Another Rudder/Prop question.

[Stephen Paterson 2Participant @stephenpaterson2]

Ok, after extensive use of search function and hours of googling… I have not found an answer that I feel is accurate enough to go with.

I'm building from scratch a barbaros class frigate (MEKO200 I think &#128556 Anyway… original

vessel has twin props with central rudder. On the DaftRascal version my question is motor size and do I want to keep twin or opt for single prop and is there a rule of thumb regarding the rudder size? Ship is aprox 960mm x 180mm.

On a plus note I tested the hull in the kids paddling pool tonight with superstructure sat on and just under 700g of lead as ballast to compensate for motor servo's esc and batteries. it sat slightly high BUT…it appeared stable and kept a true enough bearing when gently pushed.

It's a start! 😂🙈

[Stephen Paterson 2Participant @stephenpaterson2]

[ashley needhamParticipant @ashleyneedham69188]

Stephen. There is no rule of thumb for using single or twin shafts. It boils down to personal preference. Obviously a single shaft setup is slightly cheaper and easier, but it is nice to have the right amount of props for the type of vessel being made (another personal view).

I would say a low power mfa 540/1 type brushed motor would provide sufficient go for a single shaft, and in the event that you found this wasn't fast enough then there are other 540 or 600 motor options that would fit straight in for more power.

For twin shafts, a pair of 385 type brushed motors would be adequate for your vessel, or even 380`s or 400`s for more grunt. Cheap option, mounts all the same so if you were unhappy with the 385`s, a swap would be very easy.

I always fit as large a rudder as is consistent with not looking too odd to provide maximum manoeuvrability. A large rudder can always be cut down….enlarging a small one is more difficult. I like to use nylon clamp style tillers, as these can be done up just tight enough to hold secure, but are easily tweaked for balance etc by hand at the pondside. I replace the standard nut/bolt with a longer bolt and a small nylock locking nut, to maintain clamping pressure over a period of time.

A single rudder between twin shafts is never the best option, but if the rudder can be made a bit longer that it might otherwise be, so that at full deflection some of it is in the wash of (whatever side) a prop, this can help immensely.

Use slimline shafts perhaps for a twin setup, fatter standard one for a single.

Ashley

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[Charles OatesParticipant @charlesoates31738]

There are advantages to each way of doing the installation. A single motor is easier and cheaper, but if the real thing has 2 shafts, you'll probably regret doing it that way later.

Each person has their own way of doing things, my way would be to install 2 shafts, 2 motors ( 385 motors should be perfect) As the original has 1 rudder, stick with that and use a mixer to the speed controllers. That will give you excellent maneuverability. You could also consider the excellent combined ESC and mixer that Action electronics make.

Chas

Forgot to say that the 385 motors can be run on 6 to 15 volts, for this model a 7.2 volt NiMH battery will be more than enough, you'll spend most of the time throttled back.

Don't mix up the 385 motors with the 380 ones, they look the same but are completely different.

[Stephen Paterson 2Participant @stephenpaterson2]

Ashley and Charles, thank you both so much. I really appreciate the time taken to reply with helpfull and constructive input.

I have a ridiculous tendancy of over-complicating things such as the motor issue I theorised a single motor set up

would put vessel out of balance and therefore thought best to design and fabricate a simple geared drive unit that would allow twin props to turn into each other thereby eliminating any corkscrew effect. 😬🤔😯🙈

I think the twin motor will be route of choice but for rudder I will make my own out of brass or alloy. (I'm funny that way&#128514

It is most probable many months yet before I can start to see the build nearing completion But… I will

update build thread tomorrow with latest pics. Currently managing 3-4 hours per night on it, having said

that I've built rally cars in less

tkme 😂😂😂😂

[ashley needhamParticipant @ashleyneedham69188]

Stephen. Can’t remember the last time I bought a rudder assembly. Always make my own.

Nothing wrong with using just one shaft/motor, however on longer/thinner hulls you can get torque steer (this is where the torque of the prop tends to steer the boat one way or another, and also induces a roll or list to one side, especially at speed) and so on which is minimised by using a twin setup.

Ashley

[Charles OatesParticipant @charlesoates31738]

Me too, like Ashley I've been making my own rudders since I was a youngster. It also allows you to use a shape that will suit the twin prop one rudder set up.

I forgot to ask what size props you were expecting to use, it might make a difference to what I posted earlier. Ashleys post reminded me of something, I presume you know about having the props turning in opposite directions, it helps keep the boat going straight, just buy / make a left and right hand prop.

Chas

[ashley needhamParticipant @ashleyneedham69188]

Ah..but Chas..which way round?? Inwards or outwards turning!!

i will answer that one..(yes really) Although in theory it should not make much difference, a couple of my boats went much better (steering mainly) one way round verses the other. It’s very easy of course to swap props and motor leads to see the difference, if there be such.

