Stark3 (Revo 3) Communication Protocol

1. Introduction

1.1 Purpose

This document is designed to guide users in communicating with the Stark3 (Revo 3) dexterous hand using RS485 or CAN FD interfaces, enabling device configuration, motion control, status acquisition, and tactile data reading.

1.2 Supported Interfaces

RS485
CAN FD

2. Modbus RTU Protocol

RS485 communication on the Stark3 hand uses the standard Modbus RTU protocol format.

2.1 Frame Format

Header / Device ID	Function Code	Data	CRC16
1 Byte	1 Byte	N Bytes	2 Bytes

2.2 Field Descriptions

Field	Description
Header/Device ID	Slave device address
Function Code	Modbus function code (e.g., `03H`: Read Holding Registers; `04H`: Read Input Registers; `06H`: Write Single Holding Register; `10H`: Write Multiple Holding Registers)
Data	Data payload, varying based on the function code and register address
CRC16	CRC-16 (Modbus) checksum, low byte first, high byte last

3. CAN FD Encapsulation Format

When using the CAN FD interface, the underlying communication still contains Modbus protocol data, which is encapsulated and transmitted within a 29-bit CAN FD extended frame.

3.1 CAN FD ID Format

The 29-bit CAN FD ID is allocated as follows:

Bits	Field	Description
28 ~ 24	Reserved	Fixed to `0`
23 ~ 16	Device ID	Slave device address
15 ~ 8	Master ID	Host device ID (defined by host)
7 ~ 0	Payload Length	Actual length of active data payload (Bytes)

Default Device ID

Device	Default Device ID (Decimal)	Default Device ID (Hexadecimal)
Left Hand	126	`0x7E`
Right Hand	127	`0x7F`

3.2 Frame Formats

Host Transmission Frame

CAN FD ID (29-bit)	Data Segment (Payload, ≤ 64 Bytes)
Device ID + Master ID + Payload Length	Complete Modbus RTU request frame (including checksums)

Device Reply Frame

CAN FD ID (29-bit)	Data Segment (Payload, ≤ 64 Bytes)
Device ID + Master ID + Payload Length	Complete Modbus RTU response frame

4. Register Map Overview

Stark3 registers are planned as follows:

Address Range	Register Type	Category
0 ~ 199	Holding Register	System Configuration
200 ~ 399	Holding Register	Motor Parameters
1000 ~ 1599	Holding Register	Control Commands
1800 ~ 1999	Input Register	System Status
2030 ~ 2999	Input Register	Motor Feedback
3000 ~ 3999	Input Register	Device Information
4000 ~ 5000	Input Register	Tactile Data

5. System Configuration Registers

System configuration registers (address range 0~199) support read/write access.

Address	Name	Access	Description
60 ~ 80	Motor Zero Offset	RW	Unit: 0.01° (transmitted as value × 100). Total 21 joints.
101	Hand Identity	RO	`1` = Right hand, `2` = Left hand
102	Restore Finger Defaults	WO	Write specific value to restore default finger parameters.
105	Buzzer Switch	RW	`0` = Off, `1` = On
106	Vibration Motor Switch	RW	`0` = Off, `1` = On
107	Touch Screen Switch	RW	`0` = Off, `1` = On
108	Device ID	RW	Default: 126 for Left hand, 127 for Right hand
109	RS485 Baudrate	RW	See 5.1 RS485 Baudrate
110	CAN FD Baudrate	RW	See 5.2 CAN FD Baudrate
112	Auto Calibration	RW	`0` = Off, `1` = On (automatically run calibration on boot)
118	Teaching Mode	RW	Write `1` to enter, `0` to exit
119	Emergency Stop	RW	Write `1` to stop all motors, `0` to resume normal operation
131	Auto-clear Motor Error	RW	`0` = Off (default), `1` = On

5.1 RS485 Baudrate

Value	Baudrate
0	1 Mbps
1	2 Mbps
2	3 Mbps
3	5 Mbps

5.2 CAN FD Baudrate

Value	Baudrate
0	1 Mbps
1	2 Mbps
2	4 Mbps
3	5 Mbps

6. Motor Parameters

The units for motor parameters are defined as follows:

Position: Degrees (°)
Velocity: Revolutions per minute (rpm)
Current: Milliamperes (mA)

💡 Numerical Scaling Details

To maintain data precision, position and velocity values are transmitted as integers using actual value × 100.

