Solo-8 Open Torque-Controlled Quadruped Robot

A light, fast, open-source research quadruped. Solo-8 has eight brushless actuators (hip and knee on each leg) with low-ratio timing-belt transmissions, so the legs are back-drivable and torque-controlled. It can jump, trot and recover from pushes, and it weighs under 2 kg.

Updated for modern use: the robot, leg and actuator documents brought together into one parts list, one print list with counts and one build guide in build order.

What you build

• 8 actuator modules: T-Motor Antigravity 4004 300KV motors with a two-stage 9:1 AT3 timing-belt reduction and optical encoders
• 4 two-joint legs (hip shell, upper-leg shell, lower leg)
• A printed body frame carrying the Master Board, 4 Micro Driver boards and an IMU
• Tethered 24 V power and Ethernet to a Linux PC

Files

• 32 print-ready STL files: body frame, hip and upper-leg shells, lower legs, belt pulleys, tensioner rollers, encoder mounts and assembly jigs
• Build guide PDF: print list, bought and machined parts, actuator modules, legs and body, wiring and first power-up
• Bill of Material PDF with quantities, notes and a shop link for every off-the-shelf part

Print settings

Large structural parts (body frame, leg shells, lower legs): PC-ABS or PETG on a good FDM printer, or SLS nylon. Small precision parts (belt pulleys, tensioner rollers, encoder mounts): tough resin on SLA or a printing service; FDM pulleys are not accurate enough. Print every part in the positive Z direction of its STL.

Electronics

• 8 brushless motors with optical encoder kits
• 4 Micro Driver v2 boards (2 motors each) and 1 Master Board v2, talking SPI and Ethernet
• MicroStrain 3DM-CX5-25 IMU
• Current-limited adjustable bench power supply, set to 24 V

Bill of Material

Every part you need to buy, with quantities, notes and shop links, is in the Bill of Material PDF in the files of this model. The motors, encoder kits, AT3 timing belts, MR84 bearings and the IMU come directly from their makers, and the machined shafts and pulleys and the driver boards come from CNC and PCB assembly services. The build guide names each one; they are not in the shop list.

Software

Flash the Micro Driver and Master Board firmware from the Open Dynamic Robot Initiative, then run the robot control software on a Linux PC over Ethernet. Start with the robot on a stand and test one joint at a time.

Skill level

Advanced. Expect precise press-fits, bonding pulleys with adhesive, crimping fine-pitch connectors, ordering driver boards and a few machined parts, and setting up the control software on a Linux PC.

Full build guide and source

The build guide, source and all project files: https://github.com/ToolKnox/hawkridge-odri-solo8-open-quadruped-robot (Code > Download ZIP).

Safety

Use a current-limited supply and keep a power cut within reach. Brushless actuators are strong and fast: keep hands clear of the legs and belts whenever the drivers are enabled. Inspect printed pulleys and belts after every few hours of running.