Followed your description of how to build the duper without the flying machine and it doesn’t work also tried it on the flying machine and it doesn’t work either, the flying machine doesn’t work either, I’m assuming it’s user error, do you have a tutorial?
If you want it without flying machine, you need to do following:
[MINECART]
[RAIL]
[SLIME] [SLIME] [SLIME)
[OBSERVER][TNT][NOTEBLOCK]
AND A PISTON IN FRONT OF THE MIDDLE SLIME (STICKY) TO PUSH THE WHOLE CONTRAPTION.
Also the red dot of observer points into the piston.
Let me know if this works
[MINECART]
[RAIL]
[SLIME] [SLIME] [SLIME)
[OBSERVER][TNT][NOTEBLOCK]
AND A PISTON IN FRONT OF THE MIDDLE SLIME (STICKY) TO PUSH THE WHOLE CONTRAPTION.
Also the red dot of observer points into the piston.
Let me know if this works