help – 1/250 scale Yamato

[john hutchinson 1Participant @johnhutchinson1]

Having built plastic kits for nearly 50 years I have after a couple of years reading Model Boats Magazine decided to put one on the water.

I have a part built Doyusha 1/250 scale IJN "Yamato", and my question is can I just stick an RE280 motor on the end of the gear box and use the kit supplied gearbox and props? If so what voltage motor should I use and how do I the RC control the whole thing?

Also can I use the supplied plastic rudder with a servo and tiller arm to steer it?

Any information to help this beginner gladly appreciated.

John

[john hutchinson 1Participant @johnhutchinson1]

[Colin BishopModerator @colinbishop34627]

I'm not familiar with the kit although there is quite a bit on line about it which suggests that there used to be running gear available which used four 280 type motors.

You say you have a gearbox on yours which presumably operates all four shafts?

As the model is around 42 inches long I think you would need something rather more powerful than a single 280. My thought would be to fit a small brushless type which would fit in easily whilst still giving sufficient power. No doubt one of our members could suggest something suitable. If you want to stick with a conventional brushed setup then I'd think you would need a low drain 540 type.

Without seeing it I don't think we could comment on the rudder but if it is very old then theplastic could be a bit brittle, it might be better to fit a small commercial metal rudder instead. If the existing rudder is to scale then I suspect you might need something a bit oversize anyway as with a single motor you won't be able to use the propellers to help turn the model.

Colin

[ashley needhamParticipant @ashleyneedham69188]

I would use 4 motors as the gearbox is likely to be noisy. MFA 385’s would be my choice. It is a big boat with room to fit the components easily (from looking at you tube!)

What access will you have to get to these components when finished?

Ashley

[Ray Wood 3Participant @raywood3]

Hi All,

I would never disagree with Ashley on principle as he has done more floating than most but you would be in danger of having an offshore power boat rather than a battleship, scale speed only needs to creep along in relative terms ! 280's X 4nr ??

Regards Ray

[Colin BishopModerator @colinbishop34627]

Another, halfway house, option would be two 385 motors, each driving one shaft and with a pulley drive to the adjacent shaft.

I would agree with Ray that if you have four motors then 280s should be adequate.

Decisions…..!

Colin

[Malcolm FraryParticipant @malcolmfrary95515]

I would go for 4 of 385 motors, but it is well to remember that you can run them on a lower voltage than the max stated on the label. 4 brushless motors will probably mean 4 ESCs, with brushed motors you have the choice of how many ESCs you fit. One driving them all, 2, each driving a pair, one per motor. You also get plenty of choice of how much individual control you get. 15 volt motors on 6 volts should be about right.

Gearboxes supplied in plastic kits have a reputation for being noisy. A large plastic hull tends to act as a loudspeaker cabinet, so eliminating a dodgy gearbox with direct drives tends to be a lot quieter.

Not familiar with the details of this kit and its rudder area, but if it can be arranged with a good enough rudder shaft tube, yes.  If not, a rudder is one of the simpler things to knock up out of brass rod, sheet and tube.

Edited By Malcolm Frary on 23/11/2020 10:06:09

[Dave Cooper 6Participant @davecooper6]

Just a few thoughts :

For a beginner to RC boats (like me), it may be best to keep things simple eg single motor /ESC /single commercial rudder.

I don't know how you're planning to operate the model, but at 'harbour' speeds the rudder(s) may not be all that effective – so, going "multi-motor" gives extra steering assistance.

Build a simple balsa kit boat first to gain RC experience before going scale ???

Most importantly, have fun !

Dave C

ps For suitable kits, I'm sure the experts on the forum can advise you better then me

[Charles OatesParticipant @charlesoates31738]

I too would fit 4×385 motors, I'm basing that on running 2 similar ships with those motors. Plenty of advantages, inexpensive, plenty of torque, huge speed range depending on the voltage used and very simple to set up. Simplest installation can use one speed controller, then add another to get added steering assistance later, when knowledge and experience has grown. Four motors doesn't mean four times faster, but it does mean the model can accelerate quickly, and more importantly, stop in a shorter distance when a collision is impending.

The only thing to bear in mind, is access, we would like some idea of how good it is so we can advise on placement of all the gubbins. Some pictures would help.

Charles

[john hutchinson 1Participant @johnhutchinson1]

[john hutchinson 1Participant @johnhutchinson1]

Firstly thank you for the replies! Photos of the hull and the instructions. The "one in/4 out" gear box is shown with the props as supplied, and sits on the 4 mounting points to the left of the motor base plate. I assume the second gearbox [6 on the plan] is to drive the radar as a long square rod is slotted into it.

[ashley needhamParticipant @ashleyneedham69188]

Ordinary 280s I think are 3v max however MFA list several types and some 12v ones might be ok to run on a 6 cell Nimh pack.

Dont get any “fast” speed 280s as they are pretty fierce.

Colins idea has merit using two 385 and pullies/gears.

Are the tubes moulded in the hull and all you get is the shafts?

Ashley

[Ray Wood 3Participant @raywood3]

Hi All,

The running gear they supply looking at the photo ie stern tubes looks like a wire in a tube with is not up to the task of 280 power in my view ? we are in danger of over thinking this ! is there anything wrong with 1 motor and the gearbox supplied ??

