Not long ago, I bought myself a great little RC plane. It was a 3 channel Firebird Phantom. I got it off hobbyzone.com for $60. Great value, great plane.
Well, this little plane came equipped with ACT (anti-crash technology). It keeps the plane more stable, and keeps the little bird from spiraling out of control. It also keeps you from doing fun flips and barrel rolls. I used the plane for about 5 minutes before I turned off the ACT. After a few flips and turns, my plane started spiraling towards the ground. I should have let go of the accelerator and pulled up. Instead, I gunned the engine and pulled upwards. Its little foam wings were no match for the engine and gravity working together, and a terrible crash ensued. After throwing a small temper tantrum, I collected the remains of the plane and headed home.
The damage was extensive. The tail section snapped in half and one of the servos died. The plane came equipped with two servos, one for the left elevator and one for the right. So even if I fixed the tail it would only be able to turn right or go straight. Since my plane was thrown out of the 3D arena, it's now time to transform it into a craft that will only need to handle 2 Dimensions. A boat!
Remember that each boat is unique. Don't stick exactly to my plan. Consider this a suggestion to what you should do with your defunct rc boat/plane/car.
Step 1: Dismantle It!
The first thing you need to do is liberate your RC's soul. Unscrew every single screw, snap fused pieces, do what you need to do to get the basic machinery out of its casing. If you are dismantling this type of plane, make sure you don't snap the push rods or break the antenna, you can cut out the ACT sensors, you wont be needing them any more. Make sure to keep the rest of the innards intact though.
Once everything is out, plug in the battery and power up the control. Play with it and see how the controls make things move. Now would be the time to find out if the servos still work, if you are good with a soldering iron you might be able to fix broken parts. Now is the time to brainstorm and figure out how you are going to make your vehicle move and turn. Visualize it, draw pictures if you like, just make sure you have some sort of plan.
Step 2: Start Building!
This was my third attempt at making this boat. The first didn't work because all the circuitry was exposed and water splashed onto it. The second one was more elevated but only balanced on two 20 ounce coke bottles. It flipped in the bathtub. Whatever you do, make sure that your boat's "brain" is hidden from the water. I put all the circuitry into an old butter container. If my boat flips, water will probably leak in, but at least it's splash proof. The butter top is part of the boats hull, all the electric stuff is glued into the tub part, that way it can be easily removed.
The first thing i did was stick the main chip inside the butter tub. I then made a hole for the wires that lead to the engine and another for the antenna. I waterproofed them with a glue gun (I actually did all the pasting and waterproofing with my glue gun.)
I then punched a hole through the back with one of the steel push rods. The push rod is attached to the servo and will control the rudder. This is the only hole I didn't waterproof since the push rod needs to move back and forth through it. It's small enough to not be a problem though.
Next, I built a tail and rudder from some unused ziploc Tupperware. The hinge was a problem though. It needed to be strong enough to handle the push and pull of the push rod, but pliable, since the servo isn't that strong. I ended up using the hinge of a Tic-Tac box top. The hinge is a live hinge, because it has no moving parts, just a flexible polypropylene membrane. I aligned the hinge with the push rod since it would be absorbing the push rod's force. The top hinge is just some scotch tape. I pasted a little tab onto the rudder side of the hinge and attached the push rod to it. When the servo pulls, the rudder turns to starboard, when pushed, the rudder turns to port.
Next, I cut out the flat side of the tic tac box (to minimize air resistance) and used it as an engine mount. I hot glued the engine to the top. When used, the engine gets hot, but not hot enough to melt the glue or weaken it significantly. The engine and controls of the boat are now complete.
Step 3: Build the Hull
For my previous prototypes, the hull was a simple catamaran made of two 20 ounce coke bottles. It didn't provide nearly enough balance or flotation for my little boat. It is probably better to err on the side of safety rather than on the side of confidence. A large stable boat isn't going to break any speed records, but it will outlast a boat that is zippy-but-tippy. If you do make the hull too large, you can always modify it later, you should start big though.
I used two ~50 ounce water bottles glued to two 20 ounce water bottles to make a simple catamaran design. It's nice and stable but doesn't present too much resistance in the water. I had originally planned on a tri-hull, but that didn't work out. I attached the two hulls with 4 lengths of plastic (pieces of a broken clothes hanger.) One at each tip, and two in the middle (suspending the butter tub). Since the two middle spreaders are glued to the butter tub top, the the power unit of the boat can just be clipped in.
Step 4: Try It Out and Find Out You Screwed Up
Unless your project was meticulously planned and brilliantly executed, you'll find out that something went wrong. Chances are things wont be as bad as mine though...
My bathtub isn't very big, so there were some problems with the boat that weren't evident until I took it out to a nearby artificial pond/lake. Firstly, you might notice that on most boats and airplanes, the rudder is placed as far back as possible. My boats rudder was plop in the middle, it didn't work worth a bean. I had been under the impression that my boat would go so fast that a rudder in the water might cause it to turn too violently and flip over. I was wrong.
The hulls were also way too big. The boat was terribly slow in the water. Such a big thing is just too difficult to turn. Another problem I encountered was the butter tub. All the electronics were glued into the tub. The tub was attached to the hulls by being clipped onto its top. If the tub were to be accidentally unclipped during a voyage, I would loose all my electronics.
Step 5: Back to the Drawing Board
I needed to get rid of the butter tub, make the hulls smaller, and create some sort of turning device that worked. I ripped off the 20 ounce water bottles in the back, and got rid of the butter tub.
The biggest problem for me was that I needed to waterproof the container where the electronics would be but I would still need easy access to it (for easy changing of batteries.) What I finally decided to do was cut a large oval out of one of those 20 ounce water bottles and paste all the electronics in there. To waterproof it, I cut out the bottom of a Ziploc bag and glue the bottom edge around the hole. Imagine it like a kayak spray skirt, but with a Ziploc top. The pictures explain better.
I cut up a used bic pen and used it as a tube to direct the push rod backwards and at a downward angle. Since the rudder is now going to be in the water, the push rod hole needs to be at the bottom of the container. If the boat ever flips, the bic-pen-tube will stay above water and keep the electronics dry.
Step 6: Finishing Notes.
I screwed up a lot making this boat, hopefully you can learn from me and not make the same mistakes.
-Don't give up. This was my 4th attempt at making this boat.
-Use Occam's razor! The simpler you make your boat, the bigger the chances of it working. Don't make anything unnecessarily complex, remember, you'll look smarter if you make something really simple that works than if you make a complex gizmo that just doesn't work.
-Make your hulls big, but not too big either. My first hulls were 20 oz. coke bottles. They were way too small. Then I made a boat with 140 oz. of flotation, thats just too big. Now each hull is made of 50 oz. water bottles, it seems to be just right.
-Have fun! (That's the point, right?)