FUTABA RS204MD User manual

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1M23Z06502
User’s Manual Ver.1.04
RS204MD
Command Type Servo for Robot
Instruction Manual
Caution
・Read this instruction manual before use.
・Keep this manual handy for immediate reference.
For models

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1. FOR SAFETY .......................................................................................................................................... 5
WARNING SYMBOLS................................................................................................................................................5
CAUTIONS FOR USE................................................................................................................................................5
CAUTIONS FOR STORAGE........................................................................................................................................6
2. INTRODUCTION...................................................................................................................................... 7
COMPONENTS.........................................................................................................................................................7
FEATURES .............................................................................................................................................................8
●Small and Lightweight .......................................................................................................................................8
●Interactive High-Speed TTL Communication ...................................................................................................8
●Servos for Both Command Type and PWM Type ..............................................................................................8
●Feedback(Only as Command Type) ..........................................................................................................................8
●Compliance Control ............................................................................................................................................8
●Calibration ..........................................................................................................................................................8
●Wiring from the Output Shaft............................................................................................................................8
●Horn with a mark for the reference position.....................................................................................................8
PART NAMES /HANDLING INSTRUCTIONS ............................................................................................................9
HOW TO ATTACH THE SERVO.................................................................................................................................10
PIN ASSIGNMENT OF THE CONNECTOR ................................................................................................................11
COMMUNICATION SETTINGS ................................................................................................................................11
DEFINITION OF ANGLE AND ITS RANGE................................................................................................................14
●Definition of “0 degrees” and operational range............................................................................................14
●Dead Zone(undetectable range) .......................................................................................................................14
3. CONNECTIONS...................................................................................................................................... 15
SYSTEMS ..............................................................................................................................................................15
●Systems as Command-Type Servos .................................................................................................................15
●Systems as PWM Type Servos .........................................................................................................................16
NOTES OF CONNECTION.......................................................................................................................................17
4. CONTROL ............................................................................................................................................... 19
ABSTRACT ............................................................................................................................................................19
●Switch of Command-Type and PWM-Type ......................................................................................................19
●Communication Protocol (TTL Command-Type).............................................................................................19
●Control as PWM-Type Servos...........................................................................................................................19
●Memory Map .....................................................................................................................................................20
●Servo ID ............................................................................................................................................................20
●Packet................................................................................................................................................................20
●Short Packet.................................................................................................................................................20

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●Long Packet..................................................................................................................................................20
●Return Packet ..............................................................................................................................................20
FORMAT OF PACKETS............................................................................................................................................21
●Short Packet......................................................................................................................................................21
●Long Packet ......................................................................................................................................................25
●Return Packet ...................................................................................................................................................27
MEMORY MAP ......................................................................................................................................................28
4.1. Invariable ROM Area..............................................................................................................................28
●No.0/No.1 Model Number(2 Byte, Hex, Read) ............................................................................................28
●No.2 Firmware Version(1Byte, Hex, Read) ...................................................................................................28
4.2. Variable ROM Area .................................................................................................................................29
●No.4 Servo ID (1Byte, Hex, Read/Write) .....................................................................................................30
●No.5 Servo Reverse(1Byte, Hex, Read/Write) .............................................................................................30
●No.6 Baud Rate(1Byte, Hex, Read/Write) ...................................................................................................30
●No.7 Return Delay(1Byte, Hex, Read/Write) ..............................................................................................31
●No.8/No.9/No.10/No.11 Angle Limit (2 Byte, Hex, Read/Write)......................................................................32
●No.14/ No.15 Temperature Limit(2 Byte, Hex, Read) ..................................................................................32
●No.22 Torque in Silence(1 Byte, Hex, Read/Write, for PWM) ....................................................................33
●No.23 Preparation Time (1 Byte, Hex, Read/Write, for PWM)...................................................................33
●No.24 / No.25 Compliance Margin (1 Byte, Hex, Read/Write) ........................................................................34
●No.26 / No.27 Compliance Slope (1 Byte, Hex Read/Write) ............................................................................34
●No.28 / No.29 Punch (2 Byte, Hex, Read/Write) ..............................................................................................34
4.3. Variable RAM Area .................................................................................................................................36
●No.30 / No.31 Goal Position (2 Byte, Hex, Read/Write）............................................................................37
●No.32 / No.33 Goal Time (2 Byte, Hex, Read/Write）.....................................................................................37
●No.35 Maximum Torque (1 Byte, Hex, Read/Write) ...................................................................................38
●No.36 Torque Enable (1 Byte, Hex, Read/Write）...........................................................................................38
●No.38 PID Coefficient (1 Byte, Hex, Read/Write）.......................................................................................39
●No.42 / No.43 Present Position (2 Byte, Hex, Read) ...................................................................................39
●No.44/No.45 Present Time (2 Byte, Hex., Read) .............................................................................................40
●No.46/No.47 Present Speed (2 Byte, Hex, Read).............................................................................................41
●No.48/No.49 Present Current (2 Byte, Hex, Read)..........................................................................................42
●No.50/No.51 Present Temperature (2 Byte, Hex, Read) .............................................................................43
●No.52/No.53 Present Voltage (2 Byte, Hex, Read) ......................................................................................44
5. REFERENCES ........................................................................................................................................ 45
SPECS ...................................................................................................................................................................45
.DIMENSIONS.......................................................................................................................................................45
●RS204MD ..........................................................................................................................................................46
●Dimensions with Servo Horn and Free Horn..................................................................................................47

