Electrical motors operate on the principle that two magnetic fields
within certain prescribed areas react upon each other.
- cncKITS.com Tutorial & FAQ
- information on comuter control
- Control.com - an automation and
control site with a large discussion area, and motors/motion are popular topics
- DSPs excel
in motor-control applications - motor control is a new application for DSPs that can
help to lower motor costs, give better reliability and make them consume less energy
- How Electric Motors
Work - Electric motors are everywhere! In your house, almost every mechanical movement
that you see around you is caused by an AC or DC electric motor. By understanding how a
motor works you can learn a lot about magnets, electromagnets and electricity in general.
In this edition of HowStuffWorks you will learn what makes electric motors tick.
- Electric
Motor Terminology
- Information about
different surge suppression devices - motors are inductive and can cause voltage
surges
- Inside an
Electric Motor
- Introduction To Linear
Motors - A Linear Induction Motor (LIM) is basically a rotating squirrel cage
induction motor opened out flat. Instead of producing rotary torque from a cylindrical
machine it produces linear force from a flat one. Applications are many and varied,
ranging from simple sliding doors to full control of a ten tonne vehicle.
- Motioncontrol.com - This
Motor and Motion Control Portal has a direct path for the engineers to find motion control
manufacturers and their products.
- Noise in audio/video
& R/C systems - noise can be caused by a number of things including poor power
ground schemes and poor power distribution
- Questions
and aswers on electric motors and magnetics
- Steppers,
Servos, Motors & Actuators - larnign center of tutorials
- The difference between
Stepper Motors, Servos, and RC Servos
- The
rise of VSR motors - Once obscure, variable-switched-reluctance motors are now
entering mainstream use from jet fighters to washing machines.
AC motors operate from alternating current (AC) power sources. The
magnetic fields typically are generated using coils on the rotor and stator, and the field
movement occurs naturally in the stator due to the alternating nature of the input power.
These motors are inexpensive to build and operate, reliable, and usually run from standard
line power. The power supply frequency determines the speed of an AC motor, so if operated
from line power, the speed of rotation is always the same. Variable frequency power drives
control the speed of AC motors, but such drives are expensive.
AC induction motor is the most common motor used in industry and
mains powered home applicances. AC induction motors offer users simple, rugged
construction and easy maintenance. An ac induction motor consists of two basic assemblies
- stator and rotor - and is analogous to an ac transformer with a rotating secondary. The
motor’s name comes from the alternating current (ac) induces into the rotor by the
rotating magnetic flux produced in the stator. Motor torque is developed from interaction
of currents flowing in the rotor bars and the stator’s rotating magnetic field. The
magnetic field rotates at synchronous speed, the motor’s theoretical top speed that
would result in no torque output. In actual operation, rotor sped always lags the magnetic
field’s speed. Typical slip values range 2-5% at running speed, but can be large at
motor startup. Slip also increases with load. The actual rotation speed of AC induction
motor depends on the motor design. The rotation direction is controlled on the order of
the phases applied to the motor. If you change the order of two phase wires, you can
change the rotation direction. Protection of induction motors is necessary to avoid motor
failures when something goes wrong. It is somewhat hard to protect an AC induction motor
against overload with normal fuses, because at startup those motors take, for some time,
much higher current than is allowed for continuous operation. The thermal overload relays
are suitable for overload protoction of AC motor operated on hours duty or uninterrupted
duty. There are also more advanced protection relays which provide phase-failure
protection, temperature compensation, ON/OFF inidication and manual/automatic reset.
Induction motors are available in an extremely wide size range from
very small units to hundreds of kW. Some common input voltages are 230, 460, and up to 575
V for 60-Hz operation (up to 690 V for 50-Hz-rated units). AC induction motors are
designed to run from three phase power. Small AC induction motors are also sometimes used
in single-phase power applications, and in those applications special arrangements needs
to be done to make the motor to start properly and have the righ kind of fields in the
running time (this usually needs start capacitors and/or running capacitors).
There are also other AC motor types than AC induction motors. Here
are many different low power motor types. Permanent Split Capacitor Motors are designed
for single speed applications using single phase power. These motors require continuous
duty, motor run capacitors connected in the auxiliary winding circuit to produce starting
torque Synchronous designs provide exact speed from No-Load to Full Load, asyncronous
motors have regulation uusally less than 3% speed change from No-Load to Full Load.
