Printer Farm with access control: Using Power Panic?
Dear community and Prusa team,
I am planning to build a new printer farm with Prusa MK4 at my university. Students are supposed to use the printers themselves, but I want to implement an access control system to make sure only the students from our course can use the system.
Our favorite option for an access control system will switch individual relais on & off, hencing causing a power outage for our printers.
How well do Prusa MK4 printers handle recurring power outages? I read about the "Power panic" function, but I couldn't find any information, if switching the printer via a power outage is equally good as using the build-in switch or if it is worse.
I would be happy to hear your opinions on this question!
Best regards,
Hendrik
Best Answer by Walter Layher:
It might not be best practice to suddenly shut off a printer with fully heated hotend via a relay. The heat creep could damage the plastic parts in the extruder if the fan cannot cool the hotend down. It is better to wait a few minutes to let the fan cool down the hotend. If the bed is heated up for ABS it could also be bad if the fans are suddenly shut off. I am using Octoprint and the Tasmota plugin, which allows me to define a cool-down interval before shutdown.
RE:
Hi Hendrik,
MK4 printers have four ways to be "fed" with files to be printed:
1) The USB drive can store g-code files that can be stored on a PC and brought to the printer by connecting the pen drive. The user is offered the most recently copied file as the default to be printed on the printer's display.
2) The printer's USB port allows it to connect the printer to a PC where some software can stream a g-code file to the printer (uncommon and requiring the PC the on all the time may not be a popular choice).
3) The MK4 has Wifi and Ethernet connectivity and includes an internal web server (PrusaLink) that allows anyone that knows the printer's username and password to operate the printer remotely.
4) Prusa Connect is a web service that allows you to send and start jobs on your printer remotely. It is linked to a given PrusaAccount.
The problem with removing the power from a printer is that if it were printing something when the power is removed, it would offer a chance to continue when powered back on (but that is only available for a user operating the printer using the display).
I reckon you might create a web service on a local server that could handle your local user's access and implement the user access policies you need (which would use Prusa Link on your printers, shielding the details about printer's credentials to the users).
RE: Printer Farm with access control: Using Power Panic?
Thank you very much for the extensive reply and trying to solve my problem, misan! I don't want to go too much into the details of our system here, but we want to use Prusa Link to transfer the data (Option 3)
For me the central question remains: Is switching via a fuse harmful to the printer or is it equally "sustainable" as using the built-in power button?
RE: Printer Farm with access control: Using Power Panic?
You are welcome.
The built-in power switch works, AFAIK, the same as if the switch is elsewhere (power strip switch) or a relay, provided printers are idle when you power them down.
You may want to check this resource: https://github.com/prusa3d/Prusa-Link-Web to learn more about Prusa-Link
And some of the relevant info in the knowledge base: https://help.prusa3d.com/article/prusa-connect-and-prusalink-explained_302608
Please note that remote operation may be prevented whenever the printer "thinks" some physical intervention of the user is needed. For example, after a print is over, the user has to come to pick up the printed part and set the printer into a state where a new remote print might be initiated.
The bottom line is that, while what you want is within reason, it is not a functionality that is at the moment embedded in the printers so some DIY work will be needed.
RE: Printer Farm with access control: Using Power Panic?
You're not going to do any harm to the printer by turning the circuit off. I do it slightly differently, by putting each printer on a smartplug so they can be turned on or off remotely. "Alexa, turn off Prusa Green" etc.
RE: Printer Farm with access control: Using Power Panic?
It might not be best practice to suddenly shut off a printer with fully heated hotend via a relay. The heat creep could damage the plastic parts in the extruder if the fan cannot cool the hotend down. It is better to wait a few minutes to let the fan cool down the hotend. If the bed is heated up for ABS it could also be bad if the fans are suddenly shut off. I am using Octoprint and the Tasmota plugin, which allows me to define a cool-down interval before shutdown.
RE: Printer Farm with access control: Using Power Panic?
It might not be best practice to suddenly shut off a printer with fully heated hotend via a relay.
I don't disagree with you. Just saying that I've been using a Smartplug for almost three years across all of my printers, without any issues. In all fairness, the hotend is probably way more often than not either cold or at 170 idling temperature when I turn them off.
RE: Printer Farm with access control: Using Power Panic?
Just don't give users without much experience the option to shut off their printers this way! 🙂
RE: Printer Farm with access control: Using Power Panic?
Thank you for this discussion! The point, that the fan for cooldown is shut off by switching via a fuse, seems to speak against this solution, as I don't want to compromise the printers' longevity.
I might come back to you after further discussion with my colleagues and happy to share some ideas for access control then.
RE: Printer Farm with access control: Using Power Panic?
Please bear in mind hotend temperature can be remotely measured with PrusaLink, so you could still have a safe power down if you make sure the hotend is back to room temperature before shutdown is performed.