Overview This page provides complete technical specifications for the Brushless Actuator Module Core. Specifications apply to both v1.0 and v1.1 modules, which are functionally identical.
Torque Output 2.5 Nm @ 12A continuousPeak torque higher depending on thermal limits
Gear Ratio 9:1 total reductionDual-stage: 3:1 × 3:1
Encoder Resolution 20,000 counts/rev at microcontroller5,000 pulses/rev per channel (quadrature)
Control Mode Torque-controlled Current-based motor control
Physical Specifications Dimensions Parameter Value Notes Segment Length 160mm End-to-end module length Motor Diameter 45mm Rotor outer diameter Output Bearing OD 32mm Outer diameter Output Bearing ID 25mm Inner diameter for mounting Codewheel Diameter 26mm Optical encoder codewheel Codewheel ID 7mm Motor shaft mounting
Weight Breakdown Total Assembly
Core Components
v1.1 ODRI Kit
Component Category Weight Complete Module 150g Core components (no shell) 95g Shell structure ~55g
Component Weight Quantity Subtotal Motor 53g 1 53g Encoder/Codewheel 5g 1 5g Machined Parts - - 5.9g - Motor shaft 3.2g 1 3.2g - Motor pulley 0.6g 1 0.6g - Center pulley 2.1g 1 2.1g 3D Printed Parts - - 11.3g - Encoder mount 0.3g 1 0.3g - Center pulley (T30) 4.2g 1 4.2g - Output pulley (T30) 6.7g 1 6.7g - Tensioner rollers 0.2g 2 0.4g Timing Belts - - 4.5g - First stage (150mm) 1.5g 1 1.5g - Second stage (201mm) 3.0g 1 3.0g Bearings - - 16g - Output bearings 6.9g 2 13.8g - Transmission bearings 0.4g 3 1.2g - Tensioner bearings 0.4g 2 0.8g Fasteners 2.9g - 2.9g TOTAL CORE - - 95g
Component Weight ODRI Encoder Kit (complete) 11g - Motor shaft assembly 4.6g - Center pulley ~2.1g - Encoder head ~5g - Codewheel (included)
Motor Specifications T-Motor Antigravity 4004 300kV Electrical
KV Rating : 300 RPM/VConfiguration : 3-phase WYE (Star)Pole Pairs : 12Slots : 18Magnets : 24Continuous Current : 12A Mechanical
Type : Brushless outrunnerRotor Diameter : 45mmWeight : 53gBearings : IntegratedShaft : Custom prepared Encoder Specifications Parameter Specification Type Optical incremental encoder Resolution 5,000 pulses/revolution per channel Counts 20,000 counts/rev (quadrature) Output Type Two-channel quadrature + index (ABZ) Output Voltage 5V logic Codewheel 26mm diameter, 625 cycles per revolution Weight 5g (encoder + codewheel) Mounting Custom 3D printed bracket
Accuracy : The high 5,000 cpr resolution provides excellent position accuracy for torque control applications.
Transmission Specifications Dual-Stage Timing Belt System Overall
First Stage
Second Stage
Parameter Value Total Reduction 9:1 First Stage 3:1 (10T → 30T) Second Stage 3:1 (10T → 30T) Belt Type AT3 GEN III Tooth Pitch 3mm Backlash Minimal (custom profile)
Component Specification Motor Pulley 10 teeth, aluminum Center Pulley 30 teeth, 3D printed Belt Length 150mm (50 teeth) Belt Width 4mm Belt Weight 1.5g Reduction 3:1
Component Specification Center Pulley 10 teeth, aluminum Output Pulley 30 teeth, 3D printed Belt Length 201mm (67 teeth) Belt Width 6mm Belt Weight 3.0g Reduction 3:1
Timing Belt Details Conti Synchroflex AT3 GEN III
Material : Heavy-duty polyurethane with steel cord reinforcementProfile : AT3 (3mm pitch)Generation : GEN III (latest version)Total Weight : 4.5g both beltsManufacturer : Continental (Contitech)
Custom Tooth Profile : Pulley tooth profile is modified from standard AT3 to reduce backlash. Do not substitute with standard AT3 pulleys.
Bearing Specifications EZO Stainless Steel Miniature Bearings Output Bearing EZO 61705 2RS VA
Outer Diameter: 32mm
Inner Diameter: 25mm
Thickness: 4mm
Weight: 6.9g each
Quantity: 2
Type: Deep groove ball bearing
Seals: 2RS (rubber seals both sides)
Material: Stainless steel (VA)
Transmission Bearing EZO MR84 VA
Outer Diameter: 8mm
Inner Diameter: 4mm
Thickness: 2mm
Weight: 0.4g each
Quantity: 3
Type: Miniature ball bearing
Seals: Open
Material: Stainless steel (VA)
Tensioner Bearing EZO 683 2Z VA
Outer Diameter: 7mm
Inner Diameter: 3mm
Thickness: 3mm
Weight: 0.4g each
Quantity: 2
Type: Miniature ball bearing
Seals: 2Z (metal shields)
Material: Stainless steel (VA)
Alternative : Chrome steel bearings can be substituted for lower cost, but stainless steel is recommended for corrosion resistance.