Split Phase motors are designed for single speed applications using
single phase power. The specially designed auxiliary winding produces starting torque and
is then disconnected by an internal, mechanical, centrifugal starting switch. start or run
capacitor is required. However, an electrolytic start capacitor may be connected in series
with the auxiliary winding to increase starting torque and reduce starting current.
Many AC fans use a shaded-pole motor construction. It is a simple
inexpensive single phase AC motor which is generally used for fan applications.
Written-Pole motors are special single-phase AC motors which can change the position of
magnetic poles while the motor operates.
Last but not least is a motor type called "universal
motor". It is basically constructed like brush-type DC motor which has both rotor and
stator coils. This motor is constructed so that when coils are wired in one way, it
rotates to the same direction, no matter if AC or a DC in any direction is applied to it
(changing of rotation direction needs changing the connection of coils). This type of
motor is used generally on home appliances which run on AC power and have wide speed
adjustment range. This type of home appliances are for example elecric drills with speed
control, vacuum cleaners with power control and some washign machines. The speed of an
"universal motor" can be easily controlled using PWM control methods (phase
control of AC power).
In some AC motor applications devices called motor starters are
needed. AC motor starters are intended to start and accelerate motors to normal speed, to
ensure continuous operation of motors, and to provideo protection against overloads
(switch power of if overload occurs). There are many different type of starters. They all
provide protection against overloads (quite often use thermal electrical relays for motor
protection, sometimes more advanced electronic circuit). Direct-on-line (full-on) AC
starters start and accelerare motor to full speed by connecting full line voltage
immediatly to motor. Reduced voltage AC starters start and accelerate motor to normal
speed by connecting the line voltage to motor in increasing steps. Delta-star starters
start three-phase motor in star-connection (reduced start current) and then operate motor
at delta wiring (full power). Two-step auto-transformer starters start and accelerate the
AC induction motor with rediced torque to normal speed. Rheostatic rotor starters start an
AC induction motor by cutting out resistors inserted in the rotor circuit.
Some single phase motors use "capacitor start" method.
Some of those motors need capacitor start unit which connect the starting capacitor to
motor when it is powered up and disconnects that capacitor when the motor has started.
Generally electrical motors draw a large current when they started.
A 5HP 240v 3ph motor mave have a full load rating of about 15 amps but on initial start it
may draw 90 amps or more for the brief period of starting time. The mains connector blades
have to be able to handle this brief current surge without arcing. To get this working
installers sometimes need to go to larger rated plugs which have better contact mating
characteristics - hence the HP rating in some mains plugs. Mains plug ratings are really
based on current handling capability, and the horsepower rating is derived from that,
based on the current required by a given size motor to start.
Across-the-line industrial motor starters are made in sizes up to
those capable of carrying 600 amperes. Contacts of power relays used for motor control
must be capable of opening at six to eight times the rated steady current in case a motor
should stall.
General information articles
- 3 phase
A.C. Motor Windings and Connection
- AC Induction Motor
Designs, Types - Worldwide popularity of ac induction motors in numerous applications
has led to some standardized motor designs. The National Electrical Manufacturers
Association, (NEMA, Washington, D.C.) has developed specifications for so-called NEMA
design A, B, C, and D motor types. These designs are based on standardizing certain motor
characteristics such as starting current, slip, and specified torque points. This article
is a brief rundown on NEMA motor types.
- AC
Induction Motor Selection - info relating to the selection of various type of
industrial AC inductions motors and starters
- Alex's
Electronic Resource on motors and accessories - This site had many useful documents on
electric motors.
- Anatomy of an ac
induction motor
- Basic
Motor Control Schematics
- Control
by a triack for an inductive load - application note AN308 from SGS-Thomson
- Controller
provides multimode phase control - inexpensive 16C508 multichip controller can
implement a phase controller that provides a two-key, indexed processor for ac power or
other discrete, digital-signal applications
- Design
Decisions and Parameter Selections Dealing with Traction AC Drives
- Dimmer
with AC motor? - Normal light dimmers may have some problems with an inductive load,
such as a motor. Essentially, the dimmer works by chopping bits out of the AC waveform.
