A quick guide to robotic actuators
Motor selection can make or break a design. It’s not just about power; you must factor in cost, size, reliability, and scalability. The right component is not necessarily the fastest or the one with the most torque.
It’s the one that most simply answers the question of what your design needs.
This guide offers a quick overview of motor types, highlighting their pros, cons, and best use cases to simplify systems and decision making.
Brushed DC (BDC) Motors:
Brushed DC motors are internally commutated electric motors that convert direct current (DC) electrical power into mechanical rotation.
Known for their simplicity and cost-effectiveness, they feature a set of stationary magnets (stator) and rotating electromagnetic coils (rotor/armature).
How they work:
- Power Input: Direct current is supplied to the motor terminals.
- Brushes & Commutator: Carbon or graphite “brushes” maintain physical contact with a rotating segmented ring called the commutator which serves as an electrical switch.
- Magnetic Interaction: The current passes through the rotor coils, temporarily magnetizing them. This generated magnetic field pushes against the stationary magnets on the outside of the motor.
- Commutation: As the rotor spins 180 degrees, the commutator swaps the polarity of the current. This magnetic flipping prevents the rotor from locking in place and forces it to continue spinning in the same direction.
Pros:
- Very simple and cost-effective.
- Excellent starting torque (great for pulling heavy loads from a dead stop).
- Easy to control speed simply by adjusting the voltage.
Cons:
- Wear and Tear: Because the brushes constantly rub against the spinning commutator, they are a sacrificial component and will eventually wear down over time.
- Electrical Noise (EMI): The physical separation (arcing/brush bounce) of the brushes from the commutator segments creates electrical sparks and noise that can interfere with nearby microcontrollers or sensitive electronics.
- Speed Limits: Friction limits the maximum speed these motors can achieve compared to brushless alternatives.
Common use cases
Brushed motors are still widely used despite being older technology, largely because they are inexpensive to manufacture and easy to drive.
BDCs are best for simple, non‑critical motions
- Small Appliances: Hair dryers, vacuum cleaners, and kitchen mixers.
- Automotive: Power windows, windshield wipers, and seat adjusters.
- Hobbies & Robotics: RC cars, drones, and basic beginner robotics (frequently driven by small, standardized batteries).
- Power Tools: Portable cordless drills and saws.
Quick nudge
If you are adding sensors and heavy tuning to demand precision from a BDC, you likely chose the wrong motor. Step back and reassess.
Brushless DC (BLDC) Motors:
Brushless DC (BLDC) motors also run from a direct power source but commutate electronically, using a digital controller to switch current directions and generate torque.
BLDC motors eliminate mechanical brushes and use hall-effect sensors to detect the rotor’s exact position.
How they work
- Position Detection: Hall sensors or back-EMF signals track the rotor magnets.
- Signal Delivery: Position data is sent directly to the electronic controller.
- Phase Energization: The controller energizes specific stator coils in sequence.
- Magnetic Attraction: The stator coils create a rotating magnetic field.
- Rotor Movement: Permanent magnets on the rotor chase the stator’s shifting field.
- Continuous Motion: Electronic switching dynamically updates the field to maintain rotation.
Pros
- Long operating lifespan
- Very high efficiency
- No spark hazard
- Low electrical noise
Cons
- High initial cost
- Complex control electronics
- Requires 3‑phase inverter + often position sensing (encoder or observer)
- Requires specialized wiring
- Higher system weight
Common use cases
Brushless DC motors are best for traction / moving mass with high torque‑density.
- Computer cooling fans
- Drones and RC aircraft
- Electric vehicles (EVs)
- Cordless high-end tools
Quick tips:
- Factor BLDC inverter losses and wiring mass
- Confirm thermal paths in enclosed volumes
- Allocate PCB area for creepage/clearance at target voltage.
Stepper motors:
Stepper motors are electronically commutated too, but they rotate in precise, discrete angular steps rather than in a continuous motion.
They convert digital electrical pulses into fixed increments (typically 1.8° per increment, delivering 200 steps on a full 360° rotation) of mechanical rotation to provide highly accurate position control.
How they work
- Pulse Command: An external controller sends a digital electrical pulse to the motor driver.
- Phase Energization: The driver energizes a specific set of stator coils (a phase).
- Magnetic Alignment: The stator coils create a magnetic field, attracting the nearest rotor teeth.
- Step Movement: The rotor teeth snap into perfect alignment with the stator teeth, moving one precise step.
- Holding Position: The driver keeps the current flowing through those coils to lock the rotor in place.
- Continuous Motion: The driver energizes the next phase in a sequence, creating step-by-step rotation.
Pros
- Precise positioning without sensors
- Excellent low-speed holding torque
- Highly repeatable movements
- Simple open-loop control
- Simple command via step/dir + driver IC
Cons
- Low high-speed torque
- Consumes high current constantly
- Needs holding current to resist back‑drive
- Can lose steps if overloaded
- Prone to vibration and noise
Common use cases
Stepper motors are best for precise positioning and repeatable small moves
- 3D printers and CNC machines
- Flatbed scanners and office printers
- Automated medical lab equipment
- Camera pan-and-tilt platforms
Quick tip
- Budget power for stepper holding current
Considerations
Match motion requirements to motor class, then account for power electronics, wiring, sensing, and control complexity.
Consider this:
- Minimum and maximum motor speed and acceleration
- Maximum torque delivery
- Torque vs speed curve
- Operation precision and repeatability
- Size
- Weight
- Cost
Then simplify.
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