wyowilliam

I've been reading all morning on what sort of motor can go with which sort of plane, but in the end, I still haven't a clue. How does one calculate amperage of an electric motor, for example? (In order to calculate watts/ lb. for example.) Wing loading? Ugh, I should have paid more attention in math class.
Anyways - I tried to convert a 2ch plane into a 4ch one - it has a 7.2v 300mah battery, a 180 motor, and a 25amp ESC. It weighs 11.7oz with all the new servos, etc. And it drops like a rock 95% of the time.
So, is there any general rule-of-thumb as to what size motor can go with what weight of plane? Is a 180 far too small? Will a 370 burn-up my ESC? (I suspect that my flight time would now drop like a rock, but at least the thing would get in the air.) Isn't there a chart somewhere that shows some of this information?
Thanks!

Campy

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FWIW - I have found that if you use 100 watts of power per pound (16 oz) of READY TO FLY aircraft weight you will have no problems with general sport/mild aerobatic flying. Hobby City lists the watts for many of their motors as well as amps and number of cells.

For my 40 size electric conversions I usually use a Towerpro 3520 motor, 60 ampESC and a 4S lipo. I have had absolutely no problems with planes up to 7.5 lbs RTF weight.

Dsegal

> How does one calculate amperage of an electric motor, fo <

You must buy a crucial tool for electric flight, a meter such as the Wattmeter. This will read out volts, amps and watts input to your motor. And your little plane will never burn out a 25amp ESC. The issue of selecting a power system for a model is the most difficult one in electric flight. There are spreadsheets, but they won't tell what to buy in the store. The best thing is to find authoritative evidence of a system that works such as here, at the E-Zone forum, in a magazine review or from a fellow modeler.

spiral_72

Just a couple ideas. A three cell pack will help quite a bit, usually ESC's will work with a 3c pack.

I'm sure you have, but did you move your CG after all the mods? A nose heavy plane can fly like a rock......

How much more does the model weigh than it did stock? Is there any dead weight you can remove?

Is this a brushed motor? Probably not. A 180 brushed would be pretty small.

Oh, and don't take my word for it without checking; but if this is a brushless ESC/motor..... I'll pretty sure a 25A ESC will work with a 370 motor.

beau0090_99

Being this was a 2 ch plane, I am assuming it is a brushed design. I found some really great information from GWS. They make some nice little inexpensive motors and gearbox combos.

I have a Great Planes Tutor, balsa 3ch plane that I added ailerons to. I bought the recommended power source which is a 280 spd motor (which is a designator from the company that makes the motor - Mabuchi). This combo from Electrifly puts out a stated 8 oz of thrust, which would be great if I flew indoors, but I like to fly in parks that have a little bit of wind, so I quickly determined through trial and error that I needed more thrust. The plane is 16 oz with the motor and the battery. So, I checked out the GWS (gwsus dot com)website under products, then EPS power systems, and the 350C has a lot of data based on the gearbox (1,2,A,B,C,D). I chose the EPS-350C-CS which is a 300 speed motor with a 5.33:1 gear ratio and I fly with a 9x7 for speed and 10x4.7 for thrust prop. This puts out between 12 and 16 oz of thrust and draws between 9 and 10 amps of current when I use my 8.4v NiMH battery. I noticed the other motor/gearbox combos on the site, like the 300C and the others are just starting to update their specs, which is great. I would trust them.

I had to fabricate a stick type mount for the GB, but it works well now. I basically pulled out the old motor and GB and weighed them to see what would be a practical replacement.

Good luck and let us know if you have other questions.
Curtis

wyowilliam

Well, I did some math and this is what I came up with - the CG is WAY back - almost exactly 50% from the leading edge. I could add some weight in front, but I suspect it won't help as the motor IS a ferromagnetic 180 (according to the box.) with a 7" prop. (Don't know pitch.)
The weight new, before additions, was 8.85 oz. SO, I added 25% more weight (A lot of that may be hot glue - lot's of crashes.) and had the CG way off - it's amazing it flew at all.
I'll take a look at the GWS.com site and see if I can find what I need.
You think an 8.4v power system will fry my 7.2v electronics?