Duet controlling 4th axis

minim

I have a cnc mill that have a Fanuc control system. I want to add a 4th axis to this but for now I want to control it with a stepper motor just for indexing. The machine can send a binary signal for let's say 10 degrees movement. Can the duet read a signal like this and control a closed loop stepper that have an external driver? I need a nema34 or maybe a nema 23 so I don't think the driver in duet is powerful enough.

dc42

The Duet can control a Nema 23 motor if you choose one with an appropriate current rating. I test Duets at max current (2.4A) using Nema 23 motors rated at 2.8A. This is a good match. Running stepper motors at full rated current is not normally desirable, because they get very hot when you do that.

RepRapFirmware on the Duet can control up to 9 axes. Normally you would include the additional axes as additional parameters in the GCode commands (any or all of U, V, W, A, B, C). You could use a M581 trigger to cause 10deg movement on receipt of a trigger signal, but you would have to be careful to keep it synchronised to the main GCode stream.

minim

@dc42 thank you for the info. I suspect that nema23 will have too low torque to hold when milling steel so that's why I'm looking at bigger 34 or a high amp 23 but I'll do some math and see if it will work with 23.. The "original" 4th for my machine usually run a 0,75kW servo like the rest of the machine but then again this is sitting on a worm gear with 90:1 reduction and I have to gear it down even further since 90:1 doesn't add up with full steps of the stepper motor and 360 degrees..

I only need to control this one axis since the fanuc control does the rest. I need features like rigid tap where it sync spindle speed with movement among other thing that would be hard to do with the duet (I guess?). Also I'm not sure how the duet would handle encoder signals and servo control? The control system is rock solid and industrial but it's a pita to change the ladder since it has to be done in dos and burned into two uv eproms. Would love a control system upgrade but I'm sure it will cost more than I would like it to cost..

minim

Is it worth going for one of these closed loop variants instead of running it directly off a duet? Oh and how do I configure the duet for cnc use? I want to use it just as a indexer so I don't need all the temperature and other stuff in the webui.

https://www.ebay.com/itm/12NM-DSP-Closed-Loop-Stepper-Motor-Nema34-23-Hybrid-Servo-Driver-Power-Supply/122420276298?hash=item1c80d12c4amg92V7d7eazrnaYQYUe2g_Q

dc42

@minim said in Duet controlling 4th axis:

Is it worth going for one of these closed loop variants instead of running it directly off a duet?

It may be, if you can afford it!

Oh and how do I configure the duet for cnc use?

https://duet3d.dozuki.com/Wiki/Configuring_RepRapFirmware_for_a_CNC_machine

minim

@dc42 good things. I started rewriting the DWC to be better suited for running just one axis (4th). Gotta love open source

minim

Cleaned out a lot of stuff that was not needed for running a rotary table. While doing this I saw that additional axes like the A axis I have removed here was parametrized so that it wouldn't show when it was not mapped. Why not include something like this for a cnc mode or modes in general so we could customize the web interface more?

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minim

@dc42 can the board handle it if I increase the current above the firmware limit of 2,4A? I could really use a beefy nema23 or 34

wilriker

@minim said in Duet controlling 4th axis:

@dc42 can the board handle it if I increase the current above the firmware limit of 2,4A? I could really use a beefy nema23 or 34

Currently the 2.4A are limited in firmware. So if you set it any higher in M906 will still cap it at 2.4A.

I would guess that if you recompile the firmware with a higher limit and some very aggressive cooling (of the backside of the board) it might handle more than 2.4A but also I am pretty sure that this will void the warranty.

dc42

As @wilriker says, you can increase the firmware limit if you like but that will void the warranty.

minim

@dc42 said in Duet controlling 4th axis:

As @wilriker says, you can increase the firmware limit if you like but that will void the warranty.

Yeah I assumed that. I'll sort out the firmware limit but I just wondered if the board could handle it. Have you experimented with how much it takes to make ? Since trinamic rates it higher the chip itself should handle it as long as I take care of the heat?

dc42

Trinamic only rates the chip above about 2.4A peak for short durations. AFAIR the higher rating they give is for 6 full steps per second or higher.