Although most servo motors have similar specifications on paper, there are many aspects to consider when picking what type is best for a particular application.
One of the most important and obvious requirements for a servo motor is determining the load. The main loads of interest for a servo motor are what the motor shaft will be rotating in any capacity. Any parts connected to the motor shaft will apply a load inertia. Specifically, the inertia of the load needs to be less than that of the inertia generated by the motor for the motor to function as intended. The moment of inertia for the motor is typically found on the datasheet. Oftentimes, designers will use a safety factor to make sure that the motor will still be capable of efficiently turning and handling a load that might not be exactly what was expected.
Electronic Control Functions
Another requirement for the servo motor that needs to be defined are the intended electronic control functions of the motor. In other words, before a servo motor is selected, the designer must know what kind of motion sequence or function the motor needs to be capable of before making a selection. The programmability and functions available with the included drive need to be considered.
Speed and Torque
Once the motion sequence has been established for the motor, the next step is to determine how fast the motor is required to turn and how much torque the motor needs to provide. Both of these characteristics will be a result of knowing the load in addition to how the load will be moved. Between similarly sized servo motors, it can be expected that a motor that provides higher speed will not produce as much torque as a motor that is only capable of a lower speed. It is important that when making a servo motor selection to not pick a motor that will be constantly running at its maximum speed. Continuous maximum output from the servo motor will decrease its lifespan and increase its maintenance time.
Once the relative speed and torque requirements have been defined, the designer needs to select a power source that will be capable of powering the motor. This is not so much a step in the selection of the servo motor itself, but is something to consider if there is a limit to how much power can be supplied to a possible motor. A voltage requirement will determine the maximum power delivered by a motor in general.
Environmental and Installation Conditions
The environment that the servo motor is being installed in should play a large role in determining what servo motor to select. As a result of fast-moving and rotating parts, heat will be generated by the servo motor and transferred to the surrounding area, heating up the motor as well. The amount of heat produced by the motor also affects its performance, which is also typically denoted on the datasheet.
The physical size of the motor and what the motor is being installed onto also play an important role when considering the environment and installation conditions of a servo motor. While it might be easy to go with a large motor that fits within budget to oversatisfy torque requirements, the motor might not end up fitting in the preferred orientation if the designer is not careful.
The last, but not the least, important factor when selecting a servo motor is the quality. Depending on the allowed budget for the purchase, factors such as efficiency, accuracy, and reliability of the motor can and should be considered if the motor is intended for long-term use. If the motor is going to be used in a highly specific and calibrated application, then a cheap servo motor with poor motion control will probably not meet the requirements of the application over time.