ETX-80 DIY ELECTRIC FOCUSER Last updated: 18 February 2009

Sent:	Wednesday, February 18, 2009 11:03:25
From:	Chris Vickers (chris@bubla.co.uk)
Firstly may a say thanks for a great site, it has provided me with many
ideas and answered many questions for my ETX-80.

With my etx-80 i always had the common problem of focusing it without
knocking it off line. I thought the flexible focuser would be a
solution, but none would fit my scope. I then went onto looking at an
electric focuser, again no commercial products were available for the
80. One thing I did not want to do was drill any holes, or glue anything
onto my shiny etx-80, you never know when she may have to go on flebay
to be upgraded!

I found this site  http://emediadesigns.com/focuser/ for a Celestron
8SE, and using the info there started on construction. I will not go
into continuous servo rotation mods, there are plenty of webpages
available via Google.  Servos were no problem as i had several kicking
about, and the rest of the bits came mainly from Maplin here in the UK,
apart from the cable which came from ebay already fitted with a 3.5mm
jack on one end.

The main change I made to start with was to put the socket on the servo
at 90 degrees so it came out of the side, this was to give me the
clearance around the focus knob.

I used O rings as suggested by Brian, but they slipped badly, and I
couldn't get enough grip. This was a real problem until I found a couple
of plastic gears from a electric model plane. A small one was drilled
out until it fitted snugly on the servo, the bigger was then drilled out
until it clipped on top of the ETX-80 focus knob. I have not glued it at
all on there, it is just a tight fit. I bent up a quick bracket from
some thin metal which the servo is glued too. It is attached to the
telescope with the screw used to hold in place the cover to the focuser
gear. A slightly longer screw was need here. I also used a bit of thin
double sided servo tape to make it more secure.

One adaption I made to the box, was to put in an extra switch (push to
make contact) with this you can just tap it to move the focuser a tiny
amount. The direction of the servo is controlled by the DPDT switch,
which is on-off-on with locking both ways. The potentiometer controls
the speed of the servo.

I can now focus easily without moving the scope, which is especially
useful at higher magnifications. I hope this may be of help to other
people, and I am sure it can be adapted for other etx scopes.

All the best
Chris Vickers
Ipswich, UK.

Go back to the Tech Tips page.

Go back to the ETX Home Page.