Parts

All the parts for Ally's shell were cut using a mitre saw and then pre-drilled in a drill press. The aluminium was polished with Silvo silver polish and then painted with several coats of Incralac metal lacquer to preserve the finish.


Side

The pieces of Ally's shell were initially bolted loosely together and then gradually tightened until everything fitted together as closely as possible. Once the symmetry of the shell was checked and adjusted, the bolts were removed one by one and replaced with aluminium rivets.


Front

Ally's shell was designed around a 30cm by 30cm square of aluminium and the major structural elements are 40mm aluminium angles riveted together and reinforced with steel brackets. Using a large framed manual mitre saw it was possible to cut the aluminium so accurately that only hair-line cracks remain between the assembled pieces.


Base

The motors and battery are installed using brackets and supports cut from aluminium channels and angles. The battery is a 6 volt 10 amp hour sealed lead acid battery maintained by an on board charging circuit based on the UC3906 integrated circuit from Texas Instruments. The motors are Hitech HS815 Sail Winch servos modified for continuous rotation. Hobby servo motors don't get much more powerful than these. The wheels are directly bolted to the servo splines, which is ok so long as the robot is not carrying a load. This will have to be upgraded to a chain drive in the near future.


Under

The battery is positioned between the main drive wheels at the rear of the robot. The front of the robot is supported by a single castor wheel. This arrangement should make the robot less likely to topple over if it gets too close to the edge of anything precipitous like stairs.


Testing

Open

Ally fitted with a prototype bump sensor. The bump sensor is not only able to detect collisions from the front hemisphere of the robot, but also from the sides when the robot is turning. It absorbs the shock of an impact through the flexible plastic bar and spring-loaded supports.


Closed

The bump sensor can be retracted and locked in a closed position. The moving parts are lubricated with molybdenum grease and bolted together. The nuts are prevented from undoing using a thread locking compound from Permatex.


Wall

The micro-switches mounted on the base of the bump sensor are triggered as soon as the bar strikes an object. Even when travelling at full speed the robot has ample time to stop using its active braking system.


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