Mario's Lego Robotics Archive

Golia

Golia was built to attend a robotic Sumo challenge during the fifth ItLUG Legofest, where came third of seven competitors. See the Events - Legofest V section of the ItLUG site if you want to find out some more details about that event and the other competitors.

Golia's architecture is very simple: a differential drive robot whose main peculiarity in the locomotion system is the indirect control of the motors. Those are not directly connected to the RCX, but instead supplied by two battery boxes driven by two polarity inverters (5120). The latters are controlled through two motors connected to the RCX.
Globally Golia features 6 motors devoted to propulsion: 2 driving motors on the left wheel, 2 on the right one, and 2 control motors to drive the switches.
I adopted this technical solution to avoid the current limitations imposed by the RCX motor control circuit.

As for localizing the opponent, Golia uses a simple but effective system: two long antennas that at the beginning of the match stay in upright position (to complain with the turnament rules that fixed a maximum size of 32x32 studs) but then are lowered by a seventh motor.
The antennas are very flexible to prevent they got damaged during the match. They are connected to two rotation sensors that decode their position. But for the software, written in NQC, the sensors are coded as passive (raw mode). This solution proved to be more affordable as it's not affected by possible count losses, a problem the RCX firmware suffers once in a while.

Golia mounts a light sensor directed to the floor that's used to detect the white border of the field.

The software is rather simple and considers three possible modes:

  • Search: Golia runs freely on the field, doing pseudo-random length turns when reaches the border.
  • Aim: when one of the antennas detects a touch, Golia turns in that direction to face the opponent.
  • Engagement: when both the antennas detect the opponent this means Golia's facing him, and so Golia goes straight trying to push him off the field.

Front view.

Bottom view, detail of a wheel and its gearing.

Close-up of the mechanics of the antennas: the gearbox is connected to a motor (not in the picture) that lowers the antennas at the beginning of the match. The white 24t clutch gear inside it removes the need of a very precise timing when lowering the antennas and allows them to raise when pushed during a collison without getting damaged.

The switch that controls the left wheel.

Golia's ready for the fight, with the antennas still upright.

Golia engages Borg (by Sergio Lorenzetti).

My puppy Laika (3 months) stares at that strange thing.

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