I am building a myFocuserProM based on Arduino Uno, a shield board PCB prototype, that will host a DRV8825 and a Temperature probe. This is for astrophotography and my plan is to control the focuser using NINA. I have a few questions:
1) Are the voltage regulator and ceramic capacitors needed if I don't plan using the focuser unless it is connected to a pc via USB? the Arduino will get its power from the USB and the motor from 12V plug.
2) What is the purpose of the 100uf Capacitor? Is it mandatory?
3) Is there any practical difference between a Nema 14 with 1.8 degrees micro stepped to 1/16 and a Nema 14 with 0.9 degrees micro stepped to 1/8. The first one has higher torque (14Ncm vs 11Ncm)
4) Is there a way to change the microstep definition in ASCOM? F.e. when focuser is turned on, then I want it to perform a fast out to initial position (so no need to micro step) but then when autofucusing I need micro steps, and at the end of the session I want it to go back to in without micro step)
Many thanks for this project, this will be my second DIY focuser, first one is a myDCfocuser.
Daniel
Additional info:
6 inch Newtonian F5 - CFZ is 55 microns single step should be 5 - 6 microns.
Orion 2 inch Crayford focuser 4mm shaft moves 12.6mm for full revolution
12600 microns divided by 3200 (either 400 x 8 or 200 x 16) gives 3.9375 microns per step.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
1) Are the voltage regulator and ceramic capacitors needed if I don't plan using the focuser unless it is connected to a pc via USB? the Arduino will get its power from the USB and the motor from 12V plug.
Yes, but you will need to connect GND of the Arduino to GND of the 12V
2) What is the purpose of the 100uf Capacitor? Is it mandatory?
The 100uF bipolar capacitor is needed for the drv8825. It muse be mounted as close as possible to the drv8825 oubs VMOT and GND.
From the Datasheet 10.1 Bulk Capacitance, and covers a range of requirements, including minimizing the voltage ripple levels of the 12V supply to the DRV8825
3) Is there any practical difference between a Nema 14 with 1.8 degrees micro stepped to 1/16 and a Nema 14 with 0.9 degrees micro stepped to 1/8. The first one has higher torque (14Ncm vs 11Ncm)
I find it hard to accept that one would get more torque from microstep of 1/16 compared to 1/8. If one needs to use anything more than 1:2 micro-stepping then the next option would be to consider a geared motor. Nema14 I think would provide less torque than a Nema17,
the figures quoted for torque on the datasheet are for FULL stepping only. Every time you microstep, there is a loss of around 30+% for each microstep. If a full step was 16. If the torque as 15Ncm then
From full to 1/2 = 15 - 30% of 15 = 15 - (15/100*30) = 15 - 4.5 = 10.5
From 1/2 to 1/4 = 10.5 - 30% of 10.5 = 10.5 - 3.15 = 7.35
From 1/4 to 1/8 = You have probably realized where this is headed now
4) Is there a way to change the microstep definition in ASCOM? F.e. when focuser is turned on, then I want it to perform a fast out to initial position (so no need to micro step) but then when autofucusing I need micro steps, and at the end of the session I want it to go back to in without micro step)
First off, that is a pretty bad idea. I am sure there are adequate warnings in the pdf about this,
I will add why in some text below, from the pdf.
because the focuser saves the position of the focuser, there should be no need to do a fast anything - unless you are ripping everything at the end of each night. Without knowing your circumstances, from my own expriences, I just leave everything as is on shutdown, and then the next time I start everything back up its good to go. I do park the mount before shutdown though.
CHANGING STEP MODE INVALIDATES THE FOCUSER POSITION. YOU WILL NEED TO DO THE INITIAL SETUP AGAIN IF YOU CHANGE THE STEP MODE.
WARNING: Once the step mode is set, it should not be changed
WHY?
Step mode impacts directly on both Maxsteps and StepSize, and has a secondary impact on Push Button steps (which is derived from StepSize). Critical Focus Zone is not impacted because this is only affected by the focal ratio of the telescope.
I have a step mode of 1/2. I want to change the stepmode to Full. What will happen?
Consider that Step Mode is 1/2, Max Steps is 5000 and Step Size is 23.
And for push buttons with a value of 12 (Step-Size / 2), for each button press the focuser will move 12*23 =276 steps (276 microns).
If Step Mode is then set to Full, then the new values of MaxSteps = 2500, and Step Size = 46
BUT, when step mode is changed from ½ to Full, the myFP2ESP32 Focus Controller does not automatically adjust the values of MaxStep and StepSize.
