on your stick skills and picking what you love and hate about it. The twins sound like a big priority of yours, so implement that next, without changing anything else. You might find here that you can use differential thrust instead of rudders. Bam, not only have you saved time and made this easier on yourself, but you're already optimizing your final design before you've put #11 to foamboard.

Good luck, post updates!