Gear insertion on pager motors

Motor's back changed !

Pagers' motors are very well built, but one need to understand their construction to avoid any damage to the brushes when assembling. It is not possible to exerce any axial force on the shaft. This is a major problem when inserting gears if the gear is not loose. If the gear is loose, a drop of cyano will hold it, but if the drop is too large the risk to glue the shaft and block definitively the motor is high.

Les us consider a first frequent case, with a 12 teeth POM pinion to be inserted on the axis of a 6mm pager motor. The motor axis is 0.80 mm, the pinion 0.78 mm, so it is a perfect match, that will not stress the gear, and allow for a rather easy insertion and possible removal, but an adequate tool is required.

The 12 teeth pinions are not symetrical. It is important to look carefully, using a watchmaker lens, at the gear and notice the hole is slightly smaller at one end, and the gear side is slighthy rounded; this will facilitate the insertion of our propeller connectors. It facilitates also the insertion on the shaft, and the additional force due to the smaller extremitiy diameter increases the retention force when fully inserted. But now, be carefull; If you push the gear on the motor, the shaft may be pushed inside the motor, so for the collector that will deform the brushes.

You need an adequate tool for maintaining the axis. The motor is placed in a hole with a thin screw (less than 1.6mm) pushing on the axes, that is on the collector around the axes. Round the extremity of the screw, in order to have a regular effort. Now you can depress your gear.

Removing the gear must be done by inserting a thin V-shaped sheet of metal between the gear and the motor, and using a 0.7mm needle to press on the axis, the gear being maintaind by the sheet metal.


To be continued

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Last update: 08.05.02/jcz