Messages

721

General Mach Discussion / Question on using DC chokes on SCR drives

« on: August 28, 2010, 06:25:06 AM »

In anticipation of using a larger spindle motor, have switched from a PWM drive with separate relay reversing to a big 4 quadrant regen SCR drive that has reversing built in.

Being spoiled by the smooth PWM power, I am not satisfied with the much coarser SCR performance and have been doing some research on adding a driver or choke to the output and perhaps also a filter on the AC input. I have been able to find only references to using two legs of a very expensive 3 phase reactor filter as a choke between the drive and the motor, but I can get a plain 10A choke for 1/10 the price of the reactor.

Question: with a reversing drive, do I need a choke on each DC wire to the motor or will one choke suffice?

Question: is there any tangible benefit to adding a line filter on the A/C input to the drive relative to motor low speed smoothness?

722

General Mach Discussion / Re: Servo Drive Review. First 4 drives Gecko, Viper, Rutex, Leadshine

« on: August 24, 2010, 08:22:09 PM »

I've kept the original SEM servo motors which are rated at about 140v, 25A.  The rating put them outside the capabilities of Gecko's which were my first choice.

I've been trying to buy these motors on ebay and I keep getting sniped each time. What do you think of the motors in general?

To give the Dugongs a real test, I have decided to use one for my spindle drive controller.  The mill has a 5Hp DC motor which is pretty big physically.

For that big brute motor, you should include a BIG braking resistor on the Dugong. The drive uses the resistor automatically . . a nice feature . . and it should be fairly indestructible so long as it has the big resistor to dump to.


Incidentally, I have added the Granite Devices VSD drive to that review and I will be adding the MR-C and J2S series Mitsubishi industrial drives as well once I have some more experience with them (and get some time). The review link does not change, so hitting it again always gets the latest version.

723

General Mach Discussion / Re: High speed spindle recommendations

« on: August 24, 2010, 08:03:43 PM »

I am thinking it may be worth a shot, have a couple of angular contacts and would be simple to make up a housing and shaft. If the box screws up its no big deal as I got 2 of them for £12
So what do you think?

Hard to say without knowing the ratio, but if I am thinking correctly, the original input shaft should be the center pinion and the output would be the planets, so 'arse for tit' the high speed would be the center pinion driven by the planets, which is a good arrangement for a speeder. The gear set will *probably* hold up if the planets are on (or can be put on) needle rollers. I'd say go for it. You are likely to have vibration issues, it will just depend on how bad they are and what kind of effect they have on your finish.

[50,000 RPM is] quite a bit faster than I need, tool I have is rated to 20,000rpm in stainless I think so anywhere between 15 and 20K would suit me.

The point I was making here is that the speed change ratio is minimized if you start with a source closer to the target speed.

Interesting as in funny watching me screw up?

We all get a 'turn in the barrel' so to speak. I specialize in frying electronic components. I get paid to know about things mechanical, so it is more embarrassing when I break the hard stuff.

724

General Mach Discussion / Re: High speed spindle recommendations

« on: August 24, 2010, 05:18:06 PM »

Wow  I did not realize you were trying to drive the high speed engraver off the main mill spindle. Almost 4:1 speed increase with a single belt is pretty optimistic.  Going the other way is a whole different animal. If you are now thinking about using gears, you would be well advised to seek out a planetary set. Consider yourself so advised 

In my setup, I am shooting for 40k to 50k rpm, but I'm starting with a pre-balanced 30,000 RPM tool motor.  In any case, good luck and please keep posting your results. This is interesting to follow.

725

General Mach Discussion / Re: High speed spindle recommendations

« on: August 24, 2010, 11:59:19 AM »

So where does the 3,000 RPM fit into the puzzle  . . .  3,000 at the motor and 14,750 at the spindle? Is that what you have?

726

General Mach Discussion / Re: High speed spindle recommendations

« on: August 24, 2010, 11:44:19 AM »

Sorry to be dense, but I'm not following this at all. How do you engrave at 1,475 RPM   

727

General Mach Discussion / Re: High speed spindle recommendations

« on: August 24, 2010, 11:16:27 AM »

Wasn't this project for a 22,000 RPM spindle?

728

General Mach Discussion / Re: Switched out my PC and now Mach3 is unhappy

« on: August 23, 2010, 07:33:44 PM »

Thanks!

Back on topic, I am starting to use my new computer and I found some interesting behavior that I want to contribute to the kernel speed discussion. On my new setup, I can run 100K kernel thru the first BOB, but not thru the second. I have not seen this mentined before in speed discussions and it really did not occur to me until today when I was trying to run the 100K stream thru the second BOB to the 4th axis.

In this case the drive has a 4 place LED that can display (among other stuff) the pulse frequency coming into the drive. On the X axis testing (BOB number one) it was showing the 100k steady. Now I have it on the 4th axis on BOB number2 and it is shows unstable anything over 60k.

Bottom line is that the computer, which is always suspect number one, is not necessarily always the culprit.  The BOB has to be able to pass the stream thru it's optos and other circuits at that speed as well.  Seems obvious now, but it never occurred to me before.

729

General Mach Discussion / Re: Disabling an axis via mach

« on: August 23, 2010, 08:55:46 AM »

Enable/disable *should* be doable on any device that can tollerate having its 'motivation' cycled.

For example, if your dispenser is electric, you might be able to simply use a MACH output to trigger a relay to switch off the power to the dispenser. If this could be done transparently to your dispencer control routine, then that control could continue to operate, but simply not dispense anything.

If the dispenser is air powered, you might be able to install a solenoid operated valve to kill the air supply.

Even in the case of a servo or stepper drive that has no 'disable/enable' function, the step signal coming from Mach could be interrupted between the BOB and the drive, although in such case, re-homing would need to be considered as Mach would no longer have an accurate axis position.

I am using MACH outputs to enable/disable as well as activate/deactivate a variety of devices, electronic, pneumatic and mechanical. The output fuction is easy to use with MACH. More challenging is getting an action to be triggered automatically by a specific event or combination of conditions without using G-code.

730

General Mach Discussion / Re: Switched out my PC and now Mach3 is unhappy

« on: August 23, 2010, 08:36:28 AM »

I had thought about buying some Yaskawas that I saw for a decent price but decide I would just stick with what I know and like. I now have at least one spare drive for all that I use, even a spare for the 22KW drive thats on the Lathes spindle

You are wise, ObeeWan!  Spares is a definate consideration. I don't want to end up like I did with the DC servos having a different brand on every axis. Pretty expensive to have spares that way! I have been paying attention to 'general availability' as an important parameter since I can't aford to buy a bunch of new drives at this level. Mitsubishi J2S are adequate for my needs and nearly always available for reasonable prices from 200watt to 750watt, which is the range I am interested in at the moment.

The older Allen Bradley drives I didnt rate quite so much but they were still ok but lacked some I/O that the newer ones have.

Again, I have to agree that the I/O is really a huge difference between the 'hobby' and 'industrial' levels. Lack of same was a real frustration with the inexpensive DC servo drives I was trying to use previously. 

Question; what are the series of the 'older' and 'newer' models of the Allen Bradleys you are using?
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