Need Help!- Confused about limit switches

[ssutton]

Wiring up my G540 I am confused about the 4 inputs. I would think that there should be a limit switch at the end of travel in both directions on every axis for a total of 6 inputs. How do you guys set up your limit switches with just 4 inputs?

BTW I am using Mach3, have not installed it yet.

[Fastest1]

Mach knows which direction the axis is traveling. You can use 1 or 3 inputs depending on your needs. I use 1 input and have 1 switch on each axis. They are all wired in series. The negative to the way I run my machine is that I cant use "ref all" and have all 3 axis' moving at the same time. My machine during the ref process moves one axis at a time til all 3 axis are homed. Also I run "soft limits", this is a measured distance from the limit switch set by software upon approaching the software limit the machine will slow and stop with a reset in Mach. If you use a switch at both ends of axis, you will get 3 axis simultaneous homing which does look really cool but to a hobbyist is the time savings significant? Also with a switch at each end you dont need soft limiits as there is a physical switch. Though this does use 3 inputs. Dont forget an input for a probe and or touchplate. Hope this helps. It takes a little while to understand the many ways you can use switches and I am sure someone will add in or corrrect my inaccuracies.

Originally Posted by ssutton Wiring up my G540 I am confused about the 4 inputs. I would think that there should be a limit switch at the end of travel in both directions on every axis for a total of 6 inputs. How do you guys set up your limit switches with just 4 inputs? BTW I am using Mach3, have not installed it yet.

[Fastest1]

Having said the above, what machine are you running? Is it imperative you run home switches in the beginning? If this is your first time to build a cnc machine there will be a bit to learn in using Mach/Gcode/Steps per unit and the other settings that are going to become your new vocabulary. I do think that home switches are the way to go whether it be 1 per axis or 3 (3 switches can be used per axis, 1 at each end as a limit and 1 where "home" is to be). In setting up your machine and mach you will have some time to familiarize yourself with it all. However if your plan is to install limit switches and they are in a location that requires disassembly of the machine or just unnecessary work then by all means install them now and you could just run the wiring to a common access point for your G540 which you can choose when to connect them.

[mmcp42]

I'm developing driver software
believe me, limit switches have saved any number of high-speed self-destruct incidents!

[Fastest1]

I agree, however if this is a persons first foray into cnc, there will be quite a few stumbling blocks on the way. Sometimes just the reassurance that something in this pile of parts will move is enough to rejuvenate oneself into completion. Not a substitute for accuracy or safety. Hence why I prefaced it with, what kind of machine are you building? My Sherlines were never in any real danger from my mistakes in learning (well besides those ugly scars on my clamps, LOL)

Originally Posted by mmcp42 I'm developing driver software believe me, limit switches have saved any number of high-speed self-destruct incidents!

[ger21]

How do you guys set up your limit switches with just 4 inputs?

Wire them all in series to one input.

[jason75]

I am about to build an FLA100 and also will be using Mach3 and the Gecko G540.

What is the best way to set up home switches and over travel limits?

[hemsworthlad]

Several ways to approach limit's and home switch's.
1: Utilise the same switch's as both limit switch and home switch's, Mach knows the differance when in use between when the switch is to be treated as a home switch or limit. Doing it this way you can just use 1 input with all the switch's wired in series connection.
This approach works ok but does have things to watch out for and depends on switch location.!
IE: When mach homes you tell it in which direction to travel + or - to find the home switch. Now if using the same switch for both home and limits and while working your machine crash's and fly's by the limit it will trigger the switch stopping motion.
Now the only way to get it off the switch or regain movement is to override the limts and reverse off back off the switch. Now if for any reason you accidently over ride the limits and then try to home but dont reverse the machine over the switch Mach will automaticly search for the limit in the direction you told it but will never find the switch because you didnt move the machine back.!
Because you use the same switch for both job's you also have no way to tell mach to stop and it will crash into the hard stops, No big deal in some case's but could be disaterous in others.?

