Story

I have an automatic anvil replacement system using redstone. An observer detects when the existing anvil breaks, and then the ceiling opens up allowing one anvil to fall down.

Problem

The replacement anvils fall from the ceiling which is about 20 blocks high. From that height, the anvils almost always end up chipped after they fall.

I want to add some redstone near the bottom that will stop an anvil from taking damage after it falls 20 blocks.

I have tried a dispenser that shoots out water as the anvil gets close, but it seems that water doesn't break an anvil's fall.

I also had pistons that pop out of the wall one by one, but it takes way too much time for an anvil to reach the floor.

Core question

Find a way to stop an anvil from taking damage when it hits the floor using a redstone contraption.

Solution 1:

The Wiki states:

An anvil can be damaged and destroyed from falling. If it falls from a height greater than one block, the chance of degrading by one stage is 5% × the number of blocks fallen.

So dropping it from 20 blocks height practically assures damage.

Unfortunately, slime blocks on moving pistons only exacerbate the problem - the entire 'downwards' route of an anvil is counted, so dropping it onto a well-timed pushed slime block even a short distance, and then bouncing it several times will lead to the damage.

Summing up, the only way is to drop it one block at a time.

Solution 2:

If you push an anvil into the side of a honey block with a slime launcher, the anvil will slowly slide against it like any other entity, preventing damage.

It's also good to note that the anvil falling entity stays displaced after losing contact with a honey block, so a continuous wall of honey blocks is not necessary. If you end up using this in-between-freefall method, it's important to not have any other blocks directly between the 2 disconnected parts of a honey wall as that would drop the anvil as an item (without damage).

To answer the core question:

• If you need the floor to be flat and not have any honey showing, there's some bad news as I don't recall a hidden honey block floor double piston extender design being out there.
• If you have this against a wall, you can have the anvil falling at the edge of the room but still within it. Hide the honey block between the floor and wall and no double extender will be required except maybe in the ceiling. Also the entire column in which the anvil is going to fall is going to have to have its neighboring wall blocks retracted so as not to break the anvil into an item mid-fall
• If you don't care for hidden mechanisms, you can simply have a lone honey block within the floor and extend it when required, then retract its neighbors.
• And finally if you decide to ditch the idea of this being a redstone contraption, the honey block can just sit there above floor level all the time

Of course there may be other design decisions depending on your style but these are the ones that I've come up with that answer the question.