Beginner advice on using old RC plane kit on an RC boat

[CruisingGeorgeParticipant @cruisinggeorge]

Hi everyone. I'm new to the hobby of building model boats and am planning to build a 1/12 scale narrow boat for a scale garden canal. I'm happy with the construction of the vessel but I'm not terribly confident on what I'm doing with the RC side of things. I calculate it's going to displace around 10kg of water and I want a very slow realistic running speed.

Luckily, I have an old cessna RC plane which I have raided for my narrow boat build. That's the TX and RX sorted, along with a servo for the rudder (I assume . Beyond that, I'm not so sure where to turn for the rest of the kit. I am hoping that I can reuse either the battery and motor from the plane. The motor is one of these motors and the battery says 11.1V 1100mAh 9C continuous on it. Can anyone offer advice on whether either of these might be suitable? My gut instinct is that the battery is designed for a plane where it needs a lot of energy for a short period and is probably not appropriate, whereas the motor may be more appropriate in a more toned down set up.

The plane motor never ran in reverse and am I correct in thinking that the ESC is responsible for this? So if the existing motor is appropriate, how do I choose a compatible ESC?

The final bits I think I need are a shaft and propeller, and I've just selected a pretty basic one on Cornwall Model Boats, along with a joint and fittings to match my motor.

Finally, any tips for how to choose a rudder?

Thanks for any advice you can give.

[CruisingGeorgeParticipant @cruisinggeorge]

[Charles OatesParticipant @charlesoates31738]

Hi George, your instincts about the motor etc are all correct. it's the esc that gives reverse or forward only as in a plane. The motor you have is a high reving brushless one, great in a plane but unsuitable for a narrow boat. You need a slow reving motor that'll turn a decent size prop. I'm guessing that your model is about 1.1 meters long, and possibly a 40 mm prop. If this were my model I'd use a 540 ln motor from MFA and an mtronics viper esc. Please note that the ln suffix is important, 540 motors vary a lot and most are not right for your boat. A 7.2 volt nicad battery or 2s lipo of you prefer of above 3000 mah will be fine.

I hope that helps a bit.

Charles

[ashley needhamParticipant @ashleyneedham69188]

George. Welcome to the forum. The font of all knowledge.

To add to Charles post, the MFA motor is a 540/1, 6-15v type and this will turn a 40mm prop ok on 11v of your Lipo or even a 6 cell Nimh pack.

Reversing brushless esc tend to be dearer, but a cheap 28mm 1000Kv outrunner would do and this will turn a decent size prop.

Ashley

[Tim CooperParticipant @timcooper90034]

George

Just a thought. If the Tx is from an old aircraft model is it a 35 kHz set?

Strictly speaking it should be 40 kHz or 2.4 ghz for model boats.

Whether this matters if you are using it in the garden only, I don't know.

Tim

[Charles OatesParticipant @charlesoates31738]

I can't ever remember disagreeing with Ashley before, so this is a first. I did mean the 540LN. It only revs to 6000 on 12 volts, so around 4000 on 7.2 volts, with lots of torque, I use a couple myself. I also use that brushless in a 26inch police boat, on 7.2 volts it's very nippy, and planes beautifully, not a bit like a canal boat. I know it could be throttled down, but I would prefer a better match to the model.

The motor would probably draw around 1.5to 2 amps, so whilst the existing battery will work, it won't have a long duration and the weight isn't a problem in a canal boat which will need plenty of low down ballast.

https://www.mfacomodrills.com/motors/540ln.html

Above is a link to the motor data sheet, if you copy it and paste into your browser it will take you there.

Charles

[Brian Sweeting 2Participant @briansweeting2]

I may well be behind the times here but may years ago, about 30, I made a model narrowboat and used my dads old RC kit from his also old sailboat.

Depending on the size of your model but due to the potential short engine room area you may have problems getting the prop shaft aligned with the motor and the swim of the boat. I got over that by using a belt and pully to connect the horizontal prop shaft with the motor being mounted above the shaft. It can also allow for a larger/slower prop if required.

[CruisingGeorgeParticipant @cruisinggeorge]

Afternoon all, some cracking replies so far thanks very much.

Charles you're right the motor does seem to rev quite high, so I suppose I'd better ditch my existing motor and ESC. Thanks for your suggestion of the 540LN, I'm happy to take your advice on this although I note it's a bit weighty. I'm toying with the idea of dropping the plans down to 1/24, that would give a 60 foot boat a scale length of 30 inch and this would bring my weight limit down to 2-3Kg. Is there a motor/ESC combo you could recommend that's a bit lighter? I'd like to get the build as light as possible and then spread the ballast weight myself.

