[axle01 (Alan)]

I thought i'd have a go at making a BarnDoor Star Tracker to track the stars as the earth turns hoping to be able to get somewhere between 5 to 10 minutes shutter speeds.

First i did a lot of research to work out length, motor speed, gear ratio etc. then i got to work i started with 2 pieces of 350mm x 100mm x 10mm alloy plate and 2 pieces of 120mm x 100mm x 10mm alloy plate.

I then went to Bunnings and got 2 of the best hinges with the least amount of side play i could find.

I drilled and bolted the 2 long plates and the 2 small plates to the hinges.

I then bolted the small plate to the large plate, this is to adjust for our latitude which in my case is 19*16S.

I then mounted the ball head towards the low end of the wedge to allow the least weight resistance to the motor drive.

I had worked out that the distance from the hinge pivot point to the threaded rod mount would be 29cm so i got a length of 1/4' SS threaded rod which i bent in a 29cm radius.

The reason i use a curved rod is if i used a straight rod it would introduce tangent error which means as the angle increases the speed will change.

The gears are 80T x 20T which is 4 to 1 and the motor spins at 4RPM which on the 1/4' x 20 will give me 15* per hour which is what the earth turns at.

I got most of the motor mounting and gear mounting hardware etc from ServoCity in America, was a real pain waiting for the stuff to arrive then having to order more as i needed it.

I had a forward/reverse controller which i mounted on the bottom plate to control the speed.

Now i have it all together i did a test and it rises at 15* an hour which is what i am aiming for.