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Which 12v motor for 30" carbon prop?

Newbie help with thrust.......

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Frank Skilbeck10/07/2017 18:09:43
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Posted by David Wainwright on 10/07/2017 17:58:24:
https://hobbyking.com/en_us/turnigy-rotomax-100cc-size-brushless-outrunner-motor.html

This says it will power a 27x12 prop so 30x10 ok?

Yes, the beauty of an electric motor is it's flexibility, but while this would turn a 30 x 10 it would be at less rpm than 150cc version, and power is roughly proportional to the rpm squared, i.e. if it turns 2 twice as fast it needs 4 times the power, so you'd have to drop the volts and that would drop the amps, and the thrust.

Slickriff10/07/2017 18:24:10
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I assume you realise that 12s is not 12V. It is 12 lipo cells at 3.7V each. 12x3.7=44.4V
So this motor would spin it, but at 44V to match 100cc engine.12V would not be even close.
Slickriff10/07/2017 18:35:51
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So at 44V you would need 4 batteries in series. It would pull 180A, so 4 lithium car batteries of say 54Ah each would run the motor flat out for 18 minutes. (discharging to a point that would not be advisable).....and I am guessing be a bit heavy and bulky into the bargain.
David Wainwright10/07/2017 20:00:58
20 forum posts
Yes, this has been covered and refer to first post re what needed.

Seen 80cc motor, batteries and controller for under 500 that will produce what is needed. Didn't want a rocket.

Thrust produced by above will be more than adequate.

Thanks to those who chose to share knowledge rather than be blind to fact knowledge is only power when shared.
Paul Marsh10/07/2017 20:35:18
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I was wondering if you intend to fly your rig, I hope you know what you are doing. Also any legislation you will need, You should join the relevant club even before you spend any money. I reckon you just can't launch yourself into the air without training or licence and what I see here is a little risky - strapping a 80cc plus motor, with a 30 inch carbon prop doing 10000rpm with 44v of lithium batteries on your back, with no idea what you are doing. EEK!

Sorry, but it looks like that - getting chopped up in the air with a 30inch prop then blown up when the batteries catch fire...crook

see here:

https://www.bhpa.co.uk

Edited By Paul Marsh on 10/07/2017 20:36:55

David Wainwright10/07/2017 20:40:32
20 forum posts
Condescending? You don't know what it means!

Edited By David Wainwright on 10/07/2017 20:54:05

David Wainwright10/07/2017 20:53:27
20 forum posts
Now see here,

If you had bothered reading original post you will see it was a request for info and background as to neivity.

Not sure which part of your answer addresses this.

For your info, I trained and qualified in Derbyshire several years ago. During a session teaching, I saw folk steering their wings using cordless leaf blowers. I was never after a five grand rig, just a compact and light alternative for extra thrust.

If you would care for a lesson get in touch!

As for rpm, I'll be happy with max 5000 after doing calculations.

Thanks for the unwanted concern however. X
Biggles' Elder Brother - Moderator10/07/2017 21:03:37
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Right that's enough.

BEB

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