I made my FP2 pro using a custom prototype board and the myFP2F_DRV8825HW203_330 firmware.
I tried three different stepper motors, th efirst was a nema 14 MY14HY7-1 Stepper Motor 1.8° 50 mNm, 0.40A, the second a Adafruit Nema17 - 200 steps/rev, 12V 350mA, the last one (knowing the amps are too high a Nema 17, high torque, 1.6 A.
All stepper motors could not move my focus train using direct drive on my Zenithstar ED80II focuser. All steppers seem to be not strong enough.
What am I doing wrong?
Last edit: david laine 2024-04-12
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Assuming that you are using 12v to power the stepper motor,
Without knowing whats attached,
- the pot setting on the drv8825 may be just a bit to low?
- step mode setting
- focus lock screw too tight
I would expect that anything below full steps is probably an issue using a standard NEMA motor. If it cannot move at full steps it then would never move if it was 1/2 or 1/4 stepped. Remember there is a loss of 30% torque for each step change, meaning from full steps to 1/s step torque drops by 30%, If it is then changed to 1/4 stepping, the extra step mode torque is then 30% of what the torque at half step mode. etc.
As a way to see to if torque is an issue (too low)
connect motor shaft to 1:10 focus knob using small belt and pulley on stepper motor
A geared system will produce more torque than a non-geared one, hence the pulley + belt
idea previous sentence introduces gears which increases torque.
Please let me know if any of the suggested changes work for you.
regards
Robert
I have this small stepper motor, runs off 5v , GM12-15BY, driven by L298N driver board. I did show this in one of the online videos I did, cannot remember which one though
Thank you Robert for your answer,
Yes, the stepper is connected to 12 Volts and of course I adjusted the amps on the DRV8825 and my focus screw is loose, I also tried in all the step mode settings. I will try to make a pulley system on the 1:10 knob this week and will let you know what the outcome is.
regards,
David
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Apologies for the stupid questions.
If the motor is disconnected from the focuser
motor rotates in both directions?
only 1 direction,
or not at all?
both directions: wiring is probably correct and thus a torque issue
1 direction: wiring issue of stepper wires
not all all : pot current setting, wiring, or timerone class library issue
Regards
Robert
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Hi Robert,
no need to apologies, there are no stupid questions when toubleshooting!
The stepper moves in both directions, without hickups when removed from the focuser.
Regards,
David
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Fo most nema motors, full stepped, 12v
if on the bench, the stepper moves, but can you stop the shaft from turning by holding the shaft between your fingers, which is simulating a load?
I adjusted the amps on the DRV8825*
what was it set to?
So if the multi-meter was inserted into one coil of the motor, and stepmode = full and coil power = on, a small move like 10 steps should result in the meter showing the current, for the adafruit stepper that would be 350mA. and for the MY14HY7-1 motor 400mA
It will be big ask to use the NEMA stepper motors (200 step, full stepped) to move most focus trains, which is why a planetary geared motor, or a belt-pulley system is used for most systems.
here are some calculations for you comparing various motors
MY14HY7-1 Holding Torque 50 mNm
5 N*cm
0.05 Nm
So your Adafruit is stronger than the MY14HY7 by a factor of about 4 times
No point trying with the MY14HY7
But the Adafruit is much less than a PG5, at 0.2 vs 1.212 for the PG5
Just as a further, the PG27 has a holding torque of 26Nm, which compared to all of the above, in a class of its own.
If your imaging train (camera, filter wheel etc) weights about 4kg, the PG27 will push/pull that vertical straight up with ease, whereas the others will not.
Regards
Robert
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hello,
I made my FP2 pro using a custom prototype board and the myFP2F_DRV8825HW203_330 firmware.
I tried three different stepper motors, th efirst was a nema 14 MY14HY7-1 Stepper Motor 1.8° 50 mNm, 0.40A, the second a Adafruit Nema17 - 200 steps/rev, 12V 350mA, the last one (knowing the amps are too high a Nema 17, high torque, 1.6 A.
All stepper motors could not move my focus train using direct drive on my Zenithstar ED80II focuser. All steppers seem to be not strong enough.
What am I doing wrong?
Last edit: david laine 2024-04-12
Hi David
Assuming that you are using 12v to power the stepper motor,
Without knowing whats attached,
- the pot setting on the drv8825 may be just a bit to low?
