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Old Oct 26, 2010, 11:09 AM
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Sydney, Australia
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Build Log
Billing Boats 'Polar' trawler

This is my first RC boat i'm building. I used to be into them as a youngster, but my Dad did most of the work. It is the Billing Boats 'Polar' modern style fishing trawler. It is an old kit though, the date on the plans is 1987. I hope you guys will point out anything i'm doing wrong with the build.

This is where i'm up to so far. i added a lot of extra internal bracing, Billings really skimped in this area:
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Attatching prop tubes (stuffing tube, is that what it means?):
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This bracket will be used for the steering servo:
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I made these for the motor mounts, though i'm thinking of a Graupner mini gearbox. Thoughts on this??? Is it better to direct drive or have a gearbox?
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The Billings kit comes stock with these plastic couplings, will thse last with careful use?
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A few shots of the Polar next to the other boat i'm working on, Billing Boats Colin Archer (this will be kept static). If i varnish the deck it will come up as looking too clean and yellow, what timber stain will give it more of an aged, weathered appearance?
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This hull is very thin and flimsy. The first glue i used on it (Tarzan's Grip) melted the plastic, leaving depressions that i will need to fill. Epoxy has worked fine with no ill effects.
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One problem with the hull, the bow is twisted slightly to the right (when looking directly at the photo). it has straightened up a bit as i've added the bulkheads and deck beams, but i don't think adding the deck will sort it out. i'm worried as the front masts (for fishing nets) will be out of allignment with the rear masts.
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Old Oct 26, 2010, 11:26 AM
Veni, Vidi, Feci
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Joined Dec 2004
12,300 Posts
Looks like a neat old kit.
Before trusting too much in that epoxy, please flex some of the joints and see what happens (or try it on some scrap). Epoxy only appears to stick to ABS, but it can pop right off!
Glues that I have used that work pretty well on ABS:
- Stabilit Express, 2-part methyl-methacrylate (NOT an epoxy). $$, and this is what Robbe recommends on ABS hulls.
- PL Premium polyurethane construction adhesive, only available in caulking tubes at Home Depot. Joints need to be able to breathe for the stuff to set. Sticks quite well.
-Amazing Goop, from most hardware stores. More flexible than PLP, and also sticks tenaciously.
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Old Oct 26, 2010, 09:14 PM
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United States, NJ, East Brunswick
Joined Nov 2008
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Will agree with Patmat on the use of Stabilit Express on ABS plastic. I used it on my Happy Hunter for all of the internal parts, even some of the cabin work, applying it on the interior joints for adhesion and stiffingin purposes.

Just be careful with the mix and only mix a little bit at a time. If I recall, the stuff stinks pretty bad and is a bear to remove if you get in places it shouldn't be.

Scott
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Old Oct 27, 2010, 07:50 AM
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United States, ID, Rexburg
Joined Sep 2008
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I am not sure whether the couplers (known as dogbones in R/C cars) will last for a long time, due to being plastic. The good news is that several different Cars/Trucks use them so replacing them is not too difficult. I would run them (make checking the plastic parts for wear part of your post run checklist) until the plastic cups start to wear. Then find replacements, either online or at a local hobby shop.
Foo
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Old Oct 27, 2010, 09:09 AM
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Sydney, Australia
Joined Oct 2010
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Thanks for the replies guys. the epoxy seems to hold okay? I messed up gluing in the rudder post and wooden block and was able to break it off from the hull a few days later, though it took a LOT of force (at the time i was going to scrap the kit).

With the dogbones i'm wondering if i'll be able to buy metal replacements in the same size, otherwise i should get them now before mounting the motors?

What are your thoughts on gearing the motors down? Will they and the ESC burn out if i'm only ever cruising at half throttle? i've been reading about 'cavitation' etc with the props if they are spinning too fast. i like the idea of this all in one unit:
http://www.cornwallmodelboats.co.uk/...r_1139_20.html

no photos for a few days till the postman comes with the motors and batteries.
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Old Oct 27, 2010, 09:31 AM
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Graupner gearbox: NOOOOOOOOOOOOOOOOOOOOOO!

See my article on gearing:
http://matthewsmodelmarine.wordpress...all-geared-up/

The coupling shown can also be an issue (or not). To avoid binding, it must have lots of internal clearance, and clearance makes noise. See for example how badly the original coupler runs in Bristol Bay trawlers.
Ideally, two fixed shafts (motor and prop shaft in this case) must intersect PERFECTLY to allow use of a single ball like this. Since perfection is rare, it's better to use a true dogbone (having TWO balls), or a double u-joint... these joints allow for some shaft misalignment.
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Old Oct 29, 2010, 09:45 AM
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Very informative read, thankyou. What about the other Graupner gearbox you mention, the '1700' series?
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Old Oct 29, 2010, 09:50 AM
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1700 is a sweet unit, for 400 size motors. iirc, available with & w/o motor. What size are your props? And what battery voltage do you plan to run with?
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Old Oct 29, 2010, 10:05 AM
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a 400 size motor is the same (dimensions) as a mabuchi 380? as i have a pair of 380's. the props are 35mm diameter, and i will be running it on 7.2 volts. what ratio should i get, 1.85 or 2.33? i think the 380 spins to 12000rpm
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Old Oct 29, 2010, 10:14 AM
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A 35mm prop can be happy to a max of about 10,000 rpm, probably you won't need anything like that to drive at a scale speed. I'd go conservative with the 2.33.

Or, just get a couple of cheap 500 size slow motors for direct drive. See for example the Integy lathe motors:
http://www.rcgroups.com/forums/showthread.php?t=906148

The 45T or 55T motors might be a good start.
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Old Oct 29, 2010, 10:19 AM
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2.33 it is. Thanks heaps for your input. i already have the motors on their way so i'm stuck with them
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Old Nov 01, 2010, 12:30 PM
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Sydney, Australia
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I decided to fibreglass the inside of the hull. Firstly i gave the inside of the hull a thorough sanding with 100 grit sandpaper. Then i laid down some chopped mat fibreglass and resin. The mat was way too thick but i think i did okay for a first time fibreglassing effort. this has made the hull a lot more heavy, but feels solid now. Also by taping the end of the hull to a board while the fibreglass set straightened out the warp.

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I'll clean up the fibreglass dags to make it look a bit more presentable. Also i added a rudder post support beam and 2 winglets to help support the deck.

Next step i have to cut the scuppers out. i'm nervous about this as you don't really get a second chance. Then it will be painting the hull. What type of filler should i be using? I'm in Australia though so probably won't have the same brand names as you guys.
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Old Nov 02, 2010, 07:58 AM
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Regarding the dogbones (I am not sure if you ever reached a decision on them), I know an old trick the R/C car guys use help keep them from wearing and starting to chatter a little with wear. Find a small O-ring, the same size as the inside of the cup of coupler, insert it (then put the dogbone back in to retain it) and it to keep the coupling from chattering, contributing to the wear of the cup. I have used it on a old Tamya Blackfoot truck a lot of years ago and cut the wear on the cups (very soft cast aluminum in that case) about in half (and I ran the heck out of that truck).
Foo
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Old Nov 02, 2010, 09:49 AM
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I ended up buying some universal couplings while i was getting the gearboxes. This was supposed to be a cheap first build!
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Old Nov 02, 2010, 10:47 AM
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see, Boat definition
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