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R/C Combat Vehicles

First Steps In Constructing An R/C Combat Vehicle


The large scale used for R/C Tank Combat makes it possible to outfit vehicles with all of the equipment needed to wage scale warfare, but it also makes it more difficult, but not impossible, to find scale vehicles to purchase. Fortuntately, the process of constructing an R/C combat vehicle is relatively straight-forward and all of the required parts can be purchased or constructed from parts purchased from surplas catalogs, hardware stores and flea markets. This article focuses on the initial steps that can be taken to start building an R/C combat vehicle.

NOTE: This is a living-document that is intended to include lots of information from lots of people. So, if you have any additions or changes to suggest, including lessons learned, please do so and help the next generation of builders.


Picture Books

You should start the construction process by purchasing a picture book of military vehicles from your local bookstore, borrowing one from your local library or borrowing one from a friend. (It better be a good friend, because they probably won't get it back in the same shape after it's been tossed around your shop for a couple of months!!!) They come in all shapes and sizes, detailing dozens to hundreds of vehicles. You don't need anything expensive at this point or even 100% historically accurate, you just need to browse through a large number of vehicles so that you can select the right for you. Such books usually don't give any scale drawings, but they usually give the basic statistics that are sufficient to get started.


Vehicle Selection

Most people who are interested in R/C tank combat for the first time ask the following question sometime in their first conversation: what's the best vehicle to build?" Fortunately (yes fortunately), there is no answer to that question. The rules have been deliberately designed to make all vehicles competitive. Heavy tanks have more fire-power and greater armor than other vehicles, but they are also usually the slowest vehicles on the battlefield. Armored cars have more speed and turning capabilities, but they carry less ammo and can be destroyed more easily.

And don't worry too much about size either (hasn't she been telling you that for years now ...) Here again, the rules result in all vehicles, whether built in 1/6 scale or 3 feet long, to be roughly the same size. Sure, some vehicles have more "target area" than others, but during a battle there are plenty of other tactical and strategic actions that quickly make such differences meaningless. (If a heavy tank gets behind you, the size of your tail-end probably doesn't matter ... just kiss it goodbye.) In fact, for your first vehicle, a slightly larger hull makes it easier to fit in all of the equipment and work on the vehicle in the shop and, more importantly, on the battlefield.

Given the inherent balance designed into the hobby, you are free to build whatever type of vehicle suits your personal tastes, heritage, or dreams. Naturally, for your first vehicle, you don't want to build something that is extremely difficult to make or operate, but in practice all vehicles have basically the same problems to tackle during construction, so don't worry too much about such issues. The only rule that applies to all vehicles is: Keep It Simple Stupid (KISS).

The trade-offs are numerous and, as such, there is no best vehicle. If the vehicle you build suits your intended battling style, then you will probably be successful (assuming, of course, that you can hit the broad side of a barn while evading pursuit).


Information and Plans

Once you've selected one or more vehicles that are interesting to you, start doing some Internet searches and you'll probably find at least one site devoted to that vehicle. You should also post your vehicle selections to the R/C Tank Combat mailing list and ask if anyone has information about those vehicles or has found other sites for them. Over time, the R/C Tank Combat web site will accumulate information about lots of vehicles, but it will never be a one-stop location for information, so get used to asking fellow battlers for help. Besides, if you're going to be battling alongside those same battlers one day, you might as well learn to trust their advice.

You probably won't find scale plans for your vehicles on the Internet or in most books that you find, unless you are fortunate enough to find a book that focuses on your vehicle. Even still, the plans will almost certainly be drawn to a different scale than what you have chosen for your combat vehicle. Fear not, however, because lofting plans from one size to another is as simple as using a calculator. Accumulate as many drawings and photos of your vehicles as possible and compare all of them to determine the necessary size of each component. Keep in mind, you only need some basic measurements (like length, width, height) to get going. Real photos, a ruler and a calculator can then be used to model everything else.

Another great source of 3D plans is your local hobby store (or hobby catalog) that sells inexpensive plastic combat vehicle models. It is probably safe to assume that every combat vehicle, from every nation and every era has a corresponding plastic model. With a little bit of time and some glue, you can construct a model for your model; your 3D Plans. Then, just make everything larger and you're on your way.


Wheels

Once you've selected a vehicle, gathered the basic scale information and a collection of photos, it's time to start building the wheel/track assembly. Start by determining the scale size of the wheels relative to the vehicle length and then acquire or build as many wheels as needed. Here again, the R/C Tank Combat mailing list is your best starting point, asking other battlers for references to catalogs, Internet sites or stores where they found similar wheels.

