Quote
realthor
Very interesting idea, the two can be combined you know. I was going to suggest the following scenario (has already been explained somewhere above but doesn't hurt):
1) read the hardcoded X_travel and Y_travel (say 250mm and 250mm) for a bed that is 200x200
2) assume Y is at the far-est position, namely touching the close Y clamps (it has to go all the way of 250mm before reaching the far-end Y clamps)
3) reduce motor current to a low value but enough to be able to get the carriage there in a decent time without skipping too many steps (+increase microstepping to 32 -steppers must be able to work with those values so if you have 1/256 steppers why not)
4) command a travel of 300mm so you are sure it touches the other side
5) increase motor current to 1/2 of normal (keep microstepping)
6) travel 250mm back to the start
7) increase current to 100% and reduce microstepping to whatever value suits your needs

Quote
dc42

Quote
realthor

Very interesting idea, the two can be combined you know. I was going to suggest the following scenario (has already been explained somewhere above but doesn't hurt):
1) read the hardcoded X_travel and Y_travel (say 250mm and 250mm) for a bed that is 200x200
2) assume Y is at the far-est position, namely touching the close Y clamps (it has to go all the way of 250mm before reaching the far-end Y clamps)
3) reduce motor current to a low value but enough to be able to get the carriage there in a decent time without skipping too many steps (+increase microstepping to 32 -steppers must be able to work with those values so if you have 1/256 steppers why not)
4) command a travel of 300mm so you are sure it touches the other side
5) increase motor current to 1/2 of normal (keep microstepping)
6) travel 250mm back to the start
7) increase current to 100% and reduce microstepping to whatever value suits your needs.

Increasing microstepping when driving against the physical endstop wont help. The motor won't just stop when it hits the endstop, it will keep jumping back by an amount corresponding to about 2 full steps whatever microstepping you use. For a typical build with 1.8deg motors and 80 steps/mm @ 16x microstepping, that's 0.4mm of movement.

For a CoreXY machine, I still think that a better solution is to use one IR Z probe to home all three axes. The Ormerod uses it to home both X and Z, but with the bed moving in the Y direction and the gantry in the X direction, there wasn't anywhere you could put a Y homing tab. On a CoreXY machine, I can't see any reason why you can't have a homing tab for Y as well as one for X.

Quote
realthor

Very interesting idea, the two can be combined you know. I was going to suggest the following scenario (has already been explained somewhere above but doesn't hurt):
1) read the hardcoded X_travel and Y_travel (say 250mm and 250mm) for a bed that is 200x200
2) assume Y is at the far-est position, namely touching the close Y clamps (it has to go all the way of 250mm before reaching the far-end Y clamps)
3) reduce motor current to a low value but enough to be able to get the carriage there in a decent time without skipping too many steps (+increase microstepping to 32 -steppers must be able to work with those values so if you have 1/256 steppers why not)
4) command a travel of 300mm so you are sure it touches the other side
5) increase motor current to 1/2 of normal (keep microstepping)
6) travel 250mm back to the start
7) increase current to 100% and reduce microstepping to whatever value suits your needs.

Quote
lkcl

Quote
realthor
Nono, i've kind of given up that idea -I understood about the NO shortcomings and the exposed contacts risks- ... was focusing on switchless homing by reducing the motor current so it hits the wall, skipping steps as it thinks it's still moving, until enough coverage has been traversed to be sure it's there at the end of the rods, then coming back and counting the steps on its way.

.... blerrgh! ingenious idea but one that has me kinda shuddering at the calibration you'd need to perform, and the testing - how many printers are you planning to get through during the testing phase? :) hey i know - how about, instead of changing the current (which you can do with RepRapFirmware anyway) you change the microstepping rate to something mad like 1/256? my main objection to the "bang it against the wall" idea is that it's not very accurate, you'd get juddering down the belt, you'd be relying on the elastic properties of the belt as well and it really might not like the large steps when subjected to tension. i know they survive wall-banging but it's not a nice sound. buuut if you're using silly-ridiculously-accurate microstepping, not only would the torque be reduced but the accuracy would go up, and, also, you'd be forced to run at a much slower speed.

for the z-axis... the thought of banging the z-bed into things... you'd better have a good bed design! or have just a z-probe.

Quote
realthor
Nono, i've kind of given up that idea -I understood about the NO shortcomings and the exposed contacts risks- ... was focusing on switchless homing by reducing the motor current so it hits the wall, skipping steps as it thinks it's still moving, until enough coverage has been traversed to be sure it's there at the end of the rods, then coming back and counting the steps on its way.

Quote
realthor
Bearing touches, contact made => endstop triggered.

Quote
realthor
No objection really, maybe a bit more complexity and the fact that the simple low tech devices aren't that good (mechanical microswitches for ex). It's no secret that I like the low-tech approach of the instant direct-contact of the nozzle2bed approach for Z.

