Harmonic Drive Actuator R68 Module for Shoulder/Elbow/Knee
Product Overview
The Workhorse That Bridges Mid-Size Joints
The CrabNova R68 is the most versatile module in the lineup — the actuator you reach for when you need more torque than the R58 but don't yet need the bulk of the R83. At 830 grams with 33 Nm continuous torque (82 Nm peak), it occupies the critical middle ground in humanoid robot joint sizing. It's the default choice for elbow pitch, knee pitch, and waist yaw on mid-size humanoid platforms carrying 3–5 kg payloads.
The R68 comes in two well-differentiated variants. The Standard version (830g, R68×75.6mm) is a pure high-performance rotary actuator — 260W continuous power, 2500 RPM motor speed, and triple protocol support for maximum integration flexibility. The Upgraded version (1.15kg, R68×82.6mm) adds both an electromagnetic safety brake (0.42 Nm holding torque, ≤50ms release) and an integrated torque sensor (120 Nm range, ±0.5% FS, 300% overload tolerance). The addition of the brake is a game-changer for safety-critical joints — elbows and knees that must hold position on power loss.
At the heart of both variants is the same 101:1 harmonic drive with 30 arcsec backlash and dual 19-bit absolute encoders, driven by a high-performance servo drive running 20 kHz current loop and 10 kHz speed loop. The 5.5A rated current (16.3A peak) at 48V provides ample electrical headroom for dynamic maneuvers and transient load spikes.
🎯 Why the R68 Matters: In humanoid robot design, the elbow is often the most demanding joint — it must support the full weight of the forearm + hand + payload at maximum extension, while moving fast enough for natural arm swing. The R68's 33 Nm continuous rating means it can hold a 5 kg payload at 0.6m extension indefinitely without overheating — the benchmark for practical humanoid manipulation.
Technical Specifications
Complete Parameter List
Based on CrabNova CE-RB-R68 series specifications. Standard and Upgraded variants shown.
⚙️ Mechanical Specifications
| Parameter | R68 Standard | R68 Upgraded | Notes |
|---|---|---|---|
| Model | CE-RB-R68-101-DNN-CO-I | CE-RB-R68-101-FBT-I | — |
| Reduction Ratio | 101:1 | Harmonic drive | |
| Rated Torque | 33 Nm | Continuous | |
| Peak Torque | 82 Nm | Transient | |
| Output Speed | 30 RPM | At rated load | |
| Backlash | 30 arcsec | Harmonic drive | |
⚡ Electrical Characteristics
| Parameter | R68 Standard | R68 Upgraded |
|---|---|---|
| Rated Voltage | 48V DC | |
| Rated Power | 260 W | 264 W |
| Rated Speed | 2500 RPM | |
| Rated Current | 5.42 A | 5.5 A |
| Peak Current | 16.3 A | |
📡 Control & Sensing
| Parameter | R68 Standard | R68 Upgraded |
|---|---|---|
| Encoder | Dual encoders, 19-bit absolute (524,288 counts/rev) | |
| Control Interface | EtherCAT / CAN FD / CANOpen | |
| Current Loop | 20 kHz | |
| Speed Loop | 10 kHz | |
| Brake | — | 0.42 Nm holding, ≤50ms release |
| Torque Sensor | — | 120 Nm range, ±0.5% FS, 300% overload, RS485 |
📏 Physical Dimensions
| Parameter | R68 Standard | R68 Upgraded |
|---|---|---|
| Dimensions | R68 × 75.6 mm | R68 × 82.55 mm |
| Weight | 0.83 kg | 1.15 kg |
| Target Applications | Shoulder roll/pitch, elbow pitch, knee pitch, waist yaw | |
Key Features
Why the R68 Excels in Safety-Critical Joints
🛑 Electromagnetic Safety Brake (Upgraded)
The Upgraded R68 features a fail-safe electromagnetic brake with 0.42 Nm holding torque — enough to prevent the arm from collapsing under its own weight on power loss. With a release time of ≤50 ms and pull-in time ≤50 ms, the brake engages and disengages fast enough for real-time safety responses. This is the minimum requirement for any joint that must maintain position when unpowered — elbows, knees, and lifting axes.
🎯 120 Nm Torque Sensing (Upgraded)
The integrated torque sensor in the Upgraded variant offers a 120 Nm rated range with ±0.5% FS accuracy and an impressive 300% overload tolerance (360 Nm before damage). This means the sensor survives peak torque events that would destroy most external load cells. RS485 digital output integrates directly with your control system for impedance control, collision detection, and gravity compensation.
