900-00008 Datasheet by Parallax Inc.

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Parallax Continuous Rotation Servo (#900-00008)

The Parallax Standard Servo is ideal for adding bidirectional continuous rotation to your robotics projects.

Features

 Bidirectional continuous rotation

 0 to 50 RPM, with a linear response to PWM for easy

ramping

 Accepts four mounting screws

 Easy to interface with any Parallax microcontroller or

PWM-capable device

 Very easy to control with the PULSOUT command in

PBASIC or SX/B

 Weighs only 1.50 oz (42.5 g)

 38 oz-in torque @ 6 V

Key Specifications

 Power requirements: 4 to 6 VDC; Maximum current draw

140 +/- 50 mA at 6 VDC when operating in no load conditions, 15 mA when in static state

 Communication: pulse-width modulation

 Dimensions: approx 2.2 x 0.8 x 1.6 in (5.58x 1.9 x 4.06 cm) excluding servo horn

 Operating temperature range: 14 to 122 °F (-10 to +50 °C)

Quick-Start Circuit

Vµ = microcontroller voltage supply

Vservo = 4 to 6 VDC, regulated or battery

I/O = PWM TTL or CMOS output signal, 3.3 to 5 V; < Vservo + 0.2 V

Continuous Rotation Servo Microcontroller

GND

Vservo

White

Vss

I/O

Red

Black

Vdd

Vµ

Device Information

The Parallax continuous rotation servo relies on pulse width modulation to control the rotation speed and

direction of the serv o shaft. Before u sing the servo in a project, it is important to c alibrate the center

position of the servo in order to defi ne the pul se width value at which the servo holds still (see the

section Calibration – "Center" the Servo on page 4).

Specifications

Pin Name Description Minimum Typical Maximum Units

1 (White) Signal Input; TTL or CMOS 3.3 5.0 Vservo + 0.2 V

2 (Red) Vservo Power Supply 4.0 5.0 6.0* V

3 (Black) Vss Ground 0 V

*See Board of Education Servo Header Connection Diagram.

Power Precautions

 Do not use this servo with an unregulated wall-mount supply. Such powe supplies may deliver

variable voltage far above the stated voltage.

 Do not power this servo through the BASIC Stamp® Module's Vin pin, this can deliver voltages

above the stated voltage. See the Board of Education Connection Diagram below for jumper

settings.

 Servo current draw can spike while under peak load; be sure your application's regulator is

prepared to supply adequate current for all servos used in combination.

Board of Education Servo Header Connection Diagram

When connecting the servo to the Board of Education® servo header, be sure the jumper is set t o Vdd

(regulated 5 VDC for this board) as shown in the figure below. Failure to place the jumper at this setting

can cause damage your servo! (Note: see the Board of Education product documentation for instructions

regarding earlier board revisions that do not have a servo header with a jumper.)

Black

Red

X4 X5

15 14 13 12

Vdd

Vin

Using a Separate Power Supply on a HomeWork Board

The BASIC Stamp HomeWork Board uses a 9 V battery for a power supply. A servo can drain a fresh 9 V

battery in under 20 minutes! Foll ow these direc tions to build two servo p orts on the breadboard, and

power them with a separate battery pack.

Hardware Required

(1) BASIC Stamp HomeWork Board (serial #555-28158 or USB #555-28188)

(1) Battery pack with tinned leads (Parallax #753-00001)

(2) Parallax continuous rotation servos

(2) 3-pin male-male headers (Parallax #451-00303)

(4) Jumper wires (10-pack: Parallax #800-00016

(4) 1.5 V AA batteries

Red Red 192

√ Disconnect the 9 V battery from the board, and do not put the AA batteries in their holder yet.

√ Build the servo ports shown by the schematic and wiring diagram below.

√ Double-check to make sure the black wire with th e white stripe is connected to Vbp, the solid

black wire is connected to Vss, and that all the connections for P13, Vbp, Vss, Vbp (another one),

and P12 all exactly match the wiring diagram.

√ Connect the servo plugs to the male headers on the right side of the wiring diagram.

√ Connect the 9 V battery, and insert the AA batteries into their holder.

Vbp

Vss

P12

White

Red

Black

Vbp

Vss

P13

White

Red

Black

P15

P14

P11

P10

P9

P8

P13

P12

X3

Vdd VssVin

(916) 624-8333

www.parallaxinc.com

www.stampsinclass.com

Rev B

P15

P14

P11

P10

P9

P8

P13

P12

X3

Vdd VssVin

(916) 624-8333

www.parallaxinc.com

www.stampsinclass.com

Rev B

Port connections Servo connections by wire color

 P13

 Vbp

 Vss

 Vbp

 P12

Battery pack

solid black

wire = ground

Battery

pack black

wire with

white stripe

= Vbp

Vbp stands for Voltage battery pack.

It refers to the 6 VDC supplied by the four 1.5 V

batteries. This is brought directly to the breadboard to

power the servos for Boe-Bots built with the HomeWork

Board. Your BASIC Stam p is still powered by the 9 V

battery.

