Quote:
Originally Posted by Rod
Hi Barry,
Are you aware of Mel Bartels stepper drive system? You can find details here:
http://www.bbastrodesigns.com/BBAstr...ted_Telescopes
I built the stepper drive for my 12 inch dob and it works well, although I am still ironing out some issues with goto. You can get excellent tracking, goto and slew speeds are usually between 1.5 and 3 degrees per second. You do need an old laptop for this system but the software is free and there is a very good yahoo group that can assist you. Mel is very active in his support of those who build his system.
A friend did the electronics for mine and I made all the mechanical parts. I just made moulded epoxy gears for the reduction system. They work very well visually.
Hope that helps,
Rod. |
I had a quick look at that site and the method appears to be very similar to what I did in 1994. My main difference was that my stepper drives used a computer program to drive discrete components rather than those special chips. My budget was a lot less than the prices listed. Driving the steppers is a function of the sequence of how you excite the fields and was done via the printer port with two four bit words.
This needs a faster computer than the old PC I was using as the control loop was quite large. Later With 386 and 486 computers speed was no problem.
The program to drive the DOB 11 originally only sent commands to the controller at one per second which at high resolutions made the scope move up a stair case. I developed a method of sending commands every 100ms which was a great improvement.
I used parts from the junk box and salvaged stepper motors. I went through lots of motors looking for the ones that could drive the fastest and at one half step for each second of rotation I managed to get the fastest slew to just under 1 degree/second.
I wrote my own software and the source is free to anyone who wants it although it is written oin Qbasic and is a bit archaic by modern standards.
My main problem was getting suitable mechanics to drive the scope. I experimented with all sorts of devices using parts mainly salvaged from old computers and printers.
I spent many months refining software and mechanics but before I got everything fully working. I had a loan repaid and bought a LX200 10" classic. The stepper drive system and 8" Dob was given to my daughter.
The system worked OK from a laptop although at the time the only hand controller I had was via the games port which left a lot to be desired in speed of operation.
I occasionally get the old test board and motors out and hook it up to the computer and do dummy alignments and gotos. The motors look good slewing and tracking. Oh did I say how I tracked. I re-calculated all the coords every 100ms in the program loop at sidereal rate and sent them to the motors.
It was a lot of fun but I prefer my LX200 these days.
Barry