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[DominicS]

I'm new here, but have been playing with and making radio controlled model boats for about 6 years now. I tend to make them on the smaller scale and have 3 rules


1) The are small enough to fit into a carrier bag
2) They use single cell li-ion or Lipo batteries for powering them
3) The use brushed rather than brushless motors

And my latest build is converting a Meng 1/700 scale HMS Rodney to radio control

http://www.meng-model.com/en/contents/77/215.html

as they have a full hull rather than the Tamiya model which is a waterline model. The Meng version can be made as a waterline model and the hull is split horizontally to do this. One issue with making smaller models is that they are always too heavy, and rather than trying to lighten things to extreme and getting minimum gains, I thought I'd make the hull deeper, so that it sits on the water correctly.


To do this I assembled the hull and deck and had a guess at the weight of the superstructure, motors and propulsion, radio control equipment and battery and added some 1p's and 2p's for ballast at appropriate points in the hull. The hull then had some electrical insulation tape over the hull sections and was then put into some water to show how it sits. The model is about 320mm long, 50mm wide and has a freeboard of 12mm, so it is on the smaller size. From this test I decided that the hull needs to be 1mm deeper at the bow and 4mm deeper at the stern to sit right in the water.


To do this I used a 1mm thick piece of styrene sheet and then layered it up with 0.3mm, 0.5mm, 0.75mm, 1.0mm, 1.5mm and 2mm thickness to get the correct taper. This was glued together with superglue as I find I can get stronger bonds than I can with styrene cement.

I then decided to mill some holes in the hull bottom so that I could fit the propeller tubes going through the hull.


the hull sections ready to be glued together. note the locating pins have been extended to go though the white tapered section

the hull sections gued together


and the hull hollowed out

[dodgy geezer]

Interesting. Where do you sail them? I would have thought that the smallest waves on a lake would be too much...

[DominicS]

Interesting. Where do you sail them? I would have thought that the smallest waves on a lake would be too much...

yeah they are fine on a lake as the don't weigh much they are boyant and ride above waves if they're not too big, and wakes from other boats dont seem to cause an issue either.

The pictures below show my paddle boat in a lake and also sink, and my playmobil speedboat also in a lake and in a sink.

The biggest problem is that they are hard to see when out on a lake, so normally I only go a few feet out from the side of the lake.

[warspite]

I have a trumpeter Warspite that I want to convert, it too is of a small scale and deepening the hull sounds like a good idea, though unsure if I could do it to your standard, have the same problem with the other airfix vessels I have - one day 

[dodgy geezer]

That's a great pic of the Rodney on the lake!  Do you have a Bismarck? It looks exactly like the view that the Swordfish would have had as they lined up for attack...

[DominicS]

When I made my first boat about 6 years, I had the issue of aligning the motor and propshaft accurately, so my answer to that problem was to mount the motor to the propshaft tube, so the photo below shows a complete assembly of the propulsion units for this model, and one in pieces (and a pound coin for scale). The motors I use for a model of this size are N20 motors (normally sold with small geartrains on them), I got a few of them a while ago, and on 4.2v have 13,800 rpm without any load. Then there is the motor mounting that mounts the motor to the prop tube. The prop tube is made of aluminium rather than brass tubing to save weight. There is only one bearing on the prop tube and it is made from bronze with an O ring in it to seal the propshaft. I used an O ring rather than filling the prop  tube with grease as there is less drag, and with motors this size you don't have too much power to begin with The prop shafts are 1mm carbon fibre rods, to save weight as I tried stainless steel ones orginally. the prop shaft is connected to the motor by a piece of small nylon tubing which is a tight fit. There is also a styrene tube that the prop tube goes into and this is a light push fit and is glued into the hull of the boat. doing it this way the whole assembly can be taken apart for maintenance The propellers are 12mm diameter and are cut down from from the following props for small drones

https://www.ebay.co.uk/itm/335844411080

so thats how I attach a propeller to a motor.

to align the prop tubes correctly for gluing the styrene tubes into the hull I used a piece of scrap metal with a couple of holes in them the same size as the prop tubes and this works as an alignment guide.

and the complete assemblies in the hull of the boat

I'll leave the rudder on the boat, but its not going to be a working one, as I'll use tank steering to turn it as I've got a couple of propellers on the boat, and it saves weight not having a servo to operate the rudder.

[DominicS]

a few years ago when I got back into radio control I found that things had changed from the early 1990's when I last used it. I decided to use Flysky radio control gear as I could get these small 4 channel aftermarket receivers that work down to 3.3V so can be used with single cell Li-ion or LIPO batteries for power

https://www.aliexpress.com/item/1005005992276197.html

For this model I'm using tank steering and mixing the channels in the transmitter to do the steering, which has an issue with the above receivers as the 4 channels it uses are the same as the 4 channels on the joystick, so I needed to disable the sticks to work on two of those channels. This was done by cutting one of the legs off one of the potentiometers that the stick controls and wiring in second potentiometer (blue in the pic), so that the electronics think that the stick isnt moving in one direction. If I was using a standard 6 channel receiver this wouldnt have been a problem.


and speaking of batteries they need charging so for single cell li-ion or LIPO batteries I still use a TP4056 USB charging module, for batteries less than 1AH capacity. by changing one resistor on them I was able to reduce the charging current to 0.5A

https://www.ebay.co.uk/itm/303629601119

For this model I used these speed controllers for the motors. if you're using N20 geared motors to operate things on models they can be used as forward and reversing switches for them.

https://www.aliexpress.com/item/1005012569516901.html

I need a receiever and 2 speed controllers for this model so here they are wired up with a pound for scale.

The speed controllers are then folded above the speed controller, with some thin styrene between them and covered with heatshrink, which I think is very neat wiring.

I did try this model out on a lake with the electrics just taped to the hull with the deck taped on the hull to see how it went and it went pretty well and the tank steering worked well giving a decent turning circle without a rudder. I use a Flysky i6s tansmitter, and if you want to know how to do the channel mixing to do the steering on these, let me know and I'll post it on here. I can use different capacity batteries and change position to alter the balast when the model is completed

I did test the electrics in my grill pan, and at full power with a half charged battery (3.58 Volts),  both motors are only drawing 0.31Amps together, so even with that battery I should get an hours running. I needed 6p of ballast to keep the propellers under the water.

the gauge which shows the voltage and current draw is a USB power meter  taken out of the case, rewired with suitable connectors  and covered with heatshrink.

https://www.ebay.co.uk/itm/389054682679

For smaller models like these and power consumption under 3 Amps I use JST BEC connectors that are standard on batteries. For the power connections below 1 amp and servo connectors (on other models) I use Micro JST 1.25mm conectors.