Messages

1241

General Mach Discussion / Re: Problems threading on the lathe

« on: April 21, 2009, 04:05:46 AM »

Art,

I have a disk on my spindle and I am am willing to drill more holes in it to test your driver. How many holes (slots) and how mch larger does the main slot have to be? You can answer in ms if that's what Mach is looking at.  I'll calculate the appropriate slot size for my disk dia. and RPM.


I also am expecting a servo motor, encoder and Gecko 320 to arrive today. I plan to use it as the spindle motor for my 4th axis, so testing is as a spindle will be perfect for my purposes.

Serendipitously, I am testing a newly designed breakout board and PWM speed controller from Peter Homann as I write this. So far I am just stressing it with a looped program in Mach3, but it is dead rock steady on the output. I was unable to achive this with either his earlier DC06 or the CNC4PC speed controllers.

To anyone reading this, please note that the problem might have been with noise in and around my mill, and not the fault of the speed controllers, so I'll need to get the new setup installed in order to really know if the issue is resolved, but so far so good.

I will have a second parallel port in a couple days to hook up the second breakout to the computer. That will give me a bunch of extra pins to use.

1242

General Mach Discussion / Re: Opinion and advice - explain relationship of encoder to kernel speed

« on: April 20, 2009, 10:05:10 AM »

Excellent!

Retrofitting this little mill was my first foray into home grown CNC and it has been a lot of fun. Some setbacks, but overall not nearly as difficult as I envisioned.

I have some other commitments that will take me away from my toys for a few months and I'm thinking about selling this little mill complete. I've pretty much taken it to it's limits. When I get time to play again, I would be doing up the larger X3 with servos. Maybe the CNC Brain, or equivalent, will be working by then.

I'll look you up when that times comes and see what you think of the progress.

1243

General Mach Discussion / Re: Limit switch wiring advice needed from you electronics guys, please!

« on: April 20, 2009, 09:47:10 AM »

I am aware of the printer driver problem. There is no driver installed, and the mother board is a very high quality server board. The driver test provided with mach is a dead flat line up to 65khz.

When I was getting chips on the switches, I could see the problem clearly on the diagnostics screen, but now there are no clues, so it's going to be difficult to track down a cause for the random e-stops.

So it seems like it is down to eliminating possible causes, one of which, the consensus is, would be running the limit switches at 5v.

Is there a particular brand of mechanical switches that are considered particularly accurate?

 

1244

General Mach Discussion / Re: What size motors?

« on: April 20, 2009, 09:37:34 AM »

Bill, my sincere apologies if you felt demeaned in some way.

My comments were not directed at anyone in particular. I think some of the advice dispensed is not so much 'wrong' as it may be outdated, and out of context.

I don't think it is helpful to say steppers are 'just as good' as a blanket statement. Especially when it is obviously a newbee asking the question. Steppers are appropriate if used in such and such application, WHICH IS . . . ..  blah blah blah   BECAUASE . .  blah blah blah.  Mo' better answer.

There is a lot of conflcting information around and I know that as a newbee, I had trouble sifting thru it, primarily because AS a newbee, I had no tools to distiguish opinion from fact, or to dvine what information was missing from an answer.  I made some expensive mistakes following incomplete advice.  It cost me several hundreds of dollars to learn what an 'isolated signal' is, even though I had asked the right questions and purchased the exact components I was told to use. So, this being a forum, I share my 'experience' such as it is, like everyone else.

This is a technical forum. It's all about facts, not about personalities or one's "outlook on life". 

1245

General Mach Discussion / Limit switch wiring advice needed from you electronics guys, please!

« on: April 20, 2009, 06:11:08 AM »

Getting false estops again. First time it was swarf getting on switch contacts. Easily remedied. Now getting spooky random e-stops for no apparent reason.

One cause could be momentary induction on the 5v limit switch wires, so I read that bumping them to 24v is the solution . . again easy enough.

I'm at 'Electronics for Dummies' level, so I need some help interfacing the new 24v daisy chain back to the breakout without frying things . . . . again   .

So I would appreciate getting some advice on two possible solutions. First, a part number and wiring instructions for an optoisolator to connect the 24v limit switch loop to the breakout.

