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May 24, 2011, 06:11 PM
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Rubberband Nautilus III


A Jules Verne-style Nautilus made from PVC pipe.

He's a rubberband-powered, dynamic free-diver, similar to my previous Nautilus. I use the male pronoun because this sub is a little too evil looking to be a she :-)

We've made one trip to the pond to test. He works :-). Like my previous sub, this one is also sensitive to amount and placement of ballast. Decks awash and a slight nose down attitude allow the rubberband & prop to dive the boat. Depth is controlled by a floating squid controlling the angle of attack of the dive vanes, details in the other Nautilus thread.

This sub has an enclosed rubberband power pod: 1/2" ID PVC, 4 strands of 1/4" contest rubber, APC 5.1x4.5E thin electric prop, 1/6"brass rod as prop stop. I'd hoped this would reduce drag and make the sub cruise faster than the previous version. Not sure how the speeds compare, though. Will have to have a sub race :-). The pod is removable for winding the rubber band, which is easier to accomplish single-handed than with the previous sub's setup. We use a 5:1 winder, so putting in 300 turns is not too onerous. The sub will travel under water about 50' with this stored power.

Design, construction, and operation details of Nautilus II here:
https://www.rcgroups.com/forums/show....php?t=1405510

Bottle Brig (the Victim of Naut II and soon to be victim of Naut III *evil laugh*):
https://www.rcgroups.com/forums/show....php?t=1399486
Last edited by Brooks; May 24, 2011 at 06:43 PM.
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May 24, 2011, 09:54 PM
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Brooks, if you are not drowned (Rexburg has the same weather) do you have the video you got the pic from? Looks like it might be interesting to watch.....
Foo
May 25, 2011, 02:46 AM
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Hi Fooman, house not sunk yet. Hope you are dry too, and can continue your sea stories!

The Nautilus II sub runby video is in post #3 here:
https://www.rcgroups.com/forums/show....php?t=1409501
May 25, 2011, 07:36 AM
Registered User
Thanks Brooks, lawnmower broke down last week and lost wife's shi tzu in the backyard yesterday (LOL), now I have to take a machete to go find him! (How's that for a short sea story?)
Foo
May 26, 2011, 08:47 AM
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Perhaps I should clarify the design of this sub for the non-submariners. The familiar Disney version of the Nautilus is not anything like Verne's book version. I revere the Disney version, as do most US RC submariners. My first-ever scratch sub build was a profile Disney version. To match Verne's 1870's sub, though, one needs to look at cigar-boat hull profiles, not the Victorian, angular-design invented by Disney's Harper Goff (Or the equally interesting, if wildly divergent design, used in the movie "League of Extraordinary Gentlemen")

Verne was actually up to date on sub technology of his era. He even correctly figured out operational details of modern subs (like the fact that diving will get you out of the turbulence of a sea storm). In the 1960's, his book was pilloried as containing numerous science errors; but it turns out, it was the English translation that was full of errors, not Verne's original French book. For a modern, accurate translation of "20k Leagues Under the Sea" I can recommend the 1993 translation by co-authors Walter James Miller and Frederick Paul Walter, published by Naval Institute Press. I got mine, used paperback, for less than $10.

Dozens of interpretations of Verne's sub can be found here:
http://www.vernianera.com/Nautilus/Catalog/
May 26, 2011, 01:11 PM
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At the pond


Sub ran well in high winds and seas. As Verne said, once you get below the surface, things go better :-)

I reduced the trimtab size substantially, compared to Nautilus II and the previous Naut III cruise. The boat still dove fine. The trimtabs are meant to force the vanes into the dive configuration, opposing the vane's tendency to streamline parallel to the hull (since their axle runs fore of the geometric center of the vane, near the aerodynamic center). I realized, while working on the boat yesterday, that the larger the trimtab, the more dive vane area that was "neutralized". By their very nature, trimtabs work in opposition to the lift off a wing, no matter whether the lift is oriented up, per usual, or down, per a sub. So, the bigger the trimtab, the less total useful lift off a wing or dive vane.

