Help me, oh might CNCzone! Grant thee a sliver of thy eternal wisdom.

I am doing an X3 with Nema 23's on X,Y, and Nema 34 on Z. I don't know if it matters, but I'd like to add an MPG (Manual Pulse Generator) in the future as well. Oh, and possibly a 4th axis.

Nema 23's = 387 in-oz 3.5A, 65volt

Nema 34 = 640 in-oz 3.5A, 65 volt

PSU = 65volt/20A (DIY type)

G203V's

Thanks!

I think just about any BOB will work. Depends on your needs and how much you want to spend.
I am using C10 BOB's from CNC4PC and I'm happy with both cost and function.

Leeway,

Yes, I have been looking at cnc4pc.com also. Do you need a C10 BOB for EACH motor?

Thanks!

-Caleb105-

No. The single C10 BOB does all four axes. Take a look at the schematics for each BOB you are looking at. Most BOB's will handle 4 axes. Pins 2 thru 9 are generally step and direction pins. One of each per axis.

A BOB mainly breaks out all 25 pins on a parallel port. Many do more than that, but that is a basic BOB.

Hey Caleb,
An MPG only needs 2 inputs and power so you could use one on a single C10 along with 4 motors.
If you want to have a manual axis selector switch like is used on cnc4pc's pendant (http://www.cnc4pc.com/Store/osc/product_info.php?cPath=40&products_id=158)
you'll need another C10 to handle all the OEM trigger inputs (10 on mine).
You'll also have to get the Mach 3 Brain to process the signals.( cnc4pc gives one for 4 axis)
A switch is more convenient than jumping back and forth from the MPG and mouse.
An easier tool might be the Shuttle Xpress (http://www.contourdesign.com/shuttlepro/shuttlexpress.htm) or Shuttle Pro, I'm going to use one for my new build.
They've been on Ebay for $45.
Hoss

Lee, thanks for the BOB info.

and Hoss, thanks for the great info on the MPG's. That shuttle express looks pretty interesting.

So my big question is, which of the following would you recommend? Seems like there are tons of different models, with greatly varying prices, and I really don't understand all the differences between them:

C1
C1G
C10
C11
C11G
C11T
C23
C25 (smooth stepper?)

KL-DB25


What is the "Smooth Stepper"? Keling's got one, but it's $159!! What the heck does this do? And is it necessary?

From a different thread:



On the BOB, the only one I don't think I've ever heard a single complaint about is the PMDX. I've personally had, and continue to have, frustrating problems with my CNC4PC C11 BOB (I'm on my third revision now).

Regards,
Ray L.

The C10 is a simple breakout board, I haven't had a bit of trouble with either one I use.
the other multifunction boards like the c11, c23 have extra features like relays, speed controls etc with some gecco specific.
I like to keep things separate, less complexity to go wrong.
the smooth stepper is a USB driver, his c25 is just a breakout board for it.

So....looks like my choices are:

C10 = $25.49
PMDX 122 = $81

Is there any reason to spend the extra money on the PMDX? Seems like both the C10 and PMDX are reliable.

The PMDX has a charge pump on board the C10 doesn't.
the C4 is $22.

So....looks like my choices are:

C10 = $25.49
PMDX 122 = $81

Is there any reason to spend the extra money on the PMDX? Seems like both the C10 and PMDX are reliable.

The advantage is, if you accidentally short something, with the PMDX you'll most likely just blow up a chip on the PMDX. With the C10, you'll likely blow up the parallel port on your PC, or worse. Isolation is worthwhile. Most people will never *need* it, but it's cheap insurance.

Also, if your PC has a low-voltage parallel port, the PMDX will work fine, where the C10 might, or might not. This can cause flaky problems that can be very tricky to track down. Or the current capability of the parallel port may be marginal, and one day you'll hook up one more signal, and start getting flaky behavior. The PMDX runs from a separate power supply, so this will never be an issue.

Regards,
Ray L.

The PMDX has a charge pump on board the C10 doesn't.
the C4 is $22.

C4?

C4 is the charge pump from Cnc4pc that works with Mach, like HK said it's cheap insurance just in case.

The CNC4pc is optically isolated therefore it wont blow up your parallel port. It also needs a seperate 5v power supply.
The biggest problem with BOBS is getting the software settings set up correctly.

Clive

Whoops
Should read CNC4PC C10 board.

Whoops
Should read CNC4PC C10 board.

The C10 is buffered only, it is *not* opto-isolated.

