Motion Control and Actuators

Motion control is the art of moving a load where you want, as fast as you need, with the right force, and stopping it safely. It combines a motor, a drive, a transmission, usually a feedback device and a controller, and a mistake in any link shows up as noise, overshoot, lost steps, overheating or a part in the wrong place. This guide takes the chain one link at a time, with worked numbers and diagrams, and ends with step-by-step sizing, braking and troubleshooting. It builds on the wiring and programming in the PLC & Logic Control guide and on the networks in Industrial Communication; the motor electronics are in Power and Motor Electronics, and the mechanics of gears and belts in Gears and Belts and Pulleys.

Start here: what do you need?

I need to…	Go to
understand the parts of a motion system, motion profiles, or work out torque, speed and power	Motion Control Basics
decide between a servo, a stepper, an induction motor or a brushed motor	Choosing a Motor Technology
set up a stepper driver, choose microstepping, or stop it losing steps	Stepper Motors and Drivers
tune a servo, understand the loops, or fix overshoot and vibration	Servo Systems and Tuning
run a pump, fan or conveyor from a variable-frequency drive, or set up its parameters	AC Motors and Variable-Frequency Drives
choose an encoder or resolver, calculate resolution and frequency, or wire it	Encoders, Resolvers and Feedback
choose a ball screw, belt or gearbox, and match inertia	Mechanical Transmission: Screws, Belts and Gearboxes
size a motor and drive for a real axis, horizontal, vertical or rotary	Sizing a Motion Axis
choose or size a pneumatic cylinder, a hydraulic cylinder or an electric linear actuator	Pneumatic and Hydraulic Actuators
add a brake, stop safely, or find out why an axis misbehaves	Braking, Safe Stopping and Troubleshooting

A suggested order

If you are new to motion control, read the pages in this order. Each builds on the one before, and the previous and next links at the top and bottom of every page follow it.

1. Motion Control Basics: The parts of a motion system, open and closed loop, motion profiles, speed, torque and power, RMS torque and the four quadrants of operation.
2. Choosing a Motor Technology: Brushed DC, brushless, servo, stepper, induction and linear motors compared: torque curves, control, cost, and which to pick.
3. Stepper Motors and Drivers: Steps and microstepping, the torque-speed curve, resonance, drivers and current settings, wiring, and when a stepper loses steps.
4. Servo Systems and Tuning: Cascaded position, velocity and current loops, PID terms, tuning methods, following error, inertia ratio and stability.
5. AC Motors and Variable-Frequency Drives: Induction motor speed and slip, V/Hz control, drive setup and parameters, motor cables, derating, harmonics and braking.
6. Encoders, Resolvers and Feedback: Incremental and absolute encoders, quadrature, resolution and frequency, resolvers, Hall sensors, signal types, wiring and homing.
7. Mechanical Transmission: Screws, Belts and Gearboxes: Ball and lead screws, belts, rack and pinion, gearboxes, couplings, backlash, stiffness, linear guides and reflected inertia.
8. Sizing a Motion Axis: Step-by-step motor and drive sizing for horizontal, vertical and rotary axes, with torque, speed, inertia ratio and margin checks.
9. Pneumatic and Hydraulic Actuators: Cylinder force and air use, valves, speed control, hydraulic basics, electric linear actuators, and choosing between them.
10. Braking, Safe Stopping and Troubleshooting: Mechanical and dynamic braking, safe torque off and stop categories, commissioning, and a symptom table for motion faults.

Which motor, at a glance

Motor	Strengths	Weaknesses	Typical use
Stepper	Simple, low cost, holds position without feedback, good at low speed	Torque falls with speed, resonance, can lose steps, runs warm	3D printers, small positioning, light-duty indexing
Servo (brushless)	High speed, high dynamics, flat torque curve, efficient, fault feedback	More costly, needs tuning and a feedback device	CNC, robotics, packaging, fast pick and place
Induction on a VFD	Rugged, cheap per kW, huge range of sizes, no magnets	Less dynamic, slip, needs a drive for speed control	Pumps, fans, conveyors, spindles, mixers
Brushed DC	Cheap, simple drive, strong torque at low speed	Brush wear, noise, limited life	Toys, small actuators, automotive accessories
Linear motor, voice coil	Direct drive, no backlash, very fast and precise	Costly, limited force, heat, need good guides	Semiconductor, inspection, fast short strokes

The pages Choosing a Motor Technology and Sizing a Motion Axis turn this table into a decision with numbers.

