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Two optical encoders are required on each axis of the telescope. They measure the movement on the RA axis (left and right) and the Dec axis (up and down). The following two pictures show them respectively (the right picture shows the encoder with its cover removed, exposing the shaft, code wheel and encoder module):

RA Encoder. . . . . . . .Dec Encoder

The encoders that I'm using for the LX10 are US Digital Corporation ones (a full description of they encoders are given at this link). The part numbers that I bought are E3-2048-197 (5mm shaft for the RA axis) and E3-2048-187 (3/16" shaft size for the Dec Axis) - each costing $58. Both encoders have a 2048 cycles per revolution but because they output a quadature signal on two channels they have a final resolution of 8192 reference points per each complete revolution. This gives an accuracy of 2.6 minutes (0.04 degrees) of arc.

The RA encoder is fixed to the LX10 by first removing the RA hub cover. A central hex screw is removed and replaced by a longer 5mm screw with a shaft. This is used to attach the encoder's code wheel to. The head of this screw is removed and a nut is threaded onto it and nipped up with a spanner against the bearing retaining washer to hold it in place. This keeps the RA bearing assembly together. A small packing disc is placed into the hub recess to make it level with mount. The encoder base plate is then screw down using the two 5mm holes used by the hub cover screw. The encoder is then assembled as per the instructions provided. A centering tool is required for accurate alignment of the encoder.

The Dec encoder is mounted on the left fork arm. The setting circle is removed and an aluminium plate is screwed into place to the two factory drilled holes which exist each side of the Dec hub. A 3/16" shafted screw, with head removed and screwdriver slot cut in its place, is inserted and tightened. The encoder base plate is the fastened to the aluminium plate by two self-tapping screws. The encoder is then assembled as per instructions.

Each encoder has an IDC cable connected to it which runs to the connector box.