Regards,
Ray L.

Strange that he offers buffers and optoisolators as replacements for the C10 board.
But I am not an electronics expert so I stand to be corrected.
Regards
Clive

Strange that he offers buffers and optoisolators as replacements for the C10 board.
But I am not an electronics expert so I stand to be corrected.
Regards
Clive

Clive,

There are many errors, omissions and inconsistencies in their documentation....

Regards,
Ray L.

Ray
Yes I agree that the documentation is hastily assembled.
I have a reasonable understanding of an optoisolator, so how much protection will a buffer give if any, as I have 2 of these boards, one for my cncmill and one for the cnc lathe I am converting.

Clive

For consideration, there is also the $183 PMDX-132 BOB for Geckos. After you mount your Geckos to it this is like a giant G540:

http://www.pmdx.com/PMDX-132/

CR.

Ray
Yes I agree that the documentation is hastily assembled.
I have a reasonable understanding of an optoisolator, so how much protection will a buffer give if any, as I have 2 of these boards, one for my cncmill and one for the cnc lathe I am converting.

Clive

Some, but not as much. When an opto goes, it really can't hurt anything but the opto itself. The PC side of the opto is operating from a completely isolated power supply and completely separate login within the opto chip, so remains unaffected. With a buffer, both sides are operating from the same supply, and the logic within the chip is all connected together, so it is possible for a short to develop within the buffer chip itself that will pass excess current from the machine, through the buffer, and back to the PC, damaging the PC. This would not be the most common failure mode, but it is not all that uncommon either. So, buffered is better than unbuffered, but not as robust as opto-isolated.

Unfortunately, opto-isolated BOBs tend to get a bad rap, as there are, and have been in the past, a number of very poorly designed ones out there. When properly designed, the optos should be totally transparent to operation, even at high frequencies. Unfortunately, many BOBs are not well designed, and introduce noise and distortion into the signals they are "protecting", which causes problems that would not occur had they been properly designed.

Regards,
Ray L.

The PMDX-122 also has several jumper settigs for fault/e-stop handling, and other useful features. It also has an onboard relay. The connector on the PMDX-122 is the same used on most printers, so getting a cable for it is quite easy (not the D-sub type).

I have 5 of these bobs and I love them :)

There is really no need for opto isolation of the bob if you're using geckos. The geckos already have isolated inputs. All you're doing is just adding to the total slew rate of the components on the bob and increasing the "time of flight" for the signal from the PC to the stepper controller. Just can't be good if you're going for higher rpm.

As soon as I finish my breakout board, I plan to make a youtube video proving that all this crap added to the input of the bob, plus incorrect gluing of the logic families TTL and CMOS is the cause of "bad bob behavior". Hey that rhymes.

There is no reason a properly designed board shouldn't be able to interface with a laptop without sinking too much current, pulling down the voltage, and causing missed steppes which makes the stepper motors stall out.

How about all the other I/Os on the bob? Might be a good idea to isolate those from the parallel port.

How about all the other I/Os on the bob? Might be a good idea to isolate those from the parallel port.

Yes that makes since if you are interfacing anything other then a stepper controller that doesn't have isolated inputs already, but not as the first components the weak signal sees as it enters the bob.

If Mach 3 had more support for USB chips made by http://www.ftdichip.com/ then USB would be easier to implement, and we wouldn't even have to worry about this type of problem in the first place.

On another thought, there is no reason to have opto isolation before a relay either. I mean think about it, you already have isolation because the relay uses a small signal to charge a coil, which is isolated from the higher voltage by magnetism instead of light in opto isolation. So people who shell out extra for these boards that have opto isolation are really just throwing their money away on redundancy.

There is really no need for opto isolation of the bob if you're using geckos. The geckos already have isolated inputs. All you're doing is just adding to the total slew rate of the components on the bob and increasing the "time of flight" for the signal from the PC to the stepper controller. Just can't be good if you're going for higher rpm.

As soon as I finish my breakout board, I plan to make a youtube video proving that all this crap added to the input of the bob, plus incorrect gluing of the logic families TTL and CMOS is the cause of "bad bob behavior". Hey that rhymes.

There is no reason a properly designed board shouldn't be able to interface with a laptop without sinking too much current, pulling down the voltage, and causing missed steppes which makes the stepper motors stall out.