Quote
dc42
I tried this once on my delta printer. I use a Z probe to autocalibrate after homing, so the homing only needed to be accurate to about half a millimetre. It worked, but it was still noisy when driving the carriages against the stops, and of course homing took the same length of time as the worst-case even if the printer was almost at the home position already. My conclusion was that it is an option for making a very low cost printer, but you wouldn't want to use it otherwise.

Quote
realthor
As with most things a software solution is the best. Not only that software reducing the current while homing would prevent any damage if something was broken, but a software solution alone can replace the X and Y endstops alone. It would work like this:
- current is reduced by such amount that when the Y carriages hit the end points they "keep going", skipping steps easily (just as a torque adjustable cordless drill, when you set the dial so it skips at the right amount of force to prevent damaging the screw head)
- software knows the size of your bed (hard coded)
- printer goes for that amount of steps and then double it (what if it really was at the other side and it didn't know it). So in the ideal case it will go twice as far as it should but, by having a low current in the motors, it will hit the end and spend the other half of the distance skipping steps. In the worst case scenario it would start from the end and skip the steps for the whole "virtual" distance.
- printer comes back to the Home position for that axis by the distance that is hardcoded in your settings. basically homing. This can be done for all axes, but for Z it wouldn't matter much as you will have some sort of probe anyway to do the ABLwinking smiley.

How difficult would be in software such a setup?

Anyway for an NO circuit, reducing the current during homing would be enough to prevent catastrophic damages. That or sizing your parts so that the motors will skip steps if they hit an end even at full power (not that difficult with 3D printers torque needs, but as the desired speed of the printhead increases, so is the needed torque and so the above should be implemented - also needs digitally adjustable stepper motors).

I've found the digital current settings in Marlin & Repetier:
Marlin: Configuration_adv.h setting called DIGIPOT_MOTOR_CURRENT
Repetier: Configuration.h setting called MOTOR_CURRENT

Now if these are hard-coded values, how can they be altered during homing? This might not be as difficult of a task as I think.

Quote
realthor
I am not after fights here MKSA, the first one was a genuine question. Also the second, what is ABL? See, I accept people have different views and I really wanted NO to be better, because that's why I was after. Some people here in the forums have a hard time to understand that others can be very different and tend to put everybody in the same pot. I spend a lot of time out of my home/town/country so I am left with mostly designing, asking, educating myself, reading, etc.

So rather then proving such a short temper please try to understand that. I don't expect you to design as much as I do because you are different, have access to tools and like tinkering more than designing. I simply accept that.

Edit: about the community, as much as I love the community concept, it's not quite like that. When someone asked that I do some design to fit their situation I did it from scratch. Because I enjoyed it. It wasn't his burden, it was OUR burden. Now that's community :)

Quote
realthor
I've found the digital current settings in Marlin & Repetier:
Marlin: Configuration_adv.h setting called DIGIPOT_MOTOR_CURRENT
Repetier: Configuration.h setting called MOTOR_CURRENT

Now if these are hard-coded values, how can they be altered during homing? This might not be as difficult of a task as I think.

Quote
os3dp
I somehow had an old page. I posted but didn't see ALL the other posts before.

-os3dp

Quote
the_digital_dentist
ABL = auto bed leveling

Quote
realthor

Quote
MKSA
Different thing here. Talking about ENDSTOPs, which are BETTER to be NO.

Why is that? It is really the first time I hear that. Crashes can happen in XY as well...

Quote
MKSA
If you want an other mean to determine the Z 0 with for example a probe on the print head to provide ABL, indeed but you better make sure not to sacrifice reliability..

ABL=?

Quote
MKSA
As a matter of fact this has been discussed in an other thread and I advised you to really BUILD, TEST and give the results. Without that, there is nothing.

Yeah, it's a bit tiring :) ...as I've been patient and explained at least as many times why I can't for the time being. But well...

Quote
dc42
Building and testing is necessary and all very well, but the best designs also consider "what will be the effect if XXX happens?". For example:

Quote
grat
Also, if you wire in series with NO -> NO -> NO -> NO, then closing any particular switch will not complete your circuit. Conversely, using all NC, any switch opening will break the circuit, causing the entire circuit to go "open".

Quote
MKSA
Different thing here. Talking about ENDSTOPs, which are BETTER to be NO.

Quote
realthor
No objection really, maybe a bit more complexity and the fact that the simple low tech devices aren't that good (mechanical microswitches for ex). It's no secret that I like the low-tech approach of the instant direct-contact of the nozzle2bed approach for Z.

So I am in pursuit of similar versions of X and Y. Y is quite simple, like I said before, bearing closes the circuit when it touches two contacts on the Y Rod's clamp. X Endstop are not that easy to offload from the X carriage. All this can be done with NO mentality in mind but that increases a bit the complexity although it's more elegant (the way I imagine doing it - some sort of 2D renishaw-stule contact breaking)