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mocha
14-09-2011, 11:39 PM
**
Firstly a big thank you to everyone who has shared their experience on this site. This project would still be a vague pipe dream without your generosity.

As mentioned elsewhere, I have a trip to China coming up in just over a month and I'm hoping to use that trip to bring back some of the biggest bargains.

The research continues at a pace although not as fast as the time is counting down! I've had a chat with the guy who has access to the heavy engineering part... His Abene mill looks like a beast, but it's bound to be really useful along the way. It does of course mean that the whole design process has to be done in a rather tight timeframe which is less than ideal given my lack of understanding of the problems. Targets are design finished mid October and running before xmas! ROFL!

After trawling what feels like a majority of the internet, the design considerations so far (in no specific order as this thinking as still changing too rapidly!);

DeusExCNC

Small A3+ CNC capable of working wood, plastics and some light alloy (slowly) budget around 1000GBP

Working area of not less than 60cm x 60cm x 15cm. Overall I guess somewhere around 80cm x 80cm(?)

Design to incorporate adjustable height bed, 0-15cm, 15 to 30cm.

Box section steel frame at least 25mm x 25mm - filled with sand (thanks JAZZ!) a bit like this one, (Is there a name for the high side design?)



4537


In the above pic, along with some other changes I'm thinking that I'd add a third vertical under the top rails and possibly add a cross bar at the back roughly where the steppers are at the far end for better stiffness and also triangulate the bottom of "open" end. I have seen another similar design that uses a substantial C section for the top rail too…

20mm supported round rail on X,Y,Z haven't found a price for profiled, I expect it will be outside my budget.

This is the area giving me the most problems at the moment, currently from what I've read, I think I need;
Steppers - 23(?) 3nm? (still trying to play with Irving's excellent spread sheet)
Ball screws - X,Y; 20, 10mm pitch (approx. 800mm long) FFZD ball nuts
Ball screws - Z; 20, 5mm pitch (approx. 300mm long)

Construction
The top rails that mount the supported rail for the X to run on would seem to be the first construction problem and perhaps one of the reasons this is not a very popular design(?).

My plan is to Mig weld the end verticals (35 - 40cm ish long) to the top rails then clamp them to the big Abene mill and skim 10 thou or so off to level them up. Then invert them, clamp the machined faces to the table and weld the bottom part of the structure together. That should (I'm thinking) give me to flat and level and parallel surface on which to mount the supported rails. The "bottom" of the structure is sure to be less accurate and more uneven, so use car body filler to level it on the stand/ table with a laser level. Then finally, mill the spoil board level to the Z axis.

Setting up the X supported rails; build the Y axis, then set one of the X rails by eye and using the other side of the Y as a guide, fettle, shim and file for best fit of the Y, bolting down gradually.

Y Axis
steel gantry, design to be decided
Z Axis alloy, design to be decided



2.2kw water cooled spindle - (noise!) PC cooler mounted on Z.

Gecko G540, although the idea of a handful of the M542's / 752's and breakout board are growing on me.


70v power supply

Misc stuff:
vortex dust removal
"bitcam"
Z zero switch
Mist cooling.
temp sensors via Arduino


Still a thousand questions without answers, not least of which are;


Is the gecko g540 really worth the extra money for the fancy magic inside it??
If the Y axis supports ends up about 1m apart, whether to go with 2 steppers for the X or use just 1 and belts?





Any thoughts, suggestions or eggs most welcome! :-)

Jonathan
15-09-2011, 07:28 PM
To me that machine looks like an excellent basis and the changes you suggest sound worthwhile, particularly the triangulation. I would be inclined to leave the sides open as it may be convenient for long pieces. By all means make the steel box section that supports the rails bigger to compensate.

Milling the surfaces for the linear bearings flat is a good idea, but you want to do it after all of the welding as any subsequent welding may throw it off again. If the milling machine is big enough then it's easy enough to clamp the whole frame to the bed - the difficult bit is clamping it to the bed without distorting. If it twists when you clamp it to the bed, then reverts when you take it off then it's a waste of time...

An alternative to milling is using epoxy resin. Put barriers round the top of the box section where the rails round with a channel / tube between. Pour the resin in (couple of mm thick I reckon) and gravity will self level it extremely accurately.

You can mill the spoil board with the router when it's finished. Having an adjustable height bed is great but it's hard to keep it level when you move it!

I can highly recommend the PM752's. I've neither seen nor used the G540 in real life but I doubt the 'clever stuff' it does is worthwhile for a machine this size.

For that length I think you'd be fine with 16mm, 10mm pitch ballscrew, not 20mm diameter. The bigger screws have a higher inertia which will harm your acceleration and top speed to an extent, however the critical speed is greater so with big enough motors it would go faster. I managed to get 60m/min on my 16mm, 10mm pitch Y-axis which is a 910mm long screw, about 840mm unsupported ... which is clearly much more than enough! That is with PM752 and 3Nm Nema 23 motors. You don't want Nema 34 for a machine this size as the moment of inertia of the rotor is greater which, among other things, means they operate at lower rpm.

mocha
17-09-2011, 06:59 PM
Thanks for the help Jonathan, some good ideas there! Much appreciated!

Quick update;
The last couple of days have actually seen some progress with the first iteration of the bill of material is now complete although it's stiill going to need several more iterations before all the bugs are ironed out.