For tanks, there are basically two methods for wheel construction: build them or buy them. Building wheels has the advantage that you can make them exactly the right size and you can model them to look like the metal wheels that supported the track. The T001 wheels are made from 3/4" plywood cut into circles on the band saw, with surplus 1/4" bearings inset to support the axles. Other battlers found plastic or rubber wheels that are the right size and shape for their vehicle. (NOTE: We are talking here about the tank's boogie wheels, not the drive cogs. We will discuss tread drive cogs shortly.)

For armored cars, it is usually best to purchase the wheels/tires. Fortunately, lawn-mower and wagon wheels come in a wide assortment of styles and sizes, and are relatively cheap. Don't be afraid to get wheels that are slightly larger or smaller than the wheel size computed for your scale; it's called a "modeler's choice". Also, don't worry too much about the tread type (hard or soft) or pattern (smooth, knobby, etc). For your first operational vehicle, you should be happy to have it moving around reliably for an hour.


Motors

Once you know the diameter of your wheels, you can start acquiring your drive motors, which usually come from surplas catalogs. Surplas kiddie car motors are the motor of choice and they usually come complete with a gear assembly that runs at roughly the speed needed for combat vehicles (approx 200-400 rpm). When looking for motor/gear combinations, use the diameter of your wheels and the RPMs of the motor under load to determine how fast the vehicle will be moving under perfect conditions. Most vehicles run at 2-5 mph.

Keep note of the amp draw under load for the motors that you select. Many catalogs list only the no load amp draw for some motors, leaving you to figure out the loaded amp draw after purchasing them. Here again, kiddie car motors are designed to move about a 100 pound vehicle (car + kid) at a reasonable speed without melting the drive system. You should also be careful to note whether the motor is designed for continuous or intermittant use. R/C combat vehicles require continuous use motors (unless you plan on sitting still every 15 seconds or so!!!) Over the years, veteran battlers accumulate a large supply of various motors that didn't quite work out, so don't be afraid to start your collection now. It is always safest to buy one motor and test it out under load before plopping down lots of money to buy a complete set.

The type of motor that you buy will determine how it needs to be connected to the drive wheel. Most kiddie car motors are also designed to fit around a stationary shaft, allowing the use of free-spinning wheels. In that case, the drive cog on the motor interlocks or is connected to the drive wheel in some way and the stationary axle goes down the center of each. The tricky bit is usually how to connect the wheels and motors, give that most such wheels are made to turn freely around a shaft. Nathan Blattau solved this problem very nicely, by using a stiff rubber pipe connector. The rubber cylinder is attached to the motor drive cog on one end and the wheel hub on the other end with hose clamps.

For other motors, you'll need to fix the shaft to the wheel, support it using a bearing of some sort on the chassis and drive it from the motor using a coupler of some sort. With that arrangement, a motor can be used to drive the shaft directly or using a belt or chain, with appropriate gearing.

Kiddie car drive assemblies are easier to acquire and install (that's why they are made that way), but they may be harder to replace or work on over time then motors that drive the axle. On the other hand, finding geared motors with the proper ratios and power consumption is not an easy task; a problem that the kiddie car dudes already solved for you. So, we have another classic trade-off: time to develop vs. flexibility.


Test Chassis

For both tanks and armored cars, it is beneficial to construct a rolling test chassis that can be used to experiment with various wheel and axle configurations. A simple piece of plywood will suffice, with some wooden rails screwed or bolted to each side. Although you may want to use the test chassis as the actual hull base for your tank, that may also prevent you from experimenting with different approaches. (Once a design starts to gel, it's hard to throw it away, even if it's wrong.) So, take a little time and play with different approaches before deciding on the final version. (Most of the tanks built so far have had at least two wheel assembly versions.)

For tanks, the bogie wheels are usually mounted on stationary axles that are mounted to the chassis. Use the test chassis to determine how you want to solve that problem and what parts will be needed.

For both tanks and armored cars, the test chassis is used to develop and test the drive assembly. With just a single drive assembly mounted to the test chassis, along with 3 free-spinning wheels, the prospective drive system for an armored car can be tested. Be sure to put enough weight on the test chassis to simulate the expected battle weight of the vehicle. Tank drive systems can also be tested by building only a single track system and using free-spinning wheels on the other side. Eventually, you'll need to replace the wheels with another track system to complete your testing, but there is no need to do that until you're sure that the test motor/axle/cog combination is working properly.