Inductors, like the coils in a motor, dislike having the current through them changed
abruptly, and produce large voltage spikes which can cause the triac to self-trigger or
burn if not properly taken care of. This article tells how to do this.
- Equations
for Electrical Motors
- Generate
advanced PWM signals using 8-bit µCs - hot to generate waveforms needed for variable
speed three phase motor controlling
- Identifying
Motor Defects Through Fault Zone Analysis - This article has information on three
phase AC motor troubleshooting and measuring.
- Magnetic
Noise Reduction Method of Inverter Driven Induction Motors
- Medium
Voltage Drive Technology: A Comparison
- Motor Controlling
Application Notes from LSI Computer Systems
- Motor
Formulas - check also other useful formulas
- Motor
Starter Basics - The first purpose of a motor controller is to start and stop the
equipment. A magnetic contactor provides the traditional and still most common start-stop
control. Protection must be provided to prevent motor thermal damage due to high currents
caused by mechanical overloads. Overload relays in motor controllers are connected in the
motor current circuit between the contactor and the motor. They are provided with three
current-sensing elements, one per phase, and a control contact, which is wired to open the
contactor. Relay operation includes an inverse time characteristic; the higher the
magnitude of an overload, the shorter the time delay before opening the contactor. For
most applications, the level above which the relay senses an overload is 115% of FLA, and
the relay will hold LRA for at least 10 sec to accommodate starting of high-inertia loads.
- Motor
Starter Basics: Motor and motor branch circuit short circuit and ground fault protection
- Short circuits and ground faults occur when conductors unintentionally contact one
another, or a grounded surface due to insulation failure, equipment damage, or human
error. Protection is provided by fuses, molded-case circuit breakers (MCCBs), or motor
circuit protectors (MCPs) installed on the line side of the motor controller, either as
part of a combination starter or separately-mounted.
- Power
Factor Correction
- Rules Of
Thumb
- Synchronous
Motor Operation
- The
Selection, Connection, Reversing and Repair of Electric Motors - Selecting a motor and
connecting the electricals are the first challenges encountered after purchasing that long
coveted machine tool. There are several types of single phase AC motors in current
production in the U.S., but only two types are commonly used in powering home shop
machninist equipment.
Controlling three phase motors
The actual rotation speed of AC induction motor depends on the motor
design. If you want to change that you need to change the frequency of mains voltage (you
need special variable speed drive electronics for this) or you need to change the motor.
The rotation direction of a three phase motor is controlled on the
order of the phases applied to the motor. If you change the order of two phase wires, you
can change the rotation direction.
Protection of induction motors is necessary to avoid motor failures
when something goes wrong. It is somewhat hard to protect an AC induction motor against
overload with normal fuses, because at startup those motors take, for some time, much
higher current than is allowed for continuous operation. The thermal overload relays are
suitable for overload protoction of AC motor operated on hours duty or uninterrupted duty.
There are also more advanced protection relays which provide phase-failure protection,
temperature compensation, ON/OFF inidication and manual/automatic reset. Modern motor
protection devices (usually called electronic thermal overload relays) protect against
locked rotor conditions, running overload, high ambient temperature, lost phase and low
voltage. Motor protection devices generally use Positive Temperature Coefficient (PTC)
sensors to sense motor temperature.
- Solving Motor Failures
Due to High Peak Voltages and Fast Rise Times (dv/dt) - The evolution of power
semiconductors has been so dramatic that today an insulated gate bi-polar transistor
(IGBT) can be turned on in just 0. I micro-second. This results in the voltage rising from
zero to peak in only one-tenth of a microsecond. Unfortunately, there are many motors in
existence that do not have sufficient insulation to operate under these conditions. When
the rise time is very fast the motor insulation system becomes stressed. Excessively high
dv/dt can cause premature breakdown of standard motor insulation. Inverter duty motors
typically have more phase-to-phase and slot insulation than standard duty motors (NEMA
design B).
Using three phase motor on single phase supply
Circuits
The direct current (DC) motor is one of the first machines devised
to convert electrical power into mechanical power. Permanent magnet (PM) direct current
convert electrical energy into mechanical energy through the interaction of two magnetic
fields. One field is produced by a permanent magnet assembly, the other field is produced
by an electrical current flowing in the motor windings. These two fields result in a
torque which tends to rotate the rotor. As the rotor turns, the current in the windings is
commutated to produce a continuous torque output Permanent magnet (PM) motors are propably
the most commonly used DC motors, but there are also some other type of DC motors (types
which use coils to make the permanent magentic field also).
