Motor Controller Selection

Motor Specifications

A DC brushed motor has several specifications, three of which are key to properly pair a motor controller.

The first is the motors operating voltage range. The motor controller must be able to operate within the correct voltage range for the motor to avoid damage.

The second property is running current. This is typical the current that the motor requires to spin at maximum speed under no load.

The next specification, stall current, is the most vital in properly pairing a motor controller. Any motor when not rotating is in a stall condition. Depending on the condition in which the motor is operated the maximum stall current can be paired with the motor controllers peak current. However if the motor will be under a constant load or change direction often then peak current should not be used. In this situation the motor controllers continuous current rating should be paired to the motors maximum stall current.

Selecting a Motor Controller

We often see customers who feel their motor will only operate at light loads and therefor can use a smaller motor controller. This is typically not true. When starting from a stand still the motor will require its maximum stall current in order to startup and spin. The load will determine the amount of time the maximum current is required. Once the motor is spinning freely the current will drop proportionally. However if the motor direction is changed without a full stop the maximum stall current will be easily reached. The time it takes for the motor to fully reverse direction dictates how long the maximum stall current will be required.

An example of this would be a DC brushed motor that has a stall current of 100 amps and a running current of 15 amps. The RoboClaw 2X30 has the running current to run this motor. However since the RoboClaw 2X30 is only capable of 60 amps for brief periods it may not be able to start this motor properly.

The minimum required motor controller based on our example motor specifications would be the RoboClaw 2X60A which rated at 120 amps peak for brief periods and 60A continuous. The 2X60A would be able to easily handle frequent starting and stopping along with sudden direction changes. The only limitation being the heat that will be generated. This is where adequate cooling is critical, especially if the motor is expected to be under heavy loads and change rotation frequently.

Depending on load conditions its also possible the RoboClaw 2X60 is too small for our example motor and the next size up of RoboClaw motor controllers would be required. This is true for all motor controllers.