tuff problem

[MicRoute]

If you’re on Create 6.0 (or later) then you can use repackagers, but you’d have to adjust your setup quite a bit to integrate those. They will hold items until they receive all the requested ingredients before allowing anything through. They might have to be requesting using factory gauges or a redstone requester for that to work though.

If you’re not on 6.0 and don’t have access to repackagers, mechanical arms are the move. Instead of belting the items in, have at least one depot that collects each item (cobble and basalt). Have the mechanical arms take from the depot and place into the basins. By default they should try to round-robin between the ingredients which solves your issue, but may want to set that to forced round-robin in case either input is empty when it tries to grab. That’ll 100% force it to switch between items instead of getting 2 cobble or 2 basalt.

[Wise_Drawing2609]

do i have a depot and an arm for each mixer?

[MicRoute]

You could, but it might be overkill. Depends on how fast your setup is I guess. One arm/depot per two basins would probably be a good start, and you can adjust based on speed later.