servo control vs stepper control

[JAZZCNC]

The BoB draws such a tiny current you can tap off a spare HDD (or similar) connector inside the PC.

I wouldn't take that route.? The drives are industrial grade and servo's are powerful beast's that unlike steppers tend not to stall when the shit hits the fan.!
For this reason things like limit switch's and E-stops become very important with servo's. They are sensitive to electrical noise and for this reason I wouldn't run any e-stop or limit switch's with 5V, instead using 24V which is more industry standard. So you'll need a 24V PSU so then I'd run the BOB from that, most decent bob's will run off 24V.

[boldford]

I wouldn't take that route.? The drives are industrial grade and servo's are powerful beast's that unlike steppers tend not to stall when the shit hits the fan.!
For this reason things like limit switch's and E-stops become very important with servo's. They are sensitive to electrical noise and for this reason I wouldn't run any e-stop or limit switch's with 5V, instead using 24V which is more industry standard. So you'll need a 24V PSU so then I'd run the BOB from that, most decent bob's will run off 24V.

I wasn't suggesting he drive the CNC M/C side of the BoB from the PC. Only the PC side of the optos would come from the HDD 5v. I'm sure your PC wouldn't want you to put 24v or more up its paraport. As I stated the EL817s provide the isolation; on this BoB inbound and outbound, so your e-stop and limits etc. can go up to, say, 30v.

[Peter.]

So that board can take 5v signals from the PC and send out 24V signals to the drives? Is this an automatic thing or is it something that need to be set up via dip-switches or parameters etc?

I have some specs of the hardware now too, just pulling out the info. Seems I've been very lucky and got some nice skip-bound hardware to play with.

I have another of the one I already posted coming to me, which a 750W servo motor acting as a stepper with a step&direct drive, no resolver. A pair of Lexion LMx05 drives with 0.4kw servos & encoders and a pair of Mitsubishi MR-J2S-40A servo drives with Mitsubishi 750W (I think) servo motors & encoders. Plus a bag of other bits - pulleys,belts,rails, canbus leads etc.

I think I will start off by sourcing a breakout board and using the stepper drives for my (vertical) learning-curve. I'm not sure exactly how the servo drives will interface with the PC but I can figure the step & direct out pretty easily. I will, of course, keep a log of my progress right here, though exactly how fast that progress will be I don't know as I have a very high workload in my regular job.

[Peter.]

By the way - what does 'optically isolated' actually mean? Does it mean that the electrical signal from the PC is passed through an emitter-collector pair and out to the drives in order to keep the two circuits isloated, perhaps so that a fault on the machine can't send power back through the port?

[JAZZCNC]

I wasn't suggesting he drive the CNC M/C side of the BoB from the PC. Only the PC side of the optos would come from the HDD 5v. I'm sure your PC wouldn't want you to put 24v or more up its paraport. As I stated the EL817s provide the isolation; on this BoB inbound and outbound, so your e-stop and limits etc. can go up to, say, 30v.

Ok don't want to send this thread off course too much but think best to clear this up so not to confuse.!!

Yes I under stood what you meant but don't think you did me.? I wasn't suggesting sending 24V up the PP's chuff.!!

The 24V supply has multiple uses.!!. . . It's sent thru the limits Switch's and E-stop to help with switch bounce and noise. This is done in conjunction with 24V relays, so it powers them has well.
These control the 5V signals from the BOB, they also act has safety for other things killing power to anything attached etc, enabling a hardware driven fully safe latching E-stop system that can only be restarted when in a safe condition and the master relay engages even then this only engage after pushing a reset button.
If any of the safety switch's are tripped or some things in an unsafe condition then nothing happens.! . . . . Also In this case and the point of my comment meant to also use it to power the BOB and therefore save messing about with the 5V from HDD.

[Peter.]

So from that I gather that whatever voltage I use to power the BOB, that's the signal voltage sent to the drive? Will that BOB linked in post 3 definately run safely off 24v?

[irving2008]

So from that I gather that whatever voltage I use to power the BOB, that's the signal voltage sent to the drive? Will that BOB linked in post 3 definately run safely off 24v?

The problem I have with running this BOB at 24v is this:




The output circuit has a pull up to 'Isolating + supply'. Without knowing the value of that resistor you can't be 100% sure its not going to fry. In the manual it shows 'Isolating Supply +5v'so I would assume they are sized for 5v and not 24v supply...

[JAZZCNC]

So from that I gather that whatever voltage I use to power the BOB, that's the signal voltage sent to the drive? Will that BOB linked in post 3 definately run safely off 24v?

I wasn't referring to that particular Bob or any Bob really and so obviously it would need to support 24V but most decent Bob's feature a range of input voltages.

I wouldn't use a cheap BOB with quality Servo's and to me this BOB isn't really a quality Item, it doesn't have a Charge pump for one which is nice feature and it looks a bit small and cramped.
Cheap nasty BOB's are a pain in the arse and a large source of problems and they don't always show has plain "works or doesn't" so can cause any thing from weak signals to dropped signals to slow acting Opto's etc all of which if your unlucky to drop for it will drive you crazy. .

[boldford]

Ok don't want to send this thread off course too much but think best to clear this up so not to confuse.!!

Yes I under stood what you meant but don't think you did me.? I wasn't suggesting sending 24V up the PP's chuff.!!

The 24V supply has multiple uses.!!. . . It's sent thru the limits Switch's and E-stop to help with switch bounce and noise. This is done in conjunction with 24V relays, so it powers them has well.
These control the 5V signals from the BOB, they also act has safety for other things killing power to anything attached etc, enabling a hardware driven fully safe latching E-stop system that can only be restarted when in a safe condition and the master relay engages even then this only engage after pushing a reset button.
If any of the safety switch's are tripped or some things in an unsafe condition then nothing happens.! . . . . Also In this case and the point of my comment meant to also use it to power the BOB and therefore save messing about with the 5V from HDD.

I understood you perfectly well hence the reason why I said "I'm sure your PC wouldn't want you to put 24v or more up its paraport",
Whatever vendors BoB is used, assuming it is capable of complete opto-isolation, and you wish to maintain it, the PC side will almost certainly need to find a logic 5v since most paraports can usually sink far more current than they can source.
I realise I mistakenly suggesting the e-stop be routed back into the PC - Bad move to rely on S/W for that function!. If I did mislead anyone I apologise.

[boldford]

The problem I have with running this BOB at 24v is this:




The output circuit has a pull up to 'Isolating + supply'. Without knowing the value of that resistor you can't be 100% sure its not going to fry. In the manual it shows 'Isolating Supply +5v'so I would assume they are sized for 5v and not 24v supply...

They are 1K.