Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: wartsilaone on February 04, 2011, 09:59:55 PM

Title: Any problems?
Post by: wartsilaone on February 04, 2011, 09:59:55 PM
I want to use the following setup. Can anyone see any potential problems?

One 12v 7ah battery driving two MFA 919 motors with 11:1 gear ratio,each controlled by a viper marine 15


another 12v battery providing power to a 7.5v bow thruster,rudder servo and receiver using the BEC on a viper marine 25 mirror.
 I should add that the motors are 540's and im running 50mm props at scale speed for a ferry.
Title: Re: Any problems?
Post by: malcolmfrary on February 05, 2011, 08:30:26 AM
Not being familiar with MFA919s, the only problem I see it that a 7 and a bit volt motor will soon be unhappy with 12 volts.  Plenty of discussion on various threads on here covering just this point.
Title: Re: Any problems?
Post by: Roadrunner on February 05, 2011, 10:56:46 AM
the mfa 919 motors will draw more then the the 15A ESC can provide ( each motor is recommended to use 15A esc each as a minimum, the result will be fire!)

im currently using twin mfa 919 2.5:1 motors in my tug project, which will run off Actions p94 (twin esc & mixer unit)

using the bow thruster rated as 7.2v with a 12v is over powered and will burn the motor out in a short amount of time, have you considered a all ACTion setup using the P102 power distribution board, which will take a single 12v 7ah battery or two in parallel if you want more run time. 

that in turn should connect to a p94 twin 20A esc and mixer ( with 4 mode function ) which will run the mfa motors.

the bow thruster u are able to connect up using a 2nd single esc through the p102.

P102 (

p94 (

P93 (multi controller/esc) (

check out ACtions wiring diagram on how your setup can be done ' better' (

Also what boat are you building as 11.1 geared may not be suitable for your project if its a tug, 2.5:1 or 6:1 should be used as 11:1 is very slow and will not provide enough push/pull.

Im using 2.5:1 as the lake we sail has random currents so 2.5:1 will give me a good all round pull, but will also get me out of trouble if need's be, i am able to swap to 6:1 if im on a clear pond for the day.

11:1 is more suitable for paddle wheel boats or where slower rotation is needed.
Title: Re: Any problems?
Post by: nick_75au on February 05, 2011, 11:17:21 AM

Is this what your talking about?

If it is  you will be fine with a 15 amp controller and 50mm prop, but you wont be moving at scale speed, , you need to spin the props to at least 4000 RPM, of which the 15 amp controller will still be OK, I would recommend that you don't run the thruster on 12 volts, the mechanics don't handle the higher RPM 12 volt gives, use a 6 or 8 volt battery for it.

Title: Re: Any problems?
Post by: Roadrunner on February 05, 2011, 11:21:09 AM
This one.. (

Also Action's wiring diagram is setup using MFA's motors so he knows what hes on about, or he wouldn't suggest twin 20A esc's for mfa motors.....  %)
Title: Re: Any problems?
Post by: DickyD on February 05, 2011, 11:26:16 AM
With the 12V battery you really need a 6:1 gearing
Title: Re: Any problems?
Post by: ACTion on February 05, 2011, 11:28:52 AM
The MFA 919 Series of geared motors are also sold as Torpedo 500. The specifications can be found on the MFA/Como Drills website, on the sixth page of the full catalogue: (
The stall current of the motor is given as 8.2A in all applications. The only problem we have found with them is that they are very "dirty" electrically and benefit from a full 3-capacitor suppressor set. If you are using a 2.4GHz set then this is less important.
We recommend using the 20A ESCs as they offer a higher safety margin than the 10A version for little extra cost - "belt and braces" as it were. A 15A ESC would also be adequate - but we don't make one!
Title: Re: Any problems?
Post by: wartsilaone on February 05, 2011, 10:02:20 PM
Thanks for all your replies. It seems the general consensus is that i should use 20A speed controllers and a 7.2 battery pack just for the thruster. Ill stick with a 12v battery to power everything else. As for the motors, I chose these because i don't want my ferry to run like a speedboat.
Title: Re: Any problems?
Post by: john s 2 on February 05, 2011, 10:11:36 PM
May i suggest the use of an Action P94 mixer? It will give you good control over your model. John.
Title: Re: Any problems?
Post by: Shipmate60 on February 05, 2011, 10:15:36 PM
How big is the model and what size props will you be using?

