Just an idea, I may be bonkers......

Looking at my machine whilst wiring up the closed loop steppers and cursing the Chinese bods who don't use screened cable for the motor wires - WHY??? -there's 48V switching edges on those wires!!!!! - I suddenly thought why not put the driver modules on the machine next to the motors? That way all you have to run from the control box is low powered step/direction/enable lines which could easily live in a a bit of 26 AWG 6 core screened cable (about 4.5mm diameter) connected by M12 connectors and power which could be a few strands of 1mm2 wire twisted together*, or if you're flash some high power flexible coax like the Mogami 3082.

* actually 2 x 2 x 0.5mm2 would be better on reflection.

Denford never used shielded wiring to stepper motors, and it's never caused them any problems.

Having the drivers at the motors is nothing new, but it's not something I'd personally want to do unless the step/dir were using differential signals.

It's a cunning plan. There could be problems with dust and vibration for the drivers mounted on your gantry and don't forget that the power cables feeding the drivers, which will have to come from the control box alongside the control cables, will not have a smooth DC current flow, though you could add some filtering at each driver to reduce that.

The biggest problem I can see is that you are replacing the nice short signal cables between your controller and the drivers by several metres of 'antenna' wiring which will have to run alongside the still noisy stepper driver power cabling and the VERY noisy spindle power cabling from your VFD. It might be case of frying pans and fires in spite of your best efforts at screening. But please don't stop thinking out loud!

In my controller the break-out is mounted inside it's own screening box and has short screened cables running to the drivers leaving only about 20mm of exposed wiring. The output cables are deliberately routed away from the inputs to minimise coupling. I've cut the motor's own wires quite short and use screened cable to connect back to the drivers with all the cable screens connected only at the controller end. Limit switch inputs have 1uF capacitors across them to prevent noise-induced false triggering. I haven't had any problems since upgrading the controller to this design.

Kit

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Originally Posted by Kitwn

It's a cunning plan. There could be problems with dust and vibration for the drivers mounted on your gantry and don't forget that the power cables feeding the drivers, which will have to come from the control box alongside the control cables, will not have a smooth DC current flow, though you could add some filtering at each driver to reduce that.

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Aye, I can see that dust etc. might be a problem and was thinking of a cover to minimise that.With a suitable cable (starquad or high current coaxial) I don't think the current flow in the power line would be too much of an issue.

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The biggest problem I can see is that you are replacing the nice short signal cables between your controller and the drivers by several metres of 'antenna' wiring which will have to run alongside the still noisy stepper driver power cabling and the VERY noisy spindle power cabling from your VFD. It might be case of frying pans and fires in spite of your best efforts at screening. But please don't stop thinking out loud!

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I was thinking of using a 3 x twisted pair screened cable running to the (Lichuan) drivers with have an iso-optalator input so are effectively floatting diff., so ought to be OK. But I'm not sure I can be arsed to undo all the "conventional" wiring I've already done :cower:

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In my controller the break-out is mounted inside it's own screening box and has short screened cables running to the drivers leaving only about 20mm of exposed wiring. The output cables are deliberately routed away from the inputs to minimise coupling. I've cut the motor's own wires quite short and use screened cable to connect back to the drivers with all the cable screens connected only at the controller end. Limit switch inputs have 1uF capacitors across them to prevent noise-induced false triggering. I haven't had any problems since upgrading the controller to this design.

Kit

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Caps across the inputs are cool, been using them for years with great results.

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Originally Posted by Voicecoil

But I'm not sure I can be arsed to undo all the "conventional" wiring I've already done :cower:

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If it ain't broke, don't fix it!

Kit

The machine design is all about balancing compromise. From an electrical power drive to the motor what you propose (locating the drivers close to the motors) is a good idea - you're removing parasitic resistance and impedance from supply lines to the motor - which will impact the performance of the motor at speed. You're having to balance this with driving the digital step/dir signals over a longer length of cabling, and these are more susceptible to noise, but it's not rocket science to switch these (non-linear) resistive loads of a few volts / milliamps at 200kHz - differential drive is nice but not necessary unless you have long cable runs and a high noise environment (and you're removing a good proportion of the emissive lines by removing the high-current AC signalling to the steppers). I'd invest in a heavier gauge power cabling to the driver.

The other compromise is the mechanical aspects, and as others have said - vibration, dust etc. You are making life difficult for yourself here but this is just part of the overall design compromise.

