Scratch Built 31" Cat

So, a couple of months ago, my son and I decided to build our first joint RC project. He wanted to start with an airplane (I have some), but I figured something closer to the ground would probably be more appropriate. So, I looked online, and found some plans for a 30" cat (and, yes, it is 30", not 31"; sorry for the error in the title!).

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I had some balsa laying around (from my planes), so we got started.

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We first built the skeleton out of balsa, and sheeted the whole thing in 1/16 balsa. I reinforced the tunnel with some 1/32 ply (and a little carbon fiber), and added some foam to the front part for flotation. Cockpit was made like a model airplane, using structure to get the shape and then sheeted in balsa and fiberglass (sides were basically sculpted!).

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Then we covered the whole thing in 2oz fiberglass using epoxic resin diluted in alcohol. A couple of coats of resin and lots of sanding later, we had a somewhat smooth surface. Primered, bondoed and painted (with lots of sanding thrown in for good measure), and we had ourselves a nice looking hull. Have to say, this quarantine sure as heck motivated us to get off our buts and put some time into this boat!

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Then, my son, my daughter and I made some drawings to pick out a nice paint scheme, and my daughter came up with the octopus theme.

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Not exactly how it turned out, but certainly the inspiration... Proceeded to paint the whole boat white, getting ready for the artwork!

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Made sure to have a nice cockpit too!

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Then my wife (who used to paint) helped me with the octopus' arms. She started with some tests to see how they would turn out and what style I liked best.

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My wife got started with the octupus legs, while I put some color on the hull... and then we added some more details.

Started adding some details with watersilde stickers, and painting the top side tentacles (there has got to be 8, right?). The name PIPEX (pronounced pihpehx) is because of my son's nickname. The last RC plane I build was called PIPEX, so he came up with the OCTO PIPEX name, and we all thought it sounded cool. So we ran with the idea...

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Finally got the paint part done. Well, mostly... I still need to give it a clear coat to lock in the waterslide stickers. Sure, there are a few mistakes, but overall, it looks pretty cool, if I do say so myself! Just needs a final coat of clear to seal in the last waterslide stickers.

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Also started installing the hardware. Prop (and flex drive) is just for show, not yet installed. I also need to refenish the rear of the canopy, as there is a HUGE hole there for water to get in!

Motor will be a Leopard LBP4074-B 1800KV driving either a CNC 4216-D, CNC 4016-D or Octura X442 (depending on what she likes), and controlled by a OSE 150A ESC. Radio will be a Fly Sky FS GT5 transmitting to a FS GR3E waterproof receiver, driving an Annimos DS3218MG 20 Kg waterproof servo.

Power will come from a Tattu 4S 8000 MAh pack I had from my drone days. Yeah, I know it is a heavy pack, and that the center of gravity will be raised by having the single pack over the tunnel, but it is what I have, and with all this COVID 19 lockdowns, I prefer not to spend any more money than what I absolutely need to, as I have no idea how the economy will recover from this (which can affect all of our job status!).

I still need to figure out how I will keep everything dry inside, as the canopy does not have anything close to resembling a watertight seal. But I will get to that later on in the build. This weekend I will bend the flexdrive tube, and basically stop there because I am out of epoxy! On Tuesday I am allowed to go out (in Panama, where I live, guys can go out Tuesday and Thursday for 2 hours per day - hours set by the last number of your ID; gals get to go out Monday, Wednesday and Friday. Nobody can go out Saturday or Sunday), and hopefully the supermarket will carry some 15 or 30 minute epoxy that I can use to glue in the flex drive and the motor mount.

Before this boat, I owned a RTR nitro boat some years ago, and I bought my son a small Aquacraft Minimono in 2018, which we both run from time to time (when we are not restricted to stay at home, anyway!). This is my first scratch built RC boat, and I am happy with the results so far. A true family project!

Superb. Thanks for sharing. Hey, I thought the PA location was Pennsylvania.

Took this one today, trying out how she would float... Gotta include it here!

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Did a couple more things to this cat...

1. Changed the servo to a better servo. Installed a Savox SH-1350 Super Torque Mini Digital Servo instead of the analog one I had in there (now I have more torque, metal gears, 2 ball bearings, and LOTS more torque on the rudder!).

2. Eliminated the engine mount from the cooling line. This was suggested on another thread in here.

3. Finally installed the outlet line (it finally arrived!).

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Oh, and (I know this is for photos and not videos, but I figured is in line with this build) I did a couple of test runs in the pool... Yeah, I know I should not have, but I did...

https://youtu.be/GmolnwO8hP4

https://youtu.be/dmbMLzKOnuw

Now, some time back, when this boat was almost finished, my son asked me "how are we going to race if we only got one boat?" BEST QUESTION EVER!

CLICK HERE TO SEE HOW I ANSWERED!

Finally got around to running this boat! And man, she runs great! Everything I wanted, I got! She is not the fastest boat on the water, but I was looking for a sport boat anyway. I would venture to say that the center of gravity is spot on!

Here are some videos of that:

https://youtu.be/ZmXmY6MpfYk

https://youtu.be/L1nvDpQMfOY

Temperature was fine; motor, ESC and battery were barely warm to the touch. I guess I could try a bigger prop, but, to be honest, I am not in need of more speed. I am happy with the way it runs!

Nice job.
I have used this set of plans for over ten years and have tweaked the design to a 34” version and now run twins in it! Search scratch cat and see how I did mine.