User Manual

RoboClaw Series
Brushed DC Motor Controllers
RoboClaw Series User Manual
10
Introduction
Motor Selection
When selecting a motor controller several factors should be considered. All DC brushed motors
will have two current ratings, maximum stall current and continuous current. The most important
rating is the stall current. Choose a model that can support the stall current of the motor
selected to insure the motor can be driven properly without damage to the motor controller.
Stall Current
A motor at rest is in a stall condition. This means during start up the motors stall current will be
reached. The loading of the motor will determine how long maximum stall current is required. A
motor that is required to start and stop or change directions rapidly but with light load will still
require maximum stall current often.
Running Current
The continuous current rating of a motor is the maximum current the motor can run without
overheating and eventually failing. The average running current of the motor should not excede
the continuous current rating of the motor.
Shut Down
To shut down a motor controller the positive power connections should be removed rst after the
motors have stopped moving. Powering off in an emergency, a properly sized switch or contactor
can be used. A path to ground for regeneration energy to return to the battery should always be
provided. This can be accomplish by using a power diode with proper ratings to provide a path
across the switch or contactor when in an open circuit state.
Run Away
During development of your project caution should be taken to avoid run away conditions. The
wheels of a robot should not be in contact with any surface until all development is complete.
If the motor is embedded, ensure you have a safe and easy method to remove power from
RoboClaw as a fail safe.
Wire Lengths
Wire lengths to the motors and from the battery should be kept as short as possible. Longer
wires will create increased inductance which will produce undesirable effects such as electrical
noise or increased current and voltage ripple. The power supply/battery wires must be as short
as possible. They should also be sized appropriately for the amout of current being drawn.
Increased inductance in the power source wires will increase the ripple current/voltage at the
RoboClaw which can damage the lter caps on the board or even causing voltage spikes over the
rated voltage of the Roboclaw, leading to board failure.
Power Sources
A battery is recommended as the main power source for the motor controller. Some power
supplies can also be used without additional hardware if they have built in voltage clamps or if
used with very low current motors. Most Linear and Switching power supplies are not capable
of handling the regeneration energy generated by DC motors. Switching power supplies will
momentarily reduce voltage and/or shut down, causing brown outs which will leave the controller
in an unsafe state. The MCPs minimum and maximum voltage levels can be set to prevent some
of these voltage spikes, however this will cause the motors to brake when slowing down in an
attempt to reduce the over voltage spikes. This will also limit power output when accelerating
motors or when the load changes to prevent undervoltage conditions. Voltage clamp solutions
may be required for higher power motors when using power supplies.