Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

All home switch fixings are now done, it is amazing how long the little jobs take, this was a whole afternoon. Milled up a little block to hold the Z switch, decided it would be better outside of the axis rather than inside regards adjustment. Then had to drill two very awkward 12mm holes in the X bearing plates with a portable drill, for this I had to mill up a drill guide, still easier than dismantling the gantry.

[devmonkey]

Last of the tedious mechanical bits I think, energy chain carriers.

Attachment 28375 Attachment 28376 Attachment 28377 Attachment 28378

Next job soldering cables, lots of it, and bolting the machine stand to the floor.

[devmonkey]

Question for Doddy,

I've scoped the common mode noise and it isn't sufficient to cause a phantom step to be read at the 328p. I think the phantom steps I was detecting that I have 'fixed' by debouncing the read are actually being caused by reflections and/or induced voltage spikes as the differential pair switches. If this is correct placing a termination resistor across the pair as you do for rs485 should help do you concur?

Cheers, Joe

[Doddy]

Question for Doddy,

I've scoped the common mode noise and it isn't sufficient to cause a phantom step to be read at the 328p. I think the phantom steps I was detecting that I have 'fixed' by debouncing the read are actually being caused by reflections and/or induced voltage spikes as the differential pair switches. If this is correct placing a termination resistor across the pair as you do for rs485 should help do you concur?

Cheers, Joe

I guess you know a bit about signal theory - you're trying to match the characteristic impedance of the transmission line at both ends - just randomly throwing resistors on won't be as effective as a properly matched terminator - and yes, as per 485. What's the driving system?, have a look at that and match it.

[devmonkey]

I guess you know a bit about signal theory - you're trying to match the characteristic impedance of the transmission line at both ends - just randomly throwing resistors on won't be as effective as a properly matched terminator - and yes, as per 485. What's the driving system?, have a look at that and match it.

Just taken the DDCS apart again, the differential outputs are all driven by a standard quad differential line drivers, AM26LV31, no resistors at the transmitting end. I'm driving this through a 2m db37 cable, not twisted pair, or if it is it is highly unlikely the right pairs are twisted. Still these are EIA-422 spec drivers same as max485, etc, so I reckon I wont go wrong with 120 ohms.

It DDCS has a really nice board, has an onboard FPGA, Altera cyclone3 that does all the realtime stuff. I've taken a few photos whilst it is open.

[devmonkey]

How do people usually wire the alarm outputs of the drivers?

My plan was to place these in series with the estop but this wont actually work for me. Reason being estop unlatches the relay that switches the main contactor that switches AC into the driver PSU, this means that the drivers are unpowered until reset is pressed latching the relay, however the relay wont latch as the drivers are unpowered therefore cannot switch on their open collector alarm outputs breaking the estop circuit.

The only thing I can think of is to add another relay in series with estop, via the normally closed contact and then have the driver alarms open this relay, this has the downside that you don't know if the alarm circuit is intact until it doesn't work.

[Neale]

How do people usually wire the alarm outputs of the drivers?

My plan was to place these in series with the estop but this wont actually work for me. Reason being estop unlatches the relay that switches the main contactor that switches AC into the driver PSU, this means that the drivers are unpowered until reset is pressed latching the relay, however the relay wont latch as the drivers are unpowered therefore cannot switch on their open collector alarm outputs breaking the estop circuit.

The only thing I can think of is to add another relay in series with estop, via the normally closed contact and then have the driver alarms open this relay, this has the downside that you don't know if the alarm circuit is intact until it doesn't work.

I have wired fault outputs in series and taken that to a "servo fault" input on the motion controller. Partly for the reason you give - can't put power on the drivers via the safety relay until there is power on the drivers - and partly because I classify "fault" signals into two categories. Personal safety - when you hit estop you really want it to stop NOW so that is a safety relay task (mine cuts driver power, driver enable, and signals motion controller), and machine issue - driver fault, limit switch - and I'm happy that motion controller firmware can be trusted for that. Does DDSC have "driver/servo fault" input(s)?

[Doddy]

Section 9.1 of the TI data sheet - recommends 100R, you're not far off. It's a fast switching device - most differential drivers (not design for high speed) will have deliberately slow slew-rates to limit EMI. But, it is what it is.

[devmonkey]

Progress update:

Stand is bolted to the floor and machine is clamped to the stand. I cut some little bits of angle and use M8 bolts for the clamps. So first the stand was levelled as best a possible with some composite slate tile shims and bolted to the floor. Then the machine was levelled on top of the stand (it has an M12 bolt threaded into the bottom of each corner) and checked that each bolt was bearing weight (attempting to avoid twisting the machine), then finally it was lightly clamped at 4 points to the stand.



I cut all the cabling to length and took it indoors to solder all sensors and motors, this took a few hours and rather a lot of heatshrink.

Next I fitted all the motors and sensors to the machine and started work on the enclosure.

A few trips to screwfix to further increase my holesaw collection, then an unpleasant afternoon drilling fan, exhaust, switch, indicators and gland ports in the steel enclosure. Now mounted to the wall and cabling fed through. Will do final wiring tomorrow and maybe the first machine moves!



That ugly slot next to the glands is for the DB37 control cable to go to the DDCS control box.

Finally both drag chains were fixed.

[routercnc]

That machine is really starting to take shape. Nice work.