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●Servo Horn and Free Horn for RS20x/RS30x ..................................................................................................48
OPTION PARTS......................................................................................................................................................49
HOW TO USE “BRACKET”......................................................................................................................................51
●Fixing Brackets to RS204MD...........................................................................................................................51
●Jointing Other Parts/Servos.............................................................................................................................51
●Usage of Brackets .............................................................................................................................................52
●Dimensions with Brackets ...............................................................................................................................52
DIMENSIONS OF TERMINAL BOARD......................................................................................................................53

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1. FOR SAFETY
To use this product safely, please pay your full attention to the followings.
Be sure to read this instruction manual prior to using this product.
Warning Symbols
The warning symbols used in this text are defined as follows:
Indication Meanings
Danger Indicates a hazard that will cause severe personal injury, death,
or substantial property damage if the warning is ignored.
Warning Indicates a hazard that can cause severe personal injury, death, or substantial
property damage if the warning is ignored.
Caution Indicates a hazard that will or can cause minor personal injury, or property
damage if the warning is ignored
Symbols: :Prohibited :Mandatory
Cautions for Use
Caution
Do not disassemble or alter the servo.
Otherwise, it may cause breakage in the gear box, fire on the servo or explosion of
the battery.
Do not use any battery as a power supply other than the specified battery.
The product is designed to be operated by Futaba’s 9.6V Ni-MH battery only. Do not
use any other batteries.
Do not touch the servo case during or some time after operating the servo.
Otherwise, you may get burned on the finger as the motor or electronic circuit in the
servo gets very hot.
Do not let the servo get covered with sandy dust or water.
Otherwise, the servo may stop moving or have a short circuit. The servo is not
designed to be waterproof or dust-proof.

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Do not use this product for any application other than indoor hobby-robots.
Futaba is cleared of all responsibility to the results caused by the usage of this
product for any application other than indoor hobby-robots.
Do not turn the servo horn forcibly.
Otherwise, the servo will be damaged.
Do not leave the servo locked.
If the servo continues to be locked due to a strong external force, it may cause smoke,
fire or damage.
Cautions for Storage
Caution
Do not store the servos in the following conditions.
Places where the temperature is over 60℃or below －20℃.
Places where the Sun directly shines over the servos.
Places where it is very high in humidity.
Places where there is a strong vibration.
Places where there is a lot of dust.
Places where static electricity tends to be induced.
Places where infants can reach.
◆Storing the servos in the places shown above may cause deformation and failure of the servos, or
hazard.

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2. Introduction
Components
The following parts are included in RS204MD.
Please refer to p.50 “Optional parts”for optional parts and repair parts.
●1) Servo(RS204MD) x1
2) Servo Horn x1
3) Screw to fix servo horn x1 (M2x8 Tapping Screw)
*Servo Horn and Screw are attached to the servo.
●4) Cable (ADH-Connector, 70mm) x1
●5) Free Horn (Same as for RS30x) x1
●5) USAGE PRECAUTION x1

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Features
RS204MD is specially designed for robotic applications, having the following features.
●Small and Lightweight
RS204MD is small and lightweight servos specially designed for robots, which are 12g respectively.
●Interactive High-Speed TTL Communication
TTL bi-directional communication of a maximum baud rate of 230kbps is possible and is
used for the communication between the robot’s processor and servos.
●Servos for Both Command Type and PWM Type
RS204MD can be controlled either as the Command Type Servo for robots or the PWM Type Servo for
existing R/C servos. The type is automatically switched by the first signal sent after these products are
connected.
●Feedback(Only as Command Type)
Information of sensors on the servo such as the position, load, temperature, electric current, and the
alarm situation, etc. can be obtained via TTL communication.
●Compliance Control
With this feature, the movement of the RS204MD is controlled in accordance with the distance between
the present and target positions. This enables the robot to move very smoothly without trembling its
arms and legs and to absorb turbulence from an external force.
●Calibration
Angular position of every servo is calibrated by our standard gauge before their shipment. Even if
another RS204MD servo is employed, it does not require any bothersome work for adjusting its angular
position.
●Wiring from the Output Shaft
In order to avoid wires becoming entangled during operation, they are drawn out from the rear of the
output shaft. Another shaft is installed on the bottom case to make the center impeller structure easy to
construct.
●Horn with a mark for the reference position
凹marks are placed on the circumference of the servo horn in order to make sure the reference position
even after being built in. (one 凹for 0°position, two 凹s for 90°position, three 凹s for 180 position
and four 凹s for 270°position)

