BoB selection for closed loop steppers

Hi folks,

Trying to figure out the motion control side of things and electronics are not my strength. I'm planning to used a UC300ETH and some closed loop steppers. I am unsure of how to account for the closed loop steppers in my BoB selection. I have seen about using a combination of limit switches plus the home/Z pulse on a closed loop stepper as a way to accurately home. How many inputs would be required on my BoB to account for this? One for each limit switch plus one for each stepper encoder?

I was recommended the UB1 got it seems it might be overkill for what I want to do.

The closed loop steppers are wired to the breakout board just like open loop steppers. The loop is closed in the drive, and the UC300ETH never sees the encoder signals.

Quote:

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I have seen about using a combination of limit switches plus the home/Z pulse on a closed loop stepper as a way to accurately home. How many inputs would be required on my BoB to account for this?

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Depends on how you wire it? If you wire everything in series, maybe as few as 2? Or as many as 6 or more?
Note that you'll need to write a custom homing macro to do this.

Makes sense! I was thinking "couldn't I just wire them on the same pin" but I'm new to this stuff and wasn't sure. In anycase I just realized the steppers I am looking at don't have the Z pulse (it was the DMM servos that had it) so I'll likely be opting for some precision homing switches instead. Thank you!

Generally, the closed-loop steppers run the encoder back to the stepper driver, not the breakout board. As far as the breakout board and control software are concerned, they are just the same as open-loop steppers. The only difference is that they never "lose a step" due to a momentary mechanical overload.

If the encoders have an "index" output that triggers once per revolution; then yes, in principal you can get a very exact homing operation. Exactly how you would set that up in your particular control software I don't know; I use my own modified version of Grbl (for which I have the complete source code for, so I would just go into the homing routine and write something in C to handle it. Obviously, that's not an option for you when you are using off-the-shelf commercial control software).

However - for the hookup to the breakout board; I can tell you this much:

You will need, for each axis, at a minimum (and not counting tricks like running switches in series to reduce required IO pin count), two outputs and two inputs:

Step: Output from the breakout board to the Stepper Driver.
Direction: Output from the breakout board to the Stepper Driver.
Home: Input to the breakout board, from the axis Home Switch.
Index: Input to the breakout board, from the Stepper Motor's Encoder.

The Stepper Driver you select may also want that Index line routed to it; or it may be OK with running without it. You'll need to consult the driver's documentation for that information. In general, it's OK to run one TTL (i.e, 0 to 5 volt, digital) output to several TTL inputs (because the inputs are just "listening" and not trying to pull the line one way or the other); but it's not OK to do the reverse - what happens is one output driver ends up trying to pull the wire to 5 volts, and another tries to pull it down to 0 volts; the result being that at best they fight and nothing works, at worst you fry a chip.

The Stepper Drivers may have an Enable input on them; and your breakout board may have one or more Enable outputs that you can connect to the Stepper drivers. However, this is not strictly necessary; if the drivers don't have that input they will just be always on when there is power applied; and if you don't have an Enable output from the breakout board; then you can just wire the Stepper Driver's Enable Input whichever way makes it always on (some need that input tied to 5 volts, others need it tied to 0 volts). Or, you can run the Enable Input on the Stepper drivers thru a normally-closed contact on your Emergency Stop Switch, so that when you hit the E-stop, the motors shut down no matter what the software is doing (or not doing, as the case may be). If you choose to do this, please come back after you have made specific hardware choices with regard to the Stepper Drivers and Breakout Board; there is a bit of wiring and a resistor that's needed to make this work reliably but where it goes exactly depends on the Stepper Drivers and Breakout Board selected.

You can also add a limit switch at the far end of the machine's travel, so that if for whatever reason it hits the end; it makes the electronics stop trying to move the motors. These can be wired in series, as normally-closed switches, and connected to a single input on the breakout board. Then, when any axis goes too far, the software will just shut down the whole operation. Alternatively, if you have enough inputs on the breakout board; you could wire each limit switch to it's own input - although, practically, I don't really see the benefit of this in most cases - when the switches trip, it's going to be relatively obvious what's gone wrong, you don't really need a dialog box on the screen saying "Hey, it's the X axis, dummy!" ;)

I hope that helped, at least a little... :)

Thanks Britt! Theres a bunch of good info in there, I appreciate it. Its hard to gather it all up since it's scattered here and there... I found a handful of good Youtube videos of people documenting their builds and those have helped too. I'm ok doing the scripting, but after a bunch of searching around on CNCZone I think I'm going to get an AXBB and call it a day. Good price and will cover my homing needs (I'll grab some precision switches) and allows some expansion room and extra features if I'm up to it (Spindle control/VFD). It looks like it has atleast one output I can use for enable and the LCDA357H (https://webseite.sorotec.de/download...n/LCDA357H.pdf) I'm looking at utilizes high signal to enable the motors, so maybe I can tie all three to that forenable/ e-stopping.