DC motors operate from a direct current power source. Movement of
the magnetic field is achieved by switching current between coils within the motor. This
action is called "commutation". Very many DC motors (brush-type) have built-in
commutation, meaning that as the motor rotates, mechanical brushes automatically commutate
coils on the rotor.
Motor speed control of DC motor is nothing new. A simplest method to
control the rotation speed of a DC motor is to control it's driving voltage. The higher
the voltage is, the higher speed the motor tries to reach. In many applications a simple
votlage regulation would cause lots of power loss on control circuit, so a pulse width
modulation method (PWM) is used in many DC motor controlling applications. In the basic
Pulse Width Modulation (PWM) method, the operating power to the motors is turned on and
off to modulate the current to the motor. The ratio of "on" time to
"off" time is what determines the speed of the motor.
Sometimes the rotation direction needs to be changed. In normal
prmanent magnet motors, this rotation is changed by changing the polarity of operating
power (for example by switching from negative power supply topositive or by interchanging
the power terminals going to power supply). This directrion chanign is typicaly
implemented using relay or a circuit called an H bridge.
Besides "brush-type" DC motors, there is another DC motor
type: brushless DC motor. Brushless DC motors rely on the external power drive to perform
the commutation of stationary copper winding on the stator. This changing stator field
makes the permanent magner rotor to rotate. A brushless permanent magnet motor is the
highest performing motor in terms of torque / vs. weight or efficiency. Brushless motors
are usually the most expensive type of motor. Electronically commutated, brush-less DC
motor systems are widely used as drives for blowers and fans used in electronics,
telecommunications and industrial equipment applications. There is wide variety of
different brush-less motors for various applications. Some are designed to to rotate at
constant speed (those used in disk drives) and the speed of some can be controlled by
varying the voltage applid to them (usually the motors used in fans). Some brushless DC
motors have a built-in tachometer which gives out pulses as the motor rotates (this
applies to both disk drive motors and some computer fans).
In general, users select brush-type DC motors when low system cost
is a priority, and brushless motors to fulfill other requirements (such as
maintenance-free operation, high speeds, and explosive environments where sparking could
be hazardous). Brush type DC motors are used in very many battery powered appliances.
Brushless DC motors are commonly used in applications like DC powered fans and disk drive
rotation motors.
General information
Articles
- Answers to FAQs on
Battery Motors & Controllers
- Beakman's Electric
Motor - This article describes the worlds simplest and cheapest 'home-made' electric
motor, suitable for demonstrations, or just plain fun.
- Battery Motors & Controllers
FAQ
- DC motor speed
control matlab simulation and hardware circuits - course material
- Driving DC Motors
- application note in pdf format
- Inductive flyback catching
diodes - All inductive devices, operating in d.c. circuitry, which are switched on and
off (whether by a contact or by electronic circuitry) should have a diode connected across
their coils to catch the inductive fly back.
- Motion Control Primer:
Sizing an Industrial Motor for the Job and selecting motor type - What kind of DC moto
should be selected for industrial application.
- Motor
Charasteristics: Measurement of Lumped Parameters - Laporatory exercise documentation
in pdf format.
- Permanent
Magnet Motors and Their Applications - when you need high starting/acceleration
torque, linear speed-torque properties, and energy efficiency in a compact package,
permanent magnet DC motors are often the way to go
- Procedure for
Identifying Permanent Magnet DC Motors - DC Motor Overview, Permanent Magnet DC Motor
Equations and Transfer Functions, and Identification of DC Motor Parameters: Kb, Kt, R,
Jo, L, D, and Kf
- Weigh the
benefits of fuzzy-logic vs classical control in a disk-drive spindle - you can apply
fuzzy- and classical-control techniques to any servo-control loop, example on driving dc
3-phase, 12-pole spindle motor along with the driver electronics
Circuits
- 12V
or 24V DC Pulse Width Modulator - This circuit can be used as a light dimmer or DC
motor speed controller.
