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daleyd
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Modbus does use tcp to transport the data packets (there is a serial version which uses 232/485 protocol) but it’s much more structured than tcp/ip - the “master” device sends requests/commands and expects an answer back within a set time frame.
The clever stuff that requires fast counting is in the servo drive itself, so via Modbus you would send a command to go to for example position x at speed y, the drive then carries out the command - Modbus itself is too slow to carry out anything like that by itself.
I’ve used rives that could do “fast” stuff over comms but they typically use fast protocol like canbus or similar - a German company I used to work for used interbus which was designed by Phoenix Contact for fast speeds for sensors and drives etc.
daleyd
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No problem. I'm going to play around with this one. Enjoy your new motor.I doubt that would fit and I’d need to buy a stepper driver but apart from that…
daleyd
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Got anything in mind for it? The size of it I bet it’s got some torque on it!
Nothing planned as yet. I've got too many motors and no bench space at present.
skotl
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Apologies!Does this conversation come with sub titles for the hard of thinking?
In summary, back in the days when everything was wired (pre wi-fi) there was already a huge problem with what we referred to as "deterministic protocols", i.e. I send you a message and not only do I guarantee that you're going to receive it but I even guarantee that you'll receive it within ten milliseconds.
Loads of people invested huge amounts of time and money in coming up with protocols (I'm looking at you, QoS) that were going to address this but it was all for nought; the protocols that are under what we tend to refer to as "wifi", "ethernet", "the internet" and others are basically unreliable. Add in radio transmission (wi-fi) and you only make it less reliable or predictable.
Hence my concern that a stepper motor that could be hurtling a 100KG mass at a distant object (possibly human) was depending on this network to say "ummm... probably stop there, buddy" as its safety net.
Dale's clarification that the original stepper motor is on a proprietary, closed-loop system is very comforting. I might have got the details wrong so back to @daleyd for clarification
outofthefire
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And still for some reason i've still read all the postsDoes this conversation come with sub titles for the hard of thinking?
daleyd
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I think that about sums it up - Modbus is sending/receiving high level data, not the really time critical stuff. The real fast stuff is integral to the drive, things like encoder counting etc Modbus just wouldn’t be able to handle, unless it was a really slow motor!Apologies!
In summary, back in the days when everything was wired (pre wi-fi) there was already a huge problem with what we referred to as "deterministic protocols", i.e. I send you a message and not only do I guarantee that you're going to receive it but I even guarantee that you'll receive it within ten milliseconds.
Loads of people invested huge amounts of time and money in coming up with protocols (I'm looking at you, QoS) that were going to address this but it was all for nought; the protocols that are under what we tend to refer to as "wifi", "ethernet", "the internet" and others are basically unreliable. Add in radio transmission (wi-fi) and you only make it less reliable or predictable.
Hence my concern that a stepper motor that could be hurtling a 100KG mass at a distant object (possibly human) was depending on this network to say "ummm... probably stop there, buddy" as its safety net.
Dale's clarification that the original stepper motor is on a proprietary, closed-loop system is very comforting. I might have got the details wrong so back to @daleyd for clarification
I should have pointed out that there are also 4 universal inputs/outputs on the drive for things like limit switches, run signals etc (they can be configured by commissioning software) so for things which you wouldn’t trust to be sent via comms you would use these. There is also a Safe Torque Off input which is a proper safety rated input which has become common on industrial drives of all kinds recently - Interestingly on this itcomes with a 10 year from date of manufacture lifespan, so after 10 years they tell you not to use this anymore!
For industrial applications this would probably be integrated with other safety systems, like guard switches etc to cut power/apply braking (or whatever is required by the application) if something unsafe is detected. Typically these were always hardwired (and a lot of times still are) but even these have their own dedicated safety rated communications protocols now (profi-safe is the only one I’ve used, Allen Bradley have their own propriety guard link protocol for their own devices and there are others).
I use communications a lot in my job at work (mainly Modbus as our stuff has that as a native comms protocol built in), I wouldn’t claim to be any kind of expert but I know enough to get by. It’s good when it’s set up correctly, saves a lot of cabling and allows you to exchange a lot more info than you can just by hardwiring signals to things.
