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Author Topic: Nixie  (Read 6368 times)

red181

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Re: Nixie
« Reply #50 on: March 10, 2021, 11:26:44 pm »

it got wet today, and happy to report no apparent leaks. Before resorting to grease, or petroleum jelly to seal the Perspex top plate, I found some one side adhesive foam tape, I recall I must have bought this 3 years ago for this project, so thought I would give it a go, and it seems to have worked.


I've cut a square out of the top to allow the battery to be charged in situ if necessary, this will let the fumes out, although if the tape does keep performing, this makes the Perspex top plate much easier to remove. .


I was still unsure about the aerial, the instructions are not very clear about this, so had a choice of an old transmitter aerial, or the whip style in the picture, the latter has been used as it was a very easy fit, hopefully it will work.


Next stage is ballast, without ballast it wants to roll over in the bath water, hopefully that will not happen with ballast, then a range test and get the servos operating, and check the propshaft doesnt leak when in use, then its lake time ;)
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red181

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Re: Nixie
« Reply #51 on: March 27, 2021, 10:32:58 pm »

bath trials have gone ok, it is really difficult to get the ballast right, is this normal with rc submarines?


I've got 360g, front and 380g at rear, which seems an awful lot, Glyn Guest in the build commented he used a few coins to get his decks awash and ballasted. I also noticed that the slightest of movement and it all goes wrong, and if the decks are not wet, its very unstable. I need to think of a way to attach the lead in an easy fashion, making it easy to add or removed at lakeside. I though of a bolt front and rear under the hull,  and just use a wingnut to hold varying pieces of lead on, will this then create too much drag under the hull?


I have also had to change the prop, even in the bath when power was applied it was just a lot of cavitation and no movement with a 3 blade prop, I've now got a 45mm two blade, which moves it, but still a lot of cavitation, and this is running on a fresh 6 cell nimh. Ill have to rething the ballast securing, and then its to the lake, and hopefully not just a sink to the bottom!
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Davy1

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Re: Nixie
« Reply #52 on: March 29, 2021, 08:54:42 am »

Ballasting is always tricky with model subs - part of the "fun"!?
I use Velcro to attach external weights. (Apply a strip of self adhesive Velcro tape to the bottom of the hull. (Drag isn't a problem at normal sub speeds)
Prop selection is also often tricky and also interacts with ballasting. The prop can draw air in from the surface - this isn't actually cavitation. Keep the stern down in the water. Go for a low prop speed if you can - gearing perhaps?
Have fun and good luck!
David
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Subculture

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Re: Nixie
« Reply #53 on: March 29, 2021, 10:25:05 am »

Ventilation is a problem with any spindle sterned sub because there is no hull bottom acting as a shelf above the propeller. Once you get below the surface approximately one or two props diameter, you'll find the problem disappears. Use the throttle sparingly when on, or near the surface to avoid the 'egg whisk' effect.

Adding a fixed  or swivelling shroud/kort nozzle will help in reducing ventilation, but won't eliminate it. If you look at earlier submarines that were primarily restricted to behaving like submersible cruisers, and thus had to spend the majority of time on the surface, they tended to have the props mounted much lower and as far underneath the boats hull as packaging permitted.

Once subs could remain submerged for much or all of their patrol with the advent of nuclear and other AIP systems, the design constraints shifted and spindle sterns became the norm, where they are sited very efficiently with large diameter props that are less noisy.

MartinL

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Re: Nixie
« Reply #54 on: March 29, 2021, 05:15:24 pm »

My stretched And modified Nixie was ballasted with a sheet of lead forming the whole bottom and it still needed a couple of extra ounces added.
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red181

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Re: Nixie
« Reply #55 on: March 29, 2021, 08:40:17 pm »

thats a cool nixie Martin! I had not thought of opening up slots etc front and back top plates


If I had been wiser Davy, yes gearing, but too late now, I was treating it like  a conventional boat. What are the thoughts, much larger prop diameter, more prop blades?, Im considering what Subculture has explained, I called it cavitation, but in hindsight it was different to what I have experienced previously with boats, If I go larger diameter prop, it will have to submerge more to get the prop underwater    :embarrassed:  its quite technical this submarine stuff!


Strip of lead full length, what a great idea, then try less ballast front and back, worth a go I suppose
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Subculture

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Re: Nixie
« Reply #56 on: March 30, 2021, 10:58:08 am »

Attach the lead to the outside of the boat using rubber bands, zipties etc. slide back and forth until you have the right position for trim, then attach inside.

red181

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Re: Nixie
« Reply #57 on: April 22, 2021, 10:59:41 pm »

for God's sake!!! :(( :((


so I've been on other tasks, with rc plane sites reopening, and very favourable weather, I've been playing with them. Ba[size=78%]ck to Nixie, all ready for the first real water test outside, and I connect the battery up reversed in the tx and the smell of electrical death came out of it, so now I need  a transmitter and receiver[/size] >>:-(
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SteamboatPhil

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Re: Nixie
« Reply #58 on: April 23, 2021, 11:52:51 am »

"smell of electrical death".  {-) {-) {-) {-) {-)  sorry but its a great expression !
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Steamed up all the time

red181

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Re: Nixie
« Reply #59 on: April 25, 2021, 08:56:25 pm »

its a bonus if it also releases a deathly black cloud, which follows you almost laughing at you, then  you know your device is well and truly dead, when its just the death smell you always feel there is a chance of resurrection, bit like a steven king film.......... :embarrassed:
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