r/c servo refresher - omfc servos refresher.pdf · r/c servo refresher ... 18. servo ‘speed’ to...
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Basic ServosOptional HornsOutput Horn
Horn Screw
Connector
Mounting Screws
Grommets
Mounting Screws
Eyelets (Brass)Mounting
lFlange
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Servo Components
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General OperationGeneral Operation
(Potentiometer)
(Pulse Width)(Pulse Width Error-based)Motor Drive Signal
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SpecificationsParameter Details
Type Analog (Standard), Digital, Brushless (Digital), Waterproof, Hi‐Res,Lo‐Profile, Retract (Non‐Proportional)Lo Profile, Retract (Non Proportional)
Hookup Standard, S‐Bus (Serial)
Connector JR, Futaba
M T B h d (3 P l ) C l B hlMotor Type Brushed (3‐Pole), Coreless, Brushless
Bearing Type Bushing, Ball (Single Top, Dual)
Gear Type Nylon, Metal (Steel, Titanium), Karbonite η = 90:1 to 370:1
Speed Travel Time (Sec)* @ 60° Travel
Torque oz‐in (kg‐cm)*
Travel Angular Rotational Range (Deg)Travel Angular Rotational Range (Deg)
Voltage* Regular (4.8‐6V), High‐Voltage (6‐7.4V)
Size Micro, Mini, Mid, Wing, Wing, Sail, Standard, Sport, Giant¼ Scale 1/5 Scale 1/8 Scale in (mm) L x W x H¼ Scale, 1/5 Scale, 1/8 Scale in (mm) L x W x H
Weight g (oz)5
Trends & DevelopmentsParameter TrendsLife 5x and up
R Reduced and Adjustable Deadband (Digital)Response j ( g )Slow Start Function
Internal Processing Serial Bus, Digital, Feedback, Programmable
Smoothness Higher ResolutionDigital Brushless Proportionality Linear, Differential, ‘Expo’, Mixing
Power Consumption Brushless vs. Brushed, Hi‐Voltage, Wide‐Voltage
Power Density Power Management Importance
Magnetics Higher Flux Density
Case Design Materials, Heat Dissipation, EMI Shielding
Motor Type Coreless, BrushlessMotor Type Coreless, Brushless
Sensor Hall Effect (Contactless)
Harness Hi‐Temp, Gauge, # of Strands
Lower Backlash Lo‐Inertia Hybrid Tooth Type
Digital BrushlessHall Effect Sensor
Gearing Lower Backlash, Lo‐Inertia, Hybrid, Tooth Type, Materials, Dry Film Lubrication
Bearing Ceramic, Needle
Slow Start Function
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Connector Types (Common)Futaba “J”• Keyed with a tab on signal end• Can work with JR/HiTEC if tab trimmed• Can work with JR/HiTEC if tab trimmed
Tab
JR / HiTEC “S”JR / HiTEC “S”• Known as ‘Universal’• Compatible with Futaba ‘J’
Airtronic “Z”Airtronic “Z”• Compatible with JR / HiTEC’
Airtronic “T” (Obsolete)• Reversed Polarity• Not compatible with any other types 7
Analog vs Digital•Looks for pulse within 0.02 sec (20 ms or 50 pulses/s)•Compares duration to prior pulse
Analog
Compares duration to prior pulse•If change in pulse duration > Deadband
position change•Lookup new angle and compare to currentR d l
Digital Brushless
•Rotate towards new angle •Stop when change in pulse duration ≤ Deadband
Digital•Same as Analog input signal•However ..
Internal Microprocessor
Digital
Internal MicroprocessorConverts signal to drive motor at ≈ 300‐400HzDuty Cycle (% on) remains the same
•Reduced Deadband Faster responsei h C i•Higher Power Consumption
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Analog vs Digital ResponseAnalog vs Digital Response
(Digital)
(Analog)
Reduced Deadband Higher Power & Current Consumption Higher Power & Current Consumption
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Servo Motor TypesBrushed Brushless
N-Poles(Iron Core) Brushed Coreless Brushless Coreless(Iron Core)
• Low Inertia, Fast Spin-up• Winding Geometry limit cogging
• Low Cost• Life is Brush Limited
• Thermal Mass and dissipation• High Efficiency• Winding Geometry limit cogging
• Efficient but Thermal Limits• Med Speed ≈ 9000 RPM
• Life is Brush Limited• Slower Response (Rotor inertia)• Mechanical
• High Efficiency• Long Life bearing limited (5x)• Highest Speed. 30% Faster Response• Quieter, Cleaner
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Position FeedbackPosition FeedbackMechanical Potentiometer Hall-Effect Sensor
Voltage Divider
Used in Brushless Motor Also
Sensor
• Analog• Range of travel is Limited• Life is Wiper and Element Wear Limited• Mechanical Losses• Vulnerable to Vibration
• Solid State• Requires Magnetic Field• Varies voltage in response to magnetic field • Travel Range not limited – Arbitrary ‘Zero’• Long Life, No mechanical contact, Low Torque
fVulnerable to Vibration
•Temperature Sensitive• Bulky, Miniature Versions used
• Requires processing of output to derive position• Used in Brushless Motor and Servo Output Shaft• Compact
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ProportionalityProportionality
C t l I t1.0
'Exponential'0% x Control Input
y Servo Output
f = 0% x = y (Linear)0.4
0.6
0.8
y)
0%25%50%75%100%‐25% f = 0% x = y (Linear)
f > 0% y = fx3 + (1-f)xf < 0% x = (1-f)y3 + fy0.0
0.2
0.4
Outpu
t (y 25%
‐50%‐75%‐100%
Actual Function:Cubic (x3 or y3) !
