The Graham variable-speed transmission is a compound planetary drive in which the positive contact between the ring gear and one
end of the compound planet gear has been replaced by rolling contact between a reaction, ring and a tapered planetary roller.
The axial position of the reaction ring determines the effective diameter of the planetary roller and, thus, the speed ratio
of the drive.
The planet carrier is driven by a constant-speed motor, and the centrifugal force on the planetary rollers
supplies the traction pressure between the rollers and the ring. Two types are available. The standard (nonreversing) types
give output speeds ranging from a maximum of approximately one-third input speed in the same direction, through zero, to approximately
one one-hundredth input speed in reverse. The B (reversing) types give equal speeds of approximately one-fifth input speeds
both sides of zero. Built-in reduction or step-up gear trains are normally used to give a wider range of maximum output speeds.
Capacities range from 1/15 to 5 hp at 1,750-rpm input speeds, and drive efficiencies
range from 65 to 85 percent, depending upon the size of the unit.