Hardware — Specifications, BOM & Assembly | Robotics Center of Silicon Valley

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Complete hardware documentation: mechanical and motor specifications, bill of materials with procurement guide, CAD file access, motor ID configuration, and wiring details.

DAMIAO Motors SocketCAN Aluminum Frame Open Hardware

Source: docs.openarm.dev/hardware/ License: CERN-OHL-S-2.0 Last updated: Apr 6, 2026

1. General Specifications

OpenArm features a small human-like physique with support pillars made of MiSUMi aluminum frames for easy dimension adjustment and attachment of cameras and sensors. The base plate features evenly spaced M6 taps for mounting to surfaces.

Property	Value
Degrees of Freedom	7 DOF per arm
Design Scale	Human-scale, proportioned for ~160–165 cm person
Nominal Payload	4.1 kg (weight held for 1 min in worst posture with arms extended)
Peak Payload	6.0 kg (moved to worst posture over 3 sec, held for 1 sec)
Frame Material	Aluminum (structural), stainless steel (critical joints)
Base Mounting	Evenly spaced M6 tapped holes
Support Pillars	MiSUMi aluminum frames (adjustable)
Communication	SocketCAN (Linux CAN-bus)
Motor Type	QDD (Quasi-Direct Drive) backdrivable
CAD Files	STEP, STL, Fusion 360 (open source)
Hardware License	CERN Open Hardware Licence Version 2 — Strongly Reciprocal

Payload Note The payload value includes the end-effector weight. For example, a 1.5 kg end-effector reduces nominal payload to 2.6 kg and peak payload to 4.5 kg.

Each joint includes mechanical limits restricting motion range for safety purposes. These limits also protect internal wiring from over-rotation damage.

2. Motor Specifications

OpenArm incorporates the DAMIAO 43 series and DAMIAO 8009P motors, with different models selected for each joint to balance high payload capacity with a clean, compact appearance. Motors with cross-roller bearings are used in single-support sections for enhanced rigidity and precision.

Motor Assignment by Joint

Joint	Motor Model
J1, J2 (shoulder)	DM-J8009P-2EC
J3	DM-J4340P-2EC
J4	DM-J4340-2EC
J5, J6, J7, J8 (wrist/gripper)	DM-J4310-2EC V1.1

Detailed Motor Specifications

Parameter	DM-J4310-2EC V1.1	DM4340 series	DM-J8009P-2EC
Rated Voltage	24 V	24 V	24 V (supports 24–48 V)
Rated Current	2.5 A	2.5 A	20 A
Peak Current	7.5 A	8 A	50 A
Rated Torque	3 Nm	9 Nm	20 Nm
Peak Torque	7 Nm	27 Nm	40 Nm
Rated Speed	120 rpm	36 rpm	24 V: 100 rpm / 48 V: 200 rpm
Max No-Load Speed	200 rpm	52 rpm	24 V: 160 rpm / 48 V: 320 rpm
Reduction Ratio	10:1	40:1	9:1
Pole Pairs	14	14	21
Phase Inductance	340 μH	317 μH	61 μH (at 25 °C)
Phase Resistance	650 mΩ	760 mΩ	90 mΩ (at 25 °C)
Outer Diameter	56 mm	57 mm	98 mm
Height	46 mm	53.3 mm	61.7 mm
Weight	300 g	362 g	896 g
Encoder Bits	14-bit	14-bit	14-bit
Number of Encoders	2	2	2
Encoder Type	Magnetic (single-turn)	Magnetic (single-turn)	Magnetic (single-turn)
Control Interface	CAN	CAN	CAN

Note The actual motor used for J1/J2 is the DM8009P. Specifications are nearly identical to the DM8009 datasheet. All motors use CAN communication protocol.

3. Gripper Specifications

Property	Value
Maximum Jaw Separation	88 mm
Fully Closed State	Jaws contact each other
Rotor Travel (closed → open)	60°
Zero Point	Motor zero aligns with fully closed state
Mechanism	Ball-bearing slider blocks, rails, and linkage bearings

Custom End-Effector Integration

OpenArm supports custom end-effectors by replacing the J8_B interface part. When designing a custom attachment:

Match original hole patterns and dimensions of J8_B
Include mounting features compatible with your end-effector
Maintain structural integrity and alignment
Consider balanced mass distribution relative to the arm's axis
Plan cable routing to avoid snags during full range of motion
Design for 3D printing or CNC machining manufacturability

CAD files for the J8_B interface are available in the openarm_hardware repository.

4. Bill of Materials

All prices listed below are in Japanese Yen (¥), as the primary sourcing platform is MISUMI Japan. International buyers should check for regional MISUMI sites or alternative distributors.

Actuators (Total: ¥397,356)

Component	Qty	Model	Cost
J1, J2 motors (per arm)	4 (bimanual)	DM-J8009P-2EC	¥205,790
J3 motor (per arm)	2 (bimanual)	DM-J4340P-2EC	¥42,066
J4 motor (per arm)	2 (bimanual)	DM-J4340-2EC	¥37,387
J5, J6, J7, J8 motors (per arm)	8 (bimanual)	DM-J4310-2EC V1.1	¥112,113

Mechanical Components (Total: ¥478,518)

Component	Cost
Manufactured Arm Parts (MEVIY)	¥316,018
Off-the-shelf Arm Parts	¥34,336
Pedestal Components	¥20,222
Gripper Components	¥107,942

Electrical Components (Total: ¥84,564)

Electrical components include: 24 V / 15 A power supply, USB to CANFD converter, and emergency stop switch. PCBs and wiring harnesses are custom-designed with fabrication files provided in the repository.

