Motor Focuser Attachment to Esprit 150?

[BlueAstra]

Does anyone know the correct mounting points for a motor focuser on an Esprit 150? Looking at the bottom of the focuser there are four slotted screwheads that seem to be set in concrete. Are these the best place?  Also how do you get the focuser knobs off. The x10 knob comes off easily by undoing a screw, but there are no obvious screws for the large knobs. Again they appear to be set in concrete if you pull them. The focuser is a Pegasus cube on an L bracket.

 

[Allinthehead]

Try peeling the rubber from the focus knobs. There should be grub screws underneath.

[Laurin Dave]

This is a different focuser to the one on my 150 but I suspect that if you rotate the focus knob the grub screw will become visible in the hole in the focuser body.

Dave

 

[BlueAstra]

I have now managed to attach the Pegasus Motor Focuser to the Esprit 150. With the help of the focuser patent drawing I was able to identify some of the features on the bottom of the focuser:

A – Threaded hole for grub screw. Not sure what this is for other than to hold a spare screw for the knob fixing screws. If you screw it right in then it hits the spindle and locks it.

B – Access hole for knob locking screws. Rotate the knob until the screw is visible, loosen screw and pull off the knob.

C, D – Not sure what these are other than to hold the spindle assembly to the focuser barrel.

E – Screws to hold the bearings (12 on patent drawing) which grip the metal plate attached to the barrel.

F – Tension screw which controls the pressure of the spindle against the metal plate

G – Locking knob (221) which clamps the barrel plate and prevents any movement of the focuser.

I wanted to remove the coarse knob to attach the motor focuser. However, it was stuck and would not remove easily. I removed the x10 knob (easy), loosened the tension screw F and withdrew the spindle with the coarse knob attached. I put the spindle in a vice (taking care not to grip the plate contact area) and twisted the knob off. Once off it went on and off quite easily, so something must have been holding it. I then re-inserted it into the focuser, re-attached the x10 knob and re-tensioned screw F. I now had a bare end of the spindle to attach the focuser to.

I offered up the motor/L bracket and found the L bracket was too long. It interfered with the locking knob G. I removed some material to avoid the clash. I then set the motor position on the bracket and secured it. I removed two M3 screws at C and used two longer screws with washers to secure the L bracket. A locking cylinder connected the motor to the focuser (a selection is supplied with the motor).

I connected the temperature sensor, 12V power and USB cable, and I can now control the focuser through its own app, or via Ascom in other programs. The motor is too stiff to allow manual focus via the knobs. You can get a manual control box but it’s quite expensive.  I am currently trying to take out backlash by adjusting F, although there is backlash control in the software. I’m not familiar with focuser construction, but I was surprised that it operates by pressure of a bare metal spindle on a flat metal plate. I thought there would be some friction material between them. It remains to be seen whether it can cope with large camera loads at high declination. If not I may have to upgrade to rack and pinion.