Stöber Antriebstechnik has developed the ServoFit gear unit that has a backlash of less than three arc minutes. Martin Preece from Stober Drives in the UK says: "Much greater stiffness arises not only because four planet gears are used instead of three, but because of optimisation of the planet carrier and the use of needle bearings instead of ball bearings for the planet gears." The increased torsional rigidity reduces positioning errors under load and improves vibration behaviour, at the same time as enhancing reliability and extending life. The gearboxes are lubricated for life and are offered with motor adaptors and servo motor attachments. Right angled units are also available.
Four planets are better than three
By using four planet gears instead of the usual three, planetary gearboxes are able to deliver 35% greater torque and an 80% improvement in torsional rigidity, in the same sized gearbox
