I've decided to go with the TMC2208. Its current-handling properties appear to be the same as A4988s and the Duet doesn't really support the SPI/UART features of the 2130/2208 so the driver is going to run in "legacy mode" in either case.

That clears things up, thanks!

On this printer i'm currently using an atmega-marlin type board with A4982's onboard and it has no problems with the Z-motors, so it shouldn't be an issue. The bed levelling is a nifty idea, i hadn't thought about that. Since it's a "Mendel"-style cartesian it would be more like leveling the whole X-axis to the bed.

Since you mentioned SPI, is it actually possible to use it instead of Step/Dir? I've seen some Pololu-style TMC boards that have SPI headers on them.

Hi there, i've been reading the wiki on how to add external Stepstick-style drivers for an IDEX setup, but it has left me with a few questions that i haven't seen answered anywhere.

1. I'd prefer to use a standard RAMPS or a CNC shield, and i assume that you need to wire the 12V/24V power supply directly to the power terminals on those boards for motor power. Does the "100mm wires or less" rule apply as with the Duex boards and would it be preferrable to use a splitter the way it's shown in the Duex manual?
2. Which function would be best to assign to the external A4988 driver? Most of the time i've seen people use it for the second extruder, but i'm thinking that it's best to use it for the Z axis as that's the only one that doesn't really benefit from the increased microstepping precision of the TMC2660's and is used the least during printing.
3. Assuming i used the external driver for the Z axis, can i use it to drive both Z motors the way it's usually done for RAMPS setups, or would it be preferrable to use two A4988's since it's simple to add and costs next to nothing?