EQ3-2 motor gearbox reduction ratio

I’ve decided there’s nothing more I can do with my EQ3-2 mechanics to improve the backlash that’s painfully obvious in the DEC axis. What backlash there is left (about twelve seconds at the 8x speed when changing direction) appears to be in the motor gearbox. So I’m thinking about replacing the gearbox assuming I can find something to do so at a reasonable price.

The first step was to establish the reduction ratio of the existing gearbox. To that ends I took my spare one apart and photographed all the gears so I could load the images onto the PC and count the teeth. These are the numbers I ended up with:

  • Motor out: 12
  • Gear 1 in: 30, out: 14
  • Gear 2 in: 42, out: 14
  • Gear 3 in: 28, out: 14
  • Gear 4 in: 28, out 10
  • Final drive in: 40

I make that to be reduction ratios of 30/12, 42/14, 28/14, 28/14 and 40/10, or 5/2, 3, 2, 2 and 4, giving a total reduction ratio of 120:1.

So, the search is now on for alternative mechanisms of achieving a 120:1 reduction ratio with the minimum of backlash.

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