Suden nasty grinding sound

[Mike]

My RV just started making this nasty grindy sound when the head moves - lots of vibration but still appeared to place OK though.
Earlier in the day I had a head versus my hand crash when reloading  a feeder while running, causing the steppers to go out of sync, and when it homed it bashed the rear cover before I hit the stop button. However it placed a couple of boards fine afer restarting.
Took off the top head covbers to investigate, but apart from finding the vacuum valve screws appeared to have fallen out (it could have been like this for ages), nothing obvious, then it suddently stopped making anoise and appears fine - wonder iif maybe there is something floating around loose ? I haven;t found one of the screws, but it's possible it's been missing since I got it...
One more panel in this job to do so fingers crossed, but wondering if anyone else had experienced sudden noisiness....

[Gopher]

Some days ours does seem to have noisy/rattly hour or two but they never seem to coincide with other problems like the machine losing track of the head as you describe or the occasional wobbly when it crashes into itself or breaks a tool. Ours also seems to have taken to shaking out the odd screw - one of the excessive number holding on the Arm board in fact.

[Mike]

This happened again today. Checking at the stepper driver showed one of the stepper coils measuring 1Mohm
I eventually traced it down to a dodgy socket contact on the D37 on the base.
Looks like it has been sparking a bit. What I was surprised about was that despite the rattly motion it was staying in the right position (although parts were tending to get shaken off the nozzle!) .
Looks like the steppers are unipolar, so it would have been missing one out of 4 phases, rather than the 2 of 4 if they were bipolars.
I think it was too consistent to have been vibrating in and out of contact in time with the steps..!

 

[Gopher]

... Interesting,  so what exactly have you had to dismantle to get to the dodgy contact?
We have only so far dared to dismantle things we knew to be broken, so that's the arm covers to change the control board and the pump.

[Mike]

I replaced the D37F connector - pic is from the autopsy of the old one

[Mike]

BTW wiggling the D37 connector made the problem come & go, so that's a quick way to diagnose.
The grindy noise was worst while accelerating & decelerating - once at full speed it sounded almost normal.

[Mike]

I've subsequently found that the steppers are actually 5-phase bipolar, which explains  why they will run with a wire off without missing steps, albeit roughly.

So if you hear any sudden grindyness, especially at lower speeds, step 1 should be to check continuity at the stepper drivers. On the 5 pin connector, You should see the same low resistance (a few ohms) between each adjacent pin, and across the two outermost.

You can also check for blown outputs easily - disconnect the motor, and use a DMM diode test mode. Connect meter + to ground and check forward voltage on each output pin - should all be the same at around 0.5V. Repeat with meter - on the +36V supply.

Stay tuned for more on blown stepper drivers....

[SteveW]

'sudden nasty grinding sound', huh?
Yeah, that sounds like the one. 
I've just moved my RV1S to its new home, and was running some of the backlog of boards that had accumulated.
about 1500 components in, there's a smell of hot varnish, and any Z axis movement sounds like someone strangling a duck.
The Z stepper is _hot_ (all powered down now).
The axis moves really smoothly, and the rack and runners look fine, so I don't thin it hung up on anything.

This is the first time I've run the power box on its side, not flat. Is this a terrible plan, or was I just unlucky?
I'll chase down the actual fault, but if this is deprecated behaviour, I'll stop it!

Steve

[Mike]

Sounds like the motor was being driven more than it should have been - one coil fully on.
I'd check the stepper driver outputs with the motor disconnected. - may even be worth metering  out each of the 5 outputs to supply & ground with power off and motor disconnected, as a failed-short output will be fairly obvious. Might also be a short between motor phases.
Could be a dead hybrid on the driver (I have some spares of these), but possibly caused by bad wiring.
I'd also reccommend putting some fast blow fuses inline with the supply to each stepper driver - hopefully this would blow before the bond-wire in the hybrid in the case of a short

I'm not sure box orientation is a major issue as it's heatsunk to the rear panel.
I have a vague memory that the Z is configured differently as it needs to be energised at all times to stop slip, but the other axes reduce power when not moving. I think this is why I put a small fan next to my Z driver board.

See this vid for some issues I had, and an improvised fix for a dead hybrid.
http://www.youtube.com/watch?v=DGqH8LGjZdY

[SteveW]

Yeah - Pretty sure it's the driver. I dropped in a spare control box, and got on with the job. Must fix! Not trivial, looking at your video, but looks plenty doable. Cheers!

[Mike]

I wouldn't reccommend my fix as a permanent solution - I do have some new spare hybrids if you have a dead one.

[lurowl]

Hi Mike

I have a very similar sounding problem to what you described. In the control box, which driver card is for which axis? We have 2 machines so can swap driver card to prove that the driver card is at fault but we are unsure as to which diver card is for which axis.

[Mike]

Don't recall but the easy way to identify is to power off, and move the axis manually while metering the stepper wires at the driver to look for the voltage generated by moving.

[lurowl]

Thanks Mike, we have found out which is the troublesome driver now. I remember reading you had some spares for these at some point? Is that still the case and if so how much would you sell them for?

[Mike]

Have you verified that it is actually the output hybrid ?
I only have  a couple which I'd rather hang on to, however this is where I got them and they still appear to have stock
http://www.bdent.com/pmm5301-sanyo-25-pin-sip-integrated-circuit.html
I'd strongly recommend checking the wiring and  connectors for shorts, particularly shorts to ground - meter to disconnected motor wires on continuity beep mode and wiggle everything.
I never did find a definitive cause for mine failing though. As a precaution I added individual fast-blow fuses to all drivers.