LirEdinSun

I've been fascinated by the film Das Boot, and want to try making a RC version of U96.

I have the basic design plans for a U boat VII-C of the internet and have blown it up so the whole model should be about 1.2 meters long.

I have scaled and upgraded to propellors from the 25mmscale size to about 30mm.

rudders anddive planes will be controlled using waterproof servos.

I have several questions to ask while I'm debating thefeasability of the project.

1) is it better tohave 1 motor driving 2 propellers, or 2 motors to drive 2 propellors independantly (I've been told2 x400 size motors will be enough).

2) whatis the best way to dealwith propellor drive transmission from the water tight drycompartment housing the motor/s to the wet side, I was considering using a lubricated stuffing/cable gland to do this.

3) is it better to have a fully watertight hull and weight it down, orhave a flooded hull (with a midway dry section for the RC stuff) and add bouyancy. I am personally prefering the flooded hull idea and using the conning tower as the 'dryzone' for theRC stuff then I can upgrade the bouyancy system to include 'static diving' controls.

4) I come across the idea of a 'bilge pump' I'm guessing this is for the dry area, and I could use a 'car washer motor' for this?

Quesion 1 and 2 are my main concern, which is all to do with thepropeller drive/transmission,which will be thefirst phase of the project..

Captain Nemo12

I personally prefer two motors driving two props, you'd have to either invest in twin ESCs or a single ESC able to handle the current load of the two motors. If you chose to go with the single motor route, you will have to use a gearbox to drive both props, this eliminates the need for a second ESC altogether. As for the propeller seals, stuffing boxes are very popular, there are also specially made submarine seals for this purpose:

http://www.subtech.uk.com/acatalog/S..._Products.html

Skip Asay

Your best bet will be 2 motors (1 per shaft) and 1 speed control. With the prop separation being what it is, there just isn't enough leverage to effectively turn this boat by controlling the motors independently.

By all means, don't use anything more than a 385-400 size motor and certainly don't use a high power version. After all, you want time in the water, don't you? And I'll assume you aren't looking to build something capable of going scale supersonic, right?

Skip Asay

LirEdinSun

just want something to go fast enough for dynamic submersion until I upgrade to static. I worked out the contartment for the control gear so there is plenty of working space for upgrading.

just debating whether to have the motors in the middle compartment and have long drive shafts (500mm)or have a separate sealed compartment for the motorspositioned to be true to the original layout.

I've been told that size 400 motors operate at bout 30,000 rpm. do I connect them straight to the propeller, or do I need to 'gear it down? I've hear a 3:1 gearbox mentioned at some point.

I was just going to parrallel up the motors off the speed controller, I was wondering if any slight difference in motor speed caused the sub to skew off to one side?

Skip Asay

"I've been told that size 400 motors operate at bout 30,000 rpm."

This is a problem which has never been adequately addressed. There are literally HUNDREDS of different "400" motors as there are literally HUNDREDS of "380" and "385" motors. This is due to the fact that that number tells the SIZE of the motor but doesn't tell a thing about how many poles, windings, or size of the wire used in the windings. The difference between 380, 385, and 400 motors is the length of the armature/can. I've personally seen (or have) 385 size motors which turn @5000RPMS at 12 volts all the way up to those that turn 35,000 at 12 volts. The lesser motor draws a whole whopping 100mA (unloaded) while another draws 12+ amps UNLOADED! Look for something rated at most 12,000RPMS at 12 volts.

"do I connect them straight to the propeller, or do I need to 'gear it down? I've hear a 3:1 gearbox mentioned at some point."

3:1 is a good place to start.

Skip Asay

LirEdinSun

something I noticed, I'm looking into the RC gear off Ebay, most of the stuff on there is 35Mhz, I'm guessing thats the reserved frequency for aircraft, what frequency is best for submarines? is it 25 Mhz or 40Mhz?

jsfboat

Does anybody have a source for good plans to build a U-boat? i'd like to build one as well.

jsfboat

Nevermind, found  a link for U-boat plans (as well as other RC boat plans) which was found on uboats.net
http://www.taubmansonline.com/

LirEdinSun

I've got some fantastic plans but I can't find the link/url for it again, send me a PM with your email address and I'll send it to you, its in PDF format