Specifications

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The motor slipping in the tracks would have made this project a near impossibility
without a delicate error correction system in place. Because of these difficulties a
decision was made to use wheels connected as a direct drive to the motor.
4.2 Second Prototype
The second prototype for the mechanical design consisted of an aluminium chassis with
dual drive motors. A simple trundle wheel for stability was used to allow ‘on the spot’
steering and high manoeuvrability.
Figure 4.2 Second Chassis Prototype
The drive motors were chosen from a set of affordable ‘XU1” 12 volt cordless drills.
The speed of these motors was far too fast to attach directly to the drive wheels of the
robot however, so a gearbox was required. A worm drive seemed the logical
arrangement for this to provide high reduction, high torque and very minimal backlash.
Two windscreen wiper motors from XD Falcons were purchased from a car yard and
modified to suit the desired purpose. Due to the size of this application, batteries will
be small and therefore the motors need to be of low power consumption. Windscreen
wiper motors draw approximately 5-10 amps and so running two of these would require
a rather large battery. By replacing the original motors with the cordless drill motors,
the amperage was dropped to approximately 5 amps for both motors running
simultaneously under load. Figure 4.3 shows the small motor mounted on the gearbox.