Quick reference: formulas

Topic	Formula	Page
Angular speed	ω = 2π n ÷ 60	Motion Control Basics
Power	P = T × ω; T (N·m) = 9.549 × P (W) ÷ n (rpm)	Motion Control Basics
Trapezoid move	v = d ÷ (T − ta); a = v ÷ ta	Motion Control Basics
Torque to accelerate	T = J × α + Tfriction	Motion Control Basics
RMS torque	Trms = √(Σ Ti² ti ÷ Tcycle)	Motion Control Basics
Stepper	steps per rev = 360° ÷ step angle (1.8°: 200)	Stepper Motors and Drivers
Induction speed	ns = 120 f ÷ poles; slip = (ns − n) ÷ ns	AC Motors and Variable-Frequency Drives
Encoder resolution	counts per rev = 4 × lines (quadrature)	Encoders, Resolvers and Feedback
Reflected inertia	J = Jload ÷ N²; screw: m × (lead ÷ 2π)²	Mechanical Transmission
Cylinder force	F = P × A	Pneumatic and Hydraulic Actuators

Calculators and related guides

• Motor Torque and Inertia Matching Calculator: reflected inertia, torque and inertia ratio for a gearbox or screw.
• Gear Ratio, Torque and Speed Generator: speed and torque through a gear train.
• 4-20 mA / 0-10 V Analog Scaling Tool: scaling a drive’s analog speed reference.
• Sensors and Field Devices: limit switches, proximity sensors and the other devices around an axis.
• Motors, Drives and PID Control: connecting a drive to a PLC.

Safety

• Moving machinery can kill. Guard it, and make sure it cannot start while someone is inside. Use lockout and tagout before working on it (see Workshop Safety).
• Stored energy. Springs, raised loads, pressurized air or oil and charged drive capacitors can move or injure after the power is off.
• Vertical axes fall when a motor is released: they need a holding brake or a counterbalance (Braking, Safe Stopping and Troubleshooting).
• Use safety-rated stops (safe torque off and an emergency stop circuit) for anything that can hurt people; a program stop is not a safety function.
• High voltage. Drives work at hundreds of volts and can have dangerous touch current: only qualified people should work on them.

FAQ

Where should I start?

With Motion Control Basics for the vocabulary and the torque calculation, then Choosing a Motor Technology. If you already know what motor you have, go straight to its page and to Sizing a Motion Axis.

Servo or stepper for my project?

A stepper is the simple, economical choice for low speeds and modest loads where a lost step is not a disaster. A servo costs more but gives speed, torque headroom and fault information. Choosing a Motor Technology compares them with numbers.

Do I need a gearbox?

Often yes: a motor is most efficient fast and light, and many loads need slow and strong. A gearbox also reduces the inertia the motor sees by the square of the ratio, which makes the axis easier to control. See Mechanical Transmission.

What happened to the Actuators page?

Its content (choosing an actuator, motor basics, pneumatic cylinders, hydraulics) is now in Choosing a Motor Technology and Pneumatic and Hydraulic Actuators.

References

• Parker Hannifin, Motion control and electromechanical sizing handbooks; Kollmorgen and Siemens motion sizing guides.
• Hughes, A. and Drury, B., Electric Motors and Drives, 5th ed., Newnes.
• IEC 61800-5-2, Adjustable speed electrical power drive systems: safety requirements, functional.
• Esposito, A., Fluid Power with Applications, Pearson.

Last reviewed: October 2026. Values are typical: check the datasheets of the parts you use, and follow the machine safety standards for your region.