- A
Microcontroller Based Motor Speed Control - article with theory and circuit
- A
Microcontroller Based Motor Speed Control, Part 3 - This article describes a two DC
motor controller using 89C2051.
- Audio
amp makes efficient fan controller - with a simple modification, you can use an
audio-amplifier IC to control a fan module
- Boost
converter controls 12V fan from 5V supply - temperature-controlled PWM boost converter
allows operation of a 12V brushless dc fan from a 5V supply
- Circuit
generates fan-speed control - Fan noise is becoming a significant issue as electronic
equipment increasingly enters the office and the home. Noise is proportional to fan speed.
Consider this low-cost, self-contained analog circuit for fan-speed control. You can
easily adjust the circuit for any desired linear relationship between the fan voltage and
temperature.
- Circuit
forms dc-motor switch with brake - Controlling a small dc motor without speed control
sounds like a trivial task; a switch or a relay should suffice. However, several problems
accompany this approach. Thic circuit can be useful for designs that don't need precise
control of speed and stopping position but can benefit from enhanced deceleration.
- Circuits
provide 4- to 20-mA PWM control - are useful when you use 4- to 20-mA current-loop
signals to control a PWM signal
- Circuit
provides bidirectional, variable-speed motor control - During the development of
systems that include small motors, a simple, bidirectional motor controller with speed
adjustment may be helpful. This circuit is such a controller. A transistor-based H-bridge
allows two directions of rotation. A chopper controls the upper arms of the H-bridge,
thereby enabling the speed adjustment. This circuit is designed to work at voltages up to
15V, but can be adapted to higher voltages.
- Computer controller
for DC motors - This circuit is easy to build and use and it can control two DC motors
of any current or voltage rating, depending on the rating of the relays. The circuit also
provides two shaft encoders for positional feedback to the computer.
- DC Motor Speed
Controller - Control the speed of any common DC motor rated up to 100V (5A). Operates
on 5V to 15V. Uses NE556 to pulse-width modulate a high current switching power
transistor, TIP122. In this way motor torque is maintained. Adjustable speed control.
- DC Motor
Controller - controls small 2.5-7V motors, in pdf format, text in Finnish
- Digital
Speed Control for RC car - DC motor PWM controller that takes the 1ms to 2ms pulse
from the RC receiver and converts it into a pwm train at 1Khz
- Fan
controller adapts to system temperature
- H Bridge Motor control
- general introduction to H bridges
- H bridge switch for small
motors - simple switch circuit for reversing and stopping a motor without any control
of speed
- H-Bridge
Motor Driver - drives small DC motors up to about 100 watts or 5 amps or 40 volts
- MOSFET
switch provides efficient ac/dc conversion - suitable circuit for DC motor powering
from AC from transformer
- Motor
controller operates without tachometer feedback - used back-EMF for motor speed
controlling to make a voltage controlled motor speed controller
- Motor-control
scheme yields four positions with two outputs - This article shows how to position a
mechanical device into four discrete positions but with only two free outputs and one free
input from the control system. This circuit is designed for 24V-dc up to 2.5A motor that
comes with a worm gear.
- Nopeudensäädin
tuulettimelle - simle speed controller for PC fan, based on LM317, text in Finnish
- PCB Drill
Controller - uses a Pulse-Width-Modulation technique with current feedback to keep the
speed of cheap 12V PCB drills more constant
- PIC
Based Speed Controller - This a a controller which controls a small DC motor to two
directions at variable speed. The control signal for this circuit are normal RC servo
control pulses.
- Position
detectors provide motor-control logic - Optical sensors determine end of travel, and
an SPDT switch selects to which end to send the load.
- Programmable
source powers dc micromotors - a simple, economic, compact, and tricky way of using
the LM723 as a programmable voltage source to drive dc micromotors which can can set the
output to a value of 200 mV to 6V
- Pulse Width
Modulation DC Motor Control - controls the motor speed by driving the motor with short
pulses
- PWM
Motor/Light Controller - 12 or 24V pulse width modulator for light dimming or DC motor
controlling
- PWM Motor/Light
Controller by G. Forrest Cook
- PWM
Motor/Light Controller Variations - diagrams are for 12V operation and there are high
side (common ground) and low side (common +12V) versions
- PWM speed control -
includes theory and some example circuits
- R/C Switch
- This circuit is a so-called "Radio Controlled Electronic Switch". It can be
used to switch on/off anything electrical, whatever it is. Here are a couple of examples:
navigation lights, landing gear, sound systems, glowplug driver, bomb release, parachute,
search lights, gyros, and so on. This circuits connects to a RC car controller servo
output.
