Quick answer: Most automatic litter boxes require clumping litter — it forms solid clumps the rake can separate cleanly from the clean litter. Non-clumping, crystal, and pellet litters are usually incompatible.
Automatic rakes work by separating solid waste from loose litter. Clumping litter forms tight, firm balls the rake scoops cleanly. Non-clumping litter breaks apart and gets mixed back into the clean litter, making cycles ineffective and creating odor buildup.
Fine-dust litters can clog sensors and moving parts over time. Look for low-dust or dust-free clumping litters. Unscented formulas are better for cat acceptance — strong fragrances near the litter box deter many cats and can cause them to avoid the box.
Some automatic litter boxes (like Litter-Robot) have specific recommended litter types in their manual. Check your model's requirements — some are calibrated for specific clump firmness and may jam or give false readings with lightweight or fluffy litters.
Start with a standard low-dust clumping litter when setting up a new automatic box. Only experiment with alternatives once you understand your machine's baseline behavior.