Tracking

Analysing how the system corrects for periodic encoder errors due to the gears it has been realized that the way these corrections are applied are probably the cause for the residual periodic variations seen in altitude. The variations in the encoder values caused by the imperfect shape and/or centring of a gear are a fixed function of the turns of the gear or, equivalent, a periodic variation as a function of encoder steps. However, while in azimuth a certain amount of encoder steps will cause a certain amount of movement on the sky independent on where you point the telescope (assuming a properly balanced telescope), in altitude flexure will cause a certain amount of encoder steps to be a variable amount of movement on the sky depending on the altitude of the telescope. As the periodic error corrections are applied in degrees on the sky the correction is expected to work well in azimuth but cause residual periodic errors in altitude which vary as a function in altitude (as observed). The way the periodic error corrections are applied in the TCS software will be changed to improve the correction.