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Part Names / Handling Instructions
Fig. 2.1 Part Names
Caution
Do not remove screws to fix cases of the servo unless repair or replacement is needed.
When removing all case fixing screws, be careful not to get dust or foreign matter inside the case.
Route the cable through the free horn hole in the bottom case when using the Inward-Connector.
Bending cables strongly will cause disconnection and/or short circuit.
Output-Axis
Screw to fix cases of the servo
Free Horn
Servo Horn
Connector(Outward)
Connector (Inward)
Screw to fix cases of the servo and other parts.

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How to attach the servo
Remove some of the screws of RS204MD and use its hole to fix the servo to brackets or other frames.
Refer Fig. 2.2 for the depth of each hole.
1.8mm from each Reference-Surface of Hole (A) is Clearance Hole.
Fig. 2.2 Screw Depth
Fig. 2.3 Reference for the length of the screw to fix other parts.
Other Parts (Plate)
t=1.0mm
Hole to fix cases and other parts.
Screw Depth: up to 7mm from each Reference-Surface
*1.8mm from each Reference-Surface is Clearance Hole.
Hole to fix other parts.
Screw Depth: up to 2.5mm
Tapping Screw:1.2×5mm
(Option No.BS3472)
Tapping Screw : 1.2×3.5mm
(Option No.BS3471)
Do NOT
remove
Reference-Surface
Reference-Surface

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Pin Assignment of the Connector
The pin assignment of the connector of RS204MD is shown in Fig. 2..
Connector: ADH connector, J.S.T. Mfg. Co., Ltd.
a. Connector of the cable
b. Connectors of the servo
Fig. 2.4 Connector Pin Assignment
Communication Settings
Set your Communication parameters as follows:
Baud Rate : 115.2 [kbps](9.6[kbps]～230.4[kbps], refer p.30)
Data bit length : 8 [bit]
Parity : None
Stop Bit : 1 [bit]
Flow Control : None
③（Gray）：Signal
②（Black）：VCC(3.7-6.0V)
①（Black）：GND
①(Black）：GND
②（Black）：VCC
③（Gray）：Signal
③（Gray）：Signal
②（Black）：VCC
①（Black）：GND

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Installing/Unplugging the connector
When installing the connector, be careful not to apply excessive force to the board.Also, when
unplugging, grasp the cable and pull it out slowly.
Fig. 2.5 Installing/unplugging the connector
①Installing the connector
Push the connector from upside.
②unplugging the connector
Hold the cable and pull it upward slowly.
*Do NOT pull the cable horizontal.

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Routing the cable
Remove the bottom case before routing the cable through the hole for Free-Horn (When using the
Inward-Connector).
Fig. 2.6 Routing the cable
Caution
・Use Phillips #1 screwdriver.
・Do NOT overtighten the screws.
・Do NOT pinch the cables.
・Do NOT damage the circuit-board.
①Remove the screws
and Bottom Case.
③Install the Connector.
②Route the cable through the
hole of the Bottom Case.
④Re-Assemble the Bottom
Case and screws.
⑤Finish.

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Definition of Angle and its Range
●Definition of “0 degrees”and operational range
“0 degrees”and directions(+/-) of RS204MD are defined as fig. 2.7.
Operational range (for Goal Position) is 0±150deg, and Detectable range (for Present Position) is 0±
160 deg.
fig. 2.7 Definition of Angle
●Dead Zone(undetectable range)
The range of more than +160 degrees to less than -160 degrees in fig. 2.7 is undetectable area (“Dead
Zone”) of internal angle sensor.
When in this range, ”Present Position”(p.39 エラー! ブックマークが定義されていません。) will be
“555.5” and “Torque Enable”(p.38) will be “00H”(Torque-OFF).
To turn on the torque again, please move output-axis to Operational Range then send Torque-ON
command.
You can rotate the output-axis by hand beyond the Dead Zone since there is no mechanical limit
(stopper) on the 160 degrees and -160degrees, but please keep in mind that passing the dead zone
frequently, such as continuously rotating the output shaft, will damage the angle sensor and may be
shorten its life.
＋150deg.
Dead Zone
＋160deg.
Operational Range
(+)
Detectable Range
(+)
Operational Range
(-)
Detectable Range
(-)
－150deg.
－160deg.
0 deg.

