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[bbdave]

I am going to be taking on a Robbe u47 soon but i am interested to know what the dive actualy looks like when only using dynamic diving i have seen a video on utube but wasn't impressed how the sub looked when diving and resurfacing is it possible to submerge level with dynamic diving is it just a case of trim? the sub on the video dived bow first lifting the stern up causing the props to cavitate and when surfacing it popped out of the water bow first like a cork this may have just been the way it was being operated but it didn't sell dynamic dive to me and i'm wandereing if i may save for an engel tank before building. Also i have read much on building the u47 and other subs is the bayonett fitting worth buying for it?

[Mankster]

I've seen dynamic U-47 perform really well, though they have been ballasted down quite a bit.  Some people have reported leaks with the Robbe seaing system, though these may be buid issues.

[Sub driver]

bbdave,

I would guess that the one in the video didn't have a levelling device fitted hence the " 'bottom' up " attitude when diving . A levelling device would have altered the rear vanes to pull the stern under as the nose went down so it should have gone down level. same with the going up  too much up vane and probably power off.

I have a robbe sea wolf , modified with a leveller and it goes down level. You will DEFINATELY need a leveling device whatever route you take. 

If you can wait . the Engel tank is definately the way to go as you will end up with a better performing sub all round, but thats if you can wait ??.
With regards to the bayonet fitting its all a matter of personal choice in afraid.  (and money )

Hope this is of some use

Regards Sub.

[Subculture]

I've dealt with leaks on a couple of other folks Robbe boats. In both cases it was down to the end of the cylinder not being finished off well. Robbe supply the cylinder with a rough saw cut, and this needs smoothing off to seal effectively, as Robbe employ axial compression of the o-ring seal.

Piranha do an impressive range of upgrades for Robbe boats that are especially inviting for those considering a static dive conversion.

http://www.piranha-modellbau.de/

If run in dynamic dive mode, you must ballast the boat to decks awash, otherwise you will need very high speed for submerged running, and you will get the cork-like ascendant as soon as you chop the throttle.

There are also other, cheaper options for making your boat dive statically- you can use a water pump, gas, compressed air etc. These have all been done, so you don't need to reinvent the wheel.

Andy

[bbdave]

Thanks chaps probably all obvious stuff to you and you've probably repeated it many times but very usefull to myself. I understand if i ask 10 different people i'll get 10 different answers i'm just looking to build a nice water tight reliable sub that is capable running as scale like as i can but mostly it has to be fun i don't fancy pulling my hair out constantly so i'll try to build as simply as i can.
 A couple more questions

Can you advise me of any books that show the different variants of the Vii and colour schemes?

I have seen some resin conning towers that are available that look very good but have heard they are heavy is this a problem?

Same question with the brass deck upgrades?

[Subculture]

The resin towers will displace more water than the standard vac-formed version, so therefore this can cause problems with needing a larger ballast tank when you convert to static dive.

The brass decks will be heavier than a plastic deck. However it will be thinner, so will very likely result in a smaller ballast tank required.

What will be affected is the metacentric height of the boat.

This is the distance between the two forces acting on your boat, gravity pushing down, and buoyancy pushing up. The further apart these forces are, the more stable the boat is, and this is especially noticeable when underwater.

By adding a brass deck, and a slightly heavier conning tower, you will probably need to remove a bit of lead from the keel of your boat. This raises the centre of gravity slightly.

You can go the other way, and leave the lead in the keel, and add a bit of buoyancy in the form of polystyrene foam blocks or small air cylinders just below the waterline. This raises the centre of buoyancy, and should result in a more stable boat.

Andy

[bbdave]

Cheers Andy sounds like the build could be interesting.

[Sub driver]

bbdave

Re-books.

Type V11 u-boats by Robert C. Stern ISBN. 1-86019-855-4

Squadron signal publications type V11 U boats and Anatomy of the ship the type V11

Just a couple here but there are quite a few also seach the internet there are loads of web sites for the Type V11

Hope this is of use.

[Subculture]

If you want your U47 to dive and surface with a level attitude, then you need to make the front hydrovanes operational with an extra channel. A pitch controller helps too.

What you need to remember, is that the hydrovanes produce a pitching force that acts on the centre of gravity (C.G) of the submarine, on a Type VII, this is pretty much bang in the middle of the boat.

With rear vanes only, the boat will pitch up and down around the C.G in the exaggerated fashion you describe. With both front and rear vanes working you will control depth using the front vanes, when you command them down, the bow will pitch down, the pitch controller will sense this and actuate the rear vanes to compensate and bring the boat level- your boat should then descend and ascend on an even keel.

[bbdave]

Cheers sub driver got an order placed.

