Motor advice

[Dragos StirbuParticipant @dragosstirbu92072]

Good evening all.

Although I have built some models before, this is my first try at R/C and for this I have chosen a nice tugboat, Tai Koo (no 3, launched in 1950). Having no experience in the matter I come here to ask for advice in choosing the motors for this one. I have the 50 mm, 4 bladed propellers: prop-shop. I saw in another thread someone recommended for a tugboat this motor, would it be ok for my boat? And while we're here can I get some suggestions for ESC as well please? Any advice would be appreciated.

The model will be aprox. 90 cm long.

Thank you

Regards, Dragos

[Dragos StirbuParticipant @dragosstirbu92072]

What motors for tugboat

[Ray Wood 3Participant @raywood3]

Hi Dragos,

Welcome to the forum, opinions will vary, but I think you would need the next size larger 600 – 850 to drive your4 bladed 50mm propeller, assuming your tug has a heavy displacement, with a 40 amp ESC should do the job

Regards Ray

Edited By Ray Wood 2 on 16/09/2021 14:31:39

[Dragos StirbuParticipant @dragosstirbu92072]

Hi Ray,

Thank you for the reply and the warm welcome. I have found this or this. Would the rpm be ok? I want to keep it in scale if possible.

Regards, Dragos

[Richard SimpsonParticipant @richardsimpson88330]

Hi Dragos and welcome to the forum. As Ray suggests a four bladed 50mm propeller would need a reasonable sized motor in the range he suggests but I notice your initial description says propellers.

Is this a twin shaft tug? If that is the case two 50mm propellers for a 90 cm model seems to be a bit hefty and two 850 motors would seem to be rather a lot for such a model. Can you either give us a link to a picture of the model and let us know whether it is a kit or is it going to be a scratch build? Do you have any idea what the displacement is going to be?

I found this on YouTube and wondered if this is the model you are referring to. If so they used a 90mm propeller, which appears to be a single one, and while it may also use something in the region of an 850 motor it does appear to be quite over powered:

Taikoo Tug

If so then perhaps your 50mm propeller is more realistic and you may have a comfortable excess with a 600 motor.

[ashley needhamParticipant @ashleyneedham69188]

Twin 800s would probably be better than 850s..max 5000 rpm on 12v which should be enough on 50mm props. I know my 1200mm aircraft carrier goes whizzo with twin 800 and x50 props.

ALSO, these motors are quite heavy which can be useful as you are likely fitting a reasonable amount of ballast in place.

In the 500-600 can-size motor department, 555 motors might work as they are very torque-y but need a minimum 12v to provide sufficient revs.

Ashley

[Dragos StirbuParticipant @dragosstirbu92072]

Hi all and thank you for your replies.

I am sorry for the confusion, I should have given more details.

Here is the tug, it will be scratch built. It is indeed a twin shaft tug and for the propellers I have used the dimensions in the plan. I don't know the displacement, pretty sure it can be easily calculated but never done it before as this is my first R/C build and I have quite a long list of things to learn. But I am sure will need a lot of ballast so batteries and heavy motors should help with that.

Regarding the motors, what I am trying to avoid is too much speed ( I want to keep it as close as possible to original) and overheating.

I will start a build log anyway and will most likely receive feedback there. I am about to start cutting the frames.

Dragos

PS: There is a very nice article in Model Boats vol.68 no.812 – July 2018 about this tug, built by Phil Scales.

 

Edited By Dragos Stirbu on 16/09/2021 19:10:50

[Richard SimpsonParticipant @richardsimpson88330]

Looking at that style of tug and the fact that you are using two 50mm propellers I would have thought that two 555 motors would be plenty.

[Dragos StirbuParticipant @dragosstirbu92072]

Thanks Richard. Something like this?

[Richard SimpsonParticipant @richardsimpson88330]

I would wait for other opinions as well but, if it was me, I would be happy to fit two of those.

5000 revs at 12V seems reasonable through your 50mm propellers. That is the maximum revs if you use a 12v battery and I would expect you should be able to get a good capacity 12v lead acid battery in your hull, which will provide a good proportion of the ballast you will need and a long duration.

[Dragos StirbuParticipant @dragosstirbu92072]

Thank you Richard. I have bookmarked that motor. I will wait for other opinions , of course. I still have a long way till installing the motors. I am waiting for the nozzles and shafts which are more critical to allow me to complete the hull.

I am also thinking of adding a bowthruster. The original didn't had one but considering the size it will help with manoeuvrability.

