Thor, or should that be Zeus?

[Neale]

Clive has just answered the home/limit question - Mach3 knows what you are doing so treats the switch inputs accordingly. There is a minor gotcha with this. If you use a switch with effectively no offset between on and off positions, you can get problems (to be more accurate, I had problems) with this. Z homed, then X and Y started moving. The Z switch had swapped from homing to limit function, and the slight vibration caused the Z switch to trip and stop the machine ("limit switch event"). Fortunately, the IP/M has the capability to move the axis very slightly away from the home position immediately after homing which fixed the problem.

The limit on number of inputs only applies if you are using a parallel port. That statement on the Mach3 config page is a bit misleading. There are only five input pins on a parallel port as all the others are output only, so the limit is a physical one and nothing to do with Mach3. You will be fine with the IP/A and are free to use all the ports. I doubled up my switches (combined upper and lower) mainly to reduce the number of wires needed and I still have some unused inputs on the IP/M.

Don't worry about voltages. Desertboy was talking about Arduinos and they are definitely 5V only. The IP/A will be very happy with 24V signalling, and in fact this gives much better noise rejection. The CSMIO kit is built to use the industry standard 24V signalling. No pull-up/pull-down resistors needed, but watch the wiring instuctions carefully so that you get it right. Less flexible motion controllers only have one input pin but there are two per channel on the IP/A. There are plenty of examples of how to wire NPN n/c proximity switches in series if you do a Google search - I have had four in series working reliably in testing although in practice I only wire them in pairs on my machine.

[Chaz]

Clive has just answered the home/limit question - Mach3 knows what you are doing so treats the switch inputs accordingly. There is a minor gotcha with this. If you use a switch with effectively no offset between on and off positions, you can get problems (to be more accurate, I had problems) with this. Z homed, then X and Y started moving. The Z switch had swapped from homing to limit function, and the slight vibration caused the Z switch to trip and stop the machine ("limit switch event"). Fortunately, the IP/M has the capability to move the axis very slightly away from the home position immediately after homing which fixed the problem.

The limit on number of inputs only applies if you are using a parallel port. That statement on the Mach3 config page is a bit misleading. There are only five input pins on a parallel port as all the others are output only, so the limit is a physical one and nothing to do with Mach3. You will be fine with the IP/A and are free to use all the ports. I doubled up my switches (combined upper and lower) mainly to reduce the number of wires needed and I still have some unused inputs on the IP/M.

Don't worry about voltages. Desertboy was talking about Arduinos and they are definitely 5V only. The IP/A will be very happy with 24V signalling, and in fact this gives much better noise rejection. The CSMIO kit is built to use the industry standard 24V signalling. No pull-up/pull-down resistors needed, but watch the wiring instuctions carefully so that you get it right. Less flexible motion controllers only have one input pin but there are two per channel on the IP/A. There are plenty of examples of how to wire NPN n/c proximity switches in series if you do a Google search - I have had four in series working reliably in testing although in practice I only wire them in pairs on my machine.

Awesome, thanks.

Suppose now I need to decide if its proxy and mech or only proxy. I could do mech as primary home / limit and proxy as limits via E Stop circuit.

[Chaz]

My drive will likely support limits too although Id have to undo some of the wiring already done to accommodate this.

[Davek0974]

On my IP/A setup i used mechanical limits and mechanical homes, two limits and one home per axis.

My limits are a high power circuit (24v contactor circuit as opposed to a logic circuit) as they are wired to a PILZ relay for the safety circuit which cuts all power to the drives if tripped - I really did not want to risk runaway blowing the end brackets off my table :)

The homes are inboard of the limits and i use home-offset to set the locations.

It all works well here.

When using mechanical switches, get quality ones with Gold-flashed contacts, these will not degrade under logic levels, normal switches rely on an arc to keep the contacts clean - these will fail pretty fast at logic voltages.

[Chaz]

On my IP/A setup i used mechanical limits and mechanical homes, two limits and one home per axis.

My limits are a high power circuit (24v contactor circuit as opposed to a logic circuit) as they are wired to a PILZ relay for the safety circuit which cuts all power to the drives if tripped - I really did not want to risk runaway blowing the end brackets off my table :)

The homes are inboard of the limits and i use home-offset to set the locations.

It all works well here.

When using mechanical switches, get quality ones with Gold-flashed contacts, these will not degrade under logic levels, normal switches rely on an arc to keep the contacts clean - these will fail pretty fast at logic voltages.

How do I know if they have gold flashed contacts? Quick look at RS doesnt seem to show that level of detail and their details are normally fairly generous.

[Clive S]

When using mechanical switches, get quality ones with Gold-flashed contacts, these will not degrade under logic levels, normal switches rely on an arc to keep the contacts clean - these will fail pretty fast at logic voltages.

In my opinion standard switches will be fine. (remember logic levels are 5V) the op is using 24 V.

[Neale]

On the whole it's the current being switched that matters rather than the voltage itself. A friend who worked on older systems that used extensive mechanical switching reckoned that increasing switch current to something around 10mA improved contact reliability. Sticking in pull-up/down (depending on how you arrange the switching) resistors of around 2K2 for a 24V system would be about right.

However, consider the failure modes. For limit switches, we are forcing contacts apart. It is very unlikely that contacts will get welded together to the point that they will not separate although it's possible that contact corrosion will stop them "making". This is at least a safe failure mode. I have no idea what the likely failure modes of proximity switches are, but I suspect that they give more repeatable homing positions. This is all pointing at mechanical limit switches and proximity homing switches - which has already been suggested.

On my own machine I have gone proximity switch all round, but I'm only using Nema 23 3Nm steppers which will probably stall before doing major damage.

[Davek0974]

Yes it needs a little current on a normal switch, i think gold flashed ones will be listed as suitable for logic levels or PLC inputs, sometimes have a very low max current as well, unlike the usual power switches.

With servos, we have index homing so accuracy in the switch is not needed - it works really well and insanely repeatable. On steppers as you said, damage is unlikely but the torque from a servo is frightening. :)

[Chaz]

Argh, broke my long 10mm endmill and did some damage to the Z Axis, not too bad, just cosmetic but cant finish a slight hole enlargement I need to do. Pics to follow.

[Desertboy]

Yes it needs a little current on a normal switch, i think gold flashed ones will be listed as suitable for logic levels or PLC inputs, sometimes have a very low max current as well, unlike the usual power switches.

With servos, we have index homing so accuracy in the switch is not needed - it works really well and insanely repeatable. On steppers as you said, damage is unlikely but the torque from a servo is frightening. :)

I'm wondering if the honeywell microswitches might be what I want (They're gold contacts, £3 each), or rob an old lady for servos lol.

I'm pretty certain I've sent working servo stepper motors to the scrap yard because I didn't understand what I had at the time lol.