Machined Parts Specifications v1.0 Custom Machined Parts Motor Shaft
Motor Pulley
Center Pulley
Parameter Specification Material Stainless steel 1.4301 Stock Size 4mm diameter h9 tolerance Tolerance 3.97mm - 3.99mm Finish Precision ground Weight 3.2g Features Custom ends for codewheel and bearing Drawing motor_shaft.PDF
Parameter Specification Material Aluminum Teeth 10 Profile AT3 custom (modified) Weight 0.6g Machining Form cutter or Wire EDM Drawing motor_pulley_at3_t10.PDF
Parameter Specification Material Aluminum Teeth 10 Profile AT3 custom (modified) Weight 2.1g Machining Form cutter or Wire EDM Drawing center_pulley_at3_t10.PDF
v1.1 ODRI Kit Parts Component Material Specification Included in Kit Motor Shaft Assembly Stainless steel + aluminum Pre-assembled with bearings and pulley ✅ Center Pulley Aluminum 7075 10 teeth, AT3 profile ✅ Encoder Head PCB/optical Broadcom AEDT-9810-Z00 ✅ Codewheel Glass/metal 5000 cpr, mounted on shaft ✅
The ODRI Kit (v1.1) eliminates all custom machining requirements while providing identical performance to v1.0.
3D Printed Parts Specifications Part Name Weight Teeth Material Print Method Encoder Codewheel PWB Mount 0.3g - Resin SLA/Polyjet/Multijet Center Pulley T30 4.2g 30 Resin SLA/Polyjet/Multijet Output Pulley T30 6.7g 30 Resin SLA/Polyjet/Multijet Tensioner Roller 10mm 0.2g - Resin SLA/Polyjet/Multijet
Print Quality Critical : Tooth profiles must be precise and concentric. FDM printing is NOT recommended for pulley parts.
Available Tensioner Roller Sizes
10.0mm (default)
10.5mm
11.0mm
11.5mm
Multiple sizes allow fine-tuning of timing belt tension.
Electrical Specifications Motor Connections Parameter Specification Connector Type 2mm gold-plated bullet connectors Wire Gauge 0.50 mm² (LiY cable) Quantity 3 phase wires Current Capacity 12A continuous, higher peak
Encoder Connections Parameter Specification Connector Type Hirose DF13 5-pin socket Wire Gauge 0.14 mm² (LifY cable) Signals 5 (A, B, Z, VCC, GND) Voltage 5V logic Wire Colors Red, yellow, black, white, green
Torque-Speed Curve Continuous Operation
Rated Torque : 2.5 Nm @ 12ARated Speed : Variable (motor-dependent)Efficiency : High (timing belt transmission)Thermal Limit : Depends on cooling Peak Performance
Peak Torque : >2.5 Nm (short duration)Peak Current : >12A (thermal limited)Control Bandwidth : High (direct drive feel)Backdrivability : Excellent (low friction) Control Characteristics Parameter Specification Control Type Torque (current) control Sensor Type Incremental encoder Position Resolution 20,000 counts/rev output shaft Velocity Estimation From encoder differentiation Torque Estimation From motor current Response Time Fast (low inertia)
Material Summary Comparison Table: v1.0 vs v1.1 Specification v1.0 v1.1 Notes Total Weight 150g 150g Identical Torque Output 2.5 Nm @ 12A 2.5 Nm @ 12A Identical Gear Ratio 9:1 9:1 Identical Encoder Resolution 20,000 counts/rev 20,000 counts/rev Identical Machined Parts Custom ordered ODRI Kit Different sourcing Assembly Time Longer Shorter Kit pre-assembled Cost Lower (if machining available) Higher (kit premium) Trade-off Machining Required Yes No Key difference Performance Excellent Excellent Functionally identical Compatibility Full Full Interchangeable
Tolerances and Fits Critical Dimensions Interface Nominal Tolerance Fit Type Motor shaft diameter 4.0mm h9 (3.97-3.99mm) Clearance to bearing Codewheel bore 7.0mm +0.05mm Press fit to shaft Output bearing OD 32mm Standard Press fit to pulley Output bearing ID 25mm Standard Clearance to shaft Pulley tooth profile AT3 custom ±0.05mm Critical for backlash
Environmental Specifications Parameter Specification Notes Operating Temperature 0°C to 50°C Typical lab/field use Storage Temperature -20°C to 60°C Standard conditions Humidity 20% to 80% RH Non-condensing IP Rating IP20 Not sealed, indoor use Shock Resistance Moderate Designed for legged robots Vibration Good Low-backlash transmission
These specifications are for standard laboratory and indoor robotic applications. Additional sealing or protection may be needed for harsh environments.
Quality and Standards Component Quality
Bearings : EZO precision miniature bearingsTiming Belts : Continental GEN III industrial gradeMotor : T-Motor hobby-grade (high performance)Encoder : Broadcom industrial optical encoderFasteners : DIN/ISO standard metric hardware
Design Standards
License : BSD 3-Clause (open source)Design Origin : Max Planck Institute / NYU researchDocumentation : Complete technical drawings providedTesting : Validated in multiple research platforms
Related Pages
Actuator Module v1.0 Detailed v1.0 documentation
Actuator Module v1.1 Updated v1.1 with ODRI Kit
Authors : Felix GrimmingerLicense : BSD 3-Clause LicenseCopyright : © 2019-2021 Max Planck Gesellschaft and New York University