Ashley

[Charles OatesParticipant @charlesoates31738]

Ahhh, another can of worms. I've read posts in the past saying "do it this way, or do it that way" Full size practice is xxxxxx. Like many ordinary time served modellers, I've tried all the permutations. Guess what, there was no difference in the performance in any of the models I've made.

I'm quite sure there are modelers out there who have noticed something, but after 55 years and too many boats to count I never worry about it. I'm far more concerned with deteriorating eyesight, co-ordination, and glueing myself to the blasted model……..Again.

Chas.

[ashley needhamParticipant @ashleyneedham69188]

Only my Alvis Stalwart and TG Lotus sub showed and significant difference with handing, and oddly they are both tunnelled props. A couple of others have showed small differences, but nothing significant.

The Alvis would not steer properly at all until I swapped the props?

RN practice I believe is to have props rotating up wards in the middle, but that’s not to say a model should be the same.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Twin prop rotation is a subject which has been done to death on at least one other Forum. The general concensus is that there is no correct way – outward rotation suits some types of model while inward suits others. I guess the solution is to try both and see which works best for your model.

Dave M

[Stephen Paterson 2Participant @stephenpaterson2]

Thank you for the replies.

Bit of trial and error so far.

Hull is watertight and surprisingly well balanced, I mounted a single prop to find it induced quite a roll on initial powering even at a gentle start it seemed to want to capsize. So…

So far I have settled on as per Ashleys advice twin 385 motors which I am going to have rotating in and upwards.

Coupled to 35 or 40mm props whether 3 or 4 bladed I'm not sure but possibly try all

combo's.

My next question is would I run these with twin esc's or a single one. Presumably if esc each then I'd want to add a mix to the transmitter to help facilitate turning?

Rudders…. sick of trying to make my own and it just isn't what I want (plus I'm running out of 4mm brass sheeting &#128514 🙈

I have searched full internet… twice 🙄 and cannot find the rudder I want It sort of splits 2-3 with foresection remaining static and only rear section moving. Any suggestions as to where I might purchase such a thing?

[Charles OatesParticipant @charlesoates31738]

Hi Stephen, a few things there. Firstly the props, start with 35 mm 3 blade, they're usually the best match for 385 motors. You can buy a few different size plastic ones to experiment with if you want to, they're cheap and effective.

Re the speed controller, why not start out with one, if the turning circle isn't what you want then you can spend more one a twin ESC and mixer.

Lastly the rudder, you don't say what you difficulty is, but hear is my and many other peoples way of doing them.

Find some rod and tube to make the assembly, slot one end of the rod about 5 mm to take a piece of brass sheet.

The brass sheet can be any old off cut, say about 1 x 2 cm, solder it into the slot.

Next cut 2 pieces of plasticard in the shape of the finished rudder, cut a tiny slot where the post will be.

Put the plastic in very hot water to soften them, then clamp them around the metal bits until they harden.

When dry use epoxy to join them and clamp again. You can do some final shaping with sandpaper when its all set.

It takes me about an hour to make a rudder, costs peanuts and is easy to change the design if I want to.

Chas

[ashley needhamParticipant @ashleyneedham69188]

Stephen. I am not sure the flapped rudder is available commercially, but to be honest I don't think you need them. I always over-rudder these things (large rudders) and make sure the rudder has a decent movement on it….45 degrees either way. Some will say that this is inefficient, but at slower speeds its what you need. Good instant turning can be yours from stop with a quick burst of full power and a hard over rudder. ALSO of course you are in control of the rudder and do not have to use full deflection at high speeds.

Chas`s rudder method is bang on, other than invariably I simply make the rudder blade fully from sheet brass and do not skin it with plastic. I find the most difficult part is slotting the brass rudder post, but a small bandsaw makes this dead easy (if available!). Generally I use 5mm rod, and 5.5mm thin-wall brass tube for the outer (a nice sliding fit) and I think about 1.4mm sheet (from memory will check in the shed). Clamp-on nylon tillers are my favourite as they allow very easy adjustment, replacing the standard nut/bolt with a longer bolt and nyloc nut.

I have had 40mm brass three blade props on 385 motors on my Devastation for years now and they run nicely. Quite likely they are overloaded a bit but they never get hot and the additional current consumption is negligible. 40mm plastic versions have much less pitch.

One esc I would go for, the props are likely not far enough apart to make much difference (verses the increased costs of two esc and mixer). As with all these things, test first, buy later!

Ashley

[Charles OatesParticipant @charlesoates31738]

I was forgetting about the finer pitch on 40 mm plastic props, so they're OK too. Brass ones tend to be coarser so 35 mm would still be my choice.

I like a scale looking rudder on a scale model, that's why I skin them, it only takes a few mins, on other models I don't bother either.

Really there aren't many wrongs or rights, it's a fun hobby, we just do what works for us.

Chas

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