Basic Electric Vehicle/Battery Buggy
With Dark Sabre's help, I've added some pics on the Battery Buggy Image Gallery
. The vehicle above could win medals at many tournaments if it were made to the current required dimensions.
Some features of this vehicle:
Chassis: a simple rectangle of 1/4 in thick wood, available from most home repair stores. Any material could be used, but it's best to use the lightest material you can. It's also easy to drill holes for mounting components.
Wheels: Rear/Drive wheels appear to be 4in diameter "lite flight". These cost a little extra, but are considered the best by some. Many others that are less expensive (or even free if you recycle) are almost as good.
Drive axle/Transmission: One of several Tamiya gearboxes available. Assembled straight out of the box without modification.
Note: You might be able to recycle the entire rear axle with transmission and wheels from an inexpensive Radio Control vehicle.
Motor: The gearbox/transmission usually dictates what motor can be used. Motors are supplied with the Tamiya gearboxes.
Battery Box/Holder: This vehicle uses a common battery holder available from Radio Shack and others.
Steering: This is pretty basic, an articulated chassis with a vertical bolt to hold the two parts together and act as a pivot point. A longer wheelbase is easier to make go straight. Use a wing nut for easier adjustment.
Distance Measuring: Classic threaded axle/wing nut system. You have to go quite a ways to better this arrangement. As the axle turns, a wing nut travels along its length. As the wing nut nears one end of its travel, it contacts a switch and turns off the motor to stop the vehicle.
Brakes: None. As long as speeds are relatively slow, brakes are unnecessary. It would be fairly simple to add "Dynamic Braking" to this vehicle.
Battery Box/Holder: Selected to hold the size/number of batteries used. Battery holders can be as simple as a piece of wood with nails driven into it to hold the batteries in place and make contact with the terminals at each end.
Batteries: Any size batteries can be used as long as they comply with the voltage and current requirements of the motor. Larger batteries are heavier and require a sturdier chassis, stronger motor, more braking force. Normal dry cells (primary cells) can be fairly expensive over time. Rechargeable batteries (secondary cells) require a greater initial outlay, but can reduce costs significantly over time.
Switches: The vehicle above uses separate start and stop switches. A common slide switch, located near the center of the chassis, is used to start the vehicle. This type of switch can require significant force to actuate and may cause the vehicle to move before it is actuated. It may pay to investigate other options that take less force. The stop switch is a lever switch (sometimes referred to as a micro switch) is located near the wheel in the upper left of the vehicle as shown. As the wing nut travels on the axle, it contacts the lever on the switch and depresses it to stop the vehicle. These switches are available from Radio Shack and many other electronic/robotic suppliers.
Wires: Almost any electrical wire can be used. A common source is recycled 4-conductor telephone wire. It can be separated into individual wires by removing the outer cover. Solid wire (has only 1 large strand of wire inside) is stiffer and easier to work with, but breaks sooner when flexed. Stranded wire (has several thin strands of wire inside) is more difficult to work with, but doesn't break as easily when flexed.
Motor: Motors determine the voltage and current capacity needed from the batteries and must be mechanically compatible with the transmission/gearbox used. Motors are usually supplied as part of commercially available transmissions/gearboxes. Another source for gearboxes/transmissions is old (or not so old) battery operated screwdrivers. The batteries may even be recycles if they are still good.
Dynamic Braking - Uses the drive motor to slow the vehicle. When the electrical current is turned off, the motor/vehicle begins to coast and the motor begins to act as a generator. The force required to turn the generator is proportional to the current (not voltage!) generated. When the generator is connected to an open circuit (infinite resistance), no current flows and the force needed to keep the generator rotating is only that needed to overcome friction. If the generator output terminals are connected together with a low resistance connection (short) the current in the circuit increases which, in turn requires more force to turn the generator. This acts as a brake to slow the vehicle.