- Servo
pulse to PWM converter - attemps to be an interface to convert pulses from R/C
receiver to a dual PWM(Pulse Width Modulation) signal required by an H-bridge
- Simple PWM
controller - 555 timer based PWM motor control project for electric fan or other DC
motor
- Simple µC
acts as dedicated motor control - PIC16C84 circuit accepts control words from an 8-bit
digital bus and controls motor
Servo control is a closed loop control system for electric motors.
The motor used in servo control are usually DC motors (although AC servo is also
possible). The servo system uses a sensor to sense motor position/speed. Servo control has
a feedback circuit which changes the drive power going to motor according the control
input signals and the seignal from sensors. The opearating power fed to the motor is
usually controlled usign PWM method.
Servo control is usable over varietyof compled motion profiles.
Those may involve the following: control of either velocity and/or position; high
resolution and accuracy; velocity may be either very slow, or very high; and the
application may demand high torques in a small package size.
Because of the additional components such as feedback device
(usually encoder or tachometer), complexity is considered by some to be the weakness of
the closed loop approach. Those additional components add to the initial cost and
complexity of the control system.
A Servo is a small device that has an output shaft. This shaft can
be positioned to specific angular positions by sending the servo a coded signal. RC servo
motors are small motors used in radio controlled models (cars, planes etc.). The RC servo
motors itself have built in motor, gearbox, position feedback mechanism and controlling
electronics. Those RC servo motors can be controlled to move any position just by using
simple pulse controlling. The control pulse is positive going pulse with length of 1 to 2
ms which is repeated about 50-60 times a second. RC servo motors are available in various
sizes and with different specifications. The prices vary from motor model to model (this
kind of motors typically cost around 15-20 US dollars). Those RC servo motors generally
operate form nominally 4.8V power source (somewhat higher and lower voltages are usually
OK for those motor).
Servo motor shaft can positioned to specific angular positions by
sending the servo a coded signal (PWM pulse signal). As long as the coded signal exists on
the input line, the servo will maintain the angular position of the shaft. As the coded
signal changes, the angular position of the shaft changes.
RC servo motors very useful, besides their original use, in many
kinds of small robotics experiments because they ase small, compact and quite inexpensive.
The controlling scheme is very easy to impelement with some electronics or some computer
software. You can easily build a timer circuit using 555 timer chip for generating
suitable controlling pulses or you can use small microcontroller program to do that. Or
you can write a program to do that on your PC (need some real-time support from operating
system if you try this under some multitasking operating system).
- About.com
Guide to Radio Controlled Vehicles
- Centronics
port generates narrow pulse widths - Variable-pulse-width signals are useful in
control circuitry for positioning and holding purposes in robotics and power electronics.
Frequently, the need arises for pulses with width less than 1 msec. Delays less than 1
msec are usually not available in most programming languages, so generating such pulses
can be a problem. To generate a fractional-millisecond delay you can use a PC's 8254
16-bit timer (Counter 2), which normally controls the PC's speaker. The desired pulse is
available at the PC's Centronics port through a buffer stage, which protects the port from
overload damage.
- Controlling Hobby
Servos with 0-10 volts - Generally hobby servo's require a pulse having a variable
width from 1 to 2 milli seconds, with 1.5mSec as the center position. This schematic is a
simple voltage to pulse width circuit. It doesn't get more basic than this, all components
are fairly common. The main draw back is that this circuit is not real linear.
- Futaba
compatible servo tester 1 - simple RC servo motor tester/controller based on CD4001
- Hacking
a Servo by Kevin Ross - This document describes how servo motors work and hot to
convert a servo motor to a really nice compact gearhead motor with built in electronics.
- How RC Works -
This document gives view to a typical RC signal transmission.
