View Single Post
  #1  
Old 10-10-2009, 10:04 AM
kinetic's Avatar
kinetic (Steve)
ATMer and Saganist

kinetic is offline
 
Join Date: Jun 2008
Location: Adelaide S.A.
Posts: 2,280
Motorised focuser (Bartels system)

There are many ideas on how to homebrew a motorised focuser and even a few in the
IIS archives. Here is my unit I have been making over the last few weeks.

It is a modification of a GSO 10:1 Crayford style focuser with a mini stepper motor which
interfaces to the focus option on the Bartels system.
I used a little belt reduction unit salvaged from an old bubblejet printer as the source of
stepper, belt and nylon toothed wheel. Pic 1
First I removed the black 10:1 knob from the GSO focuser which attaches with a M4
grub screw.Pic 2
I then had to turn a new knob with a shaft for the blue toothed wheel to sit
on and spin freely. Pic 3
I also turned the blue nylon wheel down so all that remained was the toothed section.
I also made a second knob which would be the pressure plate adjustment to allow
the motor to drive the focuser but slip if it came to an end travel.
All the bits shown in Pic 4 I used a slightly larger toothed belt with
the same tooth pitch to get the right motor-wheel spacing.

Pressure is applied to the clutch by turning the two adjustment screws at the end
of the knurled knob and a white nylon washer pushes on the side of the blue
nylon wheel.
Pic 5/6 Manual focus can still be done by just turning the 10:1 knurled wheel.

The electronics: I initially tried a TA7774P Stepper driver IC as the link between Mel's
SCOPE program and the motor but it was not an exact swap for the real IC needed,
the MC3479.
The MC3479 drives it much better with step and direction control direct from parallel
port pins 16 and 17.

Finally, PIC 7 is a load test with the DSI and homemade filterwheel attached.
Lifts it nicely.

Steve
Attached Thumbnails
Click for full-size image (stepper.jpg)
79.9 KB328 views
Click for full-size image (ten_to_1.jpg)
29.0 KB292 views
Click for full-size image (new_knob.jpg)
43.9 KB291 views
Click for full-size image (parts.jpg)
108.8 KB303 views
Click for full-size image (clutch.jpg)
67.2 KB345 views
Click for full-size image (clutch_plate.jpg)
62.0 KB320 views
Click for full-size image (DSI.jpg)
113.9 KB370 views

Last edited by kinetic; 10-10-2009 at 05:40 PM.
Reply With Quote