In a certain amount of applications brushless motors have to be used without any feedback system. For example harsh environments or underwater applications. Normally at least a “simple” feedback system is required for the commutation by the drive. This can be ex. Digital Hall sensors, or a simple incremental encoder.

Elmo motion control has developed a drive where there is no feedback sensor required. This means you can run the motor in open loop where the motor speed/position is measured by means of the back EMF.
A voltage applied across a motor’s winding forces the motor’s rotor to turn. The movement of the rotor through the motor’s magnetic field, however, is analogous to the behavior of a generator, and consequently the motor not only receives an applied voltage but also generates its own voltage. This voltage is referred to as back electromotive force, or back EMF, and it is proportional to the motor’s rotational speed. Back EMF can be used to determine a motor’s rotor speed and position, no sensors are required.

Some of the advantages are:

• Cost savings as there is no need for a feedback sensor
• Increased reliability, as there are no additional components ( feedback sensor, cable, connections) that can cause malfunction
• No maintenance and exchange of feedback sensor

The choice between sensored and sensorless brushless motors (and the control) is a decision based on performance, application, environment, lifespan and cost. In a situation in which you need a quick setup, precision movement and a dynamic movement, a sensored brushless motor wil probably the best choice. However, if you are looking at a long duty cycle in harsh environments, sensorless brushless motors have considerable benefits.

In both cases Eltrex-Motion can assist in selection and configuration of motors and drives.

If there are more questions about sensorless control, or questions of this is applicable for a specific application, feel free to contact us.