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HomeAircraftHelicopterHelicopter Main Discussion › Why aren't electrics motors in-line with mainshaft?
11-25-2015 07:33 PM  36 months agoPost 1
burl

rrApprentice

Port Angeles WA

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With a clutch arrangement on the motor inline with the mainshaft wouldn't it be a huge space-saver?

I expect I'll hear that motor efficiency and RPM are the issues here....

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11-25-2015 07:40 PM  36 months agoPost 2
BeltFedBrowning

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Kansas City

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You mean like this? The motor is the mainshaft!

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11-25-2015 08:45 PM  36 months agoPost 3
HeimD

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the great southwest

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And, probably more involved/expensive than just changing out a bent mainshaft. Could cause CG issues, too. Some helis are already tail heavy even with the motor up in front of the mainshaft.

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11-25-2015 09:08 PM  36 months agoPost 4
Flyin for Jesus

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Troy, IL. 62294

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Do you mean a clutch or a one-way bearing?
No need for a clutch on an electric. Motor will still spin during an auto until you get the HS low enough to let the centrifugal force unlock the clutch, then you can gain HS without engaging the clutch.

Also, if you want the motor under the MS you'd still need gears or do a direct drive. Direct drive would be hard. would have to redesign all our motors.

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11-26-2015 02:58 AM  36 months agoPost 5
burl

rrApprentice

Port Angeles WA

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Browning, yes like that. only in 500 or 600 size.

Heim, with a clutch, you'd have separation of the main rotor shaft and the motor shaft, able to be replaced separately.

Flyin', I meant clutch. Spool up would be much more gentle. Autorotation would be fully functional still. All electronics forward might restore CofG.

I'm just thinking that maybe you could do away with the large main gear to help a scale fuse fit.

Well I googled a bit and found this very interesting article.

The pioneers fought to control the forces of blade flapping and lead-lag....here those forces are actually being used for control. Amazing outside the box thinking.

http://www.3ders.org/articles/20150...nted-parts.html

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11-28-2015 11:49 AM  36 months agoPost 6
jharkin

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Holliston, MA - USA

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A few problems... To go direct drive on a 12s 700 you would need a very large high torque motor with an ultra low kV... Something like a kV of 50. Do such motors even exist? The lowest I've seen are some motors meant to replace gas engines in large fixed wing with kV of around 120-150.

And the auto performance would be hurt. In TH, the motor resistance would drag the rotor rpm down until you hit the threshold to disengage the clutch. Speaking of which you would need a centrifugal clutch that engages at around 500 rpm or so, might be hard to do as most units for nitros and gassers are made to engage between 4000 and 8000 rpm.

-Jeremy
Whiplash-G
Helix 700G
T-Rex 450 fbl conversion
alot of planks

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11-30-2015 01:10 AM  36 months agoPost 7
SkySurfer

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usa

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You still need the gearing to drive the tail rotor. So there wouldn't be any real weight savings.

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11-30-2015 01:11 AM  36 months agoPost 8
kavic5150

rrNovice

Maryland, USA

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You could manage it. But to run a brushless outrunner at its optimum speed of 50,000RPM (450 size heli) or whatever it happens to be, you'd need some type of in-line gear reduction. Planetary gears would work but that would add significant weight vs the usual pinion/main gear arrangement.

Lets take your average 600 size heli and assume its using a 520kv motor and 12s lipos. So thats 540kv * 44.4v nominal = 23,976RPM under no load.

With the load of main and tail blades its more like 21,000RPM. Just guessing here. From there lets assume your target main rotor RPM is 1,900 RPM. So you would need an 11:1 gear reduction.

Another approach would be like what JHarkin mentioned. A very low kv motor. Like this one on a 450:

http://www.helifreak.com/showthread.php?t=366956

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