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Old Oct 20, 2003, 10:15 PM
Registered User
Hervey Bay, Sunny Qld, Australia
Joined Jun 2001
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Does anybody have any experience with the Mega 16/25/xx series

Hey there,

I am thinking of buying a 16/25/4 or a 16/25/6 (more likely the 16/25/6) for my warmliner 150cm wingspan o/d glider, with a 10 x 6 or a 11 x 7 prop. The think is that since that these b/less motors are quite new I am having trouble finding people that are using these motors yet.

With the 16/25/6 it's Kv is 900 rpm/volt. Does this mean that you can put more cells in the pack before you get the the motors exceptable rev limit???

Basically I have been told that the 16/25/6 is better at turning the 10 x 6 / 11 x 7 props than the 16/25/4, but the 16/25/6's max amps are only 18 amps with the 11 x 7 prop. That's ok I guess but one other question that I need to ask is that if I run a 11 x 7 prop on the 16/25/6 at about 18 amps then am I running at the max efficiency (about 86% I believe). Then this would be good right, and thus the best motor for my application. I am looking for a climb with authority NOT ballistic vertical climbs in 3 seconds.

Thanks for any advice guys,

Cheers,
Glen
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Old Oct 20, 2003, 11:31 PM
high-speed freak
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San Jose, CA
Joined Sep 2001
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for a glider, something like a 3t mega with maxon 4.4:1 would do well turning a large prop... I'd go geared.
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Old Oct 25, 2003, 12:36 AM
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Hervey Bay, Sunny Qld, Australia
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Yes BUT...... I need advice about this motor NOT alternatives

Hey,

Thanks for the advice, but it's not really what I needed. I have looked at the 16/15/3 with a Maxon g/box BUT I prefer to not use a gearbox HENCE my reason for the Sp480 size 16/25/xx Mega preference.

Using a 16/25/xx is about the same weight as a 16/15/3 with gearbox BUT a tad shorter and DEFINATELY cheaper.

Any advice about the Kv's though. Can I use more cells with a lower Kv??? And will my efficency be at it max if I get the motor up to it's max amps???

Cheers,
Glen
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Old Oct 25, 2003, 01:56 AM
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I too have been considering this motor. Waiting for replies from actual users.

Larry
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Old Oct 25, 2003, 04:54 AM
sloping addict
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France
Joined Feb 2003
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Glenn,
assuming your complete plane w/o motor / ESC and battery weights 700g, and using Snayo HR 4/5 A cells (about the best for 20-30A) - Motocalc says:

16/25/6 DD would have to work over its amp rating and with a small prop. One setup that should work OK since you're only using throttle for 10-30 sec and losses are still low @ 37W could be:
8 cells, 9*5 Cam folder, 35A, 2:54" est runtime (less in practice), 45 climb rate at 7.8m/s, Motor eff 86.6%

Not too good, the prop sounds still too big for th emotor. A geared setup is much better, or try an Outrunner to get the biggest possible prop (12*7 would be good target) w/o raising amps too much...

I first wanted no GB, but finally chose the 16/25/3 + 4.4:1, as nothing comes close enough at full throttle for climbing efficiently. Still waiting to receive the motor....

Here you have many examples of outrunners use that will help:
http://motor.hepf.at/axi/kunden.php

Proto
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Old Oct 26, 2003, 03:33 AM
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Hervey Bay, Sunny Qld, Australia
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Hmmmmm, interesting.......

Thank you to all for the advice,

I am thinking that I might be best to go with my original idea with the 16/15/3 with a gearbox. Originally I looked at a maxon gearbox (in the ratio 3.3:1) with the 11 x 7 (my largest prop).

Is this ratio the best to get or should I go to the 3.8:1 or the 4.4:1???

My reason not to go with a gearbox, was that I might have to add an extra bulkhead at the back of the motor for support. This is what I was told by one member at my club, and also that I will lose out a bit of the efficiency with a gearbox. What do you think??? Is this true?

Cheers,
Glen
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Old Oct 26, 2003, 04:20 AM
It's a Great Day to Fly
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Melbourne Beach, Florida
Joined Jan 2002
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There is the mechanical losses in a gearbox, but typically the motor is being moved into a more efficient operating range for it.

I love the outrunners.

At 78 grams is the AXI 2808/24 driving an Aero Naut carbon folder 10 x 6 on 8 1100 mah 2/3 A cells I measured my motor at 7500 rpm 7.8 volts 15 amps. It should be about 80% efficient here.

Len
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Old Oct 28, 2003, 12:03 AM
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Hervey Bay, Sunny Qld, Australia
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The outrunners sound good too BUT ....

Hello,

I would consider the outrunner type b/less in my larger e gliders 2.5m +, BUT with this model of mine the nose front is only 32mm in diametre, and I believe that most outrunners are usually bigger in diametre to able to afford a better torque than the usually b/less motors. BUT correct me if I am wrong as I haven't really researched the outrunners that much (just what I've read in magazines such as Q & EFI).

Thanks for the suggestion.