Procuring Components

Off-the-Shelf Parts (MISUMI)

Most mechanical and fastener components are available as catalog items from MISUMI.

Visit the MISUMI website. Go to misumi.com and select your region.
Search by model number. Enter the part number (e.g., CBE4-8) in the search bar.
Confirm dimensions/specs. Verify the part matches the BOM specifications.
Add to cart and order. No drawings needed for catalog parts — model numbers are sufficient.

Manufactured Parts (MEVIY)

Some components require custom manufacturing via MEVIY, MISUMI's automated 3D machining service. Two ordering methods:

Method 1: Upload CAD File

Go to MEVIY. Visit the MEVIY website and create an account.
Upload STEP file. Download the STEP file from openarm_hardware and upload it.
Select material, finish, tolerances. Review the automated quote.
Place order. Confirm specifications and submit.

Method 2: Use Pre-registered Model Numbers (Recommended)

Visit MISUMI's search page.
Paste the BOM model number. Example: MVBLK-ASN-48S-4BGUX-L. MEVIY automatically identifies it as a custom part.
Specify quantity and order. No CAD upload required — the geometry is pre-validated.

Tip Method 2 ensures you get the exact geometry that has been validated for OpenArm. Use Method 1 only if you need to review or customize the design.

Custom PCBs (JLCPCB)

Download files. Get the Gerber + BOM + CPL files from the project repository.
Upload to JLCPCB. Go to jlcpcb.com and upload the Gerber zip file to get a quote.
Configure options. Leave default settings unless you have specific requirements. Optionally choose Remove Mark in the Mark on PCB option.
Enable PCB Assembly. Scroll to the PCB Assembly tab and enable it, then click Next.
Upload BOM and CPL files. Click Process BOM & CPL and review the parts list.
Review 2D/3D models and proceed to place the order.

Custom Wires and Harnesses (LCSC)

Go to LCSC custom cable page.
Upload wiring drawings. Use drawings provided in the openarm_hardware repository.
Input desired quantity and click Confirm your cable plan.
Submit cable order. LCSC will send a quote for final ordering.

5. Assembly Guide

Step 0: Find CAD Files

The project makes all 3D models publicly available through GitHub to promote openness and customization.

What's included in the repository:

STEP Files — For manufacturing and modification in any CAD tool
STL Files — Ready for 3D printing of all printed components
Attachments — Camera mounts, PCB hubs, and custom pieces
Wiring Diagrams — For cable manufacturing reference

Hardware License CAD files are released under the CERN Open Hardware Licence Version 2 — Strongly Reciprocal. You are free to use, modify, and manufacture, but must share modifications under the same license.

Repository: github.com/enactic/openarm_hardware

Motor ID Configuration

Before assembling, each DAMIAO motor must be assigned the correct CAN ID using the Damiao Debugging Tools software (Windows). Configuration is done over UART (serial), not CAN.

Motor ID Reference Table

Joint	Sender CAN ID	Receiver (Master) ID
J1	0x01	0x11
J2	0x02	0x12
J3	0x03	0x13
J4	0x04	0x14
J5	0x05	0x15
J6	0x06	0x16
J7	0x07	0x17
J8 (Gripper)	0x08	0x18

Motor ID Configuration Steps

Download Damiao Debugging Tools. The Windows executable is available from Damiao. Allow through Windows Defender if blocked.
Connect via UART serial at 921600 bps. Use a USB-serial adapter — not a CAN adapter for this step.
Click "ReadParam" to retrieve current motor parameters and verify connection.
Select correct Sender and Master IDs from the reference table above.
Input values into the corresponding fields in the software.
Click "WriteParam" to save settings permanently to the motor.

Power Supply Requirements for Motor Configuration

Motor	Required Current
DM-J4310 / DM-J4340	0.3 A
DM-J8009P	0.75 A

Troubleshooting — Motor starts but doesn't rotate Verify adequate power supply using the current reference above. On CANable devices, enable the 120 Ω termination resistor. Daisy-chained motors require the summed current of all connected units.

6. Wiring & Casing

Cable Types

Five cable types are needed for the full bimanual assembly:

Cable Type	Quantity
J1 & J2 cables	4
J3–J4 cables	2
J4–J7 cables	2
J7–J8 cables	2
Communication cables	2
Power extension cables	2

LCSC Connector Interference Issue There is a known interference issue with connectors from LCSC that requires a custom L-shaped connector modification. This issue does not occur with connectors from WowRobo or Cereboto. If using LCSC connectors, follow the 13-step L-shape mold procedure in the official documentation.

Casing Components

The casing requires CSPPNSB-STU-TP3-8 screws (quantity: 30) and consists of five distinct casing pieces with left/right distinction for certain components.

Hub Board Components

Required for hub board assembly:

Cap screws
T-slot nuts
Custom PCBs (fabricated via JLCPCB)
Chest covers

Note Complete wiring diagrams and casing assembly instructions with photos are available in the openarm_hardware repository and the official docs at docs.openarm.dev.

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