How to choose a power system - Page 12 - RC Groups
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Dec 21, 2009, 04:01 PM
Proud member of LISF and ESL
Originally Posted by austin.laws
Hi i have a turnigy BL 2832/06 e drive using a 60amp but im stuck which should i get a 3000mah 20c 14.8v lipo or should i get a 4000mah 15c 14.8v lipo? Im unsure?! But advice would be helpful. Thanks.

With no goals, both have exactly the same value.

Why are you unsure which to get? What is your decision criteria?

Both will handle 60 amps at the peak of their rated amperage.

The 4000 is likely bigger and heavier and will provide longer flight times.

The 3000 is likely smaller, lighter, giving better flight performance but will not last as long at the same amp load.

Since you have not mentioned cost I presume that doesn't matter.

So, which is better for you. Smaller/lighter or bigger longer lasting.

Only you can decide.
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Dec 30, 2009, 05:47 AM
Registered User
Hello all,

I am trying to convert an RC power glider to brushless and want to know if I can use a motor/ESC/battery combination:

Here are the specs for the glider:


Battery Operated 380 Motor RC Aircraft
Ready to Fly, assembly can be done in 10 mins.
Slow Speed Flying Capable
Shock Resistant ABS Plastic Fuselage and Strong Wings
2 X 17g micro servo for Rudder and Elevator Control
R/C Set included, Complete 3 Channel Radio Control
Complete Left/Right Control by Rudder
Complete Pitch Control by Elevator
Powered by 8.4V 600MAH NIMH re-chargeable battery (UK Charger included)
Can Fly as a Glider (without Motor Power)


Wingspan: 1100MM
Length: 820MM
Weight: 500g
Battery: Ni-Mh 8.4V/600MAH
Power System: 380 MOTOR
Controller: 4 channel RC Tx/Rx and 2 mini servo and 1 electronic speed controller

I am considering using this motor and ESC combo

I believe it is a brushless outrunner 110W and 18A ESC.

Now to choose a battery...

I already have two of the Ni-Mh 8.4V/600MAH that power the 380 brushed motor, but they suck. Will they work any better with the brushless motor? (is it more efficient?). I tried using the formula to calculate Watts and I got 5.04 (8.4*0.6). That don't sound right (I have 2 rugrats vying for my attention, so I might be way off the mark).

I am considering using one of the following:

Li-Po 11.1V 1000mAh
Li-Po 11.1V 800mAh
Li-Po 11.1v 1300mah
Li-Po 7.4V 800mAh
Li-Po 7.4V 350mAH
Li-Po 7.2V ???mAH

the 11.1V 1000mAh should give me the Watts I need, right?

The site is thin on details, like battery pack dimensions. The pack needs to be no more than 60Lx25Wx30D mm to fit into the glider and fairly light, which is why I am looking at the smaller batteries.

Apologies for sounding so thick, especially after the time taken to write the guide. Any advice much appreciated.
Dec 30, 2009, 09:52 AM
Proud member of LISF and ESL
Your questions are good.

Things I would want to know about the plane.

What kind of radio system? Will the brushless ESC work with it? For example, many 27 MHz FM radio systems in the US will not accept "standard" servos/ESC, etc. They are not standard systems. So I don't know if the new ESC will work. You might need a new radio and receiver.

One reviewer said he upgraded to a brushless, but we don't know if he is using the stock radio or one of his own.

I would like more info on the motor package.

110 watts is more than enough. The picture looks like an outrunner motor. Will it fit????? How will you mount it?

We don't know what voltage or amps the motor will take. It might need a 2 cell pack or it might need a 3 cell pack. Until you get the package you won't know.

Also, you have to leave room for that spinning can if it is an outrunner. You also need room for the wires that come around the can and back to the ESC.

The glider comes with a folding prop, but we don't know the specs on the prop. If you use the prop that comes in the motor package you know that will work but it will not fold. That adds more drag, but it will work.

If you want to try the folding prop that comes with the plane you can, but we don't know if it will mate up with the motor or if you will need a prop adapter.

We don't know if the ESC has a brake. If it does not, then when you try to glide the prop will freewheel, keep spinning, and place HUGE drag on the plane totally killing the glide.

So, these are the unknows as I see them.

Why not call the support center and see if they have any information/recommendations.
Last edited by aeajr; Dec 30, 2009 at 09:59 AM.
Dec 30, 2009, 11:44 AM
Registered User
Thank you aeajr, in fact my post is a modified version of a message sent to Nitrotek support. They are a bit slow in getting back to my questions, so I thought I might ask on here, too.

I am confident that the motor will fit into the fuselage, as the stock 380 motor is HUGE. Much bigger than the The folding prop might cope with the motor and it might not, I am going to have to try and see. I know I can get higher-spec folding props elsewhere.

I would also like more info about the motor package!!! Site just has a picture

This glider has definitely been upgraded to brushless Li-Po by others and
Thunderbird Glider - Brushless Upgrade (6 min 56 sec)

loads more

I think the radio set will be OK. It is quite high quality, considering the overall cost of the plane.

So, without more info about the ESC/Motor combo we won't know which Li-Po pack can be used? Is my assumption that because the ESC and motor are sold together, they will work together. The ESC can handle up to 18 Amps, no idea about the voltage.