Is though the 16/15/3 with a 3.3:1 or a 4.4:1 the best route to take without going outrunner? What is the best gear ratio for this motor with a 11 x 7 or a 10 x 6 prop???

Cheers,
Glen
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Old Oct 28, 2003, 01:30 AM
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Have you checked out the Mega USA site? They have some data on different props for all the motors. The 16/25 series is a bigger/more powerfull motor than the 16/15 series.

For the 16/25/6 see...

http://www.megamotorsusa.com/Brushle...5-6.htm?id=390

It would seem that no one has any actual experience with this motor yet. The 16/25 series just came out recently.

Good luck!

Larry
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Old Oct 28, 2003, 04:12 AM
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East Anglia, UK
Joined Sep 2002
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Re: The outrunners sound good too BUT ....

Quote:
Originally posted by Masterpiece

Is though the 16/15/3 with a 3.3:1 or a 4.4:1 the best route to take without going outrunner? What is the best gear ratio for this motor with a 11 x 7 or a 10 x 6 prop???

Cheers,
Glen
If you mean 16/15/3 and not 16/25/3 then your ratios and props are IMHO close to ideal

Maybe a little more diameter and a little less pitch - 11x5 or whatever?
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Old Oct 28, 2003, 04:23 AM
high-speed freak
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San Jose, CA
Joined Sep 2001
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for a 10x6, you might also consider a 16/15/2 4.4:1. should be right near it's max output on 10 cells. I run this on 3s lithium on a 9.5x7 at 28A, motor spec'd for 31A max continuous. I like maxing out my motors. for burst application (glider LMR) you could even prop higher.

I'd pick a 16/15/2 4.4 over a 16/15/3 3.3 because of the gearbox. I really like the maxon 4.4:1. much quiter than other boxes I've tried.
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Old Oct 28, 2003, 07:55 AM
sloping addict
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France
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Hi,
if you look at the other threads, you'll see I just got a 16/25/3 with the Maxxon gearbox. The Maxxon looks very good and is supposed to hold up to 700W. I haven't tried it yet.
However this setup requires a very big prop (17") and many cells (12-14) or you'll get poor results / stalled prop. My setup will yield to ~400-450 W for 1.5 kg AUW.
The real "hot" liners will request about 700W+ for same weight but heat losses are 4 times as much for a minimal gain (12/13 m/s raising to 16 m/s climb rate), not useful IMHO for leisure use, especially as every component in their power train is strained a lot (batteries will be trash after a few dozen flights at most)

The 16-25-6 route will lead to a small prop (8", maybe 9") and will not be a very good setup for a LMR.

I would agree with 16-15-2 recommendation, rated 38A. Don't exceed about 10 cells if you don't want to take a risk of throwing a magnet (40000 max rated RPM although some report OK at 70k) as kV is 4600. Then gear it deeply for most efficiency, Maxon 4.4:1, or even better, Reisenauer Micro-edition 5.2:1 and you'll have a winner. However this will only be a winner in relation with Sanyo 4/5 FAUP cells (7 to 10), nothing else will deliver the amps / voltage properly otherwise (bar a lot of Lipos in //). Prop that for 35-40A.
Maybe 13*11 depending on #cells (guessing there).

drawback: you'll get the performance but that costs ! You have the wallet, you choose
...Proto.
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Old Oct 28, 2003, 01:27 PM
high-speed freak
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San Jose, CA
Joined Sep 2001
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ken of megamotorsusa said 31A continuous, 45,000 rpm. are you quoting burst current? I can understand it for LMR usage.... just wondering. the /2 gets pretty warm at 30A on the ground, I think 38A would be getting pretty inefficient.
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Old Oct 28, 2003, 03:06 PM
sloping addict
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France
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Well, not sure what MEGA states exactly, the info was taken from Aircraft-world... I have a MEGA datasheet (coming with my motor) and 16-15-2 is the only one NOT listed !...

Anyway, here is an efficiency curve (for Mega 16-25-3, rated 30/50A), not taking into account heat effects. I'm not sure how accurate it is, and anyway I would not rely on it for a non LMR / non geared setup.
But you will note that Motor eff. is within about a 2% range for a very wide range of input Amps, in LMR use you *should be able* to use motor above its rating w/o decreasing efficieny (actually the overall powertrain eff. will increase). The factors to look at are RPM, and that the power runs are short enough to avoid heating effects.
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Old Oct 30, 2003, 12:04 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
6,761 Posts
Ever hear the expression - 6 on one, half a dozen on the other? If you're getting advice from Ken he's generally not far off- nor are the spec sheets on these motors- I'd take them over Motocalc.

A couple of things- making certain of your batteries and optimizing prop for airframe generally beats worrying about a couple of percent of motor efficiency. I like DD solutions a lot, and since you're not looking for ultimate performance, you'll probably be happy. One thing though- max rated current and max efficiency are generally two different numbers- and how heavy is this glider anyway? Why not just run watts/ lb (at least 100 or more) and check the pitch speed with the rpm you want.

Sam
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