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Which 12v motor for 30" carbon prop?

Newbie help with thrust.......

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David Wainwright09/07/2017 20:07:15
20 forum posts

Excuse ignorance as brand new to this hobby so please speak in dim terms although I understand a little.

I have a 30" carbon prop I want to get spinning over 10,000 rpm and run off a speed controller (have 70a one) and 12v lithium car battery.

What kind of motor would provide enough torque and speed to achieve this please?

If you're wondering, I'm building a simple paraglider fan rig. After experimenting with an 8inch prop and a cordless angle grinder I was pleasantly surprised with thrust.

Any tips in simpleton language please. Lol. Thanks in advance.
Dave Hopkin09/07/2017 21:31:42
3672 forum posts
294 photos

To get 10,000 RPM from a 12v supply with an outrunner you will be looking for a motor with a Kv rating of between 800 and 850, but to spin a 30" prop at 10k..... the norm for that sort of motor would be in the region of 11 to 13" prop

Frank Skilbeck09/07/2017 22:36:40
4423 forum posts
101 photos

Whats the propeller pitch, if that is known you can work out the power required. BTW my 18" dia by 10" pitch prop runs off a 30v battery.

Steve Hargreaves - Moderator09/07/2017 22:45:57
6711 forum posts
189 photos
Spinning a 30 inch prop at 10,000rpm would send the tips supersonic....interesting but not recommended....I doubt it would be strong enough to withstand the forces involved...

I also think you would need several kilowatts of power to get anywhere near that sort of speed....

Something is not right in the OP...are you sure it's not a 30cm prop? That would be about 12 inches & things start to make sense....
PatMc09/07/2017 23:22:09
4169 forum posts
520 photos

To get 10,000 rpm under load from 12v the motor kv would need to be about 1050. A safe current limit using a 70A esc would be about 60A. Therefore max power (input) would be around 720 Watts (just under 1HP).

David Wainwright10/07/2017 01:47:38
20 forum posts
Hi. This is the propeller I am using.Look at this on eBay
David Wainwright10/07/2017 01:48:43
20 forum posts
30" x 10" carbon prop not metric
David Wainwright10/07/2017 01:49:36
20 forum posts
Hi. 30" x 10" carbon prop mate. Thanks.
MattyB10/07/2017 02:46:23
1919 forum posts
29 photos

OP, forget rpm for now; what is your target pitch speed (the max speed of the airflow coming off the prop)? To calculate tell us the max speed you are looking to attain under power, then add 20-25%. Once we have that we can work out the rest more easily.

Andrew Ray10/07/2017 06:26:59
699 forum posts
19 photos

Frankly it sounds like too big an ask.

As for the prop you are looking at being suitable for speeds of 10,000 RPM I think you are asking for trouble. A more realistic target is around 6,000 RPM with a geared motor or big outrunner but a 12v battery will not hack it. You'll get a motor within the amp range of your ESC but you'll need something like 3 times the voltage to get a decent prop speed and probably need to use a smaller prop.

Why 10,000 RPM and 12v and what are you using it for?

Chris Bott - Moderator10/07/2017 07:23:12
6642 forum posts
1374 photos
1 articles
Hacker list a motor.the A150-10 that will spin a 30x12 at 4500 rpm. But that requires 49 Volts at 180 Amps. That's 8.8Kw for less than half the rpm requested.
Andrew Ray10/07/2017 07:29:40
699 forum posts
19 photos
Posted by Andrew Ray on 10/07/2017 06:26:59:

Why 10,000 RPM and 12v and what are you using it for?

My apologies, I see you have answered this in your original post but why 10,000 RPM?

Edited By Andrew Ray on 10/07/2017 07:30:44

Biggles' Elder Brother - Moderator10/07/2017 07:43:51
15748 forum posts
1460 photos

Hi David,

Assuming this prop has a average sort of pitch value you might expect, I'm afraid what you are asking for isn't practically possible with that battery - the current needed to deliver 10,000rpm would be huge!! Orders of magnitude beyond your 70A Speed Controller! That prop and that battery are just not a compatable pair.

It would make a lot more sense technically to start with the question "How much power do you need to fly this paraglider?" We could then work out a sensible prop/ESC/battery combination.


David Wainwright10/07/2017 08:21:56
20 forum posts
Wow. Looks like I may be using this as a ceiling fan then lol. Not sure about calculating stuff but wanted enough thrust to push around 90kg through the air so what rpm needed for 30x10 prop is unknown factor to me. Main objective is to simply achieve thrust. Obviously weight is a factor so wanted to keep battery weight low as poss. Just thought would be interesting feasibility project before having a go. Thanks for all input so far.
David Wainwright10/07/2017 08:35:30
20 forum posts
So which set up would you guys say would power it with substantial thrust? Looks like I'm back to drawing board. Oh well.
Denis Watkins10/07/2017 08:57:55
3741 forum posts
179 photos

OK David

Current electric paragliding uses 15kw set ups

This is about 20 HP

Petrol set ups are well established, and electric flight is gathering pace with the use of carbon fibre and lightweight power packs

Andrew Ray10/07/2017 09:54:22
699 forum posts
19 photos
Posted by David Wainwright on 10/07/2017 08:21:56:
Wow. Looks like I may be using this as a ceiling fan then lol. Not sure about calculating stuff but wanted enough thrust to push around 90kg through the air so what rpm needed for 30x10 prop is unknown factor to me.

This sounds like a man sized project not a model.

onetenor10/07/2017 12:10:44
1900 forum posts

I would try a recliner chair motor

David Wainwright10/07/2017 13:10:42
20 forum posts
Actually they are about 4 hp. Even the petrol ones aren't double figures. Original question did say I was after a basic device delivering thrust and I quoted angle grinder experiment

Wasn't after Frank whittle plans.
David Wainwright10/07/2017 13:12:25
20 forum posts
Using model parts hence question. Unsure why you felt this answer was needed as contribution tho. Thanks anyway.

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