SOLID Learning – Servo Robot Actuator Selected!

After discussion with educators, workshop participants, parents and interested hobbyists, the final determination for the standard type of actuator we will be using for our SOLID Learning pilot course robots is the Servo. Servos were selected because they are relatively inexpensive, have internal gears for increased torque, and can be controlled directly by a single digital TTL circuit without additional driver electronics.

Common hobby servo with 4-horned servo arm attached to output

Simplicity and cost were the most fundamental determining factors. For evaluation, I used the basic costs just for actuators and required control electronics alone in order to establish a standard across any form of control system that might be selected by our educators – which will be addressed across the upcoming week’s posts. Linear and Solid State Actuators were excluded early in the discussion due to limited stroke length and cost.

The three types of motors - DC, Servo and StepperThe three types of actuators for which cost comparisons were prepared include the DC Motor, Servomechanism, and Stepper Motor. DC Motors require an additional driver board for each two motors, while Stepper Motors require one driver board for each motor. The lowest-cost version of each component type from SparkFun, DigiKey and Adafruit were used for comparative purposes – exact costs may be slightly different in the final acquisition depending on required component size and torque requirements.

A two driver wheel robot design showing tracks with two unpowered idler wheels.The first configuration under consideration involves two powered driver wheels, whether a simple wheel or powered road wheel in a tracked form factor. This design requires any of the following:

  • 2 DC Motors and 1 Motor Driver
  • 2 Stepper Motors and 2 Motor Drivers
  • 2 Servos
DC Motors Stepper Motors Servos
Cost $35 $56 $22
Channels 4 8 2

A four-wheel drive robot, showing mechanum wheels to allow movement in any direction.

The second configuration under consideration involves four powered driver wheels, whether a simple rotary 4-wheel-drive or a more exotic form factor involving omniwheels or mecanum wheels for advanced movement options. This design requires any of the following:

  • 4 DC Motors and 2 Motor Drivers
  • 4 Stepper Motors and 4 Motor Drivers
  • 4 Servos
DC Motors Stepper Motors Servos
Cost $70 $112 $44
Channels 4 8 4

Hexapod Legged Walking Robot with three actuators per leg.

The final configuration under cost consideration involves six articulated legs, each of which has three powered control actuators to allow for fluid gait movement. This design requires any of the following:

  • 18 DC Motors and 9 Motor Drivers
  • 18 Stepper Motors and 18 Motor Drivers
  • 18 Servos
DC Motors Stepper Motors Servos
Cost $315 $504 $198
Channels 18 36 18

Obviously the integrated control electronics in Servos greatly simplify control and avoid the need for additional electronics – minimizing robot size, wiring complexity and the need for additional driver costs. The more complex the robotic actuation model, the more multiples of components that will be required. Cost differentials increase with actuation complexity, but the same electronics can be combined to form more complex configurations in group studies.

Elementary and starter robots can easily make use of 2-wheel models, while more advanced robotic control requires 4-weel models. Walking robots can make use of fewer shared actuators at the cost of jerky non-fluid movement, or can add significantly more actuators in order to gain biological levels of movement and enhanced degrees of freedom. The same servos will be able to operate all of these models. Later SOLID Learning elements may require specific alternatives, such as Stepper Motors for school-built RepRap or CNC systems. This selection of servos as an actuation standard is only for the pilot Robotics program designs.

Return to post: SOLID Learning Robot Components

Main SOLID Learning link: Introduction to SOLID Learning

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