Title: Re: Any problems?
Post by: wartsilaone on February 05, 2011, 10:22:04 PM
I want everything independant Just like the real thing so so i shouldn't need a mixer. The model is 1440mm long, 50mm props, scale speed 7cm p/s.
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Title: Re: Any problems?
Post by: Shipmate60 on February 05, 2011, 10:31:14 PM
On 12 volts these motors will only give you 1436 rpm.


It is usual to run these props about 3500 rpm.
With her windage you might struggle against any windage as the wind isn't scale!!

Title: Re: Any problems?
Post by: Roadrunner on February 05, 2011, 11:13:02 PM
I think your dismissing the p94 a bit prematurely, the p94 has 4 modes which allows you to adjust prop speed on each motor to assist in turning.

Check out the p94's pdf spec's its worth reading (

Now im no 'ferry expert' but i would have to assume that your ferry's real life counter part will turn one prop faster then the other during turning, or reverse one while the other is in a forward motion, this combined with the bow thruster makes for better manoeuvring.

I have assumed that your craft is a fixed shaft, in which case the p94 will not only do the right job for you, but will also allow better control of the craft in a scale movement, as its functions allow for the prop rotation speeds during turning in conjunction with the rudder(s)

Now i could be wrong about that given you say each prop is independently controlled like the real thing, but you also have the issues with you controlling the model via stick's which is not that easy if each motor is separate, remember your going to need a minimum of 4 channels to control this thing, both sticks forward and back for each motor , one stick controls the rudder and one for the thruster. (left and right motions)

The p94 makes it easy with its mode functions to just use one stick for forwards and reverse, leaving one full stick for your rudder and thruster .
If your craft is using something like rotating korts, then separate function of each motor would be the solution. ( i can't tell from the photo's)

Don't get me wrong i like cheap options when ever possible, but in this case i think your craft will benefit from the extra spent on its electronics.

I can't say any more, the choice is your's.
Title: Re: Any problems?
Post by: john s 2 on February 05, 2011, 11:24:16 PM
Just to add that i use a p94 on both my 4 ft Solent lifeboat and my 4ft paddler. In both cases with mode 4 i can turn the vessels in
there own length. Does of course depend on prop type Kort etc . John.
Title: Re: Any problems?
Post by: Shipmate60 on February 05, 2011, 11:40:53 PM
Why bother to keep on about mixers when the OP has already stated he wants independent control.
I am not keen on mixers for twin screws as I think I can react to Windage etc far better than a set programme.
Now 3 shafts and a mixer is almost indispensable.
If he doesn't want a mixer and more cash in his wallet that is his choice.
My concern is that with those motors the model will be severely underpowered.

Title: Re: Any problems?
Post by: john s 2 on February 06, 2011, 12:11:45 AM
Im sorry that you feel that we are keeping on. Evereyone is entiyled to there view. I fail to see why trying to help someone make
a reasoned decision is keeping on. Should we all critize each other for trying to be of help? The more info the better. Thank you
for giving your reason for not liking mixers on two prop systems.John. 
Title: Re: Any problems?
Post by: wartsilaone on February 07, 2011, 03:37:42 PM
I'm sure you all will agree that when it comes to your pride and joy running the way it should, given time and money you will do what it takes to make the necessary changes.
   I still have to conduct sea trials when I'm ready. the motors can be swapped in seconds and there is plenty of room for extra electronics.