The Search for Small Scale Speed.

[eddp]

A friend of mine recently expressed an interest in R/Cing a 1:72 scale Airfix E-Boat. I admitted that I was toying with the idea of adding R/C to a Revell 1:72 scale PT-109.

The PT is about 13" long, and the E-Boat is about 18" with proportions similar to a deep-V racing hull.

I tested the bare hull of my PT, and it will support an additional 4 ozs., floating at a slightly deep waterline. The 4 ozs. would include the radio/power system, deck/superstructure and all details.

Now anyone can but a motor in these boats and make them putt around a pond, but I want to achieve scale-like speed from plastic models of this size. Has anyone done this? Does anyone (except me, and I'm deranged) think this is possible?

There is a lot of micro R/C gear and small, powerfull motors available from the Electric Park Flyer R/C planes, so there is hope.

One of my major concerns is the availablity / construction of suitable props. (I'm not completely daft...I intend to us a single screw / single rudder config.)

This is Liberty Hall. Feel free to spit on the floor and kick the dog!

-Edd Pflum

Westmont, IL.

[leccyflyer]

Ed

What a great idea. My son and I have a Vosper RAF Rescue launch kit about 24" length- a very simple little kit of ABS mouldings. To make it look a bit more scale like I got hold of the Airfix 1:72 scale RAF Rescue launch for a few clues and it would be excellent fun to be able to motorise that one as well.

I don't know anything about leccy boats but I'll watch your thread with interest in the hope that you get this thing to work successfully.

Actually that just gave me an idea. My boy has a small toy jet ski - battery operated that squirts a jet of water for propulsion and is about the same size at the RAF Rescue launch. I wonder would it be possible to transpose that unit into the launch and do away with a prop all together. Tese are probably available from Toy's r Us.


All the best

Leccy

[Sabrejock]

Ed: I've toyed;) with the idea of using the guts and motor from a standard size servo. The motor runs in both directions and I'm sure that if you don't ask too much of it the thing could propel a small boat. It would be a very cheap controller/motor settup if it worked for you. Perhaps the contoller would power a slightly larger motor, but not much as there is no heat sink. If you think the idea has merit, let us know. Tex.

[eddp]

Sory I'm so long in replying, but I couldn't find my way back to the thread (I enter through E-Zone Magazine.) :D

I have done a litle more research: The Revell PT-109 (also PT-117, same kit different decals) hull will support about 6 oz. at a waterline which looks like it would allow planing performance. The hull itself weighs 2 oz., and the other plastic bits (deck, superstructure, details) weigh about 2.25 oz. This leaves less than 2 oz. for the R/C gear. My next step is to gather up my resources (search through piles of junk) and see what weight of system I can come up with.

Leccy: This weekend I bought a Revell Vosper MTB (early war Vosper) for $10 to check out. This boat (and the Airfix Vosper) is 70' vs. 80' for the Elco PT. That means the hull won't support quite as much weight. I haven't put it on the scales yet, but I'll keep you informed.

SabreJock: I have used the servo technique several times in the past, and it works well. I even have a Dean's "Royal Marine" WW2 Antisubmarine Trawler kit in 1:96 (18" long) that recommends the servo trick.

For fast boats, however, I am not sure the servo would put out enough power, or more specifically, enough revs. Most of the available propellors are fine pitch for slow moving scale boats, and they have to be spun at high RPM to get planing speed.

Usually adding more cells accomplishes this, but I don't want to feed more juice into the whole radio. My current (no pun) plan calls for a light 2 channel XCeiver, a micro servo for rudder, and a 5 Watt airplane ESC (no reverse) with a small electric airplane motor. I have 7-cell small battery packs that would work with this combination. If this comes in within weight, I'll try it in the test tank.

-Edd

[eddp]

I gathered together the R/C equipment for the Revell PT last night.

It included a HiTec "Feather" 4 ch. receiver, a HiTec HS-50 Servo, a Dymond "Max 1" motor (sans gearbox), a Robbe miniature stuffing box (shaft) and prop -- I forget the number. I didn't grab an ESC or rudder ass'y, but these won't weigh much.

With a disassembled Ray-O-Vac "9v" battery (7 X 150 mA NiMH) the gear weighed 2.75 oz. With 6 X 280 mA NiMH, 3 oz. and with 7 X 110 mA NiCads, 3.25 oz.

So, no matter what batery is used, the system comes out about 1 oz. over budget. Tadiron lithium cells would be lighter, but at $30 each, they're oer my budget.

I have started modifying the hull for R/C (cut a hole for the prop shaft :D ). My first goal is to see if this type of power will produce the desired performance (e.g. planing). Then I'll worry about the weight budget.

The first tests will be run without the deck, et. al., so the weight will be about 5~5.5 oz. total. I've been thinking it might be easier to build a new hull out of balsa rather than lighten the plastic one, but this kinda defeats the purpose of the exercise.

-Edd

[Sabrejock]

Edd: As you have done the servo motor drive thing, I think I will persue it with a displacement type small boat. Did you do any measurement of current acceptable to the servo electronics before letting the smoke out? They claim to use about 1/2A in short bursts but I don't think they'd stand it for extended periods. I have an old huge 1/4 scale servo which I could use. As far as a drive, I plan on using music wire in a pushrod snake inner and cobbling up a prop from shim brass to solder to the end of it.

This is fascinating. Tex.

[eddp]

Just like an electric plane, yourdraw depends on the load: the size of the prop. I'm used props of around 1"~1.25" diameter and moderate pitch with standard size servos and no problems.

I have a 15" tug boat that was powered by a standard servo. I used two, two-bladed props from the Lindburg "Blue Devil" destroyer, half lapped to make a four-blader!

By moderate pitch, I'm guessing about 30 degrees from the plane of the disk. As always, your mileage will vary.

-Edd

(I'll try to get some pictures to post.)

[Sabrejock]

Thanks. My buddy and I just cobbled up a POC model from a foam slab. Used the guts from a 1/4 scale S-34(Cannon motor). Prop was just a strip of brass bent to TLAR standard. Thing planed in my bath! Next step is a 14" PT (Not 109!!!) The beauty of this for small stuff is the elimination of the Rx Batt and tick-over slow speed.

[pbhawkin]

Hi,
I have R/C'ed a Tamiya 1/72 plastic Perkasa PT boat.
Roughy I have a speed 280 with micro ESC and BEC, 5x 500MaH Nicads operating from a Ranger 2 transmitter. It planes beautifully. I do have a standard rudder servo that operates 2x 200% oversize rudders as well.

regards
Peter

[eddp]

AFAIR, the Perkaska is a somewhat larger craft, right, about 18"?

A S280 should be great (well. ...er...actually is as you wrote.)

The Revell (Germany) S-100 Schnell Boot (E-Boat) is almost released. I saw a pre-release blurb in a British model mag. With the thin moldings Revell AG is famous for, there should be a lot of available displacement for R/C.

In the meantime, I haven't had the time to pursue the PT. Most of the "bits" are collected, it just a matter of putting it all together (for a test run, not for real.)

-Edd