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What are your thoughts on a Digital Position Readout?

Hello everyone what are your thoughts on using a Digital Position Readout on the machine to help with finding your exact zero when doing things like a tool change etc. I bet this would work great for that if you record your position when you start and then you can easily go back to it when needed very accurately

what do you think?

There’s no need for that, unless you’re not setting up the machine properly and loosing steps you should always have a precise reference point, steppers should always be engaged when the machine is off so you can do tool changes without loosing position.
Also, 500mm DRO are around 150$ each.

Or you could:

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I will sell you a procdure for doing this and not charge you $150 per axis.

(shush! Don’t tell anyone it’s built into the grbl code we can make a fortune)

Take a look at G28 and G28.1

Happy carving.

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lol you guys are killing me

IMO, using DRO scales is a good idea. Less then $120 total including shipping for all three axises. It sure would be easier to maintain calibration with a belt drive machine like the X-Carve to monitor belt stretch and any lost steps.

http://www.ebay.com/sch/m.html?_odkw=&_ssn=dbmimports&hash=item25b2e983ab%3Ag%3AVBsAAOSwl9BWHDIz&item=161915437995&_osacat=0&_from=R40&_trksid=p2046732.m570.l1312.R1.TR11.TRC2.A0.H0.XDRO.TRS1&_nkw=DRO+scale&_sacat=0

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I’d love to have that. Can’t afford it, but since Easel doesn’t show coordinates on the Main or Carve screens it would be super useful.

It would also help immensely with homing to the material origin, since you could just home the machine between each carve and then re-zero it based on where your material is located. If you accidentally moved the carriage during a bit change, no big deal. Just home, move, then set Z-zero.

What would be the best is if there was a way to feed the X/Y values back into the Arduino so it could run in a closed loop control mode. No more missing steps!

Servos or steppers with dual shafts attached to an encoder can do this.
https://www.google.com/search?q=stepper+motor+with+encoder&espv=2&biw=1536&bih=764&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi8vujGiZTKAhUBRT4KHTbQB0kQ_AUIBygC
It makes for a complex system!
Also I always wondered, once you lost a step, then what?
Yes you will know you lost a step, but how does one recover?

In a closed loop system if there is no verification the command was carried out it is tried again before the next command is sent, If on the second try there is still no positive confirmation then the system goes into a safe mode since something mechanical must not be working correctly.

Still not quite there. You need an independent verification that the move occurred correctly. You can have an encoder witness the turn of the motor shaft, but that doesn’t cover the case where the belt slips a tooth.

Good plan, Need a better processor to handle all that.

I think the Arduino could handle it, but it would be a major software change.

Ah. That’s a good point. I guess that’s why higher end systems use gears or screws as well. Those won’t slip.

The DPR unit being discussed directly measures the position of the spindle carriage position. So any belt or pulley slip would be seen.

Actually, it can’t. It’s not a matter of processor power. Grbl takes up almost all of the resources. One of the reasons enhancements are a little difficult to work in. More code space and more memory would do the trick (oh, and a little more I/O capability).

Yes, I was pointing out the difficulties with relying on the encoders mentioned above. The DPR system would be an example of an independent verification system.

Has anyone seen DROs with a serial or I2C output - something that will output a value? This could be implemented in Mach3 as there is a way to pass z,y,x coordinates to the serial port. That would be cool for coolness sake but IMHO totally unnecessary if you can just put a mark at 0,0 as a reference.

The LoboCNC used positional encoders which affords some nice capabilities.

so im not skookum on grbl what does g28 and g28.1 do?