Goto and tracking

After building a second version of the telescope the only thing that was missing was a tracking and goto capability, which I considered to be too difficult for me to build. That was until I met some members of the Almere Astronomy Society (SSA) on a public event in march 2006. They were just starting a workshop on how to build Goto control.

Goto Controller

The system that they were building was initially designed build by Martin Cibulski from Germany. This system is essentially a microcontroller for micro-stepping stepper motors that you mount on your alt-azimuth mount. Building such a Goto control for a telescope consists of roughly three phases. 1) The construction of the computer and handcontroller, this is a matter of getting the parts and soldering according to a plan. 2) Programming the computer. 3) The mechanical adjustment of the telescope. In October 2006 the Goto control was nearly finished and programming the different parameters could start. I made as spreadsheet to calculate slew speeds, gear ratios and how much arcsec a microstep would be.

Mechanical adaption

The mechanical adaptations to the telescope took more time. A computer-controlled telescope requires a more precise construction then a Dobsonian. In order to adapt the telescope I had to rebuild the entire rocker. Stepper motors and gearing had to be mounted and the bearing surfaces needed to be changed to stainless steel. The lightweight telescope gained some kilos because of this and weighted about 33 kg without a battery. I was very happy with the conversion to Goto control which was finished in December 2007. The amount of objects that I could observe in one night tripled, and high magnifications where a lot more comfortable to use.

Refiguring the mirror

Unfortunately this didn’t mean that I had a perfect telescope. During this conversion to Goto I had discovered that my main mirror was seriously flawed. It had a huge amount of astigmatism. It had not gone unnoticed to me that when magnifying more than 150x stars weren’t really dots, but I’d always  put it down to seeing or my eyepieces. Now that I had some Naglers there was no getting around it. Testing the mirror gave some daunting results, the mirror got to ½ PV. Buying a new mirror was not an option so in the end a friend used a machine and a lot of skill to refigure the great mirror to a PV of 1/8.


Total rebuild