projects / 1

7-DOF Quasi-Direct-Drive Collaborative Robot Arm

payload/mass ~1:1 (10 kg) reach 1.11 m structural mass 10 kg actuators RobStride QDD × 7 bus Decentralized CAN status In Progress (Hardware Complete)

A commercial-grade 7-DOF collaborative robot arm inspired by the Flexiv Rizon and Universal Robots UR series. Features a high-strength 3D-printed PETG link structure, quasi-direct-drive actuators, decentralized CAN bus architecture, and a 1:1 peak payload-to-mass ratio (~10 kg). Development Status: Full mechanical assembly and manual joint articulation are validated; autonomous trajectory control and ROS 2 / MoveIt2 integration are under active development.

Manual articulation test showing smooth multi-joint movement across all 7 degrees of freedom

Fully assembled 7-DOF robot arm with parallel-jaw gripper mounted on heavy base pedestal

[01/02] 7-DOF Manual Articulation Validation: Manually demonstrating multi-joint backdrivability, smooth range of motion, and structural balance across all 7 axes before autonomous commissioning.

Elite payload-to-weight ratio: a 10 kg custom 3D-printed arm rated for a ~10 kg peak payload at full 1.11 m horizontal extension, and a 3–5 kg continuous working payload.
Cut ~2 kg of structural mass through slicer parameter optimization — an isotropic 7% gyroid infill matrix maximizes torsional rigidity per gram.
Industrial cobot architecture & surface modelling: Uniform cylindrical links, ergonomic surface-modelled joint transitions, interlocking spigot structural joints, and slip-ring internal routing.
Complex CAD assembly: Managed a 5,000+ component model with multiple subassemblies, configurations, and sub-configurations to design and validate complex moving systems (SpeedPaks dropped rebuild times from 10 minutes to seconds).
Decentralized CAN bus & transient-safe power: Daisy-chained RobStride QDD actuators communicating over differential CAN with localized buck regulation isolating logic from motor inductive spikes.

01CAD & Surface Modelling

Sculpted in SolidWorks using multi-guide boundary surfaces and lofts to achieve continuous cylindrical cobot contours, packaging seven high-torque RobStride actuators with sub-millimeter internal tolerances.

01.1 External Assembly & Kinematic Surfacing

Outer link curvature, ergonomic knuckle geometries, and workspace reach envelopes engineered for cobot collaborative aesthetics and clean tool mounting.

Full arm isometric SolidWorks CAD assembly

Shoulder and base hub mounting CAD detail

Elbow joint articulation and clearance CAD

Spherical wrist pitch and yaw clevis CAD

Interlocking spigot lip interface cross section CAD

RobStride QDD actuator CAD model packaging

Multi-pose CAD reachability envelope overlay

[01/10] Full Arm Isometric Assembly: Complete 7-axis kinematic tree showing uniform cylindrical links, ergonomic joint housings, and end-effector tool flange.

01.2 Wireframe & Internal Packaging Architecture

Transparent CAD cutaways illustrating internal structural ribbing, actuator mounting clearances, nested angular contact bearing races, and central wiring conduits through the 7-axis kinematic chain.

Actuator interface and bearing seating CAD cross section

Orthogonal joint cluster internal CAD assembly

Forearm, wrist and gripper wireframe CAD kinematics

Wireframe internal cavity CAD showing raceways and clearances

[01/05] Full 7-Axis Kinematic Tree Wireframe: Transparent profile showcasing internal actuator alignment, base ballast mounting, and external control hub console.

02Cassette Ring Modular Joints

Custom 3D-printed spiral cassette rings house internal flexible wire coils to permit continuous 360° joint rotation without cable tangling or mechanical fatigue.

Internal spiral wire cavity in 3D printed cassette ring

Cassette shell and bearing lip component

Bench articulation test of cassette ring joint

Graduated stack of modular cassette rings

[01/04] Spiral Flexible Ribbon Cavity: Internal circular track guiding continuous wire expansion and contraction during continuous joint revolution.

SolidWorks CAD · Exploded Joint Stack

Exploded SolidWorks CAD view of the cassette ring joint stack with bearing races

Physical Assembly · Bench Fitup

Assembled physical cassette ring joint showing bearing race, wire exit, and 3D-printed housing

Cassette Ring Joint — CAD vs Physical — Custom spiral-coil cassette housing built to exact tolerances of the SolidWorks model, validating bearing seat fit and wire routing.

03Electrical Architecture & CAN Bus

A decentralized multi-drop CAN bus connects all seven RobStride actuators over a single shielded twisted pair, backed by transient-protected 48V DC power distribution.

