Biped Robot Bolt (6dof v1)
The Biped Bolt is a 6-degree-of-freedom bipedal robot featuring two 3DOF legs with passive ankle joints. The robot is designed for bipedal locomotion research with extended leg lengths compared to the quadruped platforms.Overview
Degrees of Freedom
6 DOF - 3 actuated joints per leg + passive ankles
Weight
1.34kg total weight
Leg Length
200mm upper and lower legs (25% longer than quadruped)
Communication
24V power / Ethernet interface wire
Key Specifications
| Specification | Value |
|---|---|
| Degrees of Freedom | 6 active DOF (3 per leg) |
| Total Weight | 1.34kg |
| Body Structure Weight | 99g |
| Leg Module Weight | 540g each |
| Upper Leg Length | 200mm |
| Lower Leg Length | 200mm |
| Power Supply | 24V over wire |
| Communication | Ethernet |
Mechanical Design
Body Structure
The compact body structure weighs only 99g and includes: 3D Printed Components (87g total):- Body Structure Front: 19g
- Body Structure Back Rev A: 14g
- Body Structure Right Side: 9g
- Body Structure Left Side: 9g
- Body Structure Bottom: 17g
- Body Structure Top (standard): 14g
- Standard Top: 14g
- Top with Vicon Markers: 15g
- Top with IMU Attachment: 15g
- Top with IMU and Vicon Markers: 16g
Biped Leg Modules
Each leg features:- Hip Abduction/Adduction (AA): Lateral leg movement
- Hip Flexion/Extension (FE): Forward/backward leg movement
- Knee: Lower leg rotation
- Passive Ankle Joint: Line contact foot for yaw stabilization
- Weight: 540g per leg
- Leg length: 25% longer than quadruped legs (200mm vs 160mm)
- Line contact feet help stabilize yaw orientation
- No yaw control (no leg rotation DOF)
Hip Height
The hip height varies with lower leg angle:- At 45° lower leg angle: ~280mm
- At 60° lower leg angle: ~320mm
- At 90° lower leg angle: ~400mm
Electronics System
Master Board v2
Master Board
Central control board for the biped
- Weight: 19g
- Ethernet communication
- SPI interface to motor drivers
- Documentation
Micro Driver Boards
Micro Driver Stack (3 cards):- Weight: 47g total
- Each board controls 2 brushless motors
- 3 boards control all 6 actuators
- Located in body structure
Inertia Measurement Unit
Lord Microstrain 3DM-CX5-25- Weight: 13g
- Mounted to top element of body structure
- Label pointing downward
- Same orientation as robot coordinate system
- Product Page
- X: -0.13mm
- Y: -6.35mm
- Z: 77.40mm
Wiring Configuration
Actuator Module Wiring
| Joint | Motor Phases | Encoder Wire |
|---|---|---|
| Hip AA (RHAA, LHAA) | 20cm | 28cm |
| Hip FE (RHFE, LHFE) | 27cm | 33cm |
| Knee (RK, LK) | 35cm | 42cm |
Additional Wiring
Robot Interface Wire
- Ethernet Wire: 6m (4 conductors)
- Power Wires: 6m (24V and ground)
Internal Wiring
- SPI Wires: 3x 10cm (5 conductors each)
- IMU Wire: 25cm (4 conductors)
- Motor Phase Wires: 18x 11cm
Assembly Components
Hip AA Bearings
Stainless Steel Bearings ET2520 2Z VA- Dimensions: 25mm x 20mm x 4mm
- Weight: 3.4g each
- Quantity: 2 required
Fasteners
Body Structure:- M3x8 Socket Head Cap Screws: 18 (body structure)
- M3x8 Socket Head Cap Screws: 6 (Hip AA modules)
- M2.5x25 Socket Head Cap Screws: 4 (micro driver stack)
- M2x5 Socket Head Cap Screws: 2 (master board)
- M2x20 Socket Head Cap Screws: 2 (master board)
- M2.5x16 Slotted Screws: 3 (IMU - polyamide plastic, shorten to 13mm)
Helicoil Thread Inserts
- M3 x 4.5mm: 24 inserts (1.5xD, Böllhoff 41890030045)
- M2.5 x 3.75mm: 4 inserts (1.5xD, Böllhoff 41890250375)
Bill of Materials
| Component | Quantity | Notes |
|---|---|---|
| Biped Leg 3DOF Right Side | 1 | Custom assembly |
| Biped Leg 3DOF Left Side | 1 | Custom assembly |
| Master Board v2 | 1 | Custom electronics |
| Micro Driver Board v2 | 3 | Custom electronics |
| IMU (3DM-CX5-25) | 1 | Extended measurement range |
| Hip AA Bearings (ET2520 2Z VA) | 2 | Stainless steel |
| Body Structure 3D Printed Parts | 1 set | Multiple top plate options |
| Master Board Protection | 1 | 3D printed |
| Micro Driver Stack Spacer | 8 | 3D printed |
| Fasteners | Various | Stainless steel |
| Helicoil Inserts | 28 total | M3 and M2.5 sizes |
| Vicon Markers (optional) | 8 | Ø 9.5mm with M4x10 set screws |
Robot Stand
A custom stand is available for the biped: Stand Components:- Stand Attachment: 23g (3D printed)
- Aluminum Profiles (Item Size 8):
- Back: 70cm
- Top: 25cm (tap M8x1.25 thread)
- Bottom: 30cm
- Side: 45cm
- Angle Brackets: 4x 90-degree 40mm brackets
- End Caps: 4
- Rubber Feet: 3
Coordinate System
The robot coordinate system origin is located at the center of the body structure. The IMU coordinate system shares the same orientation as the robot coordinate system, with the offset documented in the IMU section. For detailed coordinate system conventions, see Conventions.Vicon Object for Motion Capture
Body Structure Top with Vicon Markers- Weight: 23g (top element alone)
- Total weight with markers: 106g (complete body structure)
- 8 markers (Ø 9.5mm)
- Used for base state estimation
Robot Calibration
A dedicated calibration tool is available for the biped. See the Biped 6dof Calibration Tool documentation.Design Considerations
Why No Leg Rotation?
Why No Leg Rotation?
The biped has no leg rotation degree of freedom, meaning the yaw angle of the robot cannot be actively controlled. The line contact of the feet helps stabilize the yaw orientation passively.
Extended Leg Length
Extended Leg Length
Compared to the quadruped robots, the upper and lower leg lengths were increased by 25% (from 160mm to 200mm) to provide appropriate proportions for bipedal locomotion.
Passive Ankle Joints
Passive Ankle Joints
Each leg features a passive ankle joint with line contact feet. This design helps the robot maintain balance and provides compliance during ground contact.
Applications
The Biped Bolt is designed for:- Bipedal locomotion research
- Balance and stability control
- Walking and running gaits
- Machine learning for humanoid robots
- Underactuated control strategies
Related Resources
Biped Leg Assembly
Complete biped leg build instructions
Electronics Wiring
Detailed wiring guide and schematics
Actuator Modules
Core actuator module documentation
CAD Model
Interactive 3D CAD viewer