 White

 Red

 Black

 Red

Whi

te

HomeWork Board with

servo ports built on the

breadboard, with a separate

battery pack power supply

for the servos.

T T To center the servo, program your h 20 ms. Sample calibration code is P8X32A microcontroller, and SX/Bf product page at www.parallax.c0m. For centerlng Parallax Continuous Rotation Servo Sends a 1‘5 ms pulse approx everu 2% ms )) iclkmode = xtall t pllle ' System clock 4 8% MHz

Calibration – "Center" the Servo

The servo has a pot entiometer access port, right above the plac e where the cable attaches to the case.

The port allows the user to adjust the servo to hold completely still when receiving a 1.5 ms pulse width.

This is the value in the "center" of the range of control pulses the servo will accept.

To center the servo, program your host device to deliver a 1.5 ms pulse, continually refreshed ever y

20 ms. S ample calibration code is giv en below f or all BASIC Stamp model s, Spin for the Propeller ™

P8X32A microcontroller, and SX/B for the SX chip. All are avail able for downl oad from th e 900-00008

product page at www.parallax.com.

Connect the servo to your microcontroller's I/O pin. The example programs below specify an I/O pin.

BASIC Stamp Calibration Code - for all BS2 models

√ Connect the servo to BASIC Stamp 1/O pin P12, or update the ToServo PIN declaration.

√ Run the program, and gently twist the potentiometer adjustment screw until the servo does not

turn or vibrate.

NOTE: Calibrating the servo may take some patience. The potentiometer is very

sensitive so a very light touch will be required.

' CenterParallaxCrServo.bs2

' {$STAMP BS2}

' {$PBASIC 2.5}

#SELECT $Stamp

#CASE BS2, BS2E, BS2PE ' PULSOUT Duration units are 2 us for these models

Center CON 750

#CASE BS2SX, BS2P, BS2PX ' PULSOUT Duration units are 0.8 us for these models

Center CON 1875

#ENDSELECT

ToServo PIN 12 ' connect servo to I/O pin P12, or change it here

DO

PULSOUT ToServo, Center ' ToServo pin outputs 1.5 ms pulse

PAUSE 20 ' refresh pulse every 20 milliseconds

LOOP

Propeller Chip Calibration Code – for P8X32A

√ Download and unzip the Propeller code file from the 900-00008 product page.

√ Connect the servo signal pin to Propeller I/O pin P0.

√ Run the program CenterParallaxServo.spin, and gently twist the potentiometer adjustment screw

until the servo does not turn or vibrate.

NOTE: Calibrating the servo m ay take some p atience.

The potentiometer is very sensitive so a very light touch will be required.

{{ CenterParallaxServo.spin

For centering Parallax Continuous Rotation Servo

or holding Parallax Standard Servo at 90° position.

Sends a 1.5 ms pulse approx every 20 ms }}

CON

_clkmode = xtal1 + pll16x ' System clock → 80 MHz

_xinfreq = 5_000_000 ' Using 5 MHz external crystal oscillator

servoPin = 0 ' Servo signal to this I/O pin-change if needed

PUB CenterServo | tInc, tc, tHa, t

ctrsEB‘ .ﬂ] 1= servoPm d1rs[servoP1n]~~ ‘ Set up cgcle and hlgh Klmes tHa := tInc . 15am repeat ' Repeat PHM signal t t: tt ' Calculate next cycle repeat Parallax Con direction are romtion, d servo: Vdd \lss Vdd (5 V) V35 (0 V)

ctra[30..26] := %00100 ' Configure Counter A to NCO

ctra[8..0] := servoPin

frqa := 1

dira[servoPin]~~

' Set up cycle and high times

tInc := clkfreq/1_000_000

tC := tInc * 21_500

tHa := tInc * 1500

t := cnt ' Mark counter time

repeat ' Repeat PWM signal

phsa := -tHa ' Set up the pulse

t += tC ' Calculate next cycle repeat

waitcnt(t) ' Wait for next cycle

Communication Protocol

The Parallax Continuous Rotation Servo is controlled through pulse width modulation. Rotational speed

and direction are determi ned by the d uration of a high pulse, i n the 1.3– -1.7 ms range. In order for

smooth rotation, the servo needs a 20 ms pause between pulses. Below is a sample timing diagram for a

centered servo:

As the length of the pulse decreases from 1.5 ms, th e servo will gradually rotate faster in th e clockwise

direction, as can be seen in the figure below:

Likewise, as the length of the pulse increases from 1.5 ms, the servo will gradually rotate faster in the

counter-clockwise direction, as can be seen in the figure below:

Vdd (5 V) V55 (0 V) 4— 1.7ms <— 17="" ms=""><— 20ms="" —=""> T ﬁ

Voltage and RPM: Maximum RPM will vary with input voltage; 50 RP M @ 5 V is typical. Using

regulated Vdd as the sup ply source will reduce fluct uations in RPM for a given pulse width that might

otherwise occur with unregulated battery supplies.