I will wait and see what Nitrotek support say and post it here, in case anyone else wants to do this. I reckon it's worth it, as the stock motor and battery combo is simply awful. It struggles to get into the air and once it's gliding that massive motor drags it to earth again. Those youtube vids of the brushless gliders are to die for!
Dec 30, 2009, 12:22 PM
Registered User
Ah. Perhaps I should have done a search before posting

He says he struggled to get the motor to fit, as the shaft runs the opposite way.

People are recommending getting a Li-Po battery to use instead of the Ni-MH. Could I just connect a 11.1V 1000mAh Li-Po battery to the ESC that I have at the moment?
Dec 30, 2009, 12:38 PM
Proud member of LISF and ESL
Originally Posted by amackayj
Ah. Perhaps I should have done a search before posting

He says he struggled to get the motor to fit, as the shaft runs the opposite way.

People are recommending getting a Li-Po battery to use instead of the Ni-MH. Could I just connect a 11.1V 1000mAh Li-Po battery to the ESC that I have at the moment?
The ESC you have now, I presume, is the one that came with the plane. Does it say what voltage is OK on the ESC? they usually say voltage or cell counts.

3 cell lipo is a bit high for a 380 but they are cheap to replace so why not give it a try. You plan to replace it anyway.

Yes, the ESC should work with the motor. But, DOES IT HAVE A BRAKE!!! This is critical if you are going to fly it as a glider. No brake, no good!
Last edited by aeajr; Dec 30, 2009 at 12:44 PM.
Dec 30, 2009, 02:13 PM
Registered User
This ESC has no markings, so I have no idea.

It's currently connected to a 8.4V/600MAH NiMH battery, so a 7.4V Lithium battery like this should be OK, right?

Could I risk an 11.1V battery like this?

The following post made me think that I don't really need to replace the motor, just get more juice into it (and still be able to use the Ni-MH batteries I have spent good money on).

I am looking at the most cost effective way of upgrading what is an el cheapo Chinese clone in the first place, something I can crash without bursting into tears. The problem I have with it is that it is so underpowered that I spend all my time climbing to altitude and not enough gliding.

If the Li-Po battery does the trick, then I will be happy, but if it's still underpowered, then I will go the outrunner route. If I do, then I think that this should do the trick

I presume the 7.4V Lithium and the 8.4 NiMH batteries will work OK with this baby?

No, the ESC doesn't have a brake and I can see the prop spinning when the power is cut, however the prop folds, so this should be OK.
Dec 30, 2009, 05:48 PM
Proud member of LISF and ESL
2 cell lipo will work.

the 7 cell Nimh pack is probably 6-7 oz. The 2 cell Lipo should be 3-4. On a 17 ounce plane that is significant.

The Lipo is 8.4V fully charged and, if you get a properly sized lipo, it will probably hold its voltage than the NiMh pack, so you will probably gain in overall performance.

Again, since you plan to replace the motor, get the 3 cell and let 'er rip. If the ESC or the motor burn up, well you were going to replace them anyway. Then just make sure the motor you get can handle a 3 cell lipo.

That is what I would do.
Dec 31, 2009, 05:06 PM
Registered User
Just discovered my 380 is Rubber Ducked!

This one looks ideal

Jan 07, 2010, 02:22 PM
Registered User
Great Job.

You know what i like?

If someone could make a video. Take a couple of motors and show the amp, wat, volt and everything one could cover so that one could learn how to examen f.exam. a self rewinding motor and such.

This is great dont take me wrong. But i just forget after a while, and then i have to go through finding threads and reading half aday. If one could
Please do a video, and not one of thoes video's where you can see nothing, and you hear alot of noise and someone speaking at the end of the tunnel.

Could someone please do that

Mar 28, 2010, 04:22 PM
Registered User
FJK_12's Avatar
Wow, this thread is extremely useful! I know have a little more knowledge of power systems, an area which previously I had little knowledge.

Thanks to all who contributed to this thread!
Apr 20, 2010, 07:18 AM
Suspended Account
thanks a great way to learn ....
Jun 05, 2010, 02:43 PM
Registered User
Great work!
usefull guidelines....
Jun 13, 2010, 10:44 AM
Night flier
anybody recomend a good motor esc set up for the CM Pro Discus? Cheap is good with me i use and Model i think is about 2KG. Cheers.
Jun 19, 2010, 03:18 AM
Sic itur ad Astra
sparks59's Avatar
Just to add my two ' penneth.
A while ago I started out along a similar path with a similarly sized Chinese made Cessna foamie. The first thing I did was replace the 27Mhz equipment with 2.4Ghz as the original stuff had a range of about 100m.
The 7 cell Nimh battery was a big heavy lump and capable of keeping the plane aloft for about 2 minutes, so I pulled it out and tried a 800mAh 2s lipo, immediately better in flight and duration but the plane still weighed like a brick so flight performance was not good. I tried a 3s battery, which was probably not the best idea, the flight was lots better but the esc was toasted at the end and smoking.

I then went the whole way and tore out the 'washing machine' motor and brushed esc and put in a HXT blue wonder on a little plywood box mount, and a 12a esc. I had to cut a hole insidethe battery compartment to get the batt further forward to achieve a reasonable CG. Also replaced the horrid plastic prop with an 8x6SF prop. The only parts retained were the servo's, which are about 9g and work with the new system.

Transformation! 15 minute flights or more with a gentle throttle, great performance, good glide and easy flying characteristics.

Conclusion, rip out all of the old rubbish and replace all of it! Good luck


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