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View Full Version : help in brushless set up ?


raad
01-03-2007, 09:57 PM
al salam alaikum

hello all
I have posted a few questions on this subject and I got a lot of really helpful info .. but no experience! .I would like to get some help getting the right set up.from an earlier post by Mr. Ed

http://www.rcuniverse.com/forum/m_4938254/anchors_4938254/mpage_1/key_/anchor/tm.htm#4938254

I understood that I need 75 watts per pound to have a sports performance ... so I am in the 115 watts area that means I need a motor that delivers 115 watts , I picked a 11.1v li-po (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=3487) 1800 mah(120g),400F outrunner 2250Kv(46.5g) ,with a 5*5 prop and the 11.1 battery it should give me 171 watts and pull 15 amps with a speed of 44 MPH according to jutgofly.com or a 400T with a 7*6 prop it gives 111 watts and pulls 10 amps 62.5 MPH .

another question i have is can i use a 15A/25A for the first setup ? or should i use a 25A ESC (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=2595) ?( what do they mean by 15A/25A ?)

can anyone comment on that or suggest a set up ?

p.s. i do not know the actual weight of my plane .. but the plans had it at 15.5 Oz. flying weight

Thank u ..
Raad

ScubaSteve
01-04-2007, 01:58 PM
without knowing which ESC ur using, i'd venture to say that a "15A/25A" ESC is capable of handling 15A continuously and 25A bursts (less than 30 seconds). with that, i'd say you're probably safe using that ESC in the first setup, but honestly I'd probably just shell out for a 25A controller - the price difference the 15A model and the 25A model is probably much less than buying another 15A ESC should you fry it...

make sure you look at the thrust the motor produces with those props as well as the pitch speed.

raad
01-04-2007, 10:47 PM
hello , thank u for ur reply ...

so if i want to pull 15.5A i should go for the 25A esc ? i am trying to understand if there is a minimum !:confused: !.. i know there is a maximum ..i mean if i use a 25A ESC to get 15.5 A out of it ..it would work noramally with no problem? .. what if the 25A ESC passes more power than it should and fry the motor ? could that happen ?

thank you
Raad

raad
01-04-2007, 10:51 PM
how do i calculte the thrust into all that ?

Dr Kiwi
01-05-2007, 02:03 AM
hello , thank u for ur reply ...

so if i want to pull 15.5A i should go for the 25A esc ? i am trying to understand if there is a minimum !:confused: !.. i know there is a maximum ..i mean if i use a 25A ESC to get 15.5 A out of it ..it would work noramally with no problem? .. what if the 25A ESC passes more power than it should and fry the motor ? could that happen ?

thank you
Raad

The ESC rating is simply the maximum current one can run through it [an ESC is basically a passive object] - the motor/prop is the thing which is actively pulling the current. If, for example, the motor/prop/battery is drawing 15.5A, it doesn't matter whether you have a 25A, 35A, 80A ESC - the current drawn won't change. But if you have a 10A ESC it will fry! Bigger is better for choosing an ESC (until weight becomes a factor).

As to your question of thrust - let us know what the rpm are, and we can calculate it for you! http://www.gobrushless.com/testing/thrust_calculator.php

Cheers, Phil

raad
01-05-2007, 10:26 PM
thank u for the reply .i wanted to make sure that there is no minimum to the ESC .. i think the 25A ESC and the 400F with a 5*5 prop is the best choice ...
http://justgofly.com/tech400F_DD.htm

i wanted to know if the motors differ from one company to anoter like if it would be ny different if i get the nitroplanes brushless 400f or the justgofly 400f ? ..also what if i buy a RTF with a 4 Ch TX/RX and use that in my plane ?
is that a good idea ? its just something to get me going for now !?

thank u
Raad

tom1968
01-06-2007, 03:36 PM
Raad,

There are no hard rules as to what motors get called, but some motors with designations like "400XT" and "400F" have become very popular. Then if another manufacturer wants to copy one of these, or offer their own design in the same size and performance, they may choose to use the same name. So typically each manufacturer wants their 400F to be similar to the well known ones. In practice, some manufacturers' design and manufacturing quality is better than others, and some of their advertising is more honest than others, so the performance may be different. Sometimes very different. You have a couple of options: buy from a known name or at least from a web site that is well regarded on these forums, or take a chance on an unknown brand in hopes of saving money. People have won and lost both ways. JustGoFly has a good reputation. I don't know much about NitroPlanes but I see they openly and helpfully list their 400F manufacturer as Motor Max, so you could post specifically asking if anyone has used one of those and see if they like it.

I would recommend against buying an RTF hoping to reuse the radio, unless you want the plane for a trainer. The radio gear in RTFs is typically lower quality, usually operates on the more interference-prone 27 MHz band, and you really don't know the specs: for instance, how much current the ESC can handle. There may be a few exceptions but most people will tell you this is a bad idea.

raad
01-08-2007, 08:00 PM
al salam alaikum ,, hello again ..

again i am back to the beginning
can anyone take a look at this and give me their opinion ?

li-po 11.1 v 1800 mah 3e
http://nitroplanes.com/hiquli111810.html

and

Motor Max Motors 400F
High powered motor for 3D park fliers
400 gearbox required for larger props
2.3mm output shaft
Max continuos current 15 amps
Weight 46.5g, KV:2250
Diameter 26mm, Length w/o shaft 27.2mm
http://nitroplanes.com/40rcbrmofor3.html



