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[Chris1983]

Hi all,


First of all, I would like to point out that my boat modelling experience is none, apart from the bit I've already done. The whole story started when one day, I visited a local park with my son (6 years old). There was a man testing his RC Boats and my son asked me if we could have a look at the boats and eventually he asked me if we could build one - and this is how everything started. That was at the beginning of April.
Currently I have a hull of our project finished and thinking about choosing a motor, ESC and battery pack.
The model length is 670mm and its current weight is approx. 900g. I am thinking about 2S vs 3S battery pack and based on that I came up with the following numbers.


2S

• 3000 KV motor
• 140A ESC

3S

• 2000 KV motor
• 90A ESC

Propeller diameter 36mm.
I would like to get some advice on the topic of motor/battery/ESC selection for this type of model, I am not trying to build a speed boat, something that will be enjoyable - especially for my son.


I have one more subject I would like to get some advice on, this is in relation to the propeller shaft and the rudder. Currently I am thinking about placing everything under the hull but this might be a challenge as I should have drill the propeller shaft hole before I assembled everything and I am thinking if positioning the propeller on the stern instead would be an option.


Thank you.
Chris


Photos:

[canabus]

Hi Chris
Welcome to the forum !!!


Firstly say with the plan for prop and rudder setup.


The motors you have pick are far to high rpm( both over 20,000rpm) for both you and you son to handle first up!!


Drop  down to 900/1000kv 35mm brushless on 2S to start with.
900kv on 2S = 6400rpm and on 3S = 9900, 1000kv on 2S = 7200 and on 3S = 11100 rpm un loaded.


Some motors have three or four different kv on the same listing so you may order a few different kv ones as straight change overs for more speed.


Select a motor and ESC which handle 2 and 3S Lipo batteries.
So upgrading to 3S later you only require to change to 3S Lipo.


Canabus

[Chris1983]

Hi Canabus, thank you for your reply. I must admit the video I followed to calculate KV was most likely aimed at speed boats, therefore I really appreciate your comments, this will make my life easier.
I decided to upload a sketch of how I want to mount the propeller shaft and rudder. To be honest I have complicated things for myself already, therefore each option will be pretty challenging. Option 1 the angle of the propeller shaft is 10deg in option 2 the angle is 7 degrees. I think that with 'option 1' I could go with a shorter shaft and aim to get it inside between the first two pairs of red lines. Option 2 - I am not so sure about it. I added some dimensions just to make the things more readable. See below.

[JimG]

Option 1 is the best position for your need it would be better if you could reduce the angle by bringing the propeller closer to the hull bottom.Option 2 is the sort of position used in fast electric speedboats and would need a surface piercing propeller to work. This has the propeller running half out of the water when running as the water level follows the hull bottom when moving. Normal propellers won't work like this as they just suck in air and create a froth but little thrust. even using a surface prop you would need a high rev motor and it like to run at high speeds which is not that suitable for your son.You are in Fife so check out the Kirkcaldy Model club at Beveridge Park, I think they are still around and more likely to be at the pond now lockdown has been eased. If not you are welcome to come visit the Dundee club at Stobsmuir park on a Sunday from around midday. You would be made welcome and we have members who will gladly give you advice and help.
Jim

[canabus]

Hi Chris
Option 1 would be a better way to go !!!!


A tip for the next boat, setup and install running gear before skinning the hull.
Makes life a lot easier !!!!
I have made that mistake, but only once !!!!


Canabus

[Chris1983]

Thank you for all the suggestions. I will go with Option 1, need to get a better idea about the propeller size this will help me to position the shaft. Indeed it would be much easier to do that before I glued everything together.


Going back to the topic about the selection of motor and ESC, I got the following recommendations from one of the stores:

• https://www.hobbies.co.uk/torpedo-500-electric-motor-4-5v-to-15v
• https://www.hobbies.co.uk/catalogsearch/result/?q=RCM%2F15PP

Chris

[SteamboatPhil]

Be careful about committing yourself to propeller diameter (and pitch) nothing worse than having a shallow angle shaft and finding you need a bigger diameter propeller....been there