2005 Striker
The striker (AKA Boris or The Mammoth) is driven by two Atmel ATMega32 processors running at 4MHz, which communicate using TWI (two wire interface). It operates at 12V, which is drawn from a 1.3Ah SLA (sealed lead acid) battery. The robot consists of several wooden plates supported by threaded rods and small bolts. It uses ten Lego motors in total – six for the drive motors, two for the kicker and two for the dribbler. These are mounted using aluminium right angle pieces.
The electronics are on a custom-designed PCB (printed circuit board) which was ordered from Futurlec in Sydney. It uses three PWM-driven LMD18200 motor control chips for the omnidirectional drive and a fourth controlled by a NOR gate for the kicker logic and control. The dribbler can only be driven in one direction, and is controlled by a 90A N-channel MOSFET. The gearing used is 1:1 (Lego cogs) on the drive and dribbler motors and 36:1 on the kicker. The kicker is powered forward by a thick elastic band, and is triggered by a ratchet mechanism.
It used 4cm omniwheels which were purchased from Acroname in the US. They are made of polyurethane and have rollers built into them so that they are free to roll sideways, but can be driven forward. The second ATMega32 chip drove the motor controllers and performs the maths used to calculate wheel speeds. I've done up a page showing the mathematical formulae and how they are derived. I only have to modify this program when countering the effect of uneven drive power on either side.
The sensors are Jaycar phototransistors in lengths of black sprinkler tubing. Rather than being passed to the microcontrollers as analogue voltages, they are plugged into comparators and sensitivity is adjusted via a trimpot in a voltage divider configuration. The robot uses five infra-red sensors, but has space for eight. There are plans to implement a physical infra-red filter to reduce ambient light. The robot uses a Vector2X compass module, which is capable of reading individual degrees rather than simply eight directions. However it cannot be reset like the Wiltronics compass. It communicates with the Atmels using SPI (serial peripheral interface). The greyscale sensor consists of a blue LED and an LDR in a tube. The LDR is used as a resistor in a voltage divider to supply an analogue output.
There are several switches on the front to control the different modes (ie. direction and calibration), as well as a large power switch and a 2A fuse. The backlit LCD attached to the rear is out of a 5110 Nokia mobile, and also operates on SPI.
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