Dragos.

[ashley needhamParticipant @ashleyneedham69188]

D. How much manoeuvrability do you want?? Fitting a bow thruster is a faff, and unless you are entering steering competitions, if you have independent control of the twin props you should have plenty steering ability.

Ashley

[Dragos StirbuParticipant @dragosstirbu92072]

Thanks Ashley. I will not enter any competition for sure, so that's out. I was just thinking about the size of it, but like you mentioned, independent throttle controls should take care of that. What about some good ESC for the 555 motors? Should I look for something a bit bigger than the max amp at full load?

Dragos

[Richard SimpsonParticipant @richardsimpson88330]

Tank steering with two big props and a proportionally short hull is actually quite effective. I know there are those who complain about perfectly matching motors and props for the perfect line but with tugs that is not so much an issue and a touch of relevant trim would correct it if it was so bad to be noticeable.

As an example I have a model of an American truckable Workboat which has two large props with tank steering and no bow thruster. It can spin around within it's own length very easily.

I'm with Ashley, have a think about tank steering.

[Richard SimpsonParticipant @richardsimpson88330]

Dragos, you need a comfortable margin of safety for your speed controller. I would give Mtronics a ring and have a chat with them as regards which of their marine speed controllers they would recommend for your motors.

[Ray Wood 3Participant @raywood3]

Hi All,

I think there is a major danger of overpowering this tug, the fullsize has massive props for towing ships, and if you consider the 2 X 50mm props are already half the beam of the boat of 200mm, forget 12volts she will try to leap out of the water ! This is based upon my recently completed Oldenburg which is the same length and beam and will try and fly on 2 X 385 motors and 30mm props on 7.2 volts.

Because this is an ocean going tug her proportions are vastly different to our normal river and harbour tugs she is not a heavy displacement hull really.

Kort nozzles will be massively effective for steering, I wouldn't bother with tank steering it makes it expensive, but it's a personnel choice

Regards Ray

[Richard SimpsonParticipant @richardsimpson88330]

Tank steering was only suggested in preference to a bow thruster.

[Dragos StirbuParticipant @dragosstirbu92072]

Thank Ray,

As I said, I am still open to suggestions and will make a decision closer to when I will get to installing the motors in. For the moment, the nozzles and shafts will allow me to complete the hull but I expect this to take me a while, not having a lot of free time because of the job. That's why I have mentioned the bow thruster, that would have had to be installed now if I was thinking I need one. But that was crossed from the list and now I will see the difference between single throttle and rudder steering and tank steering.

Regarding overpowering, I assume bigger props will provide more resistance but then again the motors are bigger, so is the voltage. Still thinking about it.

Dragos.

[Kev.WParticipant @kev-w]

Dragos, I built a tug of very similar dimentions, it had two 60mm props in fixed korts, driven by a pair of 555 motors on 12v, it was easy to run at scale speeds, with just that bit more if you needed it to get out of trouble.

I used tank steering combined with twin rudders & the boat would spin in it's own length like a ballerina.

As for ESC's, I used a pair of Mtronics 15amp, with a pair of batteries, I kept each Batt. esc motor combination as 2 separate systems, so if I lost drive on one side, I could get home on the other one.

Edited By Kev.W on 17/09/2021 10:54:40

[Dragos StirbuParticipant @dragosstirbu92072]

Thank you Kev

[Dragos StirbuParticipant @dragosstirbu92072]

More goodies arrived. Now I really can crank it up and get the hull done. Hope to get the frames cut this weekend

[Dragos StirbuParticipant @dragosstirbu92072]

And the propellers

[Dragos StirbuParticipant @dragosstirbu92072]

Hello again,

Just as an end to this thread, I went with the 555 motors, tank steering so each motor with its own ESC and battery. For ESC I went with Mtroniks Viper Marine 15. Today I have received the last connectors and after some soldering I was able to test run the whole setup. Everything went fine apart from a blown fuse because I wasn't paying attention when I did connect one of the batteries to an ESC (reversed polarity). That was close

I still have to make a start on cutting the frames and the keel but I will start a build log for that and hopefully it won't take very long until I can do a proper test under load. Thank you all for advice and ideas.

Dragos

[Richard SimpsonParticipant @richardsimpson88330]

Glad you got the propulsion sorted. If possible I would try to test it out in a ballasted open hull before closing everything up.

[Dragos StirbuParticipant @dragosstirbu92072]

Will do that for sure, thanks.

Dragos

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