Angle Example: Target position 90.00° → transmitted register value is 9000.
Velocity Example: Target velocity 50.00 rpm → transmitted register value is 5000.
Current Example: Target protection currents directly use the physical value in mA.

6.1 Global Protection Current

Address	Parameter	Access	Description
200	All Joints Protection Current (mA)	WO	Configures protection current for all 21 joints at once

6.2 Single Joint Protection Current

Address	Parameter	Access	Description
201 ~ 221	Joint Protection Current (mA)	RW	Maximum allowed current for joints 0 to 20

6.3 Joint Movement Limits

Address	Parameter	Access	Description
240 ~ 260	Min Position Limit (° × 100)	RW	Physical minimum position limit for joints 0 to 20
270 ~ 290	Max Position Limit (° × 100)	RW	Physical maximum position limit for joints 0 to 20
300 ~ 320	Min Velocity Limit (rpm × 100)	RW	Minimum speed limit for joints 0 to 20
321 ~ 341	Max Velocity Limit (rpm × 100)	RW	Maximum speed limit for joints 0 to 20

7. Control Commands

Stark3 support MIT impedance control mode.

7.1 MIT Control Formula

τ = K_{p} \times (P o s R e f - P o s) + K_{d} \times (V e l R e f - V e l) + τ_{f f}

Data Scaling

$K_{p}$ , $K_{d}$ , Position, Velocity are transmitted as actual value × 100.
Current ( $τ_{f f}$ ) is transmitted directly in mA.

Example:

$K_{p}$ target = 15.00 $\to$ transmitted value = 1500
$K_{d}$ target = 0.50 $\to$ transmitted value = 50
Position target = 90.00° $\to$ transmitted value = 9000
Velocity target = 50.00 rpm $\to$ transmitted value = 5000
Current ( $τ_{f f}$ ) target = 1000 mA $\to$ transmitted value = 1000

7.2 Single Joint MIT Control

Enables standalone control of a specific joint:

Address	Parameter	Description
1050	Joint ID	Target joint number (0 ~ 20)
1051	$K_{p}$	Proportional stiffness gain (value × 100)
1052	$K_{d}$	Derivative damping gain (value × 100)
1053	Position	Target position (° × 100)
1054	Velocity	Target velocity (rpm × 100)
1055	Current ( $τ_{f f}$ )	Feedforward current (mA)

7.3 Multi-Joint MIT Control

Provides a continuous register map block for bulk updates of multiple joints:

Address Range	Target Joint	Parameter Array	Description
1100 ~ 1104	Joint 0	`[Kp, Kd, Pos, Vel, τ_ff]`	5 consecutive registers
1105 ~ 1109	Joint 1	`[Kp, Kd, Pos, Vel, τ_ff]`	5 consecutive registers
...	...	...	...
1195 ~ 1199	Joint 19	`[Kp, Kd, Pos, Vel, τ_ff]`	5 consecutive registers
1200 ~ 1204	Joint 20	`[Kp, Kd, Pos, Vel, τ_ff]`	5 consecutive registers

7.4 Bulk Parameter Controls

Enables targeted bulk updates for a single MIT parameter across all joints:

Address Range	Parameter	Description
1300 ~ 1320	$K_{p}$ List	Proportional gain ( $K_{p}$ ) for all 21 joints
1321 ~ 1341	$K_{d}$ List	Damping gain ( $K_{d}$ ) for all 21 joints
1342 ~ 1362	POS List	Target position ( $P o s$ ) for all 21 joints
1363 ~ 1383	Vel List	Target velocity ( $V e l$ ) for all 21 joints
1384 ~ 1404	$τ_{f f}$ List	Feedforward current for all 21 joints

7.5 Four-Finger MIT Control

Used to control the index, middle, ring, or pinky finger:

Address	Parameter	Description
1520	Finger Index	`1` = Index, `2` = Middle, `3` = Ring, `4` = Pinky
1521 ~ 1540	Parameter Array	Total 20 registers containing gains and references: 1. Abduction/Adduction MCP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 2. Flexion/Extension MCP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 3. PIP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 4. DIP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers)

7.6 Thumb MIT Control

Used to control the 5-DOF thumb structure:

Address Range	Parameter Array	Description
1550 ~ 1574	5-DOF Parameters	Total 25 registers in sequence: 1. CMC Flexion/Extension `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 2. CMC Abduction/Adduction `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 3. MCP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 4. IP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers) 5. DIP `[Kp, Kd, Pos, Vel, τ_ff]` (5 registers)

8. System Status

System status registers (address range 1800~1999) are read-only input registers.

