Endstop locatoins on Prusa Mendel - some questions...

Hi All,
At this stage of construction, I’m about to fit the x, y and z (min) end-stops and would appreciate some clarification on the position of these.

I’m building a Prusa Mendel ‘repstrap’ and going to use Gen6 electronics and ‘opto’ endstops. I’ve read through the wiki section on Prusa construction (http://www.reprap.org/wiki/Prusa), specifically the “Wiring and Electronics” section, paragraph #4, but found it confusing, so am attempting to clear things up with a diagram/sketch (below).



Questions:
Is Repsnapper the most popular choice of host software for the Prusa Mendel with Gen6 electronics?
With this software are my choice of positions of x, y and z Endstops going to be my best locations (see my sketch)?
Is there a ‘best’ location as such or do you just have to tell the software where your endstops are located anyway?
(Will all be revealed reasonably painlessly, once I get the software/hardware up and running?

Finally, is the side with the Y-motor really the Front of the Prusa Mendel? Does anyone know why the motor been moved to the front (it appears to be at the rear of the original Mendel)?

I’m really just trying to avoid any possible pitfalls surrounding the area of Endstop location and set-up. If anyone has pictures or blog postings that would show your location and mounting variations then I’d appreciate some links also. (I’m more interested in repstrapped endstop mountings since I’m not using printed parts).

Regards and thanks,
No.6

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[numbersixreprap.blogspot.com]

This will show you the Gen6 with opto.
[www.youtube.com]

Motor is in the front so it's easier to move the motor by turning the pulley, and it looks cool

following you in your blog, your looking great!

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repraplogphase.blogspot.com

Hi Spacexula,
Thanks for your reply. That makes good sense on why the motor is now at the front.

That video clip walk-through (you linked to above) on the endstop positions is what's adding to my confusion though, and is in the wiki also. In the audio commentary on the video the guy admits that his endstops are in the wrong position compared to the wiki instructions, but he got his positions by observing Prusa videos.

I'm sure it's no big deal where the endstops go at the end of the day, as their positions will get accommodated somehow in the software, but I'd like to establish if there is a 'standard' location for them on the Prusa Mendel, which reduces software set-up issues later.
Tks again,
No.6

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[numbersixreprap.blogspot.com]

The endstop should be at the negative end of the axis. For X that is with the nozzle over the left hand side of the bed, so the limit should be at the left hand end of the axis. For y the negative end is the front of the bed, so the switch should be at the back of the machine.

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[www.hydraraptor.blogspot.com]

Quote
nophead
The endstop should be at the negative end of the axis. For X that is with the nozzle over the left hand side of the bed, so the limit should be at the left hand end of the axis. For y the negative end is the front of the bed, so the switch should be at the back of the machine.

Doing it as described has the advantage that look down at the machine (from the front) the x, y and z axis is oriented as you would normally draw it on a piece of paper: positive x to the right, positive y is up and positive z is coming vertically from the paper towards you.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

nophead Wrote:
-------------------------------------------------------
> The endstop should be at the negative end of the
> axis. For X that is with the nozzle over the left
> hand side of the bed, so the limit should be at
> the left hand end of the axis. For y the negative
> end is the front of the bed, so the switch should
> be at the back of the machine.


Hi nophead,
Tks for the reply. I’d like to clarify something. If the negative end of the Y-axis is that front (which seems reasonable), and you say “endstop should be at the negative end of the axis”, then why are you saying “… so the switch should be at the back of the machine”? Did you mean the ‘front’ of the machine, if you are referring to the Y-axis?

With the Y endstop to the front, that would make the video in “Wiring the Electronics” section of the wiki (www.reprap.org/wiki/prusa ) correct, and the text (#4) incorrect, or at least badly described “Place the third one on the right y axis smooth rod behind the print bottom plate.”. I’m happy to submit a clearer description, and even a diagram (a neat one this time ), once clear, and someone can tell me the procedure for updating the wiki?

My interpretation of Bob’s contribution is that the Y endstop should be at the front.
Thanks again guys,
No.6

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[numbersixreprap.blogspot.com]

On CNC machines, axis movements are defined as the relative motion between the table and the tool. For us, that's motion of the extruder relative to the platform.

The reason the Y end stop seems to be at the wrong end is that the Y axis moves the platform. Unlike the X axis, which moves over the platform. It might help to imagine holding the platform still to that the whole frame has to move when you move the Y axis. With the extruder at the negative Y limit (front of the platform), the platform is actually at the back of the machine.

The original Mendel has the endstops with the motors and the Y motor is at the back of the machine and the X motor is on the left. As Bob mentioned that makes the bed match the normal XY graph orientation and as Dale mentions Y works the opposite way because the bed moves instead of the head.

If you swap both endstops it will still make correct objects, it is just the same as turning the machine round 180 and considering the back to be the front. If you swap only one axis then it will make mirror image objects .

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[www.hydraraptor.blogspot.com]

Thanks so much everyone! I think I've got it now!
The y-axis endstop goes to the rear, and conforms to the statement that the endstops are at the negative ends of the axis, because the extruder head is at the negative end of the y-axis when the table is fully to the rear of it's travel!

... the bed is moving in y-axis, not the head! Doh!

Thanks guys! Brilliant!

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[numbersixreprap.blogspot.com]