This is just a quick post on controlling DC brushless motors with no encoders. This post applies to brushless motors that typically use hall sensors for commutation. This post does not apply to the hall-less ESC (electronic speed control) motors that typically run at very high speeds and are used for things such as quadcopters and boats.
To go back to basics, brushless motors have three phases (typically) that need to be commutated. The motor controller typically knows how to commutate the motor by having a hall effect sensor on each of the three phases. The problem is, when starting from a stop (no motion) or when operating at “slow” speeds, the controller does not have all of the information it needs to optimally commutate the motor. To get that added information the controller wants to use an encoder for the higher resolution. Using the encoder, the motor controller can now know exactly where the motor is for better control. This means a few things:
So you are now in a position where you have just the halls and no encoder. What can you do about it:
When you are purchasing your motor controller you should check if it can support hall based feedback only. Some controllers do better than others at handling the lack of encoder feedback.