Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Submarines => Topic started by: bbdave on November 28, 2012, 09:06:40 pm
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These are the bits i'm considering getting for the Welman any opinions/advice on suitability etc.?
http://www.ebay.co.uk/itm/281014483451?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
http://www.ebay.co.uk/itm/390315372150?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
http://www.ebay.co.uk/itm/390315372178?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
http://www.ebay.co.uk/itm/RC-Submarine-100-Waterproof-Solenoid-valve-Air-Water-DC4-8v-18v-/271106018125?pt=US_Character_Radio_Control_Toys&hash=item3f1f2d8b4d
http://www.ebay.co.uk/itm/290519261788?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649
Dave
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Avoid like the plague- the gears are made from cream cheese. If you want a geared pump get a Kavan (best but £25-30), or one of those red things off ebay for about £6-7.
http://www.ebay.co.uk/itm/281014483451?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.ebay.co.uk/itm/281014483451?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)
Okay.
http://www.ebay.co.uk/itm/390315372150?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.ebay.co.uk/itm/390315372150?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)
Fine
http://www.ebay.co.uk/itm/390315372178?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.ebay.co.uk/itm/390315372178?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)
Looks okay, but not seen or used one, so can't comment. Servo pinch valve works just as well and is cheaper and serviceable. Your choice though.
http://www.ebay.co.uk/itm/RC-Submarine-100-Waterproof-Solenoid-valve-Air-Water-DC4-8v-18v-/271106018125?pt=US_Character_Radio_Control_Toys&hash=item3f1f2d8b4d (http://www.ebay.co.uk/itm/RC-Submarine-100-Waterproof-Solenoid-valve-Air-Water-DC4-8v-18v-/271106018125?pt=US_Character_Radio_Control_Toys&hash=item3f1f2d8b4d)
No problem. Has it got enough volume for the Welman though? Can also use medical feed bags, adapted capri-sun drinks bags- the big 330ml ones with the screw cap are easiest to convert.
http://www.ebay.co.uk/itm/290519261788?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.ebay.co.uk/itm/290519261788?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)
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Avoid like the plague- the gears are made from cream cheese. If you want a geared pump get a Kavan (best but £25-30), or one of those red things off ebay for about £6-7.
http://www.ebay.co.uk/itm/281014483451?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.ebay.co.uk/itm/281014483451?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)
Which red ones? i have seen the Kavan ones i'll see what budget is available. I may try a different bag but have no idea yet what capacity i need yet so will leave that for a while, i'm not even 100% on the WTC size yet 70-80mm most probably
Dave
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This type-
http://www.wiperblades4u.co.uk/12v-Universal-Washer-Pump-EWP13.html
Ripmax used to sell them, and they were made in France. production has now moved to China, like everything else. Quality isn't quite so good, but should be fine for the bag type system, better than the white pumps anyway.
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Well if i make my own pinch valve i will get the better pump do i need a strong servo for the pinch?
Dave
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On my Sheerline Akula it is recomended to use a ballraced servo opn the pinch valve, and to this effect I agree due to me unwittingly fitting an ordinary servo to my Vanguard which pops up rather too frequently at the moment when checked the shaft on the servo is already drifting off centre.
Regards Mark.
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This is a good place for neptune spares, I bought all my neptune dive system parts from here for my Sewolf. postage is reasonable and managed to sneak under the customs radar so no taxes :)
https://www.toysonics.com/home.php?cat=876
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I have had one of the (Chinese) red pumps on long term test here:
http://www.theassociationofmodelsubmariners.com/t286-pumps-geared-variety (http://www.theassociationofmodelsubmariners.com/t286-pumps-geared-variety)
and it looks to be OK and always fails safe. Personally I wouldn't trust any old pump off ebay. Too much at stake!
A lot of stuff on pinch valves on the Forum that you should also find interesting.
David
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I made a pinch valve up with a very inexpensive non-ballraced 9 gram servo. So far so good, but I had to use a miniature servo for space reasons. If I'd had more room, I would have fitted a standard size servo. Servos are very cheap from places like Hobbyking these days.
Couple of things to bear in mind with pinch valves. Many of the designs use a ball or rounded off shaft to pinch off the hose, these require more pressure than a pinch valve with a keener edge. I used some copper sheet folded over to make a small radius, nothing sharp at all. This was coupled with some fairly thin walled silicone tubing, which is very easy to compress.