- How Radio
Controlled Toys Work
- Parallel
Port Interface to Servos - includes example program for PC written in BASIC, also at http://ftp.cised.unina.it/pub/electronics/ftp.armory.com/SRVO/servopgm.bas
- Parallel Port Servo
Controller - gives you 256 different positions over the full range of the servo
- PIC
Based Serial Port Servo Controller - This Servo Controller uses a PIC16F84
microcontroller from Microchip to drive servo motors and digital outputs. It receives
commands from a host computer via a standard RS232 serial interface. This circuit supports
4 servo motors and 4 digital outputs. Circuit can be modified for 8 servo motors.
- PIC R/C
Servo Control Code
- RC Electronics Projects
- lots of projects published in the UK magazine Radio Control Models and Electronics
- R/C Web Directory
- Servo
Motor H-Bridge replacement - TTL driven from the TTL DIR level, based on 7404 ICs and
will provide about 150ma of current
- Servo Connector Wiring
& Command Chart - wirings and signal used with RC servo motors
- Servos
101 - basics of RC servo motor operation described
- Servo Lead
Pinouts
- Servo-Motor
101 - introduction to RC servo technology and some ideas for servo modifications
- Servo Motor Driver -
based on PIC16C71, kit from Amazon Electronics
- Servo tester -
to check the servo or speed controller without transmitter-receiver all you need is make
this simple tool
- Simple
555 based servon control circuit
- The
RC Transmission! - text explains what kind of signals are sent from the TX to the RX
of an "FM" radio control set, how they are decoded, and ideas about producing it
yourself
- Using
Servomotors with the PIC Microcontroller
- Various
Information on Servos - RC servo related information and circuits
- Various
Information on Servos - RC servo motor cross reference and example circuits
Stepper motors consist of a permanent magnet rotating shaft, called
the rotor, and electromagnets on the stationary portion that surrounds the motor, called
the stator. To move the rotor the electric magnets on the motor are activated in the right
order. Every change in this process moves the motor one step. The order in which those
electromagnets are activated determines the rotation direction.
For applications where precise measuring of a motors' rotor position
is critical, a stepper motor is usually the best choice. Stepper motors operate diffrently
from other motors; rather than voltage being applied and the rotor spinning smoothly,
stepper motors turn on a series of electrical pulses to the motor's windings. Each pulse
rotates the rotor by an exact degree. These pulses are called "steps", hence the
name "stepper motor".
Stepper motors are traditionally used in various motion control
applications. Stepper motors are quite easy to wire and control.Stepper systems are
economical to implement, intuitive to control, and have good low speed torque, making them
ideal for many low power, computer-controlled applications. They can be for example
interfaced to computer using few transitors and made to rotate usign a small piece of
software. Stepper motors provide a good position repeability. Stepper motors are video
used in robotics control and in computer accessories (disk drives, printers, scanners
etc.).
Stepper motors produce motion in discrete steps. Similar to
brushless DC motors, steppers usually have permanent magnets on the rotor and coils on the
stator with field movement provided by commutation from the power supply. Stepper motors
have a specified number of steps per revolution (typically around 200 steps/rev, or 1.8
degrees per step). Stepper motors are usually controlled by digital signals from the
controller to power drive, with one pulse corresponding to one step. Thus, the frequency
of the digital signals controls the speed of the motor. Thus, the frequency of the digital
signals controls the speed of the motor. Microstepping is an advanced control method
greatly increases the resolution of a stepper motor in applications where hevy high
resolution is needed (and added complexity is justified). Typical ways to control stepper
motor are:
- Single-Coil Excitation (Wave-drive): A-B-C-D sequence, lest power
used
- Two-Coil Excitation (Two-phase drive): AB-BC-CD-DA sequence, more
torque than Single-Coil Excitation
- Interleaved Single- and Two-Coil Excitation (Half-step):
A-AB-B-BC-C-CD-D-DA sequence, this runs the motors at half step resolution
Stepper motors have their limitations. They are available in limited
power (less than one horse power) and their rotation speed is limited (usually maximum
speed limit is about 2000 rpm). The energy effiency of stepper motors is low and stepper
motor systems have tendency to have resonances which needs to be avoided. Stepper motors
have characteristic holding torque (ability to hold the position) and pullout torque
(ability to move to the next position). Other torques can be difficult to achieve.
Therefore, precise torque control is difficult with steppers. Because of open-loop nature
of stepper motor controlling, they are not very good to be used with varying loads. It is
possible for a stepper motor to loose steps if it is loaded too much. Steppers are not
recommended for high-speed or high-power applications, or for applications requiring
precise torque control.
