End stop question (mendel v2)

Hi guys

I hope this is the correct forum to ask in and apologies if not.

I have just put together a prusa mendel v2 from parts a friend printed, and it's almost ready to use but I have a question about the end stops if someone could help please.
The whole thing is assembled and wired, and I have levelled the bed etc.

The main issue I have got is that on the Y axis, the stepper continues to move when it hits the end stop.
The first thing I need to confirm about this is which end of the machine the stop should be placed (either the side with the Y axis stepper, or the opposite end?) as I have seen both ways?
Currently the end stop for Y is beside the Y motor, so maybe it's at the wrong end?

The other axiis are fine, and stop when they are supposed to.

The setup I have got is a Melzi v2 controller (with the heatsinks on each chip), and Repetier software, but I'm not sure what I should be doing to correct this Y axis end stop thing as I'm new to this. I have searched on this but seen a variety of comments which relate to different software/controllers etc.

Secondly, (this is just curiosity) what is it that stops the steppers when each one gets to the opposite end of the axis to where the end stop is located?

One other question I have if anyone can help, relates to the vref voltage for the nema17 steppers I am using. I have seen some information stating vref should be set to 0.5-0.6v, but other sources stating 0.8v so I'm a little confused.
The x, y, and extruder steppers seem to get really warm even when I'm just doing small manual movements, but the pair of z axis motors remain cool. The z axis steppers are wired together in parallel directly at the board's terminals.
Currentlly the motors are set around 0.5-0.6v.

Appreciate any advice on this, thanks!

Problem solved re' the end stop. After checking with my friend's setup the Y end stop was positioned at the wrong end of the axis, so I've moved it to the opposite end to the motor and it's fine now.

I do have a more significant problem though it seems, just when I thought I had everything ready to go.
My X axis motor has started only moving one way for some reason and I can't figure out why.

It's not the motor, as it works fine both directions if I move it to another output. It was running ok earlier today but now only moves in one direction (away from the end stop). I've checked that the end stop switch isn't faulty (ie tricking it into thinking it was being pressed) and it's functioning just fine.

So I think it's something to do with the Melzi controller but I've no idea what. Nothing has apparently shorted/burnt/blown etc, no bad burnt smells, and the fact that the motor still controls fine in one direction suggests to me that the driver maybe hasn't blown as I'd expect it to be completely dead if that had happened.

Can anyone suggest why this might be happening at all? My printer is ready to use except for the fact this X axis is only moving one way for some reason.
Is there anything I can test on the circuit? I've pressed the reset button to no avail, and I see there are reset jumpers as well but I believe they're for loading firmware?

Thanks loads if anyone can help!!

i think the reason it only moves away from the endstop is this.

When you first power on the machine it will only move away from the minimum end stops, because whereever it was powered on it considers the zero point. trying homing the axis then you should be able to move both ways

b

As you probably know, the end stop switches are usually wired NC and C which suggests that the switch contacts are either remaining open when the motor is actuated or there's maybe an open circuit in the wiring. The motor cannot move toward the end stop if the switch is in this state because the logic thinks the X carriage is already in the home position.

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Waitaki 3D Printer

Waitaki - don't ask me why, but on my machine it appears that the switches should be NO rather than NC. I think you're right from what I've read that NC is the norm, but when wiring the end stops I asked my friend how his was set up. He tested the output from the end stops on his machine and confirmed they're NO, and get closed when pressed by their respective movement into end position by the bed or whichever axis is moving.

So I set mine the same, using the NO pins on the switches like his machine, and it worked fine until part way through yesterday when the X refused to move one way but was fine the other direction.
I can't explain why mine uses NO instead of NC, but possibly it's the use of the Melzi board instead of Ramps? I'm not yet familiar enough with the differences with these things I'm afraid.

Quote
n9jcv
i think the reason it only moves away from the endstop is this.

When you first power on the machine it will only move away from the minimum end stops, because whereever it was powered on it considers the zero point. trying homing the axis then you should be able to move both ways

b

That's an interesting suggestion thanks. I've just been and powered it up, and pressed the home button for the X axis. It turns the stepper a very short amount in the same direction it's working for, the same as if I click the manual movement arrow effectively. Since it's moving away from the end stop, if I deploy the switch by hand the motor will still operate how it was doing (because it's moving away rather than towards), and when I release the switch again it's still the same behaviour. So making it think that it's moved to the end stop doesn't appear to influence it. This behaviour all smacks of the end stop being on when it's not, but I've checked the terminals on the board and they're still open still (as my machine is set up NO, not NC remember) so this isn't the case.

No matter what I do, I cannot get the stepper to rotate in the opposite direction so far, since this problem appeared yesterday. Are there any software settings in repertoir that I can try to reset anything etc?

Is there a very specific process that I should be doing in order to home the axis as you've suggested? Perhaps I'm just making wrong assumptions about how that's done and it's not just a case of moving it to the end stop?

Thanks very much for the replies so far - I'm very grateful.

Edited 1 time(s). Last edit at 02/16/2014 05:44AM by Mr Joshua.

I have ramps not melzi, but in ramps ther is a setting to invert the logic of endstops, perhaps you have a similar setting?

I have wondered the same thing but not yet found settings for it. I'm not sure if this would mean writing new custom firmware maybe for it, and I don't have a programmer that I think is needed to load firmware onto these devices.

The fault seems to be that the circuit thinks the end stop is activated, when it definitely is not, so I'm not sure how to resolve this, or even if it's possible.

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Prusa Mendel i2 - Melzi V2

I had the same problem with my x and y axis, I tryed a million things to fix it so im not sure what actually did the trick. Im pretty sure it was after I tightened my belts and recalculated my steps per unit using the calculator on mendelmax.com. here is the link [mendelmax.com] i would give that a shot.

Have you got your X endstop on the left hand side?
Also, having them wired C and NO is not unusual - mine are like that (I use reed switches). What I had to do was change the endstop settings in firmware Have you checked your firmware settings?

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Waitaki 3D Printer