Choosing the best motor for your robotics project can be a challenging task, as there are many factors to consider, such as power, speed, torque, size, weight, efficiency, and cost. In this article, you will learn about the main types of motors used in robotics, their advantages and disadvantages, and how to select the most suitable one for your specific application.
DC motors are the simplest and most common motors used in robotics. They convert direct current (DC) electricity into mechanical rotation, and their speed and direction can be controlled by varying the voltage and polarity of the input. DC motors are easy to use, cheap, and widely available, but they also have some drawbacks, such as low efficiency, high noise, and short lifespan. DC motors are suitable for small and medium-sized robots that require basic and fast movements.
Stepper motors are a type of DC motors that can rotate in precise steps, usually from 0.9 to 1.8 degrees. They are controlled by sending pulses of current to their coils, which magnetize and align with the permanent magnets on the rotor. Stepper motors are ideal for applications that require precise positioning and speed control, such as 3D printers, CNC machines, and robotic arms. However, stepper motors also have some disadvantages, such as high power consumption, low torque at high speeds, and complex wiring and programming.
Regarding complexity: there are many examples and code libraries available for stepper motors. If you're looking for high-resolution movement, consider microstepping and gear reductions but be wary of backlash. A nice benefit of stepper motors is that you don't need encoders if you count the steps programmatically and are aware of rotation limits (for example by using momentary switches) - just make sure no skipping takes place.
Servo motors are a type of DC motors that have a feedback mechanism that allows them to maintain a specific angle or position. They consist of a motor, a gearbox, a potentiometer, and a control circuit. Servo motors are controlled by sending a pulse width modulated (PWM) signal that determines the angle of rotation. Servo motors are widely used in robotics for applications that require accurate and smooth movements, such as robotic eyes, hands, and legs. However, servo motors also have some limitations, such as limited range of motion, high cost, and sensitivity to external forces.
You can use low-resolution rotary encoders on the motor side of the servo device, which translates to a high-resolution rotary encoding of the output side (after the gear reduction)! Due to the gear reduction these motors are often quite strong so be wary of that and use a torque-limited or shearing bolt connection.
Brushless motors are a type of DC motors that do not have brushes or commutators, which are the parts that create friction and wear in conventional DC motors. Instead, they use electronic controllers that switch the current direction in the coils, creating a magnetic field that rotates the rotor. Brushless motors are more efficient, powerful, durable, and quiet than brushed motors, but they are also more expensive, complex, and difficult to control. Brushless motors are suitable for applications that require high performance and reliability, such as drones, robots, and electric vehicles.
When selecting the best motor for your robotics project, you need to take into account your design goals, budget, and technical specifications. Power, speed, torque, size, weight, efficiency, and cost are all important parameters to consider when comparing motors. Depending on the project’s requirements, you may prioritize certain parameters over others. Additionally, factors such as noise, vibration, heat, and compatibility should also be taken into account. Online tools like calculators, simulators, and databases can be used to compare different motors and find the most suitable one for your robotics project.
Don't buy motors of which the supplier or manufacturer does not have a datasheet! You can always ask for more information on the motor by emailing the manufacturer. If you design the application right and account for the limits of your motor then even with next to no maintenance there's a good chance it will outlive you! :)