Parallel Robot Clock - Hackaday One Hertz Challenge

Project Summary

The Direct Drive Parallel Robot Clock uses a human capable 6-DoF parallel robot to create precise 1-second timekeeping. A 40mm ball moves clockwise through 60 pockets arranged in a 645mm diameter circle, advancing one position every second. The system executes a complex motion sequence combining vertical translation (75.932mm span) and rotation (6° per step). Each second, the platform drops at -5.0g, breaking contact with the ball, rotates to align with the next pocket, then catches the free-falling ball with minimal impact using calculated trajectories. Motion control runs on a Teensy 4.1 at 3003Hz over Ethernet, with real-time feedback from an ARK Forward Kinematics Unit. The catch trajectory uses acceleration control for speed, while the return uses snap-controlled motion for smoothness. 

Finally, a clock that requires a PhD to set the time.How It Works

The Physics

The magic happens in two distinct phases:

Catch Trajectory (0.000s - 0.136s):

  • Platform drops at -5.0g, breaking contact with the 40mm ball
  • Ball falls freely at -1.0g while platform rotates 6° to align with next pocket
  • Platform reverses direction (+3.0g briefly, then -5.0g again)
  • Calculated timing ensures both platform and ball have identical velocities at contact
  • Minimal-impact catch at t=0.114s, followed by +5.0g deceleration to complete stop


Return Trajectory (0.136s - 0.898s):

  • Smooth snap-controlled motion returns platform and ball to starting position
  • Uses advanced S-curve trajectory planning with kinematic constraints
  • Acceleration, jerk, and snap are all continuously controlled for seamless motion


Technical Specifications

  • Clock Face: 60 pockets in 645mm diameter circle (6° angular spacing)
  • Motion Range: +40.000mm to -35.932mm vertical, ±3° rotation
  • Control Rate: 3003 Hz command rate via 100M Ethernet/UDP
  • Feedback: ARK Forward Kinematics Unit providing sub-millisecond response
  • Precision: 1-second resolution over 60-second repeating cycle

Control Parameters (Online Adjustable)

  1. g - Gravity Acceleration Coefficient (tuned to 1.0475)
  2. tC - Time of Contact (0.1136s nominal)
  3. K - Max Translational Acceleration Coefficient (5.0g)
  4. tY - Rotation Start Time (tuned to 0.017s)
  5. aY - Max Rotational Acceleration (12000°/s²)

Innovation Highlights

Advanced Motion Control

This project showcases cutting-edge open source robotics. The snap-controlled trajectory algorithm provides Online, Kinematically Constrained, Snap-Continuous S-Curve Trajectory Planning - technology typically reserved for high-end industrial applications.

Real-Time Performance

Live performance data shows exceptional tracking accuracy between commanded and actual positions. The system maintains microsecond precision while executing complex ballistic trajectories at multi-g accelerations.

Elegant Simplicity

Despite the complex underlying physics, the result is beautifully simple: a ball moving in perfect 1-second intervals around a clock face, defying gravity with each precise movement.

Build Details

Required Components

  • ARK PDK 6-DoF Direct Drive Parallel Robot
  • Teensy 4.1 Development Board with Ethernet
  • 40.00mm diameter ball (squash ball)
  • 690mm diameter × 15mm thick circular base (marine plywood)
  • 10× Clock Face Segments (3D printed)
  • Custom motion control software

Performance Data

The included graphs demonstrate:

  • Precise acceleration profiles during catch trajectory
  • Smooth snap-controlled return motion
  • Real-time tracking performance showing commanded vs actual positions


Key Achievements

  • Minimal-impact ball catching through calculated velocity matching
  • Sub-millisecond position feedback and control
  • Seamless integration of controlled motion phases