- step mode setting
- focus lock screw too tight
I would expect that anything below full steps is probably an issue using a standard NEMA motor. If it cannot move at full steps it then would never move if it was 1/2 or 1/4 stepped. Remember there is a loss of 30% torque for each step change, meaning from full steps to 1/s step torque drops by 30%, If it is then changed to 1/4 stepping, the extra step mode torque is then 30% of what the torque at half step mode. etc.
As a way to see to if torque is an issue (too low)
connect motor shaft to 1:10 focus knob using small belt and pulley on stepper motor
A geared system will produce more torque than a non-geared one, hence the pulley + belt
idea previous sentence introduces gears which increases torque.
Please let me know if any of the suggested changes work for you.
regards
Robert
I have this small stepper motor, runs off 5v , GM12-15BY, driven by L298N driver board. I did show this in one of the online videos I did, cannot remember which one though
https://www.ebay.com/itm/GM12-15BY-DC5-12V-2-phase-4-wire-Permanent-Magnet-Stepper-Gear-Motor-Metal-Gear/163265164855
Select 1:298
Torque = 1200gf-cm
That is run at full steps, 298 steps of the motor shaft moves the gearbox shaft 1 revolution
and it has huge torque that works well.
Thank you Robert for your answer,
Yes, the stepper is connected to 12 Volts and of course I adjusted the amps on the DRV8825 and my focus screw is loose, I also tried in all the step mode settings. I will try to make a pulley system on the 1:10 knob this week and will let you know what the outcome is.
regards,
David
Hi Davis
Apologies for the stupid questions.
If the motor is disconnected from the focuser
motor rotates in both directions?
only 1 direction,
or not at all?
both directions: wiring is probably correct and thus a torque issue
1 direction: wiring issue of stepper wires
not all all : pot current setting, wiring, or timerone class library issue
Regards
Robert
Hi Robert,
no need to apologies, there are no stupid questions when toubleshooting!
The stepper moves in both directions, without hickups when removed from the focuser.
Regards,
David
That would seem to indicate that the motor has insufficient torque to move the focus train.
What sort of motor is it?
Hi Robert,
I first tried with a NEMA14, from Astrosyn: https://www.astrosyn.com/product/my14hy7-1-astrosyn-stepper-motor-nema-14
Then then I took a NEMA 17 from Adafruit: https://www.adafruit.com/product/324
Both of them seem to have not enough torque to move my focus train.
With the stepper powered by 12v,
Fo most nema motors, full stepped, 12v
if on the bench, the stepper moves, but can you stop the shaft from turning by holding the shaft between your fingers, which is simulating a load?
what was it set to?
So if the multi-meter was inserted into one coil of the motor, and stepmode = full and coil power = on, a small move like 10 steps should result in the meter showing the current, for the adafruit stepper that would be 350mA. and for the MY14HY7-1 motor 400mA
It will be big ask to use the NEMA stepper motors (200 step, full stepped) to move most focus trains, which is why a planetary geared motor, or a belt-pulley system is used for most systems.
here are some calculations for you comparing various motors
MY14HY7-1 Holding Torque 50 mNm
5 N*cm
0.05 Nm
Adafruit Holding Torque 20 Ncm
200 mNm
0.2 Nm
http://www.omc-stepperonline.com/
5.18:1 Planetary Bipolar Nema17 Stepper Motor PG5
200x5.18 = 1036 steps
Holding Torque = 121.2Ncm
1212 mNm
1.212 Nm
17HS15-0404S
Bipolar, 200 steps, 1.8 degrees
Holding Torque = 0.4Ncm
4 mNm
0.4Ncm
0.004Nm
Lowest - 17HS14-0404S, 0.004Nm
MY14HY7-1 , 0.05 Nm
Adafruit, 0.2 Nm
PG5 geared. 1.212 Nm
So your Adafruit is stronger than the MY14HY7 by a factor of about 4 times
No point trying with the MY14HY7
But the Adafruit is much less than a PG5, at 0.2 vs 1.212 for the PG5
Just as a further, the PG27 has a holding torque of 26Nm, which compared to all of the above, in a class of its own.
If your imaging train (camera, filter wheel etc) weights about 4kg, the PG27 will push/pull that vertical straight up with ease, whereas the others will not.
Regards
Robert