On my machine, and I suspect many others, the motor cables aren't nearly long enough anyway, so need extending. This being the case, my motor cables (i.e. the ones actually coming out of the motor itself) terminate in a little plastic junction box somewhere near the motor and therefore quite a long way from the "sensitive" cables (step/dir, etc) which are retained within the screened control box and use differential signalling anyway. Junction box to control box is via screened CY cable. My guess is that the combination of screening and, effectively, differential motor connection work to significantly reduce emitted interference. The long "signal" wires on my machine (limit switches and e-stops) use 24V for better noise rejection. The drivers also stay away from vibration and dust in the control box with a light waft of air from a couple of low-power fans to keep them cool.

However, as Doddy says, engineering is all about compromise and there is a whole bunch of trade-offs to take into account. I went for the easy and most common configuration but that's not to say that in other cases, a different solution might not be better.

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Originally Posted by m_c

Denford never used shielded wiring to stepper motors, and it's never caused them any problems.

Having the drivers at the motors is nothing new, but it's not something I'd personally want to do unless the step/dir were using differential signals.

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I can see that as long as your limit switch wiring is well shielded then it shouldn't be a problem as far as the machine is concerned. However I'm conscious that I have some short lengths of the original unscreened cable of the limit switches in use (WHY don't they cable them with twin screened rather than the pissy miniature 3 core stuff???), and besides which I would like to be able to listen to the radio interference free whilst I'm working!

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Originally Posted by Voicecoil

I can see that as long as your limit switch wiring is well shielded then it shouldn't be a problem as far as the machine is concerned. However I'm conscious that I have some short lengths of the original unscreened cable of the limit switches in use (WHY don't they cable them with twin screened rather than the pissy miniature 3 core stuff???), and besides which I would like to be able to listen to the radio interference free whilst I'm working!

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In my Triac, the only shielded wiring were the original spindle motor tacho wires, and one of the tool carousel sensors. Everything else is unshielded, and runs in the same cable tracks as power wiring.
However, Denford always used 12 or 24V for control wiring, so noise should never be a problem.

Given the amount of effort it takes to properly and reliably shield wiring, I'm surprised more people don't use higher voltage signal wiring.

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Originally Posted by Voicecoil

and besides which I would like to be able to listen to the radio interference free whilst I'm working!

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VHF-FM is likely to be more interference free than MW-AM and DAB better again. Having spent 21 years as a BBC Transmitter Engineer before moving down under I'd also like you to be able to listen to the radio interference free whilst you're working.

Kit

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Originally Posted by Kitwn

VHF-FM is likely to be more interference free than MW-AM and DAB better again. Having spent 21 years as a BBC Transmitter Engineer before moving down under I'd also like you to be able to listen to the radio interference free whilst you're working.

Kit

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After 21 years as a T-E. I'd have thought you had had enough of radio interference and not needed to listen to it at all, even though it is free ! :glee::glee::glee:

Rob-T

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Originally Posted by Kitwn

VHF-FM is likely to be more interference free than MW-AM and DAB better again. Having spent 21 years as a BBC Transmitter Engineer before moving down under I'd also like you to be able to listen to the radio interference free whilst you're working.

Kit

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That's entirely logical, but it's perfectly possible to knock out VHF-FM. A few years back I was designing a class D (PWM) audio power amplifier which ran on similar power rails to an 80V stepper driver and with a not dissimilar switching frequency (about 300KHz IIRC). In spite of the pretty massive LC output filter, with a lead running to the loudspeaker consisting of a couple of pieces of 1.5mm2 twisted together it completely obliterated VHF reception in the workshop.

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Originally Posted by cropwell

After 21 years as a T-E. I'd have thought you had had enough of radio interference and not needed to listen to it at all, even though it is free ! :glee::glee::glee:

Rob-T

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One of the problems of being an engineer in that field is you can be more aware of the technical quality than the program content.
I was very much a talk radio man, R4 and the World Service were my favourites, but rarely watched television. I spent the last 16 of those years as a lecturer at the BBC's technical training school and was known for saying of TV "I teach people how it works, I'm not obliged to watch it". I usualy had (still have) no idea who people were talking about when discussing programmes. Unless it was David Attenbourough of course.:applouse:

Voicecoil,
If you're going to be THAT determined even the power of Auntie will have to give in. :sorrow:

It was entirely unintentional, and indeed a problem that took quite a bit of shielding (including a screened speaker lead!) to solve. So were you at Wood Norton then? A couple of colleagues of mine went through courses there, just the best training on the planet at the time: shutting it down/farming it off was probably the worst thing the BBC has done.