The Controller still thinks that MaxSteps = 5000. That means if the focuser is commanded to move to any position that is more than 2500, the Controller will attempt to drive way past what is safe and you have the potential to seriously damage your telescope focuser.
The pushbutton steps value was 12 (step size / 2). The new number should be (46 / 2) which is 23, but it is not, as changing the step mode did not change step size and recalculate a safe maximum value for push button steps.
Assuming that the user did not change Push Button steps or StepSize then the focuser settings are invalid.
Each motor step is actually now 46 microns (even though the setting for step-size was not changed by the user). One press of the puh-button moves 12 steps, so 12 *46 = 552 steps.
In all of this, the Critical Focus Zone remained the same, because it is not dependent on any of these settings. However, by changing the step mode we now have a different value for the number of steps in the Critical Focus Zone, and this will have a direct impact on focusing (manual or auto-focusing).
The end result is that even when push button steps is set to 1, the focuser will move 46 microns, twice as large as the previous 23 microns before the step mode was changed. This results in a degradation of finding good focus, in that we have now halved the number of focuser steps inside the critical focus zone.
Last edit: brownrb 2023-09-16
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Thank you for the fast answer and useful insights.
I will make sure to put the Capacitor as close as possible to the DRV8825
Re the motor I will buy a Nema 11 (6N.cm) with 5:1 PG with half step.
28HS3306A4-XG05-PW
I am not familar with that stepper, code 28HS3306A4-XG05-PW
I did a quick search on the net but could not find it.
What is the rated coil current? it would need to be around 600mA max
Did you do the calculations using a spreadsheet?
How far in mm is your focuser travel, from fully in to fully out?
I do have spreadsheets available that I can complete for you as a double check
Hi Daniel
On the worksheet in the spreadsheet
CFZ 55 microns
PG5 1/2 stepped
2072 steps (at half stepped) per motor shaft 360 degree
Each motor step is 6.08 microns
At focuser travel of 12.6 mm per rotation of knob
Number of half steps in CFZ = 9
Focuser position travel tube at maxstep = 3 rotations at 12.6mm per rotation = 37.8mm
Maxstep = 12432 (if using no safety from start-end
Hello,
I am building a myFocuserProM based on Arduino Uno, a shield board PCB prototype, that will host a DRV8825 and a Temperature probe. This is for astrophotography and my plan is to control the focuser using NINA. I have a few questions:
1) Are the voltage regulator and ceramic capacitors needed if I don't plan using the focuser unless it is connected to a pc via USB? the Arduino will get its power from the USB and the motor from 12V plug.
2) What is the purpose of the 100uf Capacitor? Is it mandatory?
3) Is there any practical difference between a Nema 14 with 1.8 degrees micro stepped to 1/16 and a Nema 14 with 0.9 degrees micro stepped to 1/8. The first one has higher torque (14Ncm vs 11Ncm)
4) Is there a way to change the microstep definition in ASCOM? F.e. when focuser is turned on, then I want it to perform a fast out to initial position (so no need to micro step) but then when autofucusing I need micro steps, and at the end of the session I want it to go back to in without micro step)
Many thanks for this project, this will be my second DIY focuser, first one is a myDCfocuser.
Daniel
Additional info:
6 inch Newtonian F5 - CFZ is 55 microns single step should be 5 - 6 microns.
Orion 2 inch Crayford focuser 4mm shaft moves 12.6mm for full revolution
12600 microns divided by 3200 (either 400 x 8 or 200 x 16) gives 3.9375 microns per step.
Hi Daniel
1) Are the voltage regulator and ceramic capacitors needed if I don't plan using the focuser unless it is connected to a pc via USB? the Arduino will get its power from the USB and the motor from 12V plug.
Yes, but you will need to connect GND of the Arduino to GND of the 12V
2) What is the purpose of the 100uf Capacitor? Is it mandatory?
The 100uF bipolar capacitor is needed for the drv8825. It muse be mounted as close as possible to the drv8825 oubs VMOT and GND.
