RC Tank Warfare community hobby forum

This is how it is designed.

All you need to do is mirror one of the props. From my experience with twin screwed boats, props turning in opposite directions are a quick way of turning a boat round. Just out of interest, what does the lever mechanism do?

Thats the rudder, unfortunately because it is central between the propshafts and very close there is no room to do much with the propshaft gears etc. There has to be room for the lever to rotate the rudder arm...it's very tight in there!

Seeing the propellors geared wrong reminded me of when I first saw the drawings that Leonardo da Vinci did for his war machine. It was designed with 4 wheel drive, but, unfortunately, if built as designed, the front and rear wheels would have rotated in opposite directions. If the great man can get it wrong, then it's no disgrace for anyone else.

Is there space to move the drive gear to about the 2 o'clock and 10 o'clock (ie have two, slightly offset to current position) on the larger gears. You still only use one motor but it'll mean the shafts counter rotate. Assuming you have the CAD for the mounting plate the hole centres should be fairly easy to move (CAD) or a fun application of O Level geometry.... A couple of UJ's should mean the motor mount is unchanged.

UJs should be avoided at all costs if possible especially in these confines. Contra rotating props are best so you cancel the torque effects of the propellers. Twin props of same rotation will cause all sorts of nasty torque roll.

tomhugill wrote:UJs should be avoided at all costs if possible especially in these confines.

Curious as to why, I've got them on the Land Rover drive shafts with minimal issues. I appreciate both ends would need to be well held down, but the section between the UJ's shouldn't go anywhere?

From my experience of model boats, subs etc you should always aim for as straight a joint as possible. Universal joints incur losses and vibrate horribly at the rpm a subsurface drive tends to run at. I have a model land rover which uses universal joints just fine but rpm the shafts run at is very low in comparison.

OK, thanks; mine are 1:1 scale!

Well I have the sub on my workbench, still in pieces, the problem I have is figuring out how to install the driveshafts and the gears so that they engage properly and actually work reliably. The way that the parts have been designed is that the motor is in one section of the hull, and the gears in another.

This means that once the transmission is assembled and the two hull sections are glued together, there is no way of taking it apart again to adjust or repair anything. It would have been better if he had designed the hull to split horizontally, so until I have resolved this I am stuck between a rock and a hard place. Everything has to be exact lengths eg propshafts, sprocket positions etc or it won't mesh up correctly. I am thinking that it would make more sense to make a container for the gears, shafts and motor so that they are all in the correct positions and meshing, and simply plug the propshafts into that...but the design of the rudder control is mm perfect and there is zero room for a casing of any sort.

I am reluctant to buy an esc etc only to discover that it isn't going to work....

This may yet end up a as static model. Interestingly there is a U-boat on Thingiverse that is designed as a small bathtub model, but one guy has scaled it up into a 6ft one?