First, thank you for the awesome work you have done on this project!
I'm in the process of building my first focuser and would like to use the home switch to set the zero position.
In my industry we always install normally closed "overtravel" switches in case the home switch fails, thus disabling any motor motion until the overtravel condition is manually fixed. The overtravel switches must be closed for any motion to happen. Is this something you would consider adding or could help me implement on my project?
My intention is to use this remotely. Or is it possible to detect a stalled motor condition and shut down that way?
Thanks,
rick
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Hi Rick
1. Additional switches pose a number of problems, availabe arduino pins, increased code complexity, and physical mounting challenges for switches. I would need to be able to see how you intend to mount and wire the switches before commenting further.
A stalled motor condition would require probably a current sensor, but the common consensus is that (depending on speed of motor) by the time its detected either damage has already occurred or its too late to be of any value.
.
Cheers
Robert
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Overtravel would require one normally closed input to the arduino. I haven't looked at the code or know how your homing rutine works.
On automated machinery, when the machine is powered on, the homing sequence starts. As long as the overtravel is closed and the home switch is open, the actuator would move slowlly towards the home switch. Once the home switch is made, the actuator backs off the switch a set amount and stops. This is set as the "zero" position in the controller.
The overtravel would mount just past the home switch in the linear direction of travel. In other words, if the tooling (focuser) didn't stop at the home switch for some reason ( broken, misadjusted, etc...) it would contact the overtravel and open the circuit. Once the overtravel input to the controller goes low, motion would stop. The code would then have to monitor the overtravel input anytime a move is requested, and only allow motion as long as the input is high. I don't know how much work this would be code wise. The hardware is easy enough. I may draw something up to illustrate what I have in mind. I don't know if I would bother with an overtravel in the opposite (outward) direction, but it would be a simple matter of wiring it in series with the first overtravel so that if either switch opened, motion would stop. Of course, if someone only wanted a single home switch they could eaily jumpper the overtavel input to the controller so it was always high.
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Once the home switch is made, the actuator backs off the switch a set amount and stops. This is set as the "zero" position in the controller. - this is how the code works now.
Another mounted switch, in series with the home position switch is not that difficult to code or a problem space wise, the detail is in the mounting and positioning. And for what benefit if its omitted? Whichever way one looks at it it is a telescope and so we often make shortcuts and assumptions.
Of course once the over limit is hit then manual intervention would be required to reset the focuser?
There is, and I would be the first to admit it, a small problem with the existing v1 home position switch in that it uses a NO switch and a default state of high for moving. With a fault condition, that is the same as a default state of high and the focuser can move,
BUT, that could also be seen as a good thing - in that the focuser still works (albeit it does not know where home or maxsteps is anymore)
Regards
Robert
Last edit: brownrb 2016-10-28
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Simpler is better, and the use of a single switch is prefered. I agree with this, my only issue is with fault detection in the home circuit since I plan to use this from a remote location.
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First, thank you for the awesome work you have done on this project!
I'm in the process of building my first focuser and would like to use the home switch to set the zero position.
In my industry we always install normally closed "overtravel" switches in case the home switch fails, thus disabling any motor motion until the overtravel condition is manually fixed. The overtravel switches must be closed for any motion to happen. Is this something you would consider adding or could help me implement on my project?
My intention is to use this remotely. Or is it possible to detect a stalled motor condition and shut down that way?
Thanks,
rick
Hi Rick
1. Additional switches pose a number of problems, availabe arduino pins, increased code complexity, and physical mounting challenges for switches. I would need to be able to see how you intend to mount and wire the switches before commenting further.
.
Cheers
Robert
Overtravel would require one normally closed input to the arduino. I haven't looked at the code or know how your homing rutine works.
On automated machinery, when the machine is powered on, the homing sequence starts. As long as the overtravel is closed and the home switch is open, the actuator would move slowlly towards the home switch. Once the home switch is made, the actuator backs off the switch a set amount and stops. This is set as the "zero" position in the controller.
The overtravel would mount just past the home switch in the linear direction of travel. In other words, if the tooling (focuser) didn't stop at the home switch for some reason ( broken, misadjusted, etc...) it would contact the overtravel and open the circuit. Once the overtravel input to the controller goes low, motion would stop. The code would then have to monitor the overtravel input anytime a move is requested, and only allow motion as long as the input is high. I don't know how much work this would be code wise. The hardware is easy enough. I may draw something up to illustrate what I have in mind. I don't know if I would bother with an overtravel in the opposite (outward) direction, but it would be a simple matter of wiring it in series with the first overtravel so that if either switch opened, motion would stop. Of course, if someone only wanted a single home switch they could eaily jumpper the overtavel input to the controller so it was always high.
Once the home switch is made, the actuator backs off the switch a set amount and stops. This is set as the "zero" position in the controller. - this is how the code works now.
Another mounted switch, in series with the home position switch is not that difficult to code or a problem space wise, the detail is in the mounting and positioning. And for what benefit if its omitted? Whichever way one looks at it it is a telescope and so we often make shortcuts and assumptions.
Of course once the over limit is hit then manual intervention would be required to reset the focuser?
There is, and I would be the first to admit it, a small problem with the existing v1 home position switch in that it uses a NO switch and a default state of high for moving. With a fault condition, that is the same as a default state of high and the focuser can move,
BUT, that could also be seen as a good thing - in that the focuser still works (albeit it does not know where home or maxsteps is anymore)
Regards
Robert
Last edit: brownrb 2016-10-28
Simpler is better, and the use of a single switch is prefered. I agree with this, my only issue is with fault detection in the home circuit since I plan to use this from a remote location.