A320
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Situational Awareness; Human-Machine Interface
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Rolling takeoff; First Officer flying; at transfer of control; First Officer powered up and almost simultaneously as Captain's hands on throttle / 40 knots 'Airspeed Alive' First Officer calls out 'you have control; you have control'; as I started to take over; [the] nose began veering right and due to low speed and long runway elected to discontinue takeoff / reject unaware of nature of the problem. Once aligned with centerline and taxi speed; 'remain seated' announced by Captain as we cleared runway. First Officer declared his rudder pedals had broke free of adjustment and went to the floor giving him no rudder authority. We elected to return to gate where maintenance locked pedals into desired position in accordance with the MEL.
A320 Captain reported a rejected takeoff and return to gate caused by the First Officer's rudder pedal adjustment failing.