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3. Connections
Systems
Systems of the robot with RS204MD are follows.
●Systems as Command-Type Servo
Systems with RS204MD as Command-Type Servos are shown in bellow:
Fig. 3.1 System with Command-Type Servos
To Control RS204MD as Command-Type Servo with USB-RS485 Converter “RSC-U485” etc., Power
Hub “TB-RV71EH 7.4V/3W”is required somewhere in the system.
The maximum number of RS204MD to be connected as TTLCommand-Type Servos is 24.
When these products are used together with RS485 Command-Type Servos, the maximum number of
the RS485 Command-Type Servo is 4.
Please note that when the Command-Type Servos are used together exceeding the maximum number,
the servos may malfunction.

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●Systems as PWM Type Servo
Fig. 3.2 Systems with PWM Type servo
Please note that the servos made by Futaba Corporation may malfunction, depending on the
specification of the controller used for PWM servos.

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Notes of Connection
RS204MD may malfunction, depending on the system configuration if they are used as TTL command
Type Servo.
Fig. 3.3 TTL Command-Type Servo / Example of Disabled Connection (1)
RS485 Command Type Servos do not work if they are connected via the Hub for 3 Wire Servo.
When both RS485 Command Type Servos and TTL Command Type Servos are used in the same system,
it is required not to create any part where three wires are placed on the route to the RS485 Command
Type Servos from a processing unit (or, USB-RS485 converter).

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Fig. 3.4 TTL Command-Type Servo / Example of Disabled Connection (2)
The servos may malfunction if more than one Hub with Power Switch for TTL Command Type Servo
(RV71EH-7.4V/3W) is connected in the same system.

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4. Control
Abstract
●Switch of Command-Type and PWM-Type
RS204MD can be controlled either as the Command-Type Servo of PWM-Type Servo.
Which Type will be applied is automatically decided by the first signal sent after the power is turned on.
The Type once decided never changes until the power is turned off.
When RS204MD is controlled by PC etc. via RSC-U485, they are operated as Command Type Servo.
When RS204MD is used by connecting to a radio control receiver or a controller for PWM-Type Servo,
they are controlled as PWM-Type Servo.
●Communication Protocol (TTL Command-Type)
The communication protocol used for TTL Command Type Servo is asynchronous half-duplex
communication. The signal line can be switched alternately for transmission or reception of data.
Normally, RS204MD stand by in a receiving mode. When they receive commands to get the data of or
the status of servos, the mode changes to a transmitting mode.After sending the data, they stand by
again in a receiving mode.
●Control as PWM-Type Servo
To control RS204MD as a PWM-Type Servo, they are operated by changing the pulse width of the
constant-frequency pulse (4ms-50ms). There is no direct relationship between the frequency, the torque,
and the speed.
The relations between the pulse width and angles (positions) are as follows.
Table 4.1Pulse Width and Angles
Pulse Width
Angle(degrees)
560μs
+144
1520μs
0
2480μs
-144
If there is no input for more than 80ms or an invalid value, less than 500μs or more than 2550μs, is input,
the RS204MD will deactivate.
(Refer p33 No.22 ).

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●Memory Map
RS204MD has its own memory area to store data necessary for its movement. This memory area is
called “Memory Map”.
This memory map is divided into two groups. One is “RAM area” in which data will be erased when the
power is turned off. The other one is “ROM area” in which data is held even after the power is turned
off.
In “ROM area”, there are three different types of parameters; parameters used only for Command Type,
parameters used only for PWM Type and those used for both Types. When these parameters are required
to be rewritten, even parameters used only for PWM Type Servo, it is required to transfer the data as a
Command Type Servo after connecting the servos to the PC with USB-RS485 converter (RSC-U485)
etc.
While the servos are operated as PWM Type Servo, rewriting the parameters cannot be executed.
Therefore, the servos are operated with the prewritten parameters.
●Servo ID
You can set “ID” numbers to RS204MD servos individually.
“ID” is used to identify servos during communication.
The default number of every servo is set to “1”.
When you use plural servos in a single communication network, give them different “ID” numbers.
●Packet
“Packet” is a block that is used for sending a command to or receiving data from RS204MD servos.
Packets are divided into the following three groups, having different formats.
●Short Packet
Short Packets are used for sending the data in the memory map toward a single servo.
●Long Packet
Long Packets are used for sending the data in the memory map toward multiple servos simultaneously.
●Return Packet
Return Packet is a packet that is sent from a servo when a return packet is requested.