‐0.6
‐0.4
‐0.2
Servo
Known as:Steering Sensitivity fn
‐1.0
‐0.8
‐1.0 ‐0.8 ‐0.6 ‐0.4 ‐0.2 0.0 0.2 0.4 0.6 0.8 1.0
Control Input (x)12
LinearityLinearityDifferential Mixing
(50% Example)x Control Inputy Servo Output
0.6
0.8
1.0
y)
(50% Example)
Variable SlopesCoupling Mixes
% Diff i l0 2
0.0
0.2
0.4
o Outpu
t (y
• % Differential • Mixing• Dual Rates• Trim Steps‐0.8
‐0.6
‐0.4
‐0.2
Servo
Trim Steps• Tx Options• Mechanical also
‐1.0‐1.0 ‐0.8 ‐0.6 ‐0.4 ‐0.2 0.0 0.2 0.4 0.6 0.8 1.0
Control Input (x)
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Accessories
ReversersS h i M i T Servo SaversSynchronizers Mounting Trays Servo Savers
Parallel Rigs for Large Scale
Billet HornsLead ExtensionsSi l
Gear Sets & Bearingsg
Signal Boosters& Safety Clips
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Tools
Analog Servo TestersDigital Servo Field Programmers
• Digital Servos have flash memory and μP• Programmable Features
Adjustable Response (Deadband Width)• Adjustable Response (Deadband Width)• Direction, Speed & Proportionality• End Points and Neutral Point• Fail-Safe
Factory Default Resets
Digital Servo Bench Programmers
• Factory Default Resets
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Handy Accessories
Servo DriversS i (L/G D )
RC Switches• Sequencing (L/G Doors)• Flash Program (Windows Based)• 6, 12, 18, 24 Servos
• Simpler than Servos & switch• Multi‐switch on Single channel
‘Servo‐Less’ Options• Electric L/G, stall protected/ , p•Solenoid Actuators / Latches• Ignition Kill (Opto) Switches
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Power Management OptionsPower Management Options
•Battery Redundancyy y•Supply Isolation•Power Conditioning•Component failure isolation•Component failure isolation
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TorqueTorque = Force x Distance
Units: 1 oz-in0.072008 kg-cm
1/16 in lb1/16 in-lb0.007064 N-m
Conversions:
1 lb = 16 oz1 kg = 2.204623 lb1 in = 2 54 cm1 in = 2.54 cm1 kg = 9.81 N (@ 1G or 9.81 m/s2)1 m = 100 cm
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Servo ‘Speed’ to RPMrpm
Arev
Arevs
sAA 10
min110
3601
min16060
60sec
Example: HiTEC P/N HS‐425BB @ 6.0v
rpmrpm 5.6216.0
1060sec16.0
Voltage (V) sec/60° RPM
4.8 0.70 ‐ 0.06 14 ‐ 167
6.0 0.62 ‐ 0.06 18 ‐ 167
7.4 0.17 ‐ 0.05 59 ‐ 200
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PowerPower = Torque x Speed (Watts)
sec312
sec60min1
min1010
60sec rad
Arevradrev
ARPM
AASpeed
NmBinoz
NminozBTorque 007064.0.1
007064.0.
radA
NmBSpeedTorquePower sec3
007064.0
WattsABPower 0023547.0
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Futaba®Torque vs SpeedD @4 8V O l
160
180
3‐P
5‐P
Data @ 4.8V Only
120
140 5 P
B/L
C/L
60
80
100
RPM
20
40
60
0
20
0 50 100 150 200 250 300
Torque (Oz‐In)21
Futaba®Analog vs Digital
160
180
Analog
Data @ 4.8V Only
100
120
140
M
Analog
Digital
60
80
100
RPM
20
40
60
00 50 100 150 200 250 300
Torque (Oz‐In)q ( )
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Futaba®Power Output12
Power Output
Analog
Data @ 4.8V Only
8
10
ut (W
)
Digital
4
6
wer Outp
2
Pow
00 50 100 150 200 250 300
Torque Output (oz‐in)
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Handy LinksHandy LinksLink Details
www hansenhobbies com Servo Wire Connectors and Toolswww.hansenhobbies.com Servo Wire, Connectors and Tools
www.rc‐base.com RC Database (Parts and Accessories Data)
www.servodatabase.com Servo Specifications and Reviews
www.servocity.com Servo Products
www.pololu.com Servo Controllers, Switches and Electronics
www.powerbox‐systems.com PRC Power Systems
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