Which Brushless Motor for Aeronaut Classic

[Martin Smith 8Participant @martinsmith8]

1000Kv or 1500Kv

[Martin Smith 8Participant @martinsmith8]

Hello new to here and model boats and about to build my second model the ever popular aeronaut classic. Whilst I accept it might not be scale speed I would like a bit more power and speed than I suspect the race 400 brushed motor is going to give bassed on the brushed motor in my aeronaut Mowe model.. Aeronaut suggest there own 880Kv motor as an alternative so I wondered if the Mtroniks G2 Hydra 15 1000Kv system motor esc combo would be a suitable alternative. I have read these forums and note the comments about not going for to high a Kv rating so thought something like Overlander Tornado Thumper V3 2830/09 1300KV Brushless Outrunner RC Motor would be as high as I should go. as I would need to upgrade the propshaft and add in a universal joint and two couplers what would be a sensible reduction in shaft length? the kit ships with a 7 inch shaft so to allow for the the coupler and joints would a 5 or 6 inch shaft be more appropriate?

Observations, comments, general wisdom or straight experience would be greatly appreciated.

[Kev.WParticipant @kev-w]

Take a look at this UTube video, it gives motor spec in the description.

Aeronaut classic

[Chris FellowsParticipant @chrisfellows72943]

Hi Martin

For these types of boats I usually suggest something around 900 to 1200kv and going up to 1300/1500kv is fine. Much more is not really needed and I note that the one in the video is 2800kv which is too high really, though it certainly shifts!

Good thing with brushless is that they can run on quite a wide range of volts so you can always increase if you want more performance.

For this sort of performance I use the alloy couplings with the rubber bit in the middle – see my Fairey builds. The UJ/Huco couplings are only really suitable for low power/speed as they can break apart. Alignment of the motor and prop shaft needs to be accurate and it's a good idea to use a solid coupling of the same length as the flexible one to achieve this. If you want to go down this route I can provide sizes of the coupling.

As for prop shaft length you need to mock it up on the drawing or keel using the motor and mount and the coupling (allowing for the distance that the motor and prop shafts go into the coupling). Many prop shafts can be reduced in length.

ModelBoatBits is one good source of couplings and prop shafts etc.

Chris

Edited By Chris Fellows on 17/05/2022 18:46:37

[Martin Smith 8Participant @martinsmith8]

Thanks for the replies and my education continues!

I will look into those couplers

I’m still considering motor options as I doubt there be space for much more than a 30mm prop so huge wattage won’t be required unless the pitch of two bladed racing props is much more aggressive, but I’ve yet to read up on that!

Im thoroughly enjoying this new hobby.

[Chris FellowsParticipant @chrisfellows72943]

Hi Martin

A larger prop can be accommodated by increasing the angle of the prop shaft, not too much though, aim for around 12 deg or having the prop shaft protrude more from the underside of the hull or a mixture of the two.

30 or 35mm is as much as you need for that boat and a 28mm dia. brushless will turn it no problem. No need for a racing prop! For me that model in the video is too fast and way above scale speed.

Clearance for the prop is one of the reasons why you need to mock up the motor and prop shaft as this will give you the length of the prop shaft required (inner and outer) and where it will go in the hull and the position of the motor mount.

This is a 30mm prop on my Fairey River Cruiser. The prop can be further away from the rudder. 

Chris

Edited By Chris Fellows on 19/05/2022 15:47:36

[Chris EParticipant @chrise]

Just to state the obvious the best motor kv is directly related to the battery that you are going to use. A 1000kv on 3S (11,1v) will turn the propeller at the same rpm as a 1500kv on 2S (7.4v).

11.1 x 1000 = 7.4 x 1500

To get the same performance the 2S pack would need to draw 50% more current than the 3S to get the same watts (voltage x amps).

[Martin Smith 8Participant @martinsmith8]

That’s the reason I’m tempted by a higher Kv motor.

3 cell for lunatic mode and 2 cell or even a 7.2v 5000mah for more scale performance.

Ive got 2, 3 and even 6 cell Lipos knocking around from my helicopters.

the build is progressing but I have to say skinning the hull proved to be pain in the ass!

[Martin Smith 8Participant @martinsmith8]

That’s the reason I’m tempted by a higher Kv motor.

3 cell for lunatic mode and 2 cell or even a 7.2v 5000mah for more scale performance.

Ive got 2, 3 and even 6 cell Lipos knocking around from my helicopters.

the build is progressing but I have to say skinning the hull proved to be pain in the ass!

[Chris EParticipant @chrise]

Sounds like a good plan to me.

[Kev.WParticipant @kev-w]

If The boat is too "lunatic" on a 3s, then calm it down by using a 2s instead.

To quote a well respected & sadly missed contributor to our hobby, "the speed of your boat, can be directly related to the movement of your 'proportional' throttle stick", i.e. if the boat is moving to fast, back your throttle off.

Modern radio's are not 2 position, otherwise you would have a switch, not a variable stick.

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