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[Windsorsub]

Good morning,
 
   Does any one know what a good propulsion set up (Motor/GearBox/Prop) would be for an 80 inch Astute? I recently built a 1:48 scale Astute class submarine with my 3D printer, and the 775 motor (turning at between 3500 - 5000 RPM) just barely moves the boat with the impeller/shroud as designed, albeit she cavitates quite a lot.


I know of people that have built this model in both 1/96 and 1/72 scale with no speed issues, so I am guessing it is due to the weight of the model on and under water.


Appreciate any help you can provode.


Dwayne Hill
Montreal, Canada
https://www.youtube.com/watch?v=OdMuhgKOiIo

[Big Ada]

Welcome to the Forum Dwayne,
You have built some lovely Models.

Len.

[Subculture]

Four points of information needed-

Brushed or brushless.

Direct drive or geared.

Diameter and pitch of propeller.

Desired speed (can only be given as a very rough estimate)

[RST]

It must be a bit annoying if you get cavitation on one of yours when the thing is barely moving. Is that a propeller or nozzle design problem? I'd be disappointed if I was damaging props or parts that way.


The video of the models look great. I suppose you can see exactly what the props are doing with an underwater camera.

[Windsorsub]

[size=0px]Brushed or brushless..... BRISHED[/size][size=0px]Direct drive or geared......... DIRECT DRIVEDiameter and pitch of propeller...... 3 3/4 inch Diameter, not sure how to explain pitchDesired speed (can only be given as a very rough estimate), Same speed as video at 22 seconds..... (she is being pushed in the video) https://www.youtube.com/watch?v=X-ke2a8gzbc[/size]

[Subculture]

I'd look for a heater blower motor from a car. Car breakers or surplus.

[tsenecal]

on my dumas Mr. Darby, which is also turning a 3.75" diameter propeller, it was using a pittman motor running 5000rpm at twelve volts...  but it was also going through  3:1 gearbox, so the propeller was spinning at 1650 rpm... and the gearbox was doubling the torque...   i would look into a gearbox to both reduce the prop rpm, and increase the torque.

[Windsorsub]

Much appreciated. Any idea where I could get a gear box....?

[Sub driver]

Hi.
If you can find one try a Robbe Navy compact, motor with the 3.3 to 1 gear reduction built into the shaft with a 600 motor, its all 1 complete unit.( motor, gearbox and 4mm shaft)
I power all my large subs with these and one with a multi bladed 3 and 3/4 inch prop no issues.(95mm)
Sub.

[tsenecal]

Much appreciated. Any idea where I could get a gear box....?

i would need to know the diameter of the motor shaft, the diameter of the motor, and the spacing of the mounting holes on the front of the motor...  then we can look for gearboxes that will fit that.

[Windsorsub]

Good evening....


It is a 775 motor, specs are here. Appreciate your help ! [size=78%]https://www.banggood.com/775-Gear-Motor-DC-12V-36V-3500-9000RPM-Motor-Large-Torque-High-power-Motor-p-1091058.html?rmmds=myorder&cur_warehouse=CN[/size]

[tsenecal]

windsorsub...

a couple more thoughts on this...

in the video you posted of the sub running its trials, at 46 seconds, there is a lovely shot of the impeller spinning up, and i don't see any signs of cavitation...


not knowing the pitch of the impeller, i really don't know if it is running too fast and cavitating, or running too slow and simply not moving enough water...

does it run just as fast at 1/3 throttle as it does at full throttle?

[Subculture]

Ventilation rather than cavitation?

Not much you can do about it with a spindle stern near the surface, other than throttle back, or dive the boat.

You can use belts rather than gears, quiet, and inexpensive. You can purchase GT2 belts and pulleys on ebay at very low cost, as they're churned out in quantity for use in 3D printers etc.

A logging device like a eagle tree unit is very worthwhile for checking things like motor RPM with props, plus power use.

[Akira]

I have a 114" Jimmy Carter in 1/48 scale. it too has an impellor turning in a shroud. I used a Pittman motor with a built in planetary gear box. The impeller turns a maximum of around 640 rpm. Even then, it is more than capable of ventilating the impeller. I would guess that your impeller is 3-4 inches in diameter. Given the size of your boat and the mass the impeller is trying to move I would aim for an rpm of around 1000-1200.Hope thhis helps

[Windsorsub]

Really appreciate your reply.
Do you think we could connect so we can chat.
Dwayne Hill

[tsenecal]

I have been looking around for anything already made that will fit that motor and there doesn't appear to be one...

the closest i have been able to find is an MFA como  belt drive, which is only 2.1:1, and it is designed for 800/850 motors with a 6mm shaft (your motor has a 5mm shaft)

there are all kinds of pinion and spur gears available that are made for 5mm shafts, they are designed to be used in larger scale r/c cars and trucks...  picking the right pinion and spur gear would allow you to get the magical 1000-1200 rpm Akira speaks of, but the gearbox itself would need to be custom made.

[HMS Invisible]

... but the gearbox itself would need to be custom made.

Here is a fun project for Dwayne could try on a 3d printer.
As the comments say, it has high ratio reduction but no feedback pot.