2: (My prefered way) Use 1 input for limit's wired in series with a switch on each end of each Axis. Then another input for home switchs again wired in series but with just 1 switch on each axis at the end you want to call home.
Doing it this way does mean Mach will referance each axis individually waiting untill it's finished before moving onto the next but it's no big deal and easier to spot if anything as gone wrong, whcih can happen.

3: If you have loads of I/O then use 1 input for each switch but most don't, even someone like me who use's a smooth stepper which gives lots of extra I/O's doesn't waste them. I wire all my limit's in series along with my E-stop and then 1 input per home switch, this then allows me to home all 3 axis at same time.

Soft limits are good and I have them enabled as well, the one thing I can tell you is that if I had to get rid of any of my switch's due to I/O restrictions it would be the limit's every time.!! . . . Home switch's are SO SO usefull I couldn't work without them and they have saved my arse so meny times because I can accurately get back to position with just the click of a buttton when some thing go's wrong and I have to hit the panic button. When ever you hit the E-stop while at any kind of resonable speed you will runout of position due to inertia essentially losing steps meaning where Mach thinks it is in relation to 0,0,0 it's not.!!. . . But with home switch's it's a simple click and your back referanced to where you started.
Soft limit's work good enough and with steppers it's no big deal if something goes wrong with the Mach and the machine hit's the stops beacuse it will usually just stall the motors any way.!

Any way after all this waffling I'd recommend wiring limit's in series on 1 input and Home's on another again in series.

Hope this helps.
Dean.

[CNC Lurker]

Keep in mind you only have 4 inputs on the Gecko (see pic). You'll probably want to save an input for an auto-Z.

[ssutton]

WOW, thanks for the information folks, I understand the various control schemes and think that I will utilize 2 limit switches per axes all wired in series together so that all 6 go to one input (the E-stop will be wired in series with these as well). I will also use 3 home switches wired in series so that each axis can be homed, these will land on one more input. That will leave 2 inputs for a possible touch sensor in the future and something else.

I am using micro-switches for the limits, they are small switches that have an "arm" with a small roller at the end. The question is, what is the best device to use for the home? Should I use a solid state device like a proximity sensor or a hall sensor with a magnet or just use another mechanical switch?


Again,
THANKS TO ALL FOR THE INFORMATION!!!!!!!!!

90% done 90% to go.....


Scott

[hemsworthlad]

Originally Posted by ssutton Again, THANKS TO ALL FOR THE INFORMATION!!!!!!!!! 90% done 90% to go..... Scott

NO you got that wrong your 0.000001% done.!! Remember you have an addiction worse than crack that can never be over come.!! . . You'll never be finished.

Depending on the accurecy you require when homing will determine the quality and type of switch to use.

On one of my machine I use high quality Honey well switch's on both H's & L's,this machine cuts Alu mainly so cant use optical proximity or magnetic switch's due to flying debre which trigger the switch's. So quality micro switch's work best for me and my use's.

I also have a smaller machine for soft materials that just use's the cheaper arm type like you describe and they work fine as well.
Basicly it all boils down to how high a repeatabilty you need from your machine.? If working to very fine tolerences then very accurate sensitve switch's are required.
That said IMO and experience the normal cheaper switch works ok when mounted to a sturdy bracket or surface that doesn't flex giving good enough repeatabilty for most diy machines cutting wood,plastics etc.

Edit: Ok you got me wondering how repeatabile the cheaper switch'c are.? So I've just quickly test my small machine(Longest Axis only) using a cheap chinese dial gauge. Out of 10 home's of varying distances from a few inch's to full travel 3ft it repeated between 0.01and 0.03mm. Which is good enough for this machine and the work it does. Some of this could also be down to the bracket the switch is attached to not being overly strong.

[restless1]

I used inductive proximity switches they wire right into thengecko g540
Easy peasy! And super accurate!