Address	Parameter	Unit	Description
1800	System Status Code	—	See 8.1 System Status Code Definitions
1801	Total Current	mA	Current consumption of the hand
1802	Total Voltage	V	Supply voltage of the hand
1803	Total Power	W	Power consumption of the hand
1804	System Temperature	℃	Temperature of the main control board

8.1 System Status Code Definitions

The status code register (1800) uses high and low bytes to indicate errors:

High 8 Bits (High Byte): Core fault flag
- 0 = Normal
- 1 = Fault
Low 8 Bits (Low Byte): Detailed exception categories
- 0 = Normal
- 1 = Communication failure
- 2 = Uncalibrated
- 3 = Temperature abnormal

9. Motor Feedback

Real-time state monitoring of the 21 joint motors via input registers (2030~2999).

Address Range	Parameter	Unit	Description
2030 ~ 2050	Motor Velocity	rpm × 100	Current rotational speed of motors 0 ~ 20
2060 ~ 2080	Motor Position	° × 100	Current angular position of motors 0 ~ 20
2090 ~ 2110	Motor Current	mA	Current drive current of motors 0 ~ 20
2120 ~ 2140	Motor Status Code	Bit field	See 9.1 Motor Status Code Definitions
2150 ~ 2170	Motor Temperature	℃	Temperature of motors 0 ~ 20 (internal or driver IC)

9.1 Motor Status Code Definitions

The motor status registers (2120~2140) use bitwise flags to report faults:

Bit	Description
0	Over-current
1	Over-voltage
2	Under-voltage
3	Over-temperature
4	Current Spike
5	Calibration Failed
8	Motor Stall
9	Calibrating
11	Motor Running

10. Device Information

Device information registers (address range 3000~3999) are read-only.

Address Range	Parameter Name	Format / Details
3030 ~ 3039	Firmware Version	RO, Big-Endian ASCII string
3040 ~ 3049	Hardware Version	RO, Big-Endian ASCII string
3050 ~ 3059	Product SN	RO, Big-Endian ASCII string
3060 ~ 3269	Motor SN	RO, Big-Endian ASCII string, 10 registers per motor SN (21 motors total)
3300 ~ 3320	Motor Firmware Version	RO, binary version representation

10.1 Encoding Details

Versions & Serial Numbers (ASCII)

Strings are stored in Big-Endian byte order inside the registers. Each uint16_t register holds 2 characters:

High Byte: Holds the first character
Low Byte: Holds the second character

Each field uses 10 registers, supporting a maximum string length of 20 characters (including trailing null \0).

Decoding Example:

Register Array (Big-Endian uint16_t)	Hexadecimal Bytes	Decoded ASCII String
`0x534E`, `0x3132`, `0x3334`, `0x3536`, `0x3738`, `0x3930`, `0x3132`, `0x3334`, `0x3500`	`53 4E 31 32 33 34 35 36 37 38 39 30 31 32 33 34 35 00`	`"SN123456789012345"`

Motor Firmware Version

The motor firmware version is stored in a single uint16_t split into:

High Byte: Major version
Low Byte: Minor version

Parsing Format: Version = V[Major].[Minor]

E.g., read value 0x0105 represents version V1.5.

11. Resistive Tactile Module

Stark3 features a high-density tactile pressure array, split between palm and finger modules.

11.1 Tactile Module Specification

Module Type	Active Points	Calibrated Resultant Forces
Palm	36	1
Thumb Tip	31	3
Thumb Pad	57	6
Four Finger Tips (each)	21	3
Four Finger Pads (each)	52	5

11.2 Tactile Control Registers

Address	Description
4000 ~ 4010	Tactile Module Enable (corresponds to module IDs 0 ~ 10)
4011	Zero-out Pressure (WO, applies to all modules)
4012 ~ 4022	Zero-out Specific Module (WO, corresponds to module IDs 0 ~ 10)
4023	Tactile Data Mode (`0` = Raw array pressure, `1` = Calibrated pressure values)

11.3 Calibrated Resultant Forces

💡 Resultant Force Definition

Resultant Force = Sum of all calibrated pressure values within the mapped sub-regions of the module.

