Actuator Module Specifications

Comprehensive technical specifications for the Open Robot Actuator Module Core v1 and v1.1

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.

Performance Specifications

Torque Output

2.5 Nm @ 12A continuous

Peak torque higher depending on thermal limits

Gear Ratio

9:1 total reduction

Dual-stage: 3:1 × 3:1

Encoder Resolution

20,000 counts/rev at microcontroller

5,000 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

Component Category	Weight
Complete Module	150g
Core components (no shell)	95g
Shell structure	~55g

Core Components

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

v1.1 ODRI Kit

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/V
• Configuration: 3-phase WYE (Star)
• Pole Pairs: 12
• Slots: 18
• Magnets: 24
• Continuous Current: 12A

Mechanical

• Type: Brushless outrunner
• Rotor Diameter: 45mm
• Weight: 53g
• Bearings: Integrated
• Shaft: Custom prepared

Encoder Specifications

Broadcom AEDT-9810-Z00

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

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)

First Stage

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

Second Stage

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 reinforcement
• Profile: AT3 (3mm pitch)
• Generation: GEN III (latest version)
• Total Weight: 4.5g both belts
• Manufacturer: 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

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

Motor Pulley

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

Center Pulley

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

Performance Characteristics

Torque-Speed Curve

Continuous Operation

• Rated Torque: 2.5 Nm @ 12A
• Rated 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

Metals

Component	Material	Specification
Motor shaft	Stainless steel 1.4301	Precision ground h9
Motor pulley	Aluminum	7075 or 6061
Center pulley	Aluminum 7075	High strength
Bearings	Stainless steel	EZO quality
Fasteners	Stainless steel A2	Corrosion resistant

Plastics

Component	Material	Method
Pulleys (T30)	Photopolymer resin	SLA/Polyjet/Multijet
Tensioner rollers	Photopolymer resin	SLA/Polyjet/Multijet
Encoder mount	Photopolymer resin	SLA/Polyjet/Multijet
Encoder screws	Polyamide (PA)	Injection molded

Composites

Component	Material	Specification
Timing belts	Polyurethane + steel	Conti GEN III
Motor wires	Copper + PVC	LiY 0.50mm²
Encoder wires	Copper + PVC	LifY 0.14mm²

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 bearings
• Timing Belts: Continental GEN III industrial grade
• Motor: T-Motor hobby-grade (high performance)
• Encoder: Broadcom industrial optical encoder
• Fasteners: DIN/ISO standard metric hardware

Design Standards

• License: BSD 3-Clause (open source)
• Design Origin: Max Planck Institute / NYU research
• Documentation: Complete technical drawings provided
• Testing: 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 Grimminger

License: BSD 3-Clause License

Copyright: © 2019-2021 Max Planck Gesellschaft and New York University