Nozzle Clog Detection
I'm working on a college team to design a mod that detecting nozzle clogs, and is focused on hobby printers using the MK3s. The mod would automatically stop the print. What kind of things would be important to people who would potentially use this mod? What kind of resources would people have to make it themselves? What would you be willing to spend making it yourself? And any general comments on this kind of mod if you have experience with doing stuff yourself.
Updates to come as we progress.
The original MK3 had a laser motion sensor to detect filament stalls. The primary issue was the sensor is designed to see metal, not filament, and some filaments were invisible to the sensor so it would fail and stop prints for no reason.
There is a user mod to add a metallic bearing that rolls on the filament and presents a solid surface to the sensor. This mod to a MK3 accomplishes what you are trying to do.
The filament sensor in MK3S detects filament run out. However, it doesn't detect a clogged nozzle. When a nozzle gets clogged or filament stuck at the beginning of PTFE tube, the sensor will keep sensing the filament in and will not trigger.
One way I see to detect both filament run out and stuck filament is using a roller connected to a potentiometer. As the filament feeds, it will turn the roller+potentiometer. The FW will compare this movement (In/Out/Stop) to the Extruder movement. It should trigger if there is a difference. Basically, a feedback system on the filament movement.
It would be worth measuring the stall current of the extruder motor when there is a nozzle clog / jam. Since the motor will continue to push filament in, right before the gear skipping (clicking noise) one should see a slightly increase in the motor current draw before it drops again and repeats the process. I am not sure if the clogged nozzle would be enough to reach the stall current, but there would definitely be a current spike. The question is "how much". An oscilloscope might come handy here.
you would need a rotary encoder ( continuous rotation) not a pot