3. Astronomy - mounts ( EQ1 with 2 arms)

This project involved fitting an old EQ mount with a fixed arm and a 2nd arm driven by a hand cranked screw - another variation on the standard barn door tracker.

This would have worked well except the bearings were too worn on the mounting (and possibly I damaged them when I took it apart). The screw and loose bearings introduced a slight wobble into the movement which I interpreted (wrongly) as a tracking error caused by poor hand cranking.

The fixed arm provides the reference point and it's to this arm that the hand cranked screw is attached to - just a 3mm 0.5mm pitch bolt in my case.

The 2nd arm is attached to the RA axis. A spring between the two arms keeps them together, while the screw bolt forces them apart at the rate of 0.5mm per minute. The distance between the screw and the centre of the RA axis was approx. 114mm - but it was hard to be accurate and I'm sure I was a few mm out.

All the elements, except for the tripod ball head mounted in place of the OTA (top right)

Three bolts screwed into holes drilled in the main drive gear serve to attach the 2nd arm to the RA axis.

The two arms would usually only move 5 - 10mm apart during a full photo session. 10mm of movement represents a total of 20mins of tracking.

The stop watch second hand is used as a guide to how fast to turn the hand cranked wheel.

The springs (far left) keep the 2nd arm close to the fixed arm. The screw bolt is what pushes the 2nd arm away, and this rotates the RA axis.

A couple of bits of meccano and some soldering produced the box. A nut was soldered onto the box and the threaded bolt screwed into place.

Apart from a wobbly bearing, the need to hand crank was the main downside to this type of approach. Still, it wouldn't be too hard to add a motor to this.