Re: Choosing a shaft encoder? We're using a track drive system and we're going to be using L.E.D. proximity sensors off of the teeth of the track gears.  The tank tracks appear to be very stable but it's still too early in the development to know how repeatable the robot movements are going to be. Although the knowledge of how far the robot has moved is of some importance, the algorithms I've been reading about only need an approximation for mapping the surrounding environment. --  James Dunn jdunn@unm.edu Chat# 14708321 Like a rose, life is sweet, with just enough thorns to make it interesting.       _,--._.-,      /\\_r-,\\_ )    .-.) _;='_/ (.;     \\ \\'     \\/S )      L.'-. _.'|-'      <_`-'\\'_.'/       *-._( \\       ___   \\\\,     ___       \\ .'-. \\\\ .-'_. /        '._' '.\\\\/.-'_.'           '--``\\('--'                 \\\\                 `\\\\,                   \\|