Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Glyn Roberts]

Hi Folk,     I am currently building the Dumas Trojan F-31 Motor Yacht,  it is 31 inches in length and 12 in beam and very light in weight. 
http://www.cornwallmodelboats.co.uk/acatalog/Dumas-Commuter-Boats-Motor-Yachts.html

As this is a departure from my usual boat size  ( Normally about 4 Foot )  I need to decide on what size motors for the twin Motor setup.  Would be nice if it was fast with a bit in reserve for my mad moments.   I envisage the props to be about 32mm  but that is open to debate.

If you have any thoughts on this matter I would be very pleased to hear them as I have had some super help on this forum in the past.

Thanks and Regards Glyn

[Glyn Roberts]

Would anyone like to make a comment on what size twin motors for this model please.   Even if its just an educated guess or a guide, would be useful. 

Regards Glyn

[unbuiltnautilus]

Okay, I will start the ball rolling..
Slow, plodding, cheap, endurance..MFA RE385 motors, 7.2v to 9.6v, up to a 5000mAh NiMh.
Bit less of the above..MFA RE540/1 motors, 7.2v to 12v, up to 5000mAh NiMhs, although the standard RE540/1 motor can be a bit 'sparky' at higher voltages. I believe MFA do a superior version of this motor, but I have no experience of it, another member on here mentioned it recently, just cannot remember who.
A bit more speed, a bit less endurance, somewhat more cost..I would go to brushless from here on out, I am now a convert! Although, so far only single screw set ups. So, hat in the ring moment, based on other peoples experience and my poor memory..28mm can outrunners, between 900kv and 1500kv. Forward only 'flight' controls are the cheapest option, ( dont forget, with brushless you will need one per motor ), Forward and reverse RC Car controls are the second cheapest option, reputable suppliers and Hobby King are available . Batteries, as long as you are not balls to the wall all the time, either high capacity niMhs again, up to 9.6v, or liPos between 7.4v or 11.1v should do the job. The higher Kv motors will work fine at the lower voltages, while the lower Kv motors like a bit more voltage to get the best out of them..now for some specifics, over to the rest of you

[Glyn Roberts]

Hi  unbuiltnautilus,  Thanks for response,  28mm can sounds right as my 4foot models use 3536 Turnigys to make them fly.   I need twin brush-less motors Forward and reverse controllers,  and have 3's lipo,  does  32mm screws sound right. 
This motor is the size suggested - https://hobbyking.com/en_us/turnigy-aerodrive-sk3-2822-1090kv-brushless-outrunner-motor.html.

Anyone, please feel free to jump in as this worked for me before getting a broad spectrum of opinion generally highlights the answer.
 
Regards and thanks Glyn

[unbuiltnautilus]

I have been testing brushless motors in a 37" KD Perkasa. The photos show it running with a Leopard 3536 960Kv motor, at 9.6v. Motor from Component Shop. The prop was a 36mm 3 blade, Graupner Carbon Hydroprop, pulling about 12 amps, it ran for about 18 minutes on a 3800mAh NiMh.
I have also tested the same boat on a Ripmax Quantum II 20 motor, same size, just 1250Kv. Maximum sensible speed was obtained at 8.4v and a current drain in the ballpark of 17 amps. I have yet to test this set up with slightly smaller props. So far, it seems that prop size can greatly effect the run time. My next prop to be tested will be a 33mm 3 blade prop, like the previous 36mm prop. Also, a standard 2 blade 35mm prop, just for reference.
I think your choice of the 33mm prop is spot on, just play with your input voltage.
Photos ripped from the Display Teams Facebook page, cheers Jamie

[Ron Rees]

Hi Glyn,


I note 'unbuilts' comments and I would go along with his recommendations re brushless set-up. In my opinion and experience it is a 'no-brainer'.


Twin 28mm diameter outrunners of about 750 to 1000 kv would be best for this size model and will give a very good performance. I would go for the slightly longer 2830 size for the extra torque. Coupled with 11.1v Li-Po's these will give a max turning speed about 8, 500 to 11,000 rpm, which to me would indicate a slightly smaller pair of props. These little motors like to run at full speed to be efficient so I use K series racing (Hydro) props from Gliders UK and would go for 28 to 30mm diameter 2 bladers to start with. They are about £4 each. I quite like the Black Turnigy and Gold Turnigy motors from HobbyKing at about £12 to £15.00 or so each.


I use the Alexander Engel 30 Amp Sub Commander speed controllers from Germany which are waterproof, can be water cooled have forward 100% and reverse 50% set up as standard. They run at about 1.5 to 2 amps each normal and no more than 4 amps fast and stay very cool. Cost about 29.00 Euros at the moment. Hobbyking do an identical ESC Part number 74071 for about £2 cheaper and quicker delivery from UK warehouse. Never had a glitch with either of them and about the same price as an MTronics 30 Amp. brushed controller.


Depending on ballast weight needed, Two 2.8 x 11.1v. Li-Pos would be nice but you can go up to a 5Amp/Hour battery if you need the weight,  Remember if you are using the BEC on one of the controllers (You need one for each motor)  you need to disconnect  the red wire from ONE of your speed controllers. Don't cut it all out just a snip and fold it back so you can use the BEC on it in another model if you wish.


You could also fit a mixer (Throttle/Rudder) and I like the Action ones from Component Shop, not essential but can be fun.


Should go like the clappers (If you push forward hard enough) but nice at tickover which you will get with this set-up.


Have Fun..........Ron.

[Glyn Roberts]

Thanks Jamie and Ron,    Just as I hoped great minds are thinking in harmony.    Its amazing how info from  some body one has never met can lift you when you feel unsure about something.  Shows that the Forum is working.
This info will also help those on similar builds to make good choices.

Regards and Many Thanks Glyn

[unbuiltnautilus]

Thanks Jamie and Ron,    Just as I hoped great minds are thinking in harmony.    Its amazing how info from  some body one has never met can lift you when you feel unsure about something.  Shows that the Forum is working.
This info will also help those on similar builds to make good choices.

Regards and Many Thanks Glyn

I can see the confusion now..it's not Jamie, it's Alan. It was Jamie's pics I pinched from our groups Facebook page.. would have made more sense if I had said 'Cheers Jamie, Alan ', but hey, any way it comes, you are welcome and it is good to share!