Others have mentioned my hose will end up damaged with this set-up, but I've seen no ill effects to date, and I keep a close eye on the hose. Also worth mentioning that the way you profile the servo arm will make a difference. You want a nice smooth cam action that gradually squishes the hose, not an 'all or nothing' type action.
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Been looking for pinch valve ideas got a couple couldn't find much on the AMS site probably hidden within the threads i have a couple of ideas to try when i get some bits up together.
Dave
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Hi Dave,
There is a lot on there - with quite a lot of photos of the different systems. I think it is in the Questions and Answers section but you will find that the search engine works well.
Let me know if you are still having problems and I will find it for you.
David
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(http://s7.postimage.org/4ki877x5m/Image0218.jpg)(http://postimage.org/image/4x9mdeffb/)
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I only made the above as a proof of the concept, but it worked so well I kept it.
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http://www.theassociationofmodelsubmariners.com/t380-pinch-valves (http://www.theassociationofmodelsubmariners.com/t380-pinch-valves)
Found the link for you, Dave!
David
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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
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you could try windscreen washer tubing
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Don't use windscreen washer tubing, it's too stiff.
For thin bore tubing, you can try Polymax. Ten pound minimum order though.
If you're using a normal size servo however, you should be alright with the thicker stuff. I used the thinner tube because I only had room for feeble little 9 gram servo, non-ballraced I might add.
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I would only recommend silicone rubber tubing. (And I have never used anything else. We should perhaps have mentioned that in our posts on the Forum but it is the obvious things that don't get mentioned!)
That's because it needs to be easy to squash and have some "spring" in it.
David
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Picture seems to have disappeared that I linked to. Let's try photobucket-
(http://img.photobucket.com/albums/v293/subculture84/Image0217.jpg)
(http://img.photobucket.com/albums/v293/subculture84/Image0218.jpg)
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I've registered on the AMS forum so will hopefully find plenty on there does the pinch have to be 100% or will a slight bleed be ok?
Now looking for a motor i'm looking for a 12v i was thinking of one of these
http://www.technobotsonline.com/mfa-motor-re-385.html
I don't need masses in the way of performance i already have a speed 500 but think that may be to big or i could go brushless
Dave
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Too small.
500 size motor minimum for a boat that size.
You could have a word with Andy Nightingale, I think he had some 555 motors up for grabs a while back, he might still have one or two.
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I'll stick with the 500 i already have then, it just seems a little on the big side but i'll give it a try.
Dave
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Depending on the 500 wind you have, it may need a gearbox to drop the RPM.
Your prop size will be about 1.5" diameter. Not sure what pitch you're going for, but assuming it is roughly the same as the diameter, you will want to be aiming at about 4-7000RPM shaft speed.
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Gosh, just got back from dropping my sub through a hole in the ice at the Barrow pond. Happy Days!
Yes, the tendency of a pinch valve to leak a little is one of the unintended benefits of the system. It has happened that people have lost their subs only for them to rise from the depths, minutes or hours later.
Try that with piston tank! (Your sub stays sunk.)
Concerning motors, I wouldn't have thought that the 1:1 Welman was exactly a zippy performer so motor choice isn't going to be too fussy.
I find myself using MFA motors more and more. www.mfacomodrills.com (http://www.mfacomodrills.com) Some gearing is a good idea (1:3 or there abouts) and the ones with integral gearboxes are very easy to fit and make chopping and changing gearboxes very easy if you get it wrong first time :} David
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If aiming for scale speed, you're only going see about one knot, as the fullsize speed was reported to be just three knots, which is slow even by midget sub standards.
Not much fun, and I'd be doubtful on the level of control from the hydroplanes at such a slow speed unless you make them larger than scale.
Personally I think a moderate walking pace would look about right for this boat. Should give the hydroplanes enough speed to work efficiently, and enough pace to make the boat entertaining to run. Also will help the model produce a more realistic wash when running surfaced.
You can always throttle back for slower speed.
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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
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It's best to get the shaft as inline as possible. Perhaps you might consider fitting the motor is a separate module
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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.
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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
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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.
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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 (http://www.theassociationofmodelsubmariners.com/t266-prop-shaft-seals)
(Sorry to keep on referring you to another Forum but it saves retyping it :D )
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
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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
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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.
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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.
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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.
(http://farm6.staticflickr.com/5167/5279884949_828bf24fe2_b.jpg)
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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