Servo - November 2008

Beta uses chain drive to power its electric hammer.

tion when building your bot.

Car vs. Tank Steering

Most robots use tank steering, which is where each side of the drive system can go forward or backward independently allowing the robot to go forward, backward, or turn in place. Car steering works just the way it sounds. The robot will drive like a large, metal remote-controlled car. One common point of confusion in tank steering is turning while reversing. With the way tank steering works, when you’re turning left from standing still, the right side wheels are going forward and the left side wheels are going backward. When you’re turning left while moving forward, the right side wheels are spinning faster than the left side in the forward direction. When going in reverse, however, the left wheels are spinning faster backwards than the right, causing it to rotate to the left while moving to the right.

External vs. Internal Wheels

Internal wheels are better

Checkmate uses a strong baseplate for component mounting.

protected and able to be supported on both sides. External wheels will prevent the robot from being hung up on a competitor’s armor if it gets lifted off the ground. External wheels can be hit easily by the opposing robot’s weapons and are subject to many more direct impacts. Which option is best depends on both the design of the robot and which features are most important to it.

Belts, Chains, and Gears

You’ve got to get the power from your motors to your wheels and weapons somehow. Belts, chains, and gears are your three options if the motor can’t have the wheel or weapon attached directly to it.

Belts are fairly lightweight and can transmit power over large gaps. There are multiple types of belts to choose from but most use tension and friction to provide enough grip on the pulleys on each side of the system to transmit power.

Chains are stronger and heavier than belts, but serve essentially the same function as belts. They

Grue uses tank style steering to maneuver in the arena.

Sewer Snake has external wheels.

Crocbot uses car style steering to maneuver in the arena.

transmit power from one shaft to another over a gap. Chains need to be aligned more precisely than belts due to their inflexibility. If they are not aligned well, the chain is likely to fall off or break.

Gears require the highest precision of the three options and are also able to be the most efficient. They are not, however, able to span the same distances that belts or chains can. Tight tolerances and proper pitch selection can result in a nearly indestructible power transfer system, however, if the pitch is too small or the gears are too loose or tight, you’re just asking for catastrophic failure.

Chassis

At the core of every competitive robot is a strong chassis. It doesn’t matter how powerful your spinning weapon is or how high your arm can flip other robots if the chassis can’t handle the forces that act on it both internally and externally. A small number of construction methods make up the majority of combat robot chassis today.