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[CezarP]

Hello everyone,
So far I have not managed to achieve much success in modeling. I have done a few plastic models, nothing significant. Finally the time has come for something more serious. On https://naval-encyclopedia.com/ I found drawings of the Russian torpedo boat Tupolev G-5. According to them and the photos I managed to draw a model which I intend to print on a 3D printer. The model is prepared in 1:20 scale and the displacement according to my calculations is about 2 kg. I stopped at the stage of selecting the electrical components. I have no idea about the choice of motors, regulators or power cells. I have only some assumptions. The maximum speed of this boat is 44 knots, so at 1:20 scale the model should move at 2.2 knots, which is about 4 km/h. That's not a very high speed, is it? With two motors, one should rotate to the right and the other to the left. Do electric model motors always rotate in one direction, or do they change direction when the poles change? Then, as I understand it, is it enough to use two propellers, left and right? I would appreciate any help in choosing motors, regulators, power supplies, or servos. Electrical engineering has been completely out of my interest so far, I need to catch up soon.

[warspite]

welcome to the site, I would look at any MTB thread to see what set up is used on a similar sized boats, but in answer to your questions, yes the motors do reverse when the poles are switched, motors tend to have a preferred rotation though, preferable to have contra rotating props so that the flow of water is concentrated into the centre, mainly for speed, check the scale threads on how to calculate the speed of 44 knots at 1:20 - its more of - does it look right, rather than actual, you will never get a true speed to look right, as to get it to plane (lift up at the front) will require a greater speed as water is at 1:1 not 1:20.

[derekwarner]

Welcome Cezar.....I don't know that too many Russian MTB's have been the subject of a build here on Mayhem, but hey, it will be good to be the first 


So scaling is relatively simple, however the Laws of Scale cannot be applied to water as it is a constant, but has an important input to a vessel speed

You are also correct, that walking speed would appear a little modest    for a model MTB

You have the understanding of twin motors OK, so some or our members with electrical drive experience in vessels of similar design will I am sure chime in & assist with recommendations for the selection of motors & control gear etc

Will enjoy following on

Derek..................[PS looks like warspite beat me as I was typing]

[tonyH]

Hi Cezar, the Tupolev type of torpedo boat hull is closer in design to the Thornycroft Coastal Torpedo Boats than the normal MTB. Look up Coastal Torpedo Boat and you may get a better idea. Mountfleet Models https://www.mountfleetmodels.co.uk/product/55ft-coastal-motor-boat/ at 1/16 as an example.
Good Luck

[JimG]

In tank testing for hulls the scaling factor for speed is normally divide the full speed by the square root of the scale. So 44 knots divided by square root of 20 (approx 4.4) gives a scale speed of 10 knots. This will give a more realistic speed for the model and should hopefully reach planing speed.
Jim

[ballastanksian]

On a model you have spent hours  and hours researching and building Cezar, I reckon you are better to play it safe on speed. It is sad to see a beautiful model spin over, crash into another boat or the jetty and need loads of drying out and/or rebuilding just because it was being sailed too fast. 10knots sounds great and it doesn't hurt to have a some extra for safety.

[CezarP]

Thanks for any suggestions. 10 knots sounds pretty good to me, it's still more than I was expecting. I'll stick with that.