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Select 1 Gearbox for each axis, (pre-mounted to standard motor).
R30, R150, R300, R600.
Unless you specify otherwise, R30 is supplied standard with DDR2-ATM systems for use on worm-gear driven mounts. If you have a large instrument or simply would like high-performance tracking & slewing you may wish to use Powemax on the back page. Note that a worm gear drive loses about 50% of the torque and this can be reduced by minimizing worm pressure. Mounts with no worm gears (low geardown ratios on main axes) such as belt or traction drives would use one of the high ratio gearboxes shown above. Call for free assistance in determining your spec's.
If you need to determine torque, use the following motor data (x gearbox ratio)...
STANDARD MOTOR: 2.0 oz-in
Rated 48 steps/rev. Includes gearbox selected from above.
NEMA23 HEAVY DUTY: 16 oz-in rated 200 steps/rev. No gearbox supplied. Use NEMA23 style, or wormgears or belting arrangements.
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Divide 1,296,000 arcseconds (1 axis revolution) by the gear ratio on your mount.
Divide the result by the motors' rated steps/revolution (our standard motors are rated at 48 steps/rev).
Divide again by 8 (the number of microsteps Dob-Driver will take for each rated motor step).
Divide again using one of the gearbox ratios shown at left.
The final result shows the nominal instrument movement in arcseconds for each "microstep" the stepper motor takes. This is the drive resolution. You should assure that it is not too large because you will see the step motion. If too small - your slew speed ability for fast pan will be poor.
Suggestions...
.3 to 1.5 A-S for best planets and hi-mag imaging (slow panning & PC-LINK slewing). More torque is available due to the higher gear ratio.
1.5 to 2.5 A-S for general all-around use & deep space photography with piggyback cameras or low-mag prime focus (fast panning & fast PC-LINK slewing). Less torque is available due to the lower gear ratio.
1.5 A-S is typical of standard Dob-Driver systems when mounted on a typical Dobsonian mount with no HRG options - this proves good for planets up to 400x visual, good for piggy or prime focus imaging up to 50x, and usually yields around 2-4 deg/sec slew speed.
Example on a worm gear driven mount...
We have a 360 tooth worm gear on Ra and a 240 tooth worm gear on Dec. We select R15 gearboxes for both axes. The resulting step-size resolution is .63 A-S for Ra, .94 A-S for Dec. Torque to the wormshaft would run about 30 OZ-IN for Ra, same for Dec. Changing to a Powermax system can simultaneously double that resolution, double the torque, and double the potential slew speed.
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Multiply the step resolution you calculated at left as follows...
x 2.0 if motor is heavily loaded.
x 6.0 if motor has a light load.
Double the above if using the Powermax ATM motors!
This will give you an idea of the range to expect even if you don't actually know how heavily loaded the motor is going to be. Note that Dob-Driver will find the fastest slew speed possible for any installation so you will always get the best possible slew speed ability regardless of the design details. Performance can be varied by changing the gearbox (or belt ratio) if more torgue is needed or conversely, if plenty of torque results and you feel a smaller ratio will move the instrument OK at higher speeds with acceptable resolution.
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