There IS a reason to have opto-isolation on all the OTHER inputs and outputs, like limit/home switches, motor controls, E-stop buttons, etc., etc. Also, there is no reason whatsoever a properly designed opto-isolation circuit should in any way impact the operation of the machine, even when driving Geckos. It is entirely possible to design opto-isolators that will run much faster than any machine will require, with low-enough signal skew as to be irrelevent. The problem is it seems many BOBs are NOT well designed, and mangle the signals. This is NOT a problem with opto-isolation in general, but simply a problem with those specific BOBs. My BOB is a perfect example. As I received it, it completely filtered out the step signals above about 40kHz. By simply re-biasing the optos, it is now quite happy at 250kHz. Few machines will ever need to go that fast. And, it is driving my G320s just fine at those speeds, despite the double opto-isolation. I'm also absolutely certain I could make it go at least 2X faster, probably faster, if I ever needed to.

Regards,
Ray L.

There IS a reason to have opto-isolation on all the OTHER inputs and outputs, like limit/home switches, motor controls, E-stop buttons, etc., etc.

So you're worried about a little 5V signal from a switch messing up your computer? Interesting. I would think most people aren't using their brand new top of the line computers that they just bought for their milling work anyway, so all this talk about how it's going to destroy your computer is pointless when used computers are practically through away these days.

So you're worried about a little 5V signal from a switch messing up your computer? Interesting. I would think most people aren't using their brand new top of the line computers that they just bought for their milling work anyway, so all this talk about how it's going to destroy your computer is pointless when used computers are practically through away these days.

First of all, many of us do not use 5V for switches. We use 12-24V, for better noise immunity. This is *necessary* and common practice on large machines (mine is a 9x49 knee mill). Not everyione here is running a little benchtop machine. Second, my computer, which I paid $100 for, is a 6 month old HP 3.6GHz pentium. And, no, I don't want it blown up, because I can't get another one at that price. Relay drivers are a *perfect* place for optos, because if the coil driver transistor fails, the relay can inject a voltage spike into the BOB, which could possibly propogate back to the PC. I'd much rather be able to replace a socketed 50 cent chip on my BOB, than have to buy a new $150 SmoothStepper or find another PC.

You could also have an accidental short in your motor drivers or power supply that ties your 5V bus to your 70V motor supply - S**t happens. Or short an AC line to a signal line. Anything like that will wipe out pretty much anything in it's path, up to the optos. Your PC will be spared. The whole idea is to protect against unplanned events, which DO occur, at least to the rest of us.

Opto isolation is insurance. Most people will never need it, but if you do, it's really nice to have it there. For me, it's a good trade-off. For you, perhaps not, but that's no reason to dismiss the entire concept. It's VERY widely used in industrial machines, and for good reason.

Regards,
Ray L.

Opto isolation is insurance. Most people will never need it

Regards,
Ray L.

Do you worry a lot?

First of all, many of us do not use 5V for switches. We use 12-24V, for better noise immunity. This is *necessary* and common practice on large machines (mine is a 9x49 knee mill). Not everyione here is running a little benchtop machine. Second, my computer, which I paid $100 for, is a 6 month old HP 3.6GHz pentium. And, no, I don't want it blown up, because I can't get another one at that price. Relay drivers are a *perfect* place for optos, because if the coil driver transistor fails, the relay can inject a voltage spike into the BOB, which could possibly propogate back to the PC. I'd much rather be able to replace a socketed 50 cent chip on my BOB, than have to buy a new $150 SmoothStepper or find another PC.

You could also have an accidental short in your motor drivers or power supply that ties your 5V bus to your 70V motor supply - S**t happens. Or short an AC line to a signal line. Anything like that will wipe out pretty much anything in it's path, up to the optos. Your PC will be spared. The whole idea is to protect against unplanned events, which DO occur, at least to the rest of us.

Opto isolation is insurance. Most people will never need it, but if you do, it's really nice to have it there. For me, it's a good trade-off. For you, perhaps not, but that's no reason to dismiss the entire concept. It's VERY widely used in industrial machines, and for good reason.

Regards,
Ray L.

So, what is this magnificent break out board that you're using? Does it have an on board relay? What voltages are required for its operation? If it has an on board rely, what voltage/current does the relay’s coil require?

