My first tank model. Features drive and steering with a subtractor, a machine-gun in the turret, and several more motorized functions.
About this creation
Propulsion: 2 x XL Motors Steering: 1 x L Motor via Subtractor Drive Type: Rear Sprocket Drive Transmission: 2-speed with 1 x M Motor Weight: 1.52 kg. Height: 14.5 cm high Length: Not including Barrel: 25 cm
---------------Including Barrel: 34.5 cm Width: 23 cm Power Source: Chassis: 7.2v Eneloop AA Batteries
---------------------Turret: 7.4v Li-Po 8878 Battery Box Extra Motorized Functions: Turret rotation with 1 x L Motor
----------------------------------Gun elevation with 1 x M Motor
----------------------------------Gun firing with 1 x M Motor
Having not built a tank before, the components of this tank were selected on what I thought would be best, rather than from experience. It was an interesting build, and taught me a lot about what work best in tanks of this scale.
The drivetrain was more complicated than it needed to be. I knew I wanted to add a transmission to the tank and thus make it more versatile, and the most efficient way to do so seemed to be with a subtractor, which would allow me to use one transmission instead of two. For those of you who don’t know what a subtractor is, the following page will be helpful: http://sariel.pl/2009/01/subtractor/. It turned out that for a large scale tank, a subtractor is inefficient and makes turning in place difficult. I used a single L motor for the turning input, geared down 8.33:1, and even with that substantial gear reduction the motor still struggled while turning in place. It would probably have been more efficient and better for performance to use two transmissions, one for each motor.
The rest of the tank was fairly standard, with trailing-arm and bogey suspensions, turret rotation, and barrel elevation. The turret and body each had their own battery box, which meant that the turret was able to make an unlimited amount of rotations. The turret itself held two motors as opposed to the body’s five; one M motor for barrel elevation and another for my favorite function: the fully-automatic elastic machine-gun.
Despite how fancy it may sound, it was as simple as possible in its implementation. It was controlled by an M motor and worm gear paired with a 24t spur gear, with drive transferred over an axle to another 24t gear. The elastics were simply attached to the hook on the front of the barrel, pulled back through the barrel, and then hooked into the teeth on the second 24t gear. As the second 24t gear turned, it would discharge the elastics one by one. The accuracy and range were both pretty decent, my only complaints with it being the tedious nature of loading it. When fully loaded, it also irritatingly pulled the barrel into a more upright position, leading me to believe that it would be better if the gun actually swiveled with the barrel.