Multimeter measuring bus termination resistance

XT30 and Molex wiring harness assemblies

ESP32 transceiver connected to motor logic for bench testing

[01/04] Bus Continuity & Resistance Check: Measuring 120 Ω terminal resistance across differential CAN-H/CAN-L lines to prevent signal reflection.

04Motor Module & Buck Regulation

High-power RobStride quasi-direct-drive actuators are paired with dedicated step-down buck regulation modules to isolate logic voltages from heavy inductive motor transients.

Direct motor wire dress and connector interface

Voltage check on actuator logic supply terminals

Buck converter integrated into motor module shell

Decoupling capacitor bank on buck regulator module

Thermal and load testing on buck converter module

Harness dressing separating DC power from CAN lines

Fully assembled joint power node ready for installation

[01/09] RobStride QDD Actuator Unit: High-torque planetary quasi-direct-drive actuator with integrated magnetic absolute encoder and CAN driver.

05Arm Assembly & Joint Conduit

Structural links were fabricated in high-strength PETG with 7% gyroid infill, assembled with spigot shear joints, and routed with central internal wiring conduits.

Animated demonstration of wiring flexing cleanly through rotating hollow joint conduit

Spigot joint mating on PETG arm link shells

Heat set insert installation into 3D printed arm links

Seating thin-section bearing into joint housing

Torquing screws on RobStride motor mount

Assembled lower arm trunk cluster on bench

Passing wire umbilical through forearm conduit

Full 7-DOF arm stood upright on workbench for inspection

Base cable strain relief collar clamping

7-DOF arm extended horizontally across bench in rest pose

[01/11] Conduit Wire Flex Demonstration: Internal wiring bundle smoothly flexing and twisting through the hollow joint center as the housing is manually rotated 180°.

06Parallel Jaw Gripper

A compact dual rack-and-pinion parallel-jaw gripper actuated by a high-torque coreless servo delivers symmetrical grasping force and swappable high-friction finger pads.

Animated demonstration of parallel gripper jaws opening and closing

Gripper mechanical SolidWorks assembly CAD

Close-up CAD of rack and pinion gear mesh

Physical gripper hardware assembled on workbench

Gripper installed on the distal wrist axis of the robot arm

[01/06] Synchronized Jaw Opening & Closing: Bench demo showing dual rack gears driven by central pinion for rapid, synchronized parallel finger travel.

07Control Hub & Power Enclosure

The standalone control hub integrates an ESP32 master controller, CAN transceiver circuitry, 48V power distribution blocks, and a master emergency-stop switch inside a fan-cooled enclosure.

Internal mounting standoffs and cable raceway CAD

Power distribution screw terminal blocks in hub enclosure

Front panel switch and safety circuit wiring

Completed control hub electronics bay with wiring combs

Completed control hub tethered to arm base harness

Control hub positioned next to weighted arm pedestal

Rear panel showing DC power jack and USB-C port

Sealed control hub with active power LEDs

[01/10] Control Hub Enclosure CAD: Ventilated base console design featuring dedicated bays for power supply, MCU, and external I/O.

08Weighted Base Mount & Stability Pedestal

To counteract heavy tipping moments at full 1.11 m horizontal extension, a custom steel mounting flange anchors the arm securely to heavy barbell ballast plates.

Arm bolted to stacked barbell ballast plates on workbench

Arm fully extended verifying base stability against overturning moment

[01/03] Weighted Base Flange CAD: Rigid heavy-duty pedestal plate with perimeter clamping holes and central conduit drop.

09Future Goals & Technical Roadmap

With physical assembly and manual kinematic validation complete, active development is transitioning to software simulation, autonomous trajectory generation, and impedance control.

URDF Generation & Kinematic Verification: Generating an accurate Unified Robot Description Format (URDF) file with exact link centers of mass, inertia tensors, joint limits, and visual/collision meshes.
High-Fidelity MuJoCo Physics Simulation: Importing the robot URDF into MuJoCo for reinforcement learning policy training, sim-to-real domain randomization, and obstacle avoidance validation.
ROS 2 & MoveIt2 Autonomous Trajectory Planning: Implementing ROS 2 Humble nodes with MoveIt2 for Cartesian path planning, collision-free obstacle avoidance, and numerical inverse kinematics (IK) solving.
Backdrivable Impedance & Gravity Compensation: Developing active feed-forward gravity compensation and Cartesian impedance control leveraging the quasi-direct-drive actuators' natural torque transparency.
Closed-Loop Gripper Tactile Control: Integrating piezoresistive pressure arrays onto parallel gripper fingertips for adaptive slip detection, compliant grasping, and delicate object manipulation.