Re: [OpenPnP] Closer loop stepper choice / Auto Squaring Y Axis

[mark maker]

> I built a CNC machine which uses two drivers for Y but these are driven by separate channels / controllers which allows them to be individually homed, squaring up the Y axis. Is this possible with OPENPNP?

Assuming this squaring would all be done in a homing sequence, and that homing sequence can be commanded via G-code, ... 

... and further assuming that from then on the Y axis is just used as a single (logical) axis letter inside the relevant G-code commands (G0, G1, G92, maybe more), and it is being reported back as such (M114), then yes! 

Meaning that OpenPnP would not be aware of that bundling and squaring, but the G-code interface should make this transparent, so it does not matter (it would surprise me, if Duet had not made sure it works like that).

BTW. I wasn't aware of the Duet 3 Mainboard 6XD with "D" as in "external Drivers" I guess. Good to know! 🙂

@other readers: be aware that the "normal" Duet 6HC does not have the headers for direct external STEP/DIR!

https://docs.duet3d.com/User_manual/Connecting_hardware/Motors_connecting_external

Another idea could be to use the Duet 3 Mini 5+ which has headers for two external drivers (for the heavy axes X and Y), and still has 5 internal drivers, which could drive the nozzles (2 x C and Z). This would allow you to put the board on the head, which can dramatically simplify the cabling. Much is then local, including down light, vacuum valves, vacuum sensors if you want them, end-switches for X and Z, plus contact-probes if you want them. Plus various voltages from the board. And it would make the drag chain lighter, or even allow for a "free-hanging" design (just power and vacuum tube, plus a few light signal cables needed).

However, unlike the 6XD, the Mini headers are just 3.3V, and would have to be protected/shifted to 5V, I guess.

_Mark

On 26.10.2023 11:13, 'Dogboy' via OpenPnP wrote:

Hello,

I have narrowed my choice of controller boards down to either a Duet 3 6XD or a Rapid Star board, as I want to use external closed loop stepper drivers.

I have been looking at NEMA 23 or 24 closed loop motors from Stepper.

However, I wanted to run the motors at 48V+ (Maybe 60v) but I have the following questions based on the following choices.

1, Frame Size: NEMA 23 or 24

2. Motors would be 2 Nm

3. I would like to use two motors for the Y axis (Either 2x 2Nm or 2x 1.2Nm)

Do you consider this to be an overkill or would this be suitable?

I know that it depends on many factors like the head weight and gantry weight etc but I would like to hear your views on what size and  type of motors are being used for perhaps higher end builds.

The Duet 3 6XD may be the best option for using external drivers as the Rapid star board only has two motor channels for external drivers, which may be ok if I use one to drive two controllers for the Y Axis (But see below).

I built a CNC machine which uses two drivers for Y but these are driven by separate channels / controllers which allows them to be individually homed, squaring up the Y axis. 

Is this possible with OPENPNP? (Both Y motors software paired but can homed semi independently. Both until one reaches home then only the second one until it reaches home)

Are the stepper online closed loop drivers and motors any good?

Thanks in advance for your replies.

Paul

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[dc42]

I thought I would mention that the Duet 3 range includes the CAN-connected Expansion 1HCL board, which can drive stepper motors with a built-in encoder, or ordinary stepper motors with our own magnetic encoder on the back. We'll be releasing Nema 23 motors with the controller and encoder built-in soon, with a direct CAN connection from any Duet 3 series main board to the motors.

[Dogboy]

Hi dc42, 

I looked at the 1HCL boards.  They would allow me to add extra heads or a conveyor etc in the future. I wasn't aware that they supported a stepper with an encoder. I will look into further - Thanks.

I will have  a look around for more info about support for NEMA 23 motors with encoders. I do like the LeadShine and StepperOnline closed loop solution. My LeadShine closed loop motors work exceptionally well with my CNC.

I also used Gecko Stepper drives (GM213V / GM215) which were incredible devices, but expensive (for previous project).

Its a shame they don't produce a closed loop version. I have to say the Gecko drives were the best I have ever used and almost bomb proof with the -V versions. (They will replace them for free if you ever destroy one of the -V drives!)

I found an Australian  company that produced stepper / Servo drivers that seemed pretty good but I cannot remember the name of the company. 

Anyway, Thanks for the info. 

Thanks

Paul 

[David Crocker]

Hi Paul,

The Expansion 1HCL board does indeed work with Nema 17/23/34 stepper motors with built-in optical encoders. We advise using 1.8deg motors only, and an encoder resolution of at least 1000ppr/4000cpr.

However, I should point out that using a motor with our own optical encoder offers some advantages:
- Absolute determination of rotary position, avoiding the need for a short calibration step after the driver and motor are powered on

- Higher resolution, resulting in greater positioning accuracy

- A wider choice of stepper motors (any stepper motor for which it is possible to glue the magnet we provide on the back of the shaft).

Best regards David

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David Crocker, Duet3D Ltd.

[Dogboy]

HI David,

Thank you for the info. That really looks good.

So, as an example (Expensive way to do this I know but...) if I had a Duet 3 6XD with 3 HCL boards to drive the X & Y axis (Two motors for Y maybe) and using the feedback (Magnet) would that in general offer an improved solution in both speed and accuracy over say using a closed loop driver and motor (4000ppr) from StepperOnline?

I know that their are many other factors here but just in general, I trying to work out the best approach.

Of course the cost of the HCL boards are pretty close to the cost of closed loop external drivers anyway, so not much extra cost using them but with the added advantage of better resolution and being able to use different motors.

I will search to see if anyone here has used this sort of setup.

One question (I will check myself), but you said "I should point out that using a motor with our own optical encoder offers some advantages:"

So, I assume that I have two options either the magnet sensor or an optical encoder, is that right? Or am I reading this wrong. I will have a look on the Duet site to check as well.

Thanks for your replies.

Paul

[Ben]

Paul, allow me to say my opinion in this issue, but I think that adding money for expensive motors and decoders and fast communication will be in vain in this case. step motors in open loop mode are quite a good solution for small P&P machine, and if you need a real fast hardware, you will not get it from step motors with encoder.

openpnp gives a good acceleration control to get a fair speed.

for faster mechanics I have experience with DC/BLDC motors with lead screw, but this is a total different story.

ben

[bing luo]

It's better to use the funds to make the mechanical structure more sturdy and precise, better linear guides, and better stepper motors. These tasks are more valuable than closed-loop control.  

Almost none of the factory's  PNP  use closed-loop motors.

[David Crocker]

Hi Paul, in my previous message I mentioned "our own optical encoder" by mistake. I meant our magnetic encoder.

I can't say whether using closed loop steppers would be of benefit to you because I don't kaveri experience with OpenPnP. The main advantage of closed loop motors is detection of when the desired position can't be achieved, allowing the operation to be paused and remedial action taken. It will also be possible soon to record the loop error and motor current needed to maintain position, which in an industrial setting could help plan preventive maintenance. However, if failure to maintain position is rare in PnP machines then it's likely that using closed loop motors is not worthwhile.

Best regards David

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