Specification:
Optics:
18” f4.5 (mirror set shared with my observatory scope)
Feathertouch Focuser with integrated Paracor, (SIPS)
Physical:
Total Weight; about 30kg
Size; will fit in the boot of my car, (except truss poles!)
Max eyepiece height; 2.1 metres
Truss poles; 20mm Al tubes covered in black heat shrink.
Electrical:
Geared stepper motors driving through toothed belts
40000 tick encoders
Nexus DSC for scope position readout
SkySafari for telescope control
Raspberry PI driving stepper motors via Phidget modules
Plate-solving digital finder finishes goto’s to 1 arc min.
This scope has been a 10 year journey, striving to reach ultimate performance in a size and weight that can be transported in my car.
Phase 1: The mirrors were removed from my observtaory equatoria fork mount and the basic UC design took shape. Ithad the usual ptfe (Teflon) pads for bearings.
Phase 2: testing with the servos showed that the PTFE bearings were giving too much friction. I replaced them with ball bearings and now it runs very smoothly and easily. Added the encoders, wifi link and starting to finish off the wiring and installation of ancillaries.
Phase 3: Having proved the drive system to work very well, the decision was made to go into small scale series production! Working with a friend we designed a compact unit built into a high quality aluminium case, laser etched panels and improved user setup and interface.
Phase 4: Modifications were undertaken between 2017 and 2019.
Changed from 'toothed wheel drive’ to ‘toothed belt drive’. Although not as elegant the performance is so much better. At the same time I introduced clutches on both axes. the scope can now be simply pushed to a new location in the sky, and the tracking drive automatically recalculates and takes over at the new position.
Phase 5: Squeezing everything into my new Mustang was getting tedious, so a rebuild was undertaken to make the scope more compact when being transported, and a bit stiffer in winds.
The Altitude drive is now via rollers on both trunnions. This gives superb motion control.
The electro-magnetic clutch shown here isn't really necessary - a simple slip clutch suffices.
A gallery of photos of the telescope is presented here for those looking for inspiration!
Recently I’ve added a digital finder scope, and ‘eFinder’. This is described here. It automatically improves GoTo accuracy to about 1 arc minute with respect to real sky RA & Dec.
I have decided that the current design no longer should be called a Dobsonian. It is so far from John Dobson’s original concept both mechanically and with the addition of tracking, GoTo and eFinder. It's an AltAz Scope!