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Context: Many previous studies have shown that the magnetic precursor of acoronal mass ejection (CME) takes the form of a magnetic flux rope, and asubset of them have become known as `hot flux ropes' due to their emissionsignatures in $\sim$10 MK plasma. Aims: We seek to identify the processes bywhich these hot flux ropes form, with a view of developing our understanding ofCMEs and thereby improving space weather forecasts. Methods:Extreme-ultraviolet observations were used to identify five pre-eruptive hotflux ropes in the solar corona and study how they evolved. Confined flares wereobserved in the hours and days before each flux rope erupted, and these wereused as indicators of episodic bursts of magnetic reconnection by which eachflux rope formed. The evolution of the photospheric magnetic field was observedduring each formation period to identify the process(es) that enabled magneticreconnection to occur in the $\beta<1$ corona and form the flux ropes. Results:The confined flares were found to be homologous events and suggest flux ropeformation times that range from 18 hours to 5 days. Throughout these periods,fragments of photospheric magnetic flux were observed to orbit around eachother in sunspots where the flux ropes had a footpoint. Active regions withright-handed (left-handed) twisted magnetic flux exhibited clockwise(anticlockwise) orbiting motions, and right-handed (left-handed) flux ropesformed. Conclusions: We infer that the orbital motions of photospheric magneticflux fragments about each other bring magnetic flux tubes together in thecorona, enabling component reconnection that forms a magnetic flux rope above aflaring arcade. This represents a novel trigger mechanism for solar eruptionsand should be considered when predicting solar magnetic activity.

A new trigger mechanism for coronal mass ejections: the role of confined flares and photospheric motions in the formation of hot flux ropes