Tutorials
Technical information
- The Stepper Motor Archive
- The Stepper Motor Archive is an online database of stepper motor data including coil
winding diagrams and electrical and mechanical data. The motivation for such an archive is
simple: There are a many surplus stepper motors on market for which data sheets are often
hard to come by.
Stepper controllers
- First
Stepper Circuit - PIC based simple stepper controller
- Remote two
wire positioner - Send power to a remote stepper motor and also control its rotation
and speed over only two wires, pdf file
- Rotary
controller positions stepping motor - uses a servo potentiometer to provide the
necessary drive pulses for a stepping motor
- Stepper Motor
Controller - very simple and inexpensive circuit built from standard components and
can easily be adapted to be controlled by a computer
- Unipolar
Stepper Motor Driver kit - Drives any 5, 6 or 8 lead unipolar stepper motor. Based on
the UCN5804 IC. All features of this IC (direction, on/off, phase control & half step)
are brought out to SPDT PCB-mounted switches.Three run modes supported.
Computer interface for steppers
- A Worked
Stepping Motor Example - running stepper motors using PC parallel port and some
electronics
- Dual Stepper
Motor Controller - Connects to the PC printer port & will drive two stepper motors
up to max. 3A each. All contained in an extended D-shell case. Will also accept 4 inputs
from external switches. DOS
based software (including source) supplied to control motors and monitor inputs.
Software will run interactively or process a text file of commands. Software even allows
manual single stepping of motors.
- PC's
BIOS interrupt drives twin stepper motors - design idea for computer controlled
stepper motor system
- Slot machine sheet
stepper motor controls - Stepper motor driver stage for two stepper motors using two
L297 driver ICs. This circuit take control bits from computer parallel port or other I/O
port with TTL signals.
- Software for Stepper
Motor Control - Simple stepper motor controlling software examples using C, C++, Turbo
Pascal, Basic and MswLogo programming languages. This page has also link the the simple
motor driver hardware suitable for the software.
- Stepper Motor Control
program Step - Step is a little utility that allows you to drive up to two 4-phase
unipolar stepper motors connected to the parallel port. It can do absolute (to a certain
angular position) or relative (clockwise or counter- clockwise by a certain angle)
movement at every speed. Angles may be measured in steps, degrees or revolutions, and
movements can be in wave, two-phase, or half-step mode. This program is made for POSIX /
Linux systems. The program documentation includes also the driver hardware circuit diagram
and circuit board design.
- Stepper motors
- how to connect to pc and useful link collection
- Tonytronic Soft Robot -
circuit and software for controlling 16 steppermotors
Desing ideas
Tachometers are used to evaluate rotational speed, generally in
revolutions per minute. The contact units have a tip that is pressed to the center of the
end of a rotating shaft. As the shaft rotates, the tachometer spindle rotates and a gear
mechanism accumulates the number of rotations. Non-contact units utilize strobe lights,
laser light or infrared technolgy to sense the rotating speed of shafts. These have the
distinct advantage of allowing speed measurement without getting close to dangerous
rotating machinery.
A tacho generator is, essentially, a small p.m. motor which is
driven as a generator and which gives an output voltage which is accurately calibrated to
be a defined measure of the rotation speed. 'Accurate' implies expensive. However in most
applications high accuracy is not actually required so you can use a small motor as a
generator. Any calibration and scaling can be done in the electronic circuitry
Other popular method for determining motor speed is pulse rate
measutemeent. For this, a sensor measures the rotation of, for instance, a gear wheel.
Sensors are available which give an output pulse whenever a metal object passes them, so
these will give a train of pulses at a rate proportional to the rate of the gear teeth
passing th sensor. These pulses have to be fed into a 'frequency to voltage converter'
(FVC) which turns the pulse rate into a variable voltage which is used instead of the
signal from the tacho generator.
- Tacho generator
feedback information - This document has general information on tachno feedback and
other motor speed controlling methods.
- Tacho generator motor
speed feedback - This page is a bit different from most in that it covers the use of
tacho generators as feedback elements in motor control systems. This page covers tacho
generator rectifier circuit for 4QD Pro-120 electric motor controllers.
