Cullamix build Part 3 – engine and electronics

Now that the hull and superstructure are basically complete and ready for all the fiddly work, we can look at the inside stuff.

Cullamix is a single engine, single rudder ship so the basic electronic package is:

Radio transmitter and receiver.

Electronic speed control.

Rudder servo and linkage, and


I’m going to add some other things, like smoke, sound and maybe lights. Cullamix didn’t have a tow winch or fire monitor – it was, after all, an English design from the 1930s, and it didn’t even have a top on the wheelhouse! A minimalist design.

The radio is a basic Spektrum DXe 6 channel with the new AR620 receiver (no antenna wires). I have a couple of these receivers and they seem to work well. I especially like the transmitter’s alkaline battery pack, because I never seem to remember to charge transmitter batteries.

Speed control is an Mtroniks 15, and the servo is a survivor from some other project.

Motor is a really nice looking belt reduction unit from MFA/Como drills, model RE800. I think its 2.5 to 1. And the prop is a 100mm/4″ 3 blade right hand from Rivabo. The red universal joint runs very smoothly. I’ve switched both my battleships to these couplers, replacing the old dog-bone style. The difference – in terms of vibration and noise – is amazing.

I buffed away most of the glossy finish on the prop with a wire wheel on the Dremel to imitate the the finish on a real ship’s prop.

Before planking the hull, I fitted a floorboard – 5″ wide and about 19″ long – to sit on top of the frames. It’s much easier to do this before planking. It’s dry-fitted in place with screws, and I’ll glue it in later. Now, I can plan out the locations of all the gear.

You can see the motor mounts and a well to accommodate the reduction gear, with a spot for the speed control. I like to use terminal blocks for most components – it saves having to use the soldering iron so much and you can move gear from one model to another more easily. This style isn’t my favourite, but they were in the parts drawer and they work. The jumpers make these into little power & ground bars. There are two – one for 12v and one for 6v components

The smoke generator will be in the middle, and batteries forward. The floorboards will be about 3/4 inch above the hull, leaving room for lead ballast under the floorboards. Probably about 20 lbs.

Rather than try to cram everything onto the lower deck, I made a small upper deck to fit just below the removable engine room cover. It holds fuses, main power switch, main power voltage/charge state indicator, the sound module and a step-down voltage converter to supply the 6v smoke generator. I’ll probably add a switch for 6v power as well.

Main power for Cullamix is 12v, and I have 6v smoke generators in various other models, so the 6v converter lets me swap kit fairly quickly. The receiver will sit on a little platform (not yet built) separate from all the other gear. These little converters are great for managing items that don’t use main battery voltage – things like lights and pumps – and they are not expensive. This one, complete with LED indicator to show voltage in or out, fully adjustable, 5 amps, was $7.50 CAD.

The LED voltmeter is handy (to the right of the power switch). When you turn on main power, it shows battery voltage and charge state. Works on lead acid or LiPo.

Lighting. I’m still wavering. I might use an aircraft lighting system. There’s many choices and they come with red, green and white pre-wired LEDs, with a control module. I’ll have to decide soon.

So that’s where we are at the moment. Now I need to start priming and painting before starting to fit all the pieces together. It should work….

1 thought on “Cullamix build Part 3 – engine and electronics”

  1. Thank you for the layout details. It’s helping me to think out what I want to do on the Steam Tug. Especially glad to see the close-up of the motor mount. I have a 3:1 reduction belt gear set to fit into mine, and I have been havering over how to fit it in.

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