MOC: RbtKpfW III Ausf. C "Schneehund"

[Lauwenmark]

The Hound: a Wolf redrawn

Although the RbtKpfW III/A (and B) made a quite satisfying exploration unit and firing platform, it wasn't without flaws: poor turning radius, underpowered offensive tactical subsystems and limited telemetry limited its use to one of a command unit. The OKL - Lego's military high command - still wanted a heavy armoured vehicle suited for offensive strikes deeply into enemy territory. Given that Heimser Waffenfabriek AG, designer of the A and B revisions, was unable to improve it further, the OKL called for help another industrial weapon manufacturer, Société des Gladiateurs, to work on the problem.

The engineers at SI rebuilt most of the chassis from scratch, only keeping the general shape. The main improvement was a much better power distribution system, finally allowing it to support a heavy artillery piece. The resulting robot, registered as Robotkampfwagen III Ausf. C "Snow Hound" was equiped with the rather powerful 10-studs Heimser's Howitzer, making it a formidable long-range artillery platform feared by many. Despite the limitations of its cannon (the 10-Heimser being long to reload and difficult to properly direct) as well as the reduced walking speed against previous versions, the RbtKpfW III/C was one of the most powerful heavy war machine of its time and played a key role in many battles.

Design notes

As said above, the chassis has been entirely redesigned from scratch. Only the head and the legs survived from the previous version.

Both pairs of legs are not fed by a single axle running from front to tail. The motor in the tail is connected to it through a pair of clutch gears. Transmission to the legs is performed by worm gears. The result is that although the robot is a little slower, it can now move with only a single motor, instead of two. This frees one for supplementary functions.

Turning is still performed as before - a pair of linear actuators control the turntable binding the front and the back parts of the robot. Since the machine is a little shorter, the maximum angle of turning is slightly bigger.

The top front engine is now not connected directly to the actuators anymore - instead, the third motor under the robot is used as a selector between the "cannon" and "turning" functions.

The selection between functions is performed by a "piano" selector system. The first picture shows a single "piano" function selector in engaged state. The "selector" clutch pushes a 2x4 L beam on which two gears are fixed: the driver gear (connected to the driver motor) and the transmission gear. The transmission gear is pushed against the output gear, hence when the driver turns, the output turns. The single picture shows the same "piano" selector in disengaged state. The selector clutch doesn't push the L beam anymore; the transmission and output gears are not connected, so when the driver turns, the output doesn't move. By grouping several of such L-beams with selector clutches at a given angle with each other, you can easily select between many different functions. "Snow Hound" uses a pair of 3x5 L-beams with 16-teeth gears; the spring mechanism is made of rubber bands attached to sliding axles hidden under the front of the robot.

The cannon is crude, ugly, but very effective - with a proper rubber band, it can throw a 10-length beam several meters away. The orange 2x4 L-beam visible on the picture holds the missile (a 10-length beam with a black pin) in place and is attached to the 16-teeth gear. That gear is blocked by a rack. When the "cannon" function is selected, the driver motor makes the rack move away from the gear, freeing it. The stretched rubber band is then strong enough to push the orange L-beam away, letting the missile free.

The control system is basically similar to the one used for the previous version of the model: an NXJ program running on the NXT exchanging data through bluetooth with a remote computer running a client java application.

Not a wonderful model by far - but at least, unlike the first I built, this one works! :) I'll probably try to improve the design of the cannon - the current one looks awful - and, of course, the software side, which is currently little more than a remote control.

Advices and opinions welcome!