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I worked out the motor drive from a previous project.
I've built an Astrolabe with a RA section which shows the 24 hours in 1 mm increments.
So 24 hours x 60 minutes = 1440 minutes and 1 minute = 1 mm This gave me a wheel with a circumference of 1440mm. Divide 1440 x Pi (3.1415) = 458.379mm diameter for the Astrolabe.
I used this formula for the diameter of the ring portion of the mount to suit the scope. The mirror box section required a ring with a diameter of 696mm. So 696mm x Pi = 2186.484mm is the circumference of the ring. To convert this into mm per minute, divide 2186.484 into 1440 = 1.518 mm would equal 1 minute of the rings circumference.
The motor/gearbox unit I purchased for my local Jaycar which has a final drive speed of 2.93 rpm at 3 volts.
I built a further reduction drive gear and a drive shaft. This in turns drives a harmonic wheel attached to the drive shaft which turns the ring.
So now the Motor drive shaft rotates at 19.30mm per minute.
The Drive shaft for the Harmonic wheel is 9.85mm x Pi = 30.943mm in circumference.
The formulation for the circumference of the Harmonic wheel is as follows,
19.30mm per minute divided by 1.518 = 12.739.
12.739 x 30.943mm = 394.18mm for the circumference of the harmonic wheel.
I hope this helps!
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