📐 40 Nm/kg Torque Density
The Standard R68 achieves an exceptional 40 Nm/kg torque density (rated) — higher than the R58 thanks to its proportionally larger torque output. At 830g, it weighs less than a liter of water while delivering enough continuous torque to hold a 5 kg payload at the end of a 0.6m arm. For the Upgraded version, the brake and torque sensor add 320g — a 38% weight increase for safety and sensing that most integrators consider well worth it.
🔌 Full Protocol Flexibility
Like its smaller siblings, the R68 supports EtherCAT, CAN FD, and CANOpen simultaneously — but at 20 kHz current loop bandwidth, it has the headroom to make full use of EtherCAT's deterministic multi-axis synchronization for coordinated arm motion. The Standard version uses CANOpen-only interface (CO-I suffix), while the Upgraded version adds EtherCAT and CAN FD for maximum integration options.
Application Scenarios
Where the R68 Is the Right Choice
💪 Humanoid Elbow Joints
The R68 is the reference design for humanoid elbows. 33 Nm continuous handles the full weight of the forearm + hand + payload at maximum extension, while 82 Nm peak provides the transient torque needed for rapid arm swing and lifting maneuvers. The Upgraded brake prevents the arm from drooping on power loss — a non-negotiable safety requirement for any robot intended to operate near humans.
🦵 Humanoid Knee Joints
The R68's 82 Nm peak torque handles walking dynamics on mid-size humanoids (up to ~50 kg total mass). The Upgraded brake is essential here — an unbraked knee collapses instantly on power loss, potentially damaging the robot or its surroundings. The torque sensor enables compliant walking gaits and terrain adaptation through impedance control.
🔄 Waist Yaw Rotation
For humanoids up to ~40 kg, the R68 provides sufficient torque for waist yaw (torso rotation) — a critical degree of freedom for reaching and manipulation. The compact 75.6mm length (Standard) fits within typical torso cross-sections, and the 19-bit absolute encoder provides the angular precision needed for coordinated whole-body motion.
🏭 Industrial Robot Arm Joints
Beyond humanoids, the R68 serves as a capable actuator for 3–5 kg payload industrial robot arms — joints 2 and 3 (shoulder and elbow) on six-axis arms. The EtherCAT interface integrates with Beckhoff, Trio, and other industrial motion controllers, while the 33 Nm continuous rating provides the thermal margin needed for 24/7 production duty cycles.
How to Choose: Standard vs. Upgraded
| Your Requirement | Recommended |
|---|---|
| The joint does NOT need to hold position when unpowered | R68 Standard (0.83 kg) |
| The joint MUST hold position on power loss (elbow, knee, lifting axis) | R68 Upgraded (1.15 kg) |
| Force control or impedance control is required | R68 Upgraded |
| Lowest weight is the priority and the load is self-locking or counterbalanced | R68 Standard |
What's Included
Package Contents
| # | Item | Qty | Description |
|---|---|---|---|
| 1 | CrabNova R68 Actuator | 1 | Fully assembled, factory-calibrated (Standard or Upgraded) |
| 2 | Communication Cable Set | 1 set | EtherCAT/CAN FD/CANOpen interface cables |
| 3 | Power Cable | 1 | 48V DC power connection |
| 4 | Brake Control Cable (Upgraded only) | 1 | 24V brake release signal cable |
| 5 | Mounting Hardware | 1 set | Socket head screws for flange mounting |
| 6 | Product Datasheet | 1 | Technical specs, mechanical drawings, and pinout |
| 7 | Software Access | — | JxServo Studio + protocol documentation |
| 8 | Calibration Certificate | 1 | Per-unit factory calibration (torque sensor for Upgraded) |
💻 Software & Resources: All CrabNova actuators are supported by JxServo Studio for configuration, tuning, and real-time telemetry. Full CANopen object dictionary, EtherCAT ESI files, and MIT impedance mode guide available at docs.juxieservo.com.
Why Buy from RobX
Sourced in China, Supported in California
US-Based PhD Technical Support
Your technical questions answered by a robotics PhD in California — in fluent English, during US business hours. We help with joint sizing, brake integration, and torque sensor calibration.
California Sample Inventory
R68 Standard and Upgraded units stocked in California. Test in your lab within days — not weeks.
DDP Pricing & Full Logistics
All pricing is DDP (Delivered Duty Paid). We handle export, freight, customs, and import duties.
Direct Manufacturer Relationship
As an authorized distributor of CrabNova (Juxie Intelligent Drive), we get priority allocation and direct engineering escalation.