Ashley what does outrunner mean in the context of motors?

Tim it's a 2.4Ghz system that I bought separately to the plane, so I'm definitely all set there.

Can anyone give some general advice on how to ensure motor, battery and ESC are compatible?

Good idea Brian but I think I will try to keep this one as simple as I can. What's the disadvantage of a smaller prop?

[Ray Wood 3Participant @raywood3]

Hello George,

This is Invictus of Allington one of my designs for a 30ft narrow boat measured from the real thing, published in Model Boats back in August 2016, it's 3/4" to the foot and comes out at 24" long. It needed 1.5lbs of steel plate as ballast with 7.2 volt nmh buggy battery and 400 size motor with 25mm 3 blade prop went fine, they are easily driven and blow all over the place in any sort of breeze on the lake

Can be made any length you like just add a longer centre section for a 60 footer bow & stern the same.

Regards Ray

Edited By Ray Wood 2 on 27/05/2022 21:03:47

[Stephen GarradParticipant @stephengarrad28964]

I bought & built the narrowboat Amelia Rose kit last year as my first model boat. On advice from my local model shop I used a Viper Marine 20amp ESC & 7.2V 2400mah Ni-Mh battery. On advice from the forum the motor that came with the kit was far too fast revving & I was recommended an MFA/Como 540LN. Absolutely spot on. Charles's advice above is exactly right. She runs just right, slow revving with plenty of torque.

Stephen

[Charles OatesParticipant @charlesoates31738]

Hi again George, if you're going for a smaller model, a 385 motor would be better, not a 380 which looks similar, but is very different.

Matching motor to esc to battery isn't difficult once you have an idea how many amps the motor will draw. An re 385 from MFA will run on a huge range of voltage from 4.5 to 15 volts, but typically on 7.2 volts it will only draw an amp or two, depending on the propeller. Even stalled it will not draw a huge current, so an esc rated up to 10amps like the mtronics viper 10 will be fine. Battery capacity for lipos and NiMH batteries are easy too, if a motor draws 2amps and the battery has capacity of 4 amp hours (4ah….4000mah) the model could run for nearly 2hours. Things are different for high amp draws, and with lead acid batteries, but that's not relevent with your model.

Hope that helps a little.

Charles.

Ps if you're interested, look for an article buried on the model boats magazine web site about models and electricity by the late great guy, Dave Milbourn.

[ashley needhamParticipant @ashleyneedham69188]

Charles. I am not sure you are disagreeing with me. I was just tidying the 540 issue to indicate the lower revving one.

Any of the motors mentioned should be happy on an Mtronics 15A esc.

As suggested, a 385 is a nice little motor and is ok on 7.2 for a 40mm prop. As you will be ballasting up, then having a heavy-ish motor is a bonus however and 540LN is able to produce more power than a 385 should you need it. I have two MFA 800s in the carrier partly just for the reason that they are v chunky.

Ashley

[Charles OatesParticipant @charlesoates31738]

Hi Ashley, you did mention the 540/1 which is a high reving much hungrier motor than the 540LN. In ye olden days, I used them in fast electric models. I blame the numbering system for motors, for a newcomer it must be a nightmare trying to tell motors apart. Thank goodness for the much easier system on brushless motors.

Charles.

[ashley needhamParticipant @ashleyneedham69188]

Having looked at the specs, I can see that indeed the LN is a truly weedy motor and also revs half as much as the /1. However MFA used to list a 6v 540 which is no longer listed, and this was more powerful thing and higher revving than the /1 even on 6v and I believe is what you would power a plane with. The LN produces approx 25 ish watts at 12v, the /1 40 ish watts at 12v…perfectly adequate of course for a canal boat or whatever, but a check with a meter to see how they are being loaded might be in order.

I have several unmarked 540s in the box and have absolutely no idea what they are, it’s difficult to tell until you put a prop on and test them with a 7.2 stick on a wattmeter.

Ashley

[Kev.WParticipant @kev-w]

I cannot understand this devotion to a 540 motor, for something of 25 – 35 inches in length, that needs thrust & slow scale speed, the 555 motor from Component Shop, is more suited. to this application, whereas the 540 is more suited to a 24" cabin cruiser that needs a bit of speed.

Edited By Kev.W on 29/05/2022 00:23:47

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