A few questions about setting up IDEX



  • 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?

  • administrators

    @Nprod

    1. As you are not connecting to a Duex and thus do not have the I2C bus to worry about the distance can be increased. how much depends on a bunch of factors but electrical noise is the one i would be most concerned about. In any case you do want to keep the ground connection low resistance so powering it the way its shown for a Duex is a good idea (i.e. Ground directly from the Duet to your RAMPs power in, short as possible).

    2. Depending on the current requirement of your Z motors, the Z axis would be a good choice.

    3. The major advantage of this would be the ability to level the bed to the X axis, assuming the Idex is laid out in such a manner that that makes sense.



  • 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.


  • administrators

    @Nprod the SPI is not instead of Step/Dir is used as well as to do things like set the current, microstepping etc. I don't think the A4982 support that. the StepSticks that do probaby have trinamics or other drivers on them.



  • The TMC3102 was Trinamic's "transition" from jumper config to SPI/Uart config. Most "stepstick" style boards for the 2103 have a jumper (just pads) that chooses which, on the bottom side (chip side), near the CS pin.

    Open = SPI
    Closed = Jumpers.

    Some boards were shipped with a zero ohm surface mount resistor as a jumper. If not present, you can "solder blob" across them as well.

    Once those pads are connected, several pins around the edge of the board become TRI STATE jumpers. They select different values when connected to VIN, GND, or left open. It is also true that no jumpers at all (pins open) selects a good set of defaults, 16x microstep with interpolation, etc.

    The point of all of this being: Run a TMC3102 for externals. They are GREAT!



  • 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.


  • administrators

    @Nprod said in A few questions about setting up IDEX:

    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.

    The TMC2208 is capable of somewhat less current than then A4988, but enough for most Nema 17 stepper motors. On the Duet Maestro we run the TMC2224 (which is almost the same chip) at up to 1.6 peak. In stepstick format, they are probably good to about 1.2A peak.


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