Regards Ray

[john hutchinson 1Participant @johnhutchinson1]

The props are fixed to the ends of a rod which passes through a tube and attaches via rubber tubing to the gear box.

I was thinking of using a replacement propshaft and prop [x4 ] with 4 separate direct drive motors running off 1 or 2 speed controller[s], but the M4 stuff I have for another project [LCM6 as seen in the last few magazines] seem far too large.

[john hutchinson 1Participant @johnhutchinson1]

My concern over the current set up is how good is the metal used for the props, shafts and tubes and will find it all rusted together after the first voyage.

[Kev.WParticipant @kev-w]

Hi John,

If you want to change the props & shafts, take a look at 'Deans Marine', they seem to specialise in scale warships, so may have something to suit.

[ashley needhamParticipant @ashleyneedham69188]

Ray has a valid point here…are we overthinking this???

I think it depends on if you want just a water model or you want it to look good out the water.

I think that you should be able to buy decent 2 or 3 mm shafts and there appears to be room to fit, looking at you tube…..so

Alternatively, working outer shafts and freewheeling inners (or vice-versa) are a possibilitiy, preserving the look but making the working bit simpler?

Ashley

[Richard SimpsonParticipant @richardsimpson88330]

I think the biggest concern with the gearbox is the potential for a distracting amount of noise. Particularly as it is mounted directly to a very large plastic hull "sounding board."

As has been mentioned access will be critical and may well restrict further modifications so I would suggest that you put the hull and running gear together and then test it to death before progressing with the superstructure. If the supplied gearbox is well built and does not generate much noise then you could use that with one motor. If it sounds horrible then you might prefer to consider four separate motors. Your decision then is do you go for one, two or even four speed controllers!

Using the kit supplied gearbox has a lot of merit so would be worth trying first. Don't forget during your trials to ballast the hull with an equivalent weight of the superstructure at an approximately realistic height to get the propellers correctly submerged and to be able to evaluate stability accurately.

[Richard SimpsonParticipant @richardsimpson88330]

Having a look through the instructions reminds me that your propellers are going to be quite a small diameter. If the manufacturer is suggesting a 280 motor through a gearbox then you would expect a single 280 motor to be man enough to power the model at around a scale speed.

I think therefore using four separate motors of 280 size or above may well lead to instability or possibly cavitation as a result of the propellers spinning too fast. Just something to think about during your evaluation stage, when I motorised a Revel 1/72nd U-Boat kit I had no room in the hull but I did want to avoid a gearbox. After discussing with SHG who had supplied running gear for a number of installations they recommended two servo motors. If I remember correctly the can is around 16mm diameter. These two motors power this model very well at a scale speed and performance. While it is nice to have a little excess power to get you out of trouble too much can be more trouble than it is worth.

There is a chap by the name of Stan Reffin who posts on the Model Boat Mayhem site who has a couple of large battle ship conversions on the go at the moment including a 1/200th Yamato and a 1/200th Arizona I would ask him for his thoughts as well on this subject.

[Malcolm FraryParticipant @malcolmfrary95515]

The single 280 will be enough to see the propellers turn and the model move, and not much more. Probably enough for the model designers to realise their intention in the circumstances that they imagined at the time. Running the numbers, 150,000 SHP on the real thing gives about 8 Watts out of the motor at scale, probably needing about 15 Watts of power into the motor(s). Way too much for a single 280, well within the capabilities of a group of 385s running on reduced voltage if the intention is to move a 10 lb model at a bit over 3 feet per second.

Cavitation is only likely if the kit props are poor – plastic kit moulded ones can have very thick blades which create more turbulence than drive. Most "cavitation" on models is actually aeration – air being sucked down from the surface. Model battleship props are likely to be far too deep to be affected.

[C V E 73Participant @cve73]

HI John please see the following links to my 1/200 scale Missouri and Yamato. Both models are fitted with 385 motors

odelboatmayhem.co.uk/forum/index.php/topic,58529.msg684583.html#msg684583.

https://www.modelboatmayhem.co.uk/forum/index.php/topic,58529.msg684583.html#msg684583

Stan

[Richard SimpsonParticipant @richardsimpson88330]

Not sure what went wrong with Stan's links but let's try again:

This is his Yamato:

https://www.modelboatmayhem.co.uk/forum/index.php/topic,58529.0.html

and this is his Missouri:

https://www.modelboatmayhem.co.uk/forum/index.php/topic,58769.msg614046.html#msg614046

Edited By Richard Simpson on 28/11/2020 16:12:08

[Charles OatesParticipant @charlesoates31738]

The model is a serious investment in time, skill and money, you obviously want to get it right. In my view the props, shafts and gearbox are poor, so replace them, use four 385s and 1 or 2 escs. Then you can enjoy using the model for a long time without having to replace things after the rest has been built. Do it well, do it once.

Just my opinion.

Chas.

[C V E 73Participant @cve73]

if you follow the links provided you will see how i have installed new motors new props in both Yamato and Missouri. Making all these changes will come at a cost but the results speak for themselves.

Stan

[john hutchinson 1Participant @johnhutchinson1]

Hi Stan,

I have joined the Model Boat Mayhem forum, now I can see all your pictures! Very useful. The 250 scale kit I have has much less detail, but is going together very quickly, photos of the build later this week.

John

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