Second, I replaced a broken limit switch (don't ask   ) with a Cherry brand and it is very inconsistent on homing. I would like to replace all of the mechanical switches with something like the NTE3100 photointerruptor. Would that be a good choice and how would one go about building a circuit out of three of those daisy chained back to the breakout?

Thanks!

1246

General Mach Discussion / Re: What size motors?

« on: April 20, 2009, 05:43:13 AM »

Bill;  Just FYI, I don't take myself all that seriously, nor do I get emotional over forum chatter. My 'opinions' are no better or worse than anyone elses, however facts are facts and I welcome any challenges in that regard.

I would like some clarification on one of your comments. You mentioned 'inrush of current' to a servo motor.

Sounds like you are implying that a servos is unpowered when not moving. If that is so, how does it have any holding power?

As to steam power, I think better to use a twelve year old kid on a hand crank.  . .  you have to feed them anyway, and it keeps them out of trouble . . .

1247

General Mach Discussion / Re: Opinion and advice - explain relationship of encoder to kernel speed

« on: April 19, 2009, 06:41:10 AM »

Overloaded; My first DC servo and Gecko 320 arrive on Tuesday, so sayeth Brown.

CNC Brain, however is not on the menu at this point, although I do plan to follow it's progress if I have the time to do so.

As I said, I only did a quick scan of the CNC Brain site and I was not aware it used linear scales, but linear scales are nothing new. I had them on my little el-cheapo Mini mill before I converted it to CNC. I had not considered getting feedback from a linear scale, but it makes a lot of sense. Absolute is always going to be more reliable than relative positioning.

Hood; I am not interested in blazing new trails in home grown retro CNC. An engineer is, by definition conservative, skeptical, anal, and only interested in facts. The CNC Brain may not be ready for prime time, but the idea is very valid and the apporoach, if it is developed fully, would solve the issues I was pointing to, and at an entry level price point. AS I have already said several times, these capabilities we have been discussing are not new. Machining centers incorporate ths technology and have for some time.

Getting anything remotely  similar for $500 or $600 would definately be something new, as are servo motors under $100 and $30 encoders, apparently.

It appears that the CNC Brain is being developed by a very small outfit, so, like most of the other suppliers to the CNC retrofit community , including Artsoft, it takes a while to get things accomplished.


I just feel strongly that discounting new technology simply because it is not fully developed or based on the cost of a single component is not a good strategy. If one were to evaluate, for example, the Gecko 540 on price alone, it would look expensive, but it has 4 drives in it. The smooth stepper has a way to go before everything is implimented the way people (including yourself) want. The only way to look at a CNC retrofit, in my opinion, it to set your criteria and then compare the total system cost of the alternatives that meet the criteria.

One of those criteria, of course can be that certain features must be fully functional right now, today. Mach has been around for quite a while and it seems they are just now getting threading to work right. I don't know of any bug free software that is under active development. I also know of no software that does not have a wish list associated with it.

There is a saying . .  'it is what it is'.

I'll say this, if I made my living off my CNC machines, I would definately be following CNC Brain and any other promising technology, unless I had the cash to plunk down on a machining center.

Lastly, were I to purchase CNC Brain, which actually would make sense in some ways as I am very interested in new technologies and at my hobby level, I don't need to make money with the machines or have tight production dealines, so beta products are not a critical issue for me . .  hell, I've had the Windoes 7 beta runing since day one availability . .  but in any event, I would not be posting the progress of CNC Brain on a Mach forum . . that would make no sense.

1248

General Mach Discussion / Re: What size motors?

« on: April 19, 2009, 05:37:15 AM »

What's better Ford or Chevy? That is an emotional or personal opinion type of debate and is therefor unresolvable. The debate betwen steppers vs servos will also be unresolvable so long as it is argued by fanboys instead of facts.

I have lost count of how many of these debates I have read and probably less than 10% of them have any facts whatsoever.

Servos are more expensive than steppers in the same way as a Corvette is more expensive that Ford Escort. It is frankly rediculous to compare those two cars based on price alone and make a blanket statement the they are both 'cars' and therefore the  Escort is 'just as good'

If your objective is to take your kid to school over surface streets at 35mph max, THEN there may be a valid argument there. If your objective is to autocross without building a race car from the ground up, then it matters zero how little the Escort costs because it is simply incapable of doing the job.

