servo control vs stepper control

**JAZZCNC** · 14-09-2012

Originally Posted by boldford

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.** · 13-09-2012

Cool, thanks again. I'll get some details of the various drives and post then up to garner your opinions on the way to make best use of them. I'll probably do a quick lash, up install on the x,y base I'm using with the stock lead screws simply to familiarise myself with the whole deal before buying new screws.

**m.marino** · 13-09-2012

Peter it depends on the type of BOB that you use. Some use very little voltage or current at all. The problem a lot of those have is making sure a good signal gets handed on to the Drivers. With you wanting to do steel, I would seriously look at a slightly higher end BOB which in turn will most likely require a higher voltage to run. I have gone up through the BOB line starting with one that I won't mention and then moving on to Roy of DIYCNC PPCPSv2 unit (gave that away to a useful home) and then on to his system 4 board set up (Which I have for sale with extension cards but not sure it is the best for your needs even though it is opto-isolated). I used that with a borrowed USB Smooth Stepper and got huge improvements in control and accuracy (Parallel port on that computer has issues).

Currently (and pretty much the last one I will ever need) using a PMDX-126 board (mains powered) with an Ethernet Smooth Stepper (was in the States and could buy them without the huge postage costs). The difference is massive. Now I am also running AM882 drivers which also make a huge difference. You are looking at running servos and therefore really want to keep as clean and solid signal reaching them as possible. So look around and ask a few folks on what would be best for you. Good luck with the build.

Michael

**Peter.** · 14-09-2012

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.** · 14-09-2012

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?

**Peter.** · 16-09-2012

Help me out here a bit folks.

After trawling through 300-odd pages of servo amplifier manual which seems to have every bit of information you could possibly want for the Mitsubishi drive - I can't for the life of me get the faintest idea how it could be connected to accept step & direction commands from Mach 3. What is the usual command process for controlling servos?

**JAZZCNC** · 16-09-2012

Originally Posted by Peter.

Help me out here a bit folks.

After trawling through 300-odd pages of servo amplifier manual which seems to have every bit of information you could possibly want for the Mitsubishi drive - I can't for the life of me get the faintest idea how it could be connected to accept step & direction commands from Mach 3. What is the usual command process for controlling servos?

Give us some model numbers etc and I'll have look for you.

**m_c** · 16-09-2012

Not all servo drives can handle step/dir. Analogue control is far more common in industrial drives, so you need a suitable interface to take the step/dir and convert them.

Search/ask on the Mach forum (www.machsupport.com/forum), as there are a couple people on there who know about servos.