Though it was hard to judge, due to the big waves, I think the sub could handle more freeboard. That is, with the new, smaller trimtabs, it had the diving power (negative lift) to pull more exposed hull underwater.

Here a couple surface shots; I had no dry hands to film subsurface runs...next time :-).
Last edited by Brooks; May 26, 2011 at 05:37 PM.
May 28, 2011, 07:14 PM
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Brig down


John, Bob, and I "Sighted Brig and Sank Same.... Several Times" :-). This sub has more mass than the it's predecessor sub; consequently, the flapper portion of the brig's keel is more reliably activated by sub ramming, resulting in foundering. One sinking was quite satisfying, with the stern settling slowly, and the brig ending up with only the bow and bowsprit exposed.

The brig's string system (the alternate way the sub can sink the brig) was not as susceptible to the new Nautilus, however, due to a) running the sub too shallow, b) faulty design of the trident spear of the sub. I've set the sub depth several inches deeper for our next cruise, and will work on refining the trident design.

This cruise was the first with squid tentacles holding the squid to the sub (red rope spun on my miniature rope walk). The tentacles added more drag, compared to the previous test cruises in which thread substituted for tentacles. I had to put in 40% more winds of the rubberband to get similar underwater performance. The band is getting old, too, (it snapped, but a field repair put the sub back in business). The sub submerges fine, but it requires a certain minimum speed to accomplish this (as do all dynamic divers). The extra drag of the tentacles was just enough to cut the underwater portion of the run in half (10 sec vs 20+ sec with the thread "tentacles). Increasing the winds restored the uw performance, though. Physics is omnipresent, whether you want it or not :-).
Last edited by Brooks; May 28, 2011 at 07:23 PM.
Jun 04, 2011, 08:23 AM
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I was not happy with the length of the underwater part of a shot. I increased the dive vane area by 40% with simple chord extentions made of clear plastic cut from a fresh strawberries container. This made a big difference: for 300 turns (60 winds of the 5:1 winder) the sub now travels 60' uw, with a 30' surface run at the end, for a total of 90' cruise. The uw portion takes about 40-45 seconds. This is 2x the previous best uw cruise time.

I am lubing the rubberband with Armor All. This seems to work, keeping the 4 strands from becoming stuck together, thus allowing a more efficient transfer of woundup energy. Armor All, though water-based, seems to be somewhat water-resistant and persists for at least an hour of pondtime; my normal rubber lube, used for aircraft, is water-soluble and does not last at sea.

Running deeper, and the new trident design, made the sub more deadly to the Brig. Under the strong winds of yesterday, I had to lock the Brig's flapper, otherwise the wave action on the hull&keel would have triggered founderings. Left with only the string trigger, the sub could now reliably (2/2) sink the brig, though. We had a several misses, it's still hard to hit that wily target :-). The Brig seems to have a mind of it's own, speeding up or turning to avoid the sub, as if Neptune himself was protecting the poor Brig sailors.

John finished varnish and paint maintenance of Bob's rowboat "Ladybug." We'll be able to send the Brig and Nautilus offshore now, which should lead to some fun attacks. Up to this point, we've had to stick to shallow, wadeable water, with only short target runs. We've had to rely on short sub attacks, constrained by either running aground, or by getting out of reach of the crook used to retrieve the vessels before they get out too far to wade after them. The winds near shore are more fickle than the winds offshore, making for erratic target courses. With the more steady offshore winds and more steady Brig course & speed, I hope to be able to use the BATAM (Brooks' Analog Torpedo Aiming Machine) to plan longer shots.

BATAM
https://www.rcgroups.com/forums/show....php?t=1415607
Last edited by Brooks; Jun 04, 2011 at 08:50 AM.


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