HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 13, 2013, 03:12 PM
Registered User
Canada, ON, Ottawa
Joined Dec 2012
9 Posts
Question
Prop size for Exceed RC Helium Brushless Motor 4500kv

Hi,

I recently purchased an Exceed RC Helium Brushless Motor 4500kv 11.5 Turn Rating of nitroplanes.com (http://www.nitroplanes.com/86ma54-2205-4500kv.html) but it doesn't give a recommended prop size. Does anyone know what a good prop size for this motor would be. I'm using it for a seaplane trainer, AUW 19 oz, and 45" wingspan.

-Thanks
richard_m is offline Find More Posts by richard_m
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 13, 2013, 09:51 PM
Registered User
Beaumont, TX
Joined Feb 2007
1,335 Posts
Unless you plan on running it with a gearbox, there is no good size prop for that motor. The KV is too high for any kind of usefull direct drive in an airplane. Pretty sure that motor is intended for helicopters.

How did you wind up choosing it?
Pete Miller is offline Find More Posts by Pete Miller
Reply With Quote
Old Jan 13, 2013, 10:03 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
As mentioned you must have a gearbox.. the motor is rated for 2s use and at 33g is probably good for only about 100W (maybe 10A-15A).. if you gear it about 3.75:1 it might be okay with perhaps a 9"-10" prop... but for a 45" seaplane I really think you need a lot bigger motor... perhaps 150W-200W to ensure it gets off the water.
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Jan 13, 2013, 10:06 PM
Registered User
scirocco's Avatar
Australia, ACT, Kambah
Joined Feb 2001
3,270 Posts
+1 on richard's comments.

BEFORE you think about the next motor, you need to determine what size prop you will run. For example, a seaplane with a pylon mounted motor will likely have highly constrained prop diameter, which will lead to a lot of power system compromises compared to say a 3D taildragger same weight and wingspan.

In looking for help, a link to the actual model will help folks frame their advice and avoid impractical suggestions.
scirocco is online now Find More Posts by scirocco
Reply With Quote
Old Jan 16, 2013, 05:38 PM
Registered User
Canada, ON, Ottawa
Joined Dec 2012
9 Posts
Quote:
Originally Posted by Dr Kiwi View Post
As mentioned you must have a gearbox.. the motor is rated for 2s use and at 33g is probably good for only about 100W (maybe 10A-15A).. if you gear it about 3.75:1 it might be okay with perhaps a 9"-10" prop... but for a 45" seaplane I really think you need a lot bigger motor... perhaps 150W-200W to ensure it gets off the water.
How did you come to the 150 to 200W. Using 100w/lbs that would be 112w. Do you really think that I need more than that? If so, would I be able to get enough power using 2s lipos (2650mah 20C) or would I need different batteries. Would you be able to recommend a motor to use.

Here's a link to the plans for the plane I'm building: http://www.rcgroups.com/forums/showthread.php?t=372857

I guess it's a good thing I only payed $9 for the motor!
richard_m is offline Find More Posts by richard_m
Reply With Quote
Old Jan 16, 2013, 05:47 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
I may be mistaken, since I've not flown a seaplane, but logic tells me that you need a fair bit of power to get it to escape the jaws of surface tension to get off the water.. once in the air you are okay. I guess a lot depends on what the wetted surface area of the hull is. Aha.. it is a floatplane! That makes it easier! Certainly, gear it for as big a prop as will fit at 15A, and try 15A/120W or so. If that's not enough go for 3s with different gearing.
Dr Kiwi is offline Find More Posts by Dr Kiwi
Last edited by Dr Kiwi; Jan 16, 2013 at 05:57 PM.
Reply With Quote
Old Jan 16, 2013, 06:05 PM
Registered User
Canada, ON, Ottawa
Joined Dec 2012
9 Posts
would it be better to buy a gearbox for it or just to buy a new motor that could run a decent sized prop without a gearbox? I don't know much about gearboxes so I don't know what their advantages or disadvantages are. Unless gearboxes are cheap, I might just buy a new motor.
richard_m is offline Find More Posts by richard_m
Reply With Quote
Old Jan 16, 2013, 06:19 PM
Registered User
Ken Myers's Avatar
Commerce Township, MI
Joined Aug 2001
4,520 Posts
Not trying to play dumb. I honestly don't understand how this motor would be used. Can someone please enlighten me? I know there are a lot more uses for outrunner motors than what I use them for, but can't understand just what this one might be used for. My only thought is maybe a small helicopter with gear reduction to the main rotor?
Ken Myers is online now Find More Posts by Ken Myers
Reply With Quote
Old Jan 16, 2013, 06:31 PM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,206 Posts
Actually Ken, I've been impressed with some small high Kv motors, deeply geared to run big props... my test motor, an el cheapo AEM12S (34g, 3800Kv) geared 3.2:1, drove a 9x5 GWS HD at 10,020rpm (37oz @ 47mph) at 250W and honestly didn't get excessively hot even static on the bench. Not bad from a 46g (engine + g/box) power unit.

As you can see from flybrushless "RPM as % of Kv x V" is still above 70% (indeed 72%) so that suggests that even a 9x5 GWS HD is not over-loading the motor.
Dr Kiwi is offline Find More Posts by Dr Kiwi
Last edited by Dr Kiwi; Jan 16, 2013 at 08:15 PM.
Reply With Quote
Old Jan 16, 2013, 07:07 PM
Registered User
Ken Myers's Avatar
Commerce Township, MI
Joined Aug 2001
4,520 Posts
Okay, I checked it out at
http://www.flybrushless.com/motor/view/114

I see there is a gear drive available. Learn something new every day. Thanks.

Seems to me that a 'little' inner runner might be better suited and lighter yet, but since I don't fly the smaller models I guess I'll never have the experience to know.

Thanks for the quick reply.
Ken Myers is online now Find More Posts by Ken Myers
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Exceed RC Helium Brushless Motor - Mounting Screws? InTr4nceWeTrust HobbyPartz.com 5 Dec 07, 2012 08:58 PM
Discussion exceed helium motors karlik XHeli 5 Oct 22, 2012 12:45 PM
Question Any problems with Exceed Helium 1600kv motors? suzukirobguy Power Systems 0 Sep 29, 2012 12:27 AM
Wanted Exceed RC Rocket 3020-600KV Brushless Motor Cabledawg1 Aircraft - Electric - Power Systems (FS/W) 0 May 25, 2012 02:54 AM
Sold Exceed Rc Helum 500 Helicopter Brushless motor $20 shipped HeliStyle Aircraft - Electric - Helis (FS/W) 1 Apr 18, 2012 08:08 PM