Subculture thanks i assumed both sets of planes were operating on the kit, but i am assuming the standard kit only the stern planes operate is this correct? is it possible to convert the fwd planes in the kit to operate or is there an after market set i will need to use?

[Subculture]

As standard the the rear vanes operate with a servo, and forward vanes are controlled passively with a rather crude affair that's best removed. AFAIK there is no after market modifcation kit, but many people have added forward vane control, and the modification is well documented on several websites. It's not a difficult or expensive modifcation.

Andy

[bbdave]

Ok things are starting to become clear now i'm doing lots of research before taking the plunge so sorry for all the questions.

I am now under the impression that the engel tank is controlled by a switch so as it fills the sub looses bouancy and submerges so for arguments sake i operate the switch until decks awash then stop, the sub will then remain at decks awash untill i either continue filling or empty the tank is this correct?

So assuming the above is true can you set a depth i.e. 12" and remain at that depth as long as the planes are not used to dive further as i assume this will upset the trim and the sub will continue to sink. true?

I guess there is a gadget for setting a max depth using pressure so the sub will automaticly surface if this is exeeded

Ok so radio wise how many channels are needed i'm guessing, Throttle (fwd.rev), rudder, planes, ballast tank, i guess the levelers etc will be be via the plane output and depth limits overiding the ballast tank switch. if i were to buy a radio what would you recomend. how or which comand outputs do you have these controls e.g.  throttle (left ratchet stick), rudder and planes (right stick), ballast (on,off,on toggle switch) or is this totaly wrong?


Sorry for the questions i'm having lots of thoughts about my sub project and i'm loving all the research an planning :)

[Subculture]

If you want to fit a ballast system, and have independent control of the vanes, then you need a minimum of five channels. Therefore you should be looking at a six channel set.

If you are fitting a piston ballast tank, then it's worth using a proportional controller. This effectively turns the tank into a big servo, and allows you to accurately control the amount of water you take on.

You can control the piston tank with a rotary pot or a linear slider.

Andy

[bbdave]

You can control the piston tank with a rotary pot or a linear slider.

Andy

Are these retro fitted to the tx or are there sets available with the already fitted?

[Subculture]

Some do, some don't!

Hitec Laser 6 has a proportional knob suitable for this kind of thing, and it's a good reasonably priced set.

http://cgi.ebay.co.uk/HITEC-LASER-6-CH-40-MHZ-R-C-SET-FOR-BOATS-BARGAIN_W0QQitemZ120217767951QQihZ002QQcategoryZ140972QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Another set worth looking at is the Polks Hobby. Although it looks like something that was designed in the '70's this set is very advanced and uses a synthesized TX and RX, which means no crystals required- ace! Price for this set is very reasonable, and If I was buying a new set today, this is the one I would get.

http://www.polkshobby.com/index1.html

Andy

[bbdave]

Thanks for the links subculture

[Mankster]

The Engel XP range of piston taks are proportionally controlled (well the last 125ml or so, but thats all you'll need really); you'll need to get the matching ballast tank switch to go with it; and it will need 2 channels to control it. Yes Engel sell a pressure sensor that attaches to the controller that will blow the tank when you exceed 6 feet or so. You can get depth controllers that will maintain your depth by adjusting your planes. The Subtech ADC1 from Pandan works well and can be use on the front planes whilst the pitch controller looks the rear. You will need to maintain some forward motion to main depth though.

I would plump for an 8 channel unit rather than 6 as the extra initial out lay is small, and the extra channels will come in useful if you want independent motor control or add sound ligths etc..

[Subculture]

You can also use Norbert Bruggens controller to proportionally control the tank, Pandan sells these in the UK, and it only needs a single channel.

There are a couple of other choices for piston tank control, but they're a bit more exclusive, and a bit more expensive.

Andy

[bbdave]

Do i just need the standard engel tank wit the two microswitches as sold by Pandan and then just add the proportional control unit to it?

[Subculture]

Engel do an upgraded end cap for their tanks that has the feedback potentiometer already fitted, although it's expensive, and it doesn't look like it would be much of an effort to modify a standard tank.

http://www.engel-modellbau.de/catalog/product_info.php?cPath=2_94&products_id=1277&osCsid=e7ec11e4572370b4c425db6b63f47cd5



I would have a word with Pandan, these tanks may be available with a pot already fitted.

Andy

[bbdave]

Thanks subculture i'll drop them an email. Isee engel sell the xp tanks direct so that maybe easyier

[kazzer]

Why go for dynamic diving when you can have a full static diving system, for less money?

see http://www.caswellplating.com/models/sdts.html


As for building these things yourself, why bother?  I tried it once, what a pain! It took me ages, because I didn't fully appreciate all the problems involved. I eventually gave up and purchased a ready made unti.

see http://www.caswellplating.com/models/bsc.html