Step & Dir into the Geckos are isolated with high speed (2 mhz) optos. (except for the 250 series). The buffering on a BOB is to improve the noise immunity of the parallel port. The outputs of a PP are logic level MOS. The pins are not designed to source over a few mills or sink more than about 10ma. The challenge of moving signals across cables over distance is that the higher the driving impedance the better antenna it makes. If you give some attention to proper design and buffer the step & dir signals you can clean them up, logic shift to full 5 V and provide a low impedance drive that will allow the use of 5 meter cables with no problems. The world of industrial electronics is a lot more challenging than logic control. Running logic level signals mixed in with high current PWM and other sources of EMI requires an understanding of grounding, isolation. shielding and differential signaling techniques that honestly baffles even some Electrical Enginners.

The opto isolation of inputs breaks ground loops, conducted noise and potentially destructive voltages. To be truly isolated the two circuits must NOT share the same ground (E.g. separate Power Supplies with separate common (grounds).

Inputs can typically be a lot slower than is needed for the step & dir signals.

All of our cards from day one have had full buffering on all step & dir, Double buffering on relay outputs and opto isolation on all inputs. We have always offered a dual power supply to drive the cards to give the isolated input power.

You can get by with ignoring the rules on smaller systems or where three is only one machine in the mix and distances are short. Toss in something like plamsa cutting or other machines and the gremlins of EMI and RFI will make you pay.

Maybe some other motor drives with straight TTL inputs need external isolation but it needs to be the right kind. Conventional optos have poor bandwidth. High speed optos are readily available but $$ compared to lower speed.

Proper documentation is always important. You should not have to take night courses in electronics to build a CNC machine!

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics

Universal Breakout Board manual at www.CandCNC.com/PDF/UBOB_Manual.pdf

Step & Dir into the Geckos are isolated with high speed (2 mhz) optos. (except for the 250 series). The buffering on a BOB is to improve the noise immunity of the parallel port. The outputs of a PP are logic level MOS. The pins are not designed to source over a few mills or sink more than about 10ma. The challenge of moving signals across cables over distance is that the higher the driving impedance the better antenna it makes. If you give some attention to proper design and buffer the step & dir signals you can clean them up, logic shift to full 5 V and provide a low impedance drive that will allow the use of 5 meter cables with no problems. The world of industrial electronics is a lot more challenging than logic control. Running logic level signals mixed in with high current PWM and other sources of EMI requires an understanding of grounding, isolation. shielding and differential signaling techniques that honestly baffles even some Electrical Enginners.

The opto isolation of inputs breaks ground loops, conducted noise and potentially destructive voltages. To be truly isolated the two circuits must NOT share the same ground (E.g. separate Power Supplies with separate common (grounds).

Inputs can typically be a lot slower than is needed for the step & dir signals.

All of our cards from day one have had full buffering on all step & dir, Double buffering on relay outputs and opto isolation on all inputs. We have always offered a dual power supply to drive the cards to give the isolated input power.

You can get by with ignoring the rules on smaller systems or where three is only one machine in the mix and distances are short. Toss in something like plamsa cutting or other machines and the gremlins of EMI and RFI will make you pay.

Maybe some other motor drives with straight TTL inputs need external isolation but it needs to be the right kind. Conventional optos have poor bandwidth. High speed optos are readily available but $$ compared to lower speed.

Proper documentation is always important. You should not have to take night courses in electronics to build a CNC machine!

TOM CAUDLE
www.CandCNC.com
Totally Modular CNC Electronics

Universal Breakout Board manual at www.CandCNC.com/PDF/UBOB_Manual.pdf

Wow, great response to the thread. Well, I'll concede that any person deciding on their breakout board, should consider environment, cost of quality components, and considerations for EMI/RFI.

I'll change my opinion to simple hobby CNC mills like the X3 don't need any more isolation other then which is provided by the geckos and relays. As Torchhead points out, good isolation does have it’s place though.

I always get a kick out of this search for super isolation.
I developed a personal strategy many years ago that although in the use of isolation components such as SSR and interfaces such as OPTO offer, I still referenced all the different systems to Earth ground, which essentially ends up at some point, to each other, including the PC power supply.
Looking through my records, I first started installing PC based systems in the late 1980's.
This has been in some the harshest industrial environments imaginable. These systems are still successfully in operation today.
Also I did not succumb to the credo that 'You must use a Industrial PC', I figured for $8,000 I could get alot of metalwork done.
The answer to the question on whether to isolate or not is personal preference, but the bottom line is, either method has to be done with due diligence.
I believe that many of the sellers of BOB's, stress the isolation method as it may be easier for many of those that use their product, may not have a background or experience to implement a uni-potential bonding system.
Some of the regular complaints of spurious switch trips etc, I swear are due to not adopting the common ground method.
Al.