Piezo20 probe and piezo kit now available
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The stall guard signal from the TMC2660 is only updated once every full step and it doesn't work at low speeds. So it's not usable for bed probing. It might be usable in place of endstop switches on a delta printer, if you then use auto calibration with a Z probe to work around the inaccuracy of homing with a resolution of only 1 full step.
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So one full step on a 0.9 deg motor with 16t pulleys and 2mm belts would be 5 microns in the centre of the bed, which would be twice as accurate as the IR probe or piezo probe which are both around 10 micron accuracy, but with 1.8 deg motors there's no accuracy advantage and near the edge of the bed accuracy would dramatically decrease?
Plus the speed would have to be too high (even with very low motor current?) to make it a useful probe?
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So one full step on a 0.9 deg motor with 16t pulleys and 2mm belts would be 5 microns in the centre of the bed, which would be twice as accurate as the IR probe or piezo probe which are both around 10 micron accuracy, but with 1.8 deg motors there's no accuracy advantage and near the edge of the bed accuracy would dramatically decrease?
No, 1 full step with 0.9deg and 16t would be 80 microns.
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Yes, I see, the online calculators presume 1/16th microstepping, yes 32mm for 1 rotation = 0.08mm! So using the stepper drivers is not a useful approach at all. Best get back to improving this piezo unit then.
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DJ
Can you tell me the Hole Spacing you have used for the rods and the mounting to the Effector.
I would like to try and incorporate the upper part into the Effector itself?
Cheers
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Hi Doug, I got the other pack of rods eventually must have been found at the delivery office somewhere.
I placed the holes visually using tinkercad, I would download the version from Lykles effector as he reworked it in proper CAD with everything correctly aligned. I can share the tinkercad if you want to copy it and edit it there, or measure on screen etc… https://www.tinkercad.com/things/4xOFf6aKRqY-mighty-hango/editv2?sharecode=geXsvoOL47aio2sexQ1VhFXhIfL_zFGPlmMLl4IOLpQ=
I have found using 4.5mm holes for the lower part on the clamp and 4mm on the upper part means assembly requires no manual easing, and slightly chamfering the acetal rods (15mm long) then tapping them in with a hammer seems to work - I've made a few of these now.
Sorry not to be more helpful. I really have to do a course on proper CAD, should have done it before now.
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Hi guy look this 3D print palpeur!!!
In cnc machine They use only "palpeur" and précision can be 0.001mm So i give you the link with ALL the stl and info and boom… It's in french So Google translate is your friend ?
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Yes Doug, I was going to do the same thing. Rework the effector for it all to fit.
The rods do interfere with the Nimble mounting places a little bit, so I was intending to move the rods a little. But that is my problem.What file format do you want?
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Lykle
could you maybe just adjust the positions so that it doesn't interfere and maybe make the Ball Spacing to be 60mm for me (I know I am asking/taking liberties but your Cad Skills are far better than mine)
I tend to use FreeCad which uses it's own format and not sure what it can import alternatively Fusion360 may do as I need to learn that anyway.
Doug
If you can do this then I Will wait to implement it till I get my Nimble?
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Hi guy look this 3D print palpeur!!!
In cnc machine They use only "palpeur" and précision can be 0.001mm So i give you the link with ALL the stl and info and boom… It's in french So Google translate is your friend ?
So this switch seems nicely made but it says the precision is 17 microns, we are easily hitting 10 microns with the Piezo, plus this is a switch - basically a large version of a microswitch, how is this going to help us with z probing? Microswitch-based hotend probes already exist but the hot end assemblies are wobbly. The switch needs much more than 0.15mm movement to trigger, it has to be able to move more than this, this creates the wobble. The feature of the Piezo probe which makes it suitable is its very sensitive and can be compressed within a mechanism that moves a tiny amount.
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Well broadly speaking I think this is the basis for the new UM3 bed probing, the probe presses on the glass which triggers a capacitative sensor underneath. I think it might be useful to start a new thread call it "new z-probe technologies" or something similar and we can discuss some of these alternative ideas there. I would like to try to keep this thread focused on the piezo z-probe and its development.
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Well broadly speaking I think this is the basis for the new UM3 bed probing, the probe presses on the glass which triggers a capacitative sensor underneath. I think it might be useful to start a new thread call it "new z-probe technologies" or something similar and we can discuss some of these alternative ideas there. I would like to try to keep this thread focused on the piezo z-probe and its development.
Hi,
Ok true i erase my reply and Start A New thread New z probes technologies…
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In any case question for the electronics experts. On the kossel XL the piezo is wired with red-positive and black-negative going into the piezo board, normal operation. On my corexy I noticed the polarity is reversed (same brand piezo) but I also get normal operation - if I reverse it on either machine it doesn't work. So why does one setup happily work with the piezo in reverse polarity compared to the other?
I've been thinking about this for a couple of days and I can't explain it.
Idris
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Are the Piezo's in the same orientation on both ie brass side up on both or down on both could that make any difference?
Just thinking out loud again
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I'll check again maybe my error. But yes they were the same way around.
Edit - no the corexy has the piezo element wired in reverse polarity, and if anything I'd say works slightly better than the kossel XL where it is the right way around. I might try reversing the polarity on the kossel XL and re-tuning the piezo board.
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So this doesn't work, if I reverse the polarity on the kossel XL I cannot tune the piezo board to get a usable output.
So two things to consider:
- my piezos are not very consistent and I bought the branded ones.
- if you cannot get it tuned with the piezo connected one way around, turn the plug from the piezo element so it is reverse polarity and being the tuning again.
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Just a quick observation on consistency: I found that the branded ones (Murata) were polarised in the opposite direction to the unbranded ones and had a wider spread of sensitivity, the most sensitive being about twice as good as the least. By comparison the unbranded ones fell into less than a 10% spread.
Mike
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I think there would be something in it to buy a lot of these and test them, how many different types did you test in total Mike?
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I purchased to batches of 10 no-name 27mm discs on ebay from two different suppliers and tested about 17 of them. I also got 10 Murata discs from Farnell and tested only 5 of them as they had to have leads soldered on and this was a destructive learning curve.
The Murata did score on giving a decent output at temperatures at just over 100C while the no-name were really poor - see http://forums.reprap.org/read.php?1,635075,655510#msg-655510
Mike
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I've soldered wires to piezo transducers before. Apart from heat damage to the piezo, the other risk is that the silver coating gets sucked off the piezo. You need to make the joints as quickly as possible, using as little solder as possible. It's best to use solder that contains silver, which some but not all lead-free solders do.