Palm & Thumb

Address	Description	Detail
4100	Palm Force	Entire palm area
4101 ~ 4103	Thumb Tip 1 ~ 3	3 sub-regions of the thumb tip
4104 ~ 4109	Thumb Pad 1 ~ 6	6 sub-regions of the thumb pad

Index Finger

Address	Description	Detail
4110 ~ 4112	Index Tip 1 ~ 3	Index finger tip sub-regions
4113 ~ 4117	Index Pad 1 ~ 5	Index finger pad sub-regions

Middle Finger

Address	Description	Detail
4118 ~ 4120	Middle Tip 1 ~ 3	Middle finger tip sub-regions
4121 ~ 4125	Middle Pad 1 ~ 5	Middle finger pad sub-regions

Ring Finger

Address	Description	Detail
4126 ~ 4128	Ring Tip 1 ~ 3	Ring finger tip sub-regions
4129 ~ 4133	Ring Pad 1 ~ 5	Ring finger pad sub-regions

Pinky Finger

Address	Description	Detail
4134 ~ 4136	Pinky Tip 1 ~ 3	Pinky finger tip sub-regions
4137 ~ 4141	Pinky Pad 1 ~ 5	Pinky finger pad sub-regions

11.4 Tactile Array Data Registers

Real-time reading of raw or calibrated array values:

Module Type	Address Range	Total Points
Palm	4200 ~ 4235	36 points
Thumb Tip	4250 ~ 4280	31 points
Thumb Pad	4290 ~ 4346	57 points
Index Tip	4350 ~ 4370	21 points
Index Pad	4400 ~ 4451	52 points
Middle Tip	4460 ~ 4480	21 points
Middle Pad	4500 ~ 4551	52 points
Ring Tip	4560 ~ 4580	21 points
Ring Pad	4600 ~ 4651	52 points
Pinky Tip	4660 ~ 4680	21 points
Pinky Pad	4700 ~ 4751	52 points

11.5 Tactile Module Index Definition

Module ID	Module Name
0	Palm Tactile
1	Thumb Tip
2	Thumb Pad
3	Index Tip
4	Index Pad
5	Middle Tip
6	Middle Pad
7	Ring Tip
8	Ring Pad
9	Pinky Tip
10	Pinky Pad

12. Joint ID Definitions

The Stark3 hand has 21 active joints. Refer to the diagram below for the ID mapping of each joint:

Stark3 (Revo 3) Dexterous Hand - Physical layout of 21 active joint motor IDs

Stark3 (Revo 3) Communication Protocol ​

1. Introduction ​

1.1 Purpose ​

1.2 Supported Interfaces ​

2. Modbus RTU Protocol ​

2.1 Frame Format ​

2.2 Field Descriptions ​

3. CAN FD Encapsulation Format ​

3.1 CAN FD ID Format ​

Default Device ID ​

3.2 Frame Formats ​

Host Transmission Frame ​

Device Reply Frame ​

4. Register Map Overview ​

5. System Configuration Registers ​

5.1 RS485 Baudrate ​

5.2 CAN FD Baudrate ​

6. Motor Parameters ​

6.1 Global Protection Current ​

6.2 Single Joint Protection Current ​

6.3 Joint Movement Limits ​

7. Control Commands ​

7.1 MIT Control Formula ​

Data Scaling ​

7.2 Single Joint MIT Control ​

7.3 Multi-Joint MIT Control ​

7.4 Bulk Parameter Controls ​

7.5 Four-Finger MIT Control ​

7.6 Thumb MIT Control ​

8. System Status ​

8.1 System Status Code Definitions ​

9. Motor Feedback ​

9.1 Motor Status Code Definitions ​

10. Device Information ​

10.1 Encoding Details ​

Versions & Serial Numbers (ASCII) ​

Motor Firmware Version ​

11. Resistive Tactile Module ​

11.1 Tactile Module Specification ​

11.2 Tactile Control Registers ​

11.3 Calibrated Resultant Forces ​

Palm & Thumb ​

Index Finger ​

Middle Finger ​

Ring Finger ​

Pinky Finger ​

11.4 Tactile Array Data Registers ​

11.5 Tactile Module Index Definition ​

12. Joint ID Definitions ​