Are there any ligher weight stepper that would work and with a higher gear ratio. I was looking at the: Gear Ratio 100:1 Planetary Gearbox With Nema 11 Stepper Motor 11HS20-0674S-PG100
If I stay with recommended 17 stepper is there any advantage to the PG100 version?
Last edit: Mark Woolridge 2016-10-09
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I assume you want 100:1 for a good reason, but you could get this with a combination of stepmode and belt drive ratio using GT2.
The problem with the smaller NEMA motors is the current gets higher to achieve reasonable torque levels. I guess the issue is weight. But if mounted directly underneath the focuser using a planetary gear, with something like a 15T GT2 pulley and belt driver to the focuser shaft using a 30 or 45T GT2 gear then that would work with a PG27 to get close to what you need.
Cheers
Robert
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Is there a reason why you want the PG100? I have found even for f5.6 refractors the PG27 is more than adequate at half steps (I can use mine at Full Steps without issue).
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Robert,
Just wanted to make sure there is enough resolution to hit critical focus. I have a 127mm f/7.1 refractor but also use it with a 0.7 focal reducer. Just figuring if I am going to build this thing get the max resolution possible without going overboard. Currently I am using a DSLR for astrophotography but would like to upgrade to filter wheel and cooled CCD sometime in the furture. Thanks for doing all this work.
Mark
Last edit: Mark Woolridge 2016-10-09
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Hi Mark
I have a Stellarvue 102T refractor used with 0.8 flattener reducer to get f5.6
Using PG27 stepper NEMA17 at half steps direct shaft connected to a large heavy 2.5" SV rack and pinion focuser I have a step size of 1.58 microns with a CFZ of 71. Using half steps I would get around 45 stepper steps within the CFZ, at full steps around 22. And I can lift a heavy AO unit, filter wheel, reducer and cooled CCD with extra cooler without issue (around 4-5kg). Some might say that was overkill :-)
Last edit: brownrb 2016-10-09
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I guess resolution, weight, torque and current are the issues you will need to resolve. If you go for a lower number stepper like NEMA11 with higher current stepper potentially you get adequate torque, but then you need to move to a different motor driver chip, bigger power supply, large case, thicker wires to carry the extra current without too much voltage drop meaning shorter cables between the driver board and the stepper etc etc
In my case I have a pretty robust sturdy mount that has large capacity, so for me weight is not a consideration. If I still had the CGEM that would be a different story altogether.
I think you will find that even the NEMA11/14 planetary geared motors will have enough torque for what you describe.
Cheers and best wishes
Last edit: brownrb 2016-10-09
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hi Mark,
i built the DRV8825_HW203_F version. and I switch to a Nema 11 PG27. trying to put my rig on a diet.
I use a DSLR and i do not have any problem with Holding Torque.i use HalfSteps
i tried belts but found direct drive to work the best.
Thanks for sharing the picture BJ. Sometimes a pciture can answer a lot of questions. I do not have any experience with the NMEA 11 as I have a fairly heavy imaging train and probably went overkill with the NEMA 17 (I figured buy once and only once), so helping out Mark and sharing your answers in relation to his query is really cool as I don't have all the answers!
R
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Are there any ligher weight stepper that would work and with a higher gear ratio. I was looking at the: Gear Ratio 100:1 Planetary Gearbox With Nema 11 Stepper Motor 11HS20-0674S-PG100
If I stay with recommended 17 stepper is there any advantage to the PG100 version?
Last edit: Mark Woolridge 2016-10-09
Hi Mark
That stepper is rated at Rated Current/phase 0.67A which at full steps is 1.54A. Meaning you are at the limits (or exceed) of current for most of the available driver chips. You would need to look at something like the ST7128 (which is supported) to drive the stepper (it is large though). http://www.omc-stepperonline.com/bipolar-stepper-motor-driver-max-3a-current-128-high-subdivision-st7128-p-244.html
I assume you want 100:1 for a good reason, but you could get this with a combination of stepmode and belt drive ratio using GT2.
The problem with the smaller NEMA motors is the current gets higher to achieve reasonable torque levels. I guess the issue is weight. But if mounted directly underneath the focuser using a planetary gear, with something like a 15T GT2 pulley and belt driver to the focuser shaft using a 30 or 45T GT2 gear then that would work with a PG27 to get close to what you need.
Cheers
Robert
Is there a reason why you want the PG100? I have found even for f5.6 refractors the PG27 is more than adequate at half steps (I can use mine at Full Steps without issue).
Robert,
Just wanted to make sure there is enough resolution to hit critical focus. I have a 127mm f/7.1 refractor but also use it with a 0.7 focal reducer. Just figuring if I am going to build this thing get the max resolution possible without going overboard. Currently I am using a DSLR for astrophotography but would like to upgrade to filter wheel and cooled CCD sometime in the furture. Thanks for doing all this work.
Mark
Last edit: Mark Woolridge 2016-10-09
Hi Mark
I have a Stellarvue 102T refractor used with 0.8 flattener reducer to get f5.6
Using PG27 stepper NEMA17 at half steps direct shaft connected to a large heavy 2.5" SV rack and pinion focuser I have a step size of 1.58 microns with a CFZ of 71. Using half steps I would get around 45 stepper steps within the CFZ, at full steps around 22. And I can lift a heavy AO unit, filter wheel, reducer and cooled CCD with extra cooler without issue (around 4-5kg). Some might say that was overkill :-)
Last edit: brownrb 2016-10-09
I guess resolution, weight, torque and current are the issues you will need to resolve. If you go for a lower number stepper like NEMA11 with higher current stepper potentially you get adequate torque, but then you need to move to a different motor driver chip, bigger power supply, large case, thicker wires to carry the extra current without too much voltage drop meaning shorter cables between the driver board and the stepper etc etc
In my case I have a pretty robust sturdy mount that has large capacity, so for me weight is not a consideration. If I still had the CGEM that would be a different story altogether.
I think you will find that even the NEMA11/14 planetary geared motors will have enough torque for what you describe.
Cheers and best wishes
Last edit: brownrb 2016-10-09
hi Mark,
i built the DRV8825_HW203_F version. and I switch to a Nema 11 PG27. trying to put my rig on a diet.
I use a DSLR and i do not have any problem with Holding Torque.i use HalfSteps
i tried belts but found direct drive to work the best.
Thanks for the feedback. The way it's mounted looks nice.
Last edit: Mark Woolridge 2016-10-18
Thanks for sharing the picture BJ. Sometimes a pciture can answer a lot of questions. I do not have any experience with the NMEA 11 as I have a fairly heavy imaging train and probably went overkill with the NEMA 17 (I figured buy once and only once), so helping out Mark and sharing your answers in relation to his query is really cool as I don't have all the answers!
R