THE NEXT ROBOT HAS TO EARN EVERY NUMBER.
The humanoid work is paused. ATH is investigating a racket-bearing robotic arm on a driven wheeled base. The design target is up to 60 m/s racket-head speed, alongside broad on-court shot coverage, fast serves and high-spin groundstrokes. That speed is a requested requirement, not measured ATH performance. The hardware, its physics model and those abilities are not validated.
ESTHER, not ATH
A published tennis robot mounted a 7-degree-of-freedom, cable-driven Barrett WAM arm and racket on a motorized tennis wheelchair. Cable drive is not the same as the QDD architecture under consideration. The researchers measured 10 m/s pre-impact racket-head speed and 1.42 m/s² autonomous base acceleration. In ball-machine court trials, 66% and 53% of shots were returned successfully in the two reported setups (15 trials each). The 60 m/s ATH design target is six times ESTHER's measured 10 m/s racket-head speed. This ratio compares targets, not proven capabilities. Those results belong to ESTHER, not our proposed robot. Read the paper.
Arm + driven base
Candidate layout: a powered wheeled chassis, a multi-joint racket arm, physical racket and stringbed contact, ball tracking and an inverse-kinematics planner. No arm, motor, gear ratio, wheel, power system or sensor stack has been selected as a verified ATH build. A component's catalog limit does not prove an assembled robot can perform a shot.
Parameter ledger
"Published" means a cited component or study number, not a certified value for ATH. Unverified cells cannot silently enter a physics simulation.
| Subsystem | Grounded reference | What remains unverified for ATH |
|---|---|---|
| Arm kinematics | Barrett describes a 7-DoF WAM with approximately 1 m reach. Its published inertial document includes link and drive data but calls itself a draft. Datasheet · inertial draft | Exact selected arm and revision; measured link inertias, joint friction/backlash, end-tool/racket geometry, self-collision and joint-specific torque-speed limits. |
| Motor and drive | HEBI R-series modules and ODrive motor characteristics publish candidate performance data. Quasi-direct-drive (QDD) is a candidate architecture class: a low-reduction transmission paired with a high-torque-density motor, not a selected ATH joint. The MIT Cheetah actuator study explains the tradeoff between reduction, reflected inertia and impact backdrivability. Neither a QDD label nor a component catalog establishes 60 m/s. | Exact motor winding, controller, gearing, voltage, current limits, torque-speed curve under load, cooling and duty cycle. For a QDD candidate, fix motor/winding, drive, voltage, gear ratio and mechanical design, then check published and measured joint torque-speed curves, reflected rotor inertia, electrical power and thermal duration against the full 60 m/s racket-tip trajectory. Joint speed alone cannot establish racket speed. |
| Wheels and court | ESTHER reports driven-wheelchair field measurements and its own drivetrain. Study | Our chassis mass/CG, wheel radius and drive, tire-court grip on each surface, slip, acceleration, braking, tipping and turning with arm motion. |
| Racket and ball | Published stringbed studies measure impact dwell and rebound under stated test conditions, not our racket. Kawazoe et al. · Washida et al. | Chosen ball/racket/string/tension: measured impact map across center, edge and rim; spin transfer, deformation, recoil, wear and high-speed aero/spin decay. Existing site racket contact is not validated. |
| Racket speed target | ATH design requirement: up to 60 m/s racket-head speed. ESTHER measured 10 m/s in its own system, not ATH. ESTHER study | Show a feasible time-resolved 60 m/s tip trajectory through the complete IK chain and measured joint torque-speed/current, reduction, reflected rotor inertia, power, thermal and structural limits. Then measure actual racket-head speed. No selected ATH hardware has passed this gate. |
| Shot and ball-exit targets | Measured impact data must tie a particular inbound ball and racket state to outbound speed, spin and trajectory; tip speed alone cannot set ball exit speed. Impact study · String study | Measure player-specific contact height, racket-head pose and velocity, outgoing ball speed/spin and landing distribution for a Nadal forehand, an Opelka serve and the wider shot set. Test the selected racket/ball stringbed at relevant inbound speeds, impact locations and angles before predicting ball-exit speed at 60 m/s. No "any shot" verdict yet. |
How the model earns trust
- Choose exact hardware revisions, acquire manufacturer curves and measure the assembled arm, base, wheels, racket and ball. Trace each parameter to a source or an experiment.
- Implement full rigid-body dynamics, wheel-court contact, three-dimensional ball flight and spin, stringbed/frame contact and inverse-kinematics shot planning within measured actuator envelopes.
- Check numerical convergence, collisions, energy and impulse accounting. Validate the full racket-head speed time history and measured ball exit speed/spin, rather than deriving either from one peak tip speed. Hold out real trajectories, impact locations, surfaces and shot types before claiming transfer to hardware.
An IK solution is only a reachable pose. It does not prove the arm can get there in time, survive the load or make the ball land. Speed, acceleration, torque, power, tire grip and contact tests must all pass.
Ball machine
Open the site's existing ball-feed simulator to explore launches. It still uses historical H2 assets; it is not an arm-on-wheels simulation or evidence that the proposed robot returns the balls. Its racket contact has not passed calibration.