If one prices out, using CURRENT pricing, servo motors and the required encoder and driver and a stepper and required driver in cases where anything resembling  equivalent performce is a criteria, then steppers and DC servos are very comperable in price.

Exactly how does one go about comparing steppers and servos? I have seen people compare the torque, but that is a completely invalid comparison because the motors are rated differently and have vastly different charactaristics. Torque is a STATIC measure. That's not an opinion, that is a fact. Moving objects requires POWER. That is also a fact. POWER is about doing work over TIME, also fact. Torque  is ONE number in the equation. I did a comparison of stepper vs servo of similar 'rated' torque and posted it in this forum. I also posted the formulas used so anyone was free to discredit them. Nobody did.  The servo was many, many times more powerfull.

A Corvette motor has 500hp and a semi diesel has only 300, therefor a Corvette engine will perform better in a semi truck than a diesel. That is simply an uneducated statement and is the type of logic that often defends stepper motors.

I have to agree with whoever said that the stepper powered full size mill that was used as an example is pitifully slow. I would add that is is also pitifully weak.

Servo motors top out early in the power game and above that there is only a choice between DC servos and AC servos. A Ford Escort gets much better mileage than a semi, so putting a Ford escort engine into the semi would result in much better mileage for the semi. This is also the type of logic that defends steppers on big machines.

It is really like comparing a pickup truck and an earth mover and saying the pickup is 'just as good' because it also can move dirt from point A to point B and it is cheaper.

Flame suit *on* 

1249

General Mach Discussion / Re: Opinion and advice - explain relationship of encoder to kernel speed

« on: April 18, 2009, 06:10:43 AM »

I did a quick perusal of the CNC brain site and I have do disagree with what's been said in this thread about it thus far.

First off, it is not exspensive. In fact, it is the opposite if one considers what is included in it's price. The CNC Brain @ $500 cost less than my 4 Gecko Drives ($600), and the CNC Brain is 6 axis. Also the 'GUI' appears to be the control software and is included. Mach is now $175. The CNC Brain also includes the functionality of the smooth stepper.

Just combining the cost of Mach and a smooth stepper together gets you a long way toward the CNC brain cost, and the functionality of both is included in the CNC Brain. I don't know at this point what kind of 'dumb' amplifiers one would need to handle the motor current, but unless they are $150 each, like a Gecko 203v, you can subtract the delta from the CNC Bain system's actual cost.

Second, it doesn't work with Mach, but there would be virtually no point to using it with Mach. IF the thing works as they claim, Mach would be a major step backward, and as I mentioned, the CNC Brain already has it's own control sofware, so it does not need Mach.

Third, there seems to be a very active forum assiciated with the device, so more than a couple of people are using it. There woud logically be little disussion about it in a dedicated Mach forum.

Lastly, anyone who can compete in the DARPA robotic challenge is cutting edge, so in my opinion, that resume' entry alone deserves respect.

I am definately going to look into this further, but from the descrition, it does exactly, precisely the kind of functions I was referring to that Mach cannot do.

Of course, there remains the question . . . does it actually work . . . but here again, in fairness, I read in the Mach forum about the relatively new smooth stepper's current limitations and what is 'planned' for the future, and nobody seems uncomfortable with that concept. This demonstrates some acknowledgement within the Mach community that new technologies need time to mature.

Obviously, I need to do a lot more homework on the CNC Brain to make an intelligent assessment, but it seems to me that the negative comments here are perhaps a rush to judgement.

1250

General Mach Discussion / Re: What size motors?

« on: April 18, 2009, 05:09:14 AM »

Take a read on the www.geckodrives.com site. Lots of good info and formulai

Make sure you do your own price checking in whatever you are considering. Also note the dates on any forum postings you pick up with a search engine.

I can't tell you how many times I read about servos being 2 or more times as expensive as steppers. My own research into pricing showed a $15 difference per axis. Insignificant.

As a newbee, I followed the advice de jour and went with steppers, albeit the most powerfull I could get in NEMA 23. Steppers make sense in some applications, but if I had it to do over . . . . 

My new servo motor should be here shortly and I will take a walk down that path in preparation for retrofitting another larger mill.