The Parts of a Cheap Airboat
ElectronicsThe first step to building a cheap airboat is picking a cheap motor. Once you have selected the motor, the rest of the boat will fall into place. This may seem like a long list, but most of the small parts come in multi-packs. Once you have a supply of the small parts, all you need are a few main parts and you can build numerous boats.
MotorThe motor and prop set up sets the size for the entire boat. To keep the boat small and manageable you want to select a fast spinning motor with a small prop. This generally also helps the boat be fast. A good start is the AX 2306N 2000kv brushless Micro Motor from HobbyKing. HobbyKing rates the motor up to 9A, but it handle more with ease. You always want extra motors. Grab a couple of these.
ESCNext, lets just pick the cheapest ESC that we can find. the Hobbyking SS Series 25-30A ESC is a good choice if it is in stock. Otherwise, the Hobbyking SS Series 15-18A ESC will work. As with the motors, the more ESCs the merrier. These tend to get damaged by water, so grab at least 2 ESCs
PropellerA good starting propeller match for the AX 2306N is a GWS EP Propeller (DD-5043 125x110mm). The DD-5043 on the AX 2306N will draw between 8-9A and should produce enough thrust for a small light boat. A pack of 6 should be plenty for now.
BatteryThe battery may be a little harder to nail down. With the motor selected, we want a 3S (3 cell) LiPo with at least 800mAh capacity. Either the ZIPPY Flightmax 1000mAh 3S1P 25C or the Turnigy 1000mAh 3S 20C Lipo Pack will work great. Nothing kills the fun faster than not having enough batteries. Get as many batteries as you can. 3 or more will keep the fun going indefinitely.
ServosYou need a single servo for an airboat to control the rudder. A simple HXT900 9g / 1.6kg / .12sec Micro Servo will do. Buy several servos. They are cheap and come in handy.
RadioIf you are just starting with boats and don't already have a radio, just grab the Hobby King 2.4Ghz 4Ch Tx & Rx V2 (Mode 2). The HK 4Ch is a super cheap system, with the cheapest spare receivers. In addition, grab some spare receivers if you can.
Battery ChargerNow, pick up a decent charger with the ability to charge any type of battery. The HobbyKing ECO6 50W 5A Balancer/Charger w/ accessories fits the bill. These fancy battery chargers need a DC voltage supply. Something like HobbyKing Power Supply 100~240v 5A will work.
MiscNow, the bits and pieces. If you've made it this far, you've got most of the major components. Just a couple more things to get you going.
- Grab some pushrods - Metal Push Rods M2xL300 (10pcs/set)
- Some snap click clevis - Nylon Snap-Click style clevis 2x8x23mm (10pc)
- Some snap connectors - Pushrod Snap Connectors 2mm (5pack)
- Some control horns - Control Horns 16x20mm (10pcs)
- A pack of connectors for connecting your battery to your ESC - JST Female 2 pin connector set (10pcs/set)
- Some 2mm connectors to connect your motor to your esc - 2mm Gold Connectors 10 pairs (20pc)
- Some screws to hold it all together - Self Tapping Screws w/shoulder M2x12 (10pcs/set)
The Raw Building SuppliesThe rest of the boat can be made from just about anything you can find at the local hardware store or dollar store.
The HullTo make the basic frame of the boat, find yourself some foam. Home Depot sells 2 types of foam that can sanded and glued fairly easily. One type is a 1 1/2" thick white foam, with a coarse visible structure. The white foam is sold in 4'x8' and 2'x4' sheets. The other type is 1/2" or 2" thick pink foam with plastic sheeting on the outside and a fine smooth texture. It is sold in 4'x8' sheets.
Usually you can find sheets of 20x30" foam board (foam with paper on either side) at any dollar store. The paper can be removed with just a little water to leave a highly flexible and easily shaped foam sheet. A good choice for more complicated designs.
The RudderThe best rudder material I've found is something called corrugated plastic. Home Depot sells 2'x3' white sheets that are 4mm thick. By cutting some of the fluting on one side, you can create quick durable, water proof, hinges. Because it is plastic, water has no effect.
Motor Mount and other woodHome Depot sells 3/8" square wooden dowels for cheap that are pretty close to the 10mm motor mount that comes with the AX 2306N Motor. With a little tape or glue, you can shim the mount to the needed dimension. For X motor mounts, you can find some 1/8"x2" strips of hardwood.
For structural supports, you can find 3/16" craft dowels at Walmart. These are about the same thickness as the foam board from the dollar store and make for good reinforcement. Various places also sell bamboo skewers for around $1 that can provide structural support and have a pointed end, which is poking through foam or corrugated plastic.
Holding it all togetherIn order to hold the boat and foam together, the best option is Gorilla glue, or some urethane based foaming glue. A lot of adhesives will melt foam, but urethane based glue will expand to fill gaps, not burn the foam, and create a light weight watertight seal.
The dimensionsIn order to create a stable airboat, make the boat at least the width of the propeller. For the smaller 5" props, an extra inch or two won't hurt. Once the width is set, double it to find the length of your boat. Again, you can add probably up to 20% in length and increase the performance of your boat.
If you want your boat to drift, ensure minimal weight to surface area. The lighter the boat and the more surface area on the bottom of the boat, the easier the boat will plane and drift. Knocking off sharp angles on the side of the boat will help it drift, as well.
WaterproofingPerhaps the most critical step, and perhaps the most difficult, it is important to ensure your components won't die if they get a little wet. The easiest way to waterproof your ESC is to remove the shrink tubing on the ESC and to coat it in epoxy. If you have thermally conductive epoxy, all the better.
A good non-corrosive silicone caulk can also help seal things up. Be careful, however, and find one that won't corrode copper if you want to use it on your electronics. A little waterproofing on the receiver won't hurt, either.
Try to make a water tight compartment for the electronics. A piece of tupperware may not look amazing, but is cheap and works in a pinch. Try to mount the electronics where water will not pool in the case that your waterproof container fails (which it probably will at some point).
The Conclusion (for now)These cheap airboats are all about having fun and experimenting. Trying different shapes and styles are half the fun. If one style doesn't work, keep trying and don't get discouraged. Enjoy!
In a future post I will go through all the steps for building scratch built boats or planes.