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[bbdave]

I thought the throttle had to be full forward or off  . Am i better mounting the motor level in the WTC then using UJs in the free flood to get the angle to shaft correct or angle the motor as in conventional boats but i think this way would be a nightmare in the WTC

Dave

[Subculture]

It's best to get the shaft as inline as possible. Perhaps you might consider fitting the motor is a separate module

[thegrimreaper]

Thanks for that similar ideas to what i was planning. I have some 6mm fuel tube but the bore is very small where can i get some thin walled tube?

Dave

Dave you could use silicon fuel tube from many good model shops their are different bores depends on the size of the fittings on the pump you decide to use.
Mark.

[bbdave]

I had considered separate modules in fact i have one of those Klick Klick type boxes for a battery compartment but i was hoping to keep all the gear and ballast bag all in one tube to save on buying endcaps.

I'll keep doodling measuring and thinking and see what else i can come up with

Also which drills cuts etc easier perspex,acrylic etc.?


Dave

[Subculture]

Perspex and acrylic are both names given to a material called PMMA. It's more brittle than most plastics, so you need to take a bit of care when drilling and cutting it, otherwise it chips and/or can crack under extreme working.

Polycarbonate (also known as lexan) and PVC sheet is close to industructible, the former is a lot more expensive, but transparent and a little tougher than PVC (not that we require that level of strength). Very different working characteristics to PMMA, the plastic is much softer, not brittle at all. Therefore it's easier to work with hand tools, coarse cutting blades etc. as it won't chip.

On the downside it doesn't polish as well, and is more easily scuffed, also it's slightly less rigid, which means it will deform easier under pressure. I find it easier to get a very smooth turned finish on PMMA than polycarbonate and PVC. Also the rigid nature of PMMA means it tends to hold a machining tolerance better.

However once again for our applications we don't need to worry too much about this sort of thing.

So in a nutshell any of the above plastics work well, PMMA needs a more delicate touch.

[Davy1]

Concerning your question about universal couplings - avoid them if you can. Outside the WTC they are not too bad but inside they take up a lot of room (length)
So a straight piece of stainless prop shaft , if you can. You do need to consider how you are going to seal the shaft. Have a look here:
http://www.theassociationofmodelsubmariners.com/t266-prop-shaft-seals
(Sorry to keep on referring you to another Forum but it saves retyping it )
If you are short of space (length) you may find that motors with fitted gearboxes start to get too long.
In that case try turning the motor through 180 degrees and use a home made reduction gear  arrangement to transfer the drive to the shaft running alongside the motor can. (Ask me to point you to a photo if you don't get the idea.)
David

[bbdave]

My main problem with space is i need to have space in the stern to allow for the control rods ect for the rear planes rudder as they operate in a unique way but achievable with enough space, i think i may sacrifice some efficiency and not have a dead true UJ for the prop shaft.

I am now at the point of figuring out the WTC size before ordering the tube and endcaps  the bag i'm looking at is 200mm x65mm do these stretch when full or do they stay the same size? as i need to know how much space to allow for the ballast bag.

Or is it worth waiting till the hull is ready and test sinking it in the bath to ascertain the ballast required and designing the WTC then i have plenty of sanding and building to do so no rush i can get the electronics pump etc ordered which will help having the bits at hand.

Dave

[Subculture]

The bag i'm looking at is 200mm x65mm do these stretch. Or is it worth waiting till the hull is ready and test sinking it in the bath to ascertain the ballast.

They don't really stretch much. I would wait until you finish the boat before buying any wtc components. Some people place bags inside a smaller plastic pipe which helps keep it in situ, and also constrains it's proportions. The pipe is vented with some holes drilled in so that the air can escape into the main hull as the bag fills with water.

Don't think you will need much of a ballast tank in a Welman if the conning tower/pod is free flood. Pictures I've seen of Welman's in the water show minimal freeboard. If you make the pod from something thin like epoxy glass sheet, or sheet metal, it will displace very little water indeed.

For the drive you can use a 500 size motor direct drive. Engel use 500 size motors on Lafayette and 212, and they're swinging larger props than you will. If you've seen either one of these models perform, you'll know that there is certainly no shortage of power. You can also use the shaft seal gland they supply, or the Thundertiger Neptune version, which is basically a knock-off of that design, although the latter uses a quaint dual dogbone coupling instead of a direct coupling (I prefer the Engel version).

Some modellers prefer geared motors becuase they give you lots of torque- usually more than required, but should the prop get entangled with weed, the motor will probably be able to chomp through it. Different strokes for different folks, as they say.

[bbdave]

The only pic i have of one in the water shows hardly any above water i assume it's fully surfaced due to the hatch being open so i will maybe only need a little ballast to submerge.

[Subculture]

Yes that's the one I've seen too. Was featured in Paul kemp's book Midget Submarines.

Seen this other one fairly recently, which shows a higher waterline, but may not be fully ballasted down in this picture.

Note the larger windows. I think this was probably a reponse to feedback from operators- the small portholes on the prototype couldn't have given much of a view to the operator. Also the germans based their biber on captured Welman's, and they had similar square cutouts for the windows.

[bbdave]

I have seen that picture but hadn't saved it i have now  no two pictures of them seem the same there's lots of differences i prefer the round ports plus thats a good close up to model from.

Dave