Battery Maintenance; Motion Control - NEX ROBOTICS SPARK V ATMEGA16 Hardware Manual

be in between 7.1 to 9V. Red and Orange are the positive terminals. Brown and Black are the
negative terminals.
Warning:
• Do not exceed 9V voltage limit else robot will get damaged.
• Battery connector socket is not reverse polarity protected. If supply is applied in reverse
polarity, it will immediately damage the robot.
• Use only good quality bench top power supply to power the robot using external supply.
Use of AC adaptor or cheap SMPS is not recommended.

3.6 Battery Maintenance

Fully charged NiMH battery will get completely discharged with in a week of storage. Always
charge the battery before use. If fully charged battery is kept in storage for about a month and
afterwards even if it's fully charged again, it can deliver only 1/3
case to restore battery to its full potential again, perform at least 2-3 charge discharge cycles.
To ensure long life, charge battery at least once a week and discharge it till robot starts giving
battery low warning. Before storage, charge the battery again.
For discharging the battery quickly, you can load any program from the "Experiments" folder of
the documentation CD.
Disconnect the battery connector if robot is to be stored for long duration of time.

3.7 Motion control

Spark V robot has two 60 RPM DC geared motors in differential drive configuration along with
the third caster wheel for the support. Robot has top speed of about 66cm per second. Using this
configuration, the robot can turn with zero turning radius by rotating one wheel in clockwise
direction and other in counterclockwise direction. Robot's motors have built-in clutch for
protection of the motor's gears from non continuous wheel stalling.
Motion control involves direction control and velocity control. Motors are controlled by L293D
dual motor driver which can provide up to 600mA of current to each motor. To change the
direction of the motor, appropriate logic levels (High/Low) are applied to L293D's direction
control pins. Velocity control is done using Pulse Width Modulation (PWM).
LEDs are connected at the input and the output stage of the motor driver for quick interpretation
of the motion commands.
Pulse Width Modulation for velocity control:
Pulse width modulation is a process in which duty cycle of constant frequency square wave is
modulated to control power delivered to the load i.e. motor.
Duty cycle is the ratio of 'T-ON/ T'. Where 'T-ON' is ON time and 'T' is the time period of the
wave. Power delivered to the motor is proportional to the 'T-ON' time of the signal. In case of
PWM the motor reacts to the time average of the signal.
PWM is used to control total amount of power delivered to the load without power losses which
generally occur in resistive methods of power control.
© NEX Robotics Pvt. Ltd. and ERTS Lab IIT Bombay, INDIA
SPARK V ATMEGA16 Hardware Manual
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