OR

justgofly

Max Current: 15 Amps.
KV: 2250
Weight: 46 grams
Shaft Diameter: 2.3mm
http://www.justgofly.com/tech400F_DD.htm


looking at a 5*5 prop or a 6*5.5 prop,
both have a max current of 15 amps...how can they pull 21 amps if the max is 15 ??

and

for the ESC i picked the tower pro 25A but they just went out of stock .. i think i will wait for it to come back or look for a cheap one somewhere else

tower-pro
Size :45 x 25 x 10mm
Weight : 22g
Continuous current limit : 25A - 30A
Maximum current limit : 40A (within 5 second)
Input voltage : 7.2V - 12V
BEC: 1.5A
High rate PWM: 8K
http://nitroplanes.com/30aelbrescsp.html


please help me pick the best setup !

thank u
Raad

Dr Kiwi
01-14-2007, 01:41 AM
The battery looks okay.

As far as the motor(s) go - they are one and the same, so I'd buy from Vinnie at Justgofly to ensure good service in case there is a problem.

Vinnie likes to push his motors in testing (in this case to 21A), just to be sure his customers don't have a problem when they run 'em at the recommended max (15A).

Personally I'd go for the best ESC I could get - your whole plane depends on it. Perhaps Tower Pro are okay, but I trust my CC Phoenix 25!

chewy
01-26-2007, 03:31 AM
The motor is rated for 15A continuous without problem with the recommended propeller. It doesn't mean that it won't go above 15A. If you put in a larger prop, then it will pull more current to swing it, until it pulls so much that you fry the windings or overheat or throw a magnet etc.

It also has a burst rating, say 21A for 30secs. This means that if you install a larger than recommend prop it may still work as long as most of your flying is not at wot (wide open throttle), which may draw 21A for longer than the 30sec limit, at which point it may overheat the motor/windings etc. If you manage your throttle, and only occasionally put in a short "burst" of wot (less than 21A for less than 30s), then it may still work. However, it is still not a recommended way, as it is hard to tell when you are flying what the exact current draw is, unless you have one of those wireless data logger with a display panel you can see on the ground. You may be drawing 18A most of the time, and that may overheat your motor as well.

Hope that helps.

chewy

virtual
01-29-2007, 07:55 AM
i'm in need of help. i've got a ST Model motor, its a 2212 model with 1250kv. its an outrunner and i'm wondering...how can i work out how many watts it is or produces, i have a 8x6 prop on it atm, thanks

danny.act
04-27-2007, 12:36 AM
i'm in need of help. i've got a ST Model motor, its a 2212 model with 1250kv. its an outrunner and i'm wondering...how can i work out how many watts it is or produces, i have a 8x6 prop on it atm, thanks


Try this:

http://www.rc-cars-planes.com/rc-watt-meter_n.html

:cool:

ScubaSteve
04-27-2007, 03:42 PM
generally, voltage * current = watts.

BUT... that doesn't account for voltage drop by the time it gets to the motor and it only predicts watts IN. to find out the watts that are actually going towards turning your prop (watts OUT) you'd have to account for any watts that are wasted as heat.

then, your watts out divided by your watts in will tell you your motor's efficiency.

RCCRASHER
05-28-2007, 07:42 PM
Can anyone answer this question?
How can I determine which brushless motor i need for any given airplane, based on the specs given not the manufacturer.

Saucerguy2
05-29-2007, 01:15 AM
You want to get to the bottom as to thrust ratio, this will tell you exactly, how much weight the motor can pull/push around with a specific prop and battery pack combo. A 1:1 ratio will get the plane to just hover and you won't have to limit what you can do aerobatics wise. Going past the 1:1 ratio and you have unlimited vertical, so basically, point the nose up give it full power and it takes off like a rocket.

I wish there was a universal formula, but with the varying size, specs, precision and weights of the motor's themselves, one rule will not apply to all of them. One word of advice though, try out different props yourself, I found not all reccomended ones are optimal for thrust ratio.

RCCRASHER
05-29-2007, 02:56 AM
How do I determine thrust.
I know the weight of my planes but I don't know how to figure thrust of my motor, propeller etc.
I do understand torque, rpm, horsepower but that apparently doesn't apply at this level.
Can anyone explain how watage, voltage, amperage and kv relate to thrust using any pitch propeller?
Or is this totally off the wall?

RCCRASHER
06-06-2007, 06:49 PM
Can anyone answer this question?
How can I determine which brushless motor i need for any given airplane, based on the specs given not the manufacturer.

You may find your answer here
http://www.ampaviators.com/index.php?option=com_content&task=view&id=67&Itemid=27

RCCRASHER
06-06-2007, 06:56 PM
I found a site that does what einstein says can be done to anything.
It reduces it to a mathmatical equation.
there are formulas, charts etc.

http://www.ampaviators.com/index.php?option=com_content&task=view&id=67&Itemid=27

Using the information found there I am building an xcel pprogram that will allow me to enter the numerical factors and solve the equations.

then I will go out and crash another plane

Saucerguy2
09-10-2007, 11:25 AM
It's a great place to go for the raw figures, now if the real world would behave in perfect harmony with zero anomolies, I'd be a happy camper on one end, dissapointed on the other since it would all resolve down to a simple formula leaving no room for exploration. Luckily the latter isn't the case. I do have to say, those guys at AA have done a very good job.