By placing an upwards-facing sticky piston with a sideways-facing observer on it that powers a block with redstone dust under it that will power the piston, one can create an infinite loop of piston extension and retraction, without the redstone dust or observer ever appearing to be powered. I believe this to be a bug because it does not conform with quasi-connectivity and the 1-tick pulse from the observer should cause the piston to not retract the observer after extending. The piston can only be stopped by breaking one of the aforementioned components or updating it while it is extended. The redstone dust does not even have to be in an orientation where it should be able to power the piston. One can start this loop by powering the piston or making the observer power the block.
Attachments
Comments 6
Shouldn't the piston being powered for only one game tick cause it to spit out the observer, though? I can't say I'm the most knowledgeable on piston mechanics but it still seems like that should be what happens. If you start the cycle by giving the piston a one-tick pulse through a different observer, it actually spits out the observer before starting the cycle.
If it's the piston itself that removes the power source, it will fully extend unless updated by an external source(just placing a note block next to it won't work. you need another piston or a different signal entirely).
btw: it's a zero-tick pulse - hence no visual
If you want to have visual confirmation if the redstone is indeed turning on for a short time: unlike pistons, which may or may not get powered depending on position(what piston gets updated first?), repeaters will always turn on
also: duplicate of MC-137638?
Can confirm in 1.17.1, if this is not a duplicate of MC-137638.
The redstone dust is actually powered for 1 game tick or so by the observer and thus causes an update to the piston, thus triggering its QC-BUD behaviour (since the sandstone block is powered as well). It turning off again causes another update to the piston which then realizes that the sandstone block is no longer powered and retracts. Repeat and go on.
But the redstone dust is not rendered as powered during that one game tick. Not sure if we have a ticket for that.