BASIC Stamp® Programming Examples

PBASIC has a PULSO UT command that sets the I/O

to an output and sends a pulse of the specified

Duration

. Since the servo needs this pulse refreshed every 20 ms for continuous operation, the PULSOUT

command is put in a coun ted FOR…NEXT loop to su stain continuous operation for the speci fied number

of cycles.

PULSOUT

,

Duration

Different BASIC Stamp m odules use different units for the P ULSOUT command's

Duration

argument.

When adapting BS2 code to another BASIC Stamp model, you may need to make adjustments. The table

below lists the PULSOUT ranges for each BASIC Stamp microcontroller. See the BASIC Stamp Manual or

BASIC Stamp Editor Help for more information.

BASIC Stamp Model 1.3 ms

(Full speed clockwise) 1.5 ms

(Center, no rotation) 1.7 ms

(Full speed counterclockwise)

BS1 130 150 170

BS2, BS2e, BS2pe 650 750 850

BS2sx, BS2p, BS2px 1625 1875 2125

The example shown below for a BASIC Stamp 2 causes a servo connected to BASIC Stamp 1/0 pin 12 to

first rotate full-speed counterclockwise for about 3 seconds, hold still f or about 3 seconds, and then

rotate counterclockwise for about 3 seconds.

' RotateParallaxCrServo.bs2

' {$STAMP BS2}

' {$PBASIC 2.5}

counter VAR Word

servoPin PIN 12 ' change I/O pin for servo signal here

FOR counter = 1 TO 100 ' Rotate counterclockwise for ~3 seconds

PULSOUT servoPin, 850

PAUSE 20

For more examples w Roboﬁts wﬂh bﬁeﬁ www.garallax.com. hold sull 2 sec, and then counterclockmse full speed for 2 sec. )) iclkmode = xxall t pllle ' Sgstem clock ~ 8% MHz servoPin = ﬂ ' Servo slgnal to thls I/O pin-change 1f needed d1ra[servoPm]~~ tInc i= clkfreq/liﬂﬂﬂiﬂﬂﬂ ' 1 ps increment tEw = tInc ' 13%E ' Elockwlse fast = 1.3 ms t = cnt ' Mark counter time phsa == -th ' Set up clockmse fast pulse

FOR counter = 1 TO 100 ' Hold still for ~3 seconds

PULSOUT servoPin, 750

PAUSE 20

PULSOUT servoPin, 650

PAUSE 20

For more examples with the BASIC Stamp 2, incl uding 2-wheeled robot maneuvers and ramping, see

Robotics with the Boe -Bot

Chapter 4 , available for free downl oad from the 28132 product page at

www.parallax.com.

Propeller™ P8X32A Application

The program below uses counter modules to rotate the servo first clockwise at full speed for 2 seconds,

then rests for 2 seconds, and rotates counterclockwise at full speed for another 2 seconds. This code can

also be downloaded from the 900-00008 product page.

{{ ServoContinuousRotation.spin

Turn Parallax Continuous Rotation Servo clockwise full speed for 21 sec.

hold still 2 sec, and then counterclockwise full speed for 2 sec. }}

CON

_clkmode = xtal1 + pll16x ' System clock → 80 MHz

_xinfreq = 5_000_000 ' Using 5 MHz external crystal oscillator

servoPin = 0 ' Servo signal to this I/O pin-change if needed

PUB CenterServo | tInc, tc, tCtr, tCw, tCcw, t

ctra[30..26] := %00100 ' Configure Counter A to NCO

ctra[8..0] := servoPin

frqa := 1

dira[servoPin]~~

tInc := clkfreq/1_000_000 ' 1 μs increment

tC := tInc * 21_500 ' Low pulse

tCtr := tInc * 1500 ' Center pulse = 1.5 ms

tCw := tInc * 1300 ' Clockwise fast = 1.3 ms

tCcw := tInc * 1700 ' Counter-Clockwise fast = 1.7 ms

t := cnt ' Mark counter time

repeat 100 ' Repeat PWM signal 100x

phsa := -tCw ' Set up clockwise fast pulse

t += tC ' Calculate next cycle repeat

waitcnt(t) ' Wait for next cycle (20 ms)

repeat 100 ' Repeat PWM signal 100x

phsa := -tCtr ' Set up the center pulse

t += (tC + 200) ' Calculate next cycle repeat

t v: (tC - 2%) ' Calculate next cgcle repeax

waitcnt(t) ' Wait for next cycle (20 ms)

repeat 100 ' Repeat PWM signal 100x

phsa := -tCcw ' Set up counter-clockwise fast pulse

t += (tC - 200) ' Calculate next cycle repeat

waitcnt(t) ' Wait for next cycle (20 ms)

Revision History

Version 2.1: corrected values in BASIC Stamp Model PULSOUT table; updated example programs to use a

constant for the servo pin.

Version 2.2: added Voltage and RPM note on p age 6. Added Usin g a Separate Power Supply on a

HomeWork Board section beginning on page 2. Updated specifications.

900-00008 Datasheet by Parallax Inc.

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