>15 axes via 3HC expansion boards

TechnomadicJim

Posting here as per @dc42 suggestion here.

I have two machines running Duet 3 main boards plus 4x 3HC expansion boards as part of a custom CNC motion control system. I currently use all 15 available axes, 13 of which are used for part feeding.

As we're firmware limited to 15 axes (main board + 3 expansion boards) I'm unable to utilise my 4th boards (axes 16-18) on both machines for further part feeding.

Is there any idea about whether >15 axes will be implemented? I can't find it now but I think I read somewhere on the forum that it was perhaps proposed for the 3.5 release.

Thanks in advance.

dc42

@TechnomadicJim that looks an interesting machine! Can you tell me a little more about how you operate the part feeders? Do they move mostly in one direction? Do they have homing switches? I am wondering whether they might be handled more easily as extruders instead of as axes. RRF on the 6HC allows up to 16 extruders already, and up to 25 axes+extruders.

TechnomadicJim

@dc42 Thanks The part feeders use sensorless homing for the four steppers that run off the 6HC. The 3HC expansion board steppers use a min end stop only (not visible in picture). I would eventually like to use sensorless homing for the part feeders on the expansion boards but this works fine at the moment.

To give you a better idea, here's a partial CAD model of the parts feeder.

The parts are stacked up on top of each other in an enclosure and drop into a recess shaped like the part once it hits it's min end stop. It then moves in the opposite direction to present the part for the next process.

I didn't think of the 25axes+extruders possibility. That's an interesting idea. I suppose an extruder can't have an end stop so that's why you ask if I have homing switches. It's not ideal but I might be able to make it work without an end stop for the time being.

dc42

@TechnomadicJim sensorless "homing" is implemented for extruders on main boards already, although it's been a while since I tested it. Basically, if you do a G1 H1 Exxx move it will stop before moving xx amount if/when the motor stalls.

TechnomadicJim

@dc42 It's working! The sensorless homing does indeed work for the extruders as suggested. Thanks again for the support.