From the Datasheet 10.1 Bulk Capacitance, and covers a range of requirements, including minimizing the voltage ripple levels of the 12V supply to the DRV8825
3) Is there any practical difference between a Nema 14 with 1.8 degrees micro stepped to 1/16 and a Nema 14 with 0.9 degrees micro stepped to 1/8. The first one has higher torque (14Ncm vs 11Ncm)
I find it hard to accept that one would get more torque from microstep of 1/16 compared to 1/8. If one needs to use anything more than 1:2 micro-stepping then the next option would be to consider a geared motor. Nema14 I think would provide less torque than a Nema17,
the figures quoted for torque on the datasheet are for FULL stepping only. Every time you microstep, there is a loss of around 30+% for each microstep. If a full step was 16. If the torque as 15Ncm then
4) Is there a way to change the microstep definition in ASCOM? F.e. when focuser is turned on, then I want it to perform a fast out to initial position (so no need to micro step) but then when autofucusing I need micro steps, and at the end of the session I want it to go back to in without micro step)
First off, that is a pretty bad idea. I am sure there are adequate warnings in the pdf about this,
I will add why in some text below, from the pdf.
because the focuser saves the position of the focuser, there should be no need to do a fast anything - unless you are ripping everything at the end of each night. Without knowing your circumstances, from my own expriences, I just leave everything as is on shutdown, and then the next time I start everything back up its good to go. I do park the mount before shutdown though.
Oh, and something else. You said you used the myFP2M board. That means you have to use the myFP2M firmware - if you tried to use myFP2 firmware the board will not work. See this thread about that issue.
https://sourceforge.net/p/arduinoascomfocuserpro2diy/discussion/general/thread/43ba8ee02a/
Regards
Robert
CHANGING STEP MODE INVALIDATES THE FOCUSER POSITION. YOU WILL NEED TO DO THE INITIAL SETUP AGAIN IF YOU CHANGE THE STEP MODE.
WARNING: Once the step mode is set, it should not be changed
WHY?
Step mode impacts directly on both Maxsteps and StepSize, and has a secondary impact on Push Button steps (which is derived from StepSize). Critical Focus Zone is not impacted because this is only affected by the focal ratio of the telescope.
I have a step mode of 1/2. I want to change the stepmode to Full. What will happen?
Consider that Step Mode is 1/2, Max Steps is 5000 and Step Size is 23.
And for push buttons with a value of 12 (Step-Size / 2), for each button press the focuser will move 12*23 =276 steps (276 microns).
If Step Mode is then set to Full, then the new values of MaxSteps = 2500, and Step Size = 46
BUT, when step mode is changed from ½ to Full, the myFP2ESP32 Focus Controller does not automatically adjust the values of MaxStep and StepSize.
The Controller still thinks that MaxSteps = 5000. That means if the focuser is commanded to move to any position that is more than 2500, the Controller will attempt to drive way past what is safe and you have the potential to seriously damage your telescope focuser.
The pushbutton steps value was 12 (step size / 2). The new number should be (46 / 2) which is 23, but it is not, as changing the step mode did not change step size and recalculate a safe maximum value for push button steps.
Assuming that the user did not change Push Button steps or StepSize then the focuser settings are invalid.
Each motor step is actually now 46 microns (even though the setting for step-size was not changed by the user). One press of the puh-button moves 12 steps, so 12 *46 = 552 steps.
In all of this, the Critical Focus Zone remained the same, because it is not dependent on any of these settings. However, by changing the step mode we now have a different value for the number of steps in the Critical Focus Zone, and this will have a direct impact on focusing (manual or auto-focusing).
The end result is that even when push button steps is set to 1, the focuser will move 46 microns, twice as large as the previous 23 microns before the step mode was changed. This results in a degradation of finding good focus, in that we have now halved the number of focuser steps inside the critical focus zone.
Last edit: brownrb 2023-09-16
Thank you for the fast answer and useful insights.
I will make sure to put the Capacitor as close as possible to the DRV8825
Re the motor I will buy a Nema 11 (6N.cm) with 5:1 PG with half step.
28HS3306A4-XG05-PW
12600 microns divided by 2000 (200 * 5 * 2) = 6.3 microns
200 steps
5:1 PG
Halfstep
I am not familar with that stepper, code 28HS3306A4-XG05-PW
I did a quick search on the net but could not find it.
What is the rated coil current? it would need to be around 600mA max
Did you do the calculations using a spreadsheet?
How far in mm is your focuser travel, from fully in to fully out?
I do have spreadsheets available that I can complete for you as a double check
Regards
Robert
Rated 0.6A
Focuser has 3 full revolutions from end to end
Hi Daniel
On the worksheet in the spreadsheet
CFZ 55 microns
PG5 1/2 stepped
2072 steps (at half stepped) per motor shaft 360 degree
Each motor step is 6.08 microns
At focuser travel of 12.6 mm per rotation of knob
Number of half steps in CFZ = 9
Focuser position travel tube at maxstep = 3 rotations at 12.6mm per rotation = 37.8mm
Maxstep = 12432 (if using no safety from start-end
Regards
Robert
Attached
Thank you very much,
I have ordered the components, and I am waiting for them to arrive.