I'll try and get an extra set of some of the elements to use initially as hot swap spares with the option of making a 4th axis after xmas...
I can't find a good reason to keep the gecko G540, so that's gone and 1610 ballscrews instead of 2005 too.

The adjustable bed might wait until I need it! the potential solution was going to be a removable second bed that could be removed.. I would put some designs up at this point but everytime I try using google's Sketchup I must be taking a stupid pill! Just can't get my head around it yet.

more to follow. :)

mocha
19-09-2011, 02:59 AM
Are there any thoughts about using 6 bearings instead of 4 on an axis, specifically here I'm thinking of 25mm supported rail?

...Which also leads me to wonder if there is anywhere to avoid or prefer with the placement of the ballnuts? Centre of mass or axis of the spindle seem to be the most logical? Does that sound reasonable? I noticed that on the picture above, (which I should apologise for not crediting to "Nhyf" on youtube before now) there was a comment about the placement of the X axis ballnut placement...

I'm trying to have the bottom of the Y axis about 150mm above the work surface, with 2/3rds of the spindle mounting plate supported on the Y axis when the spindle is at the lowest point of travel... is this something worth the effort?

Robin Hewitt
19-09-2011, 11:50 AM
Are there any thoughts about using 6 bearings instead of 4 on an axis, specifically here I'm thinking of 25mm supported rail?

You'd probably only consider 6 if the loading was too great for 4. OTOH if the loading was too great you'd want a fatter rail. It's the separation that counts.

Locating ball nuts has 2 major thoughts, keeping it rigid and avoid introducing twist. Don't put them out on a limb.

Jonathan
19-09-2011, 12:04 PM
Are there any thoughts about using 6 bearings instead of 4 on an axis, specifically here I'm thinking of 25mm supported rail?

You will reduce the contact force on each bearing. It's worth remembering that they're rated for a huge force anyway, so it may not be worthwhile. There may be other effects, such as helping with racking - not sure.


...Which also leads me to wonder if there is anywhere to avoid or prefer with the placement of the ballnuts? Centre of mass or axis of the spindle seem to be the most logical? Does that sound reasonable?

The Y-axis ballnut should be as close as you get it to between the rails and not far from the spindle. That ensures that the only thing which can flex, when you apply a force parallel to the Y-axis, is the aluminum. If the ballnut is far away then the bearings can move on the rails relatively easily, leading to quite a bit of deflection.
This is a problem on my machine at the moment:

4568

I think aligning the X-axis ballnuts with the center of mass in the XZ plane (or at least in Z) is a good plan as when the X-axis accelerates you've eliminated the turning moment about the ballnut. Ideally you would do the same for aligning the X-axis ballnut with the Z location of the cutting force, but that clearly moves so the best you can do is an average.


I'm trying to have the bottom of the Y axis about 150mm above the work surface, with 2/3rds of the spindle mounting plate supported on the Y axis when the spindle is at the lowest point of travel... is this something worth the effort?

Yes, do it - the further apart the bearing blocks are placed on any axis the stronger it will be, up to a point.

mocha
19-09-2011, 06:20 PM
thanks guys! :-)
I'm fairly happy with the state of the design for Y but the Z still needs some more work. Looks like about 150mm from the ball nut that moves the Y to the centre line of the spindle. Using HWIN 15mm rails would drop that to around 130mm, but 20 mm of those numbers are the spindle mounting plate! The Z ball nut is 94mm from the spindle centre. But it's difficult to see with these crayon drawings :rofl:

Jonathan
19-09-2011, 06:49 PM
As long as the ballnut is directly between (zero distance measured parallel to X-axis ... hard to describe) the two Y-axis rails then I think 130mm will be fine as the aluminium plate in between is very strong and should not flex much. If you have not already try setting the rails/blocks on the Z-axis into the plate - i.e. mill a slot for the rail and pocket for the blocks. That will reduce the distance further though you'll have fun fitting the Z ballnut as that will also require a cutout.

mocha
19-09-2011, 08:06 PM
Yep, I get what you mean about putting the ball nut between the rails. I might save the pocketing for V1.1 (if it turns out to be a problem!) I'm already surprised at the amount of machining that the design is going to require, I had thought of this as just bolting it together, ha!

JAZZCNC
19-09-2011, 09:14 PM
I wouldn't drop the Gecko's I have a G540 here and it's beautifull bit of kit, thou that said I would go with 203v's much more flexable with extra growing room. That said I'm slightly bias because thats what's on my machine. IMO they are the Dog's b@#/?ks and worth the extra.

m_c
19-09-2011, 10:37 PM
The main benefit of Gecko's is the microstep to full step morphing, plus they're small!

I've got 2 G251s in my lathe, and can't fault them.
I did think about getting the G540, but it wouldn't of fitted in the control housing, and I already had the SmoothStepper and C23 break out board so didn't really need any of the additional features of the G540. If I was to start from scratch, I probably would go for the G540, as it does most things you need (inputs/outputs/0-10V speed control) in one plug and play package. Just add power, a parallel cable, some steppers and resistors, and you're good to go.
If you do still consider the G540, look at the GC-02 and GC-04 connectors from www.homanndesigns.com (http://www.homanndesigns.com), as they make wiring even simpler!
Also, the Gecko customer appreciation sale must be about due, so if you're not in any hurry, keep an eye out to get the drives even cheaper than what the UK importer charges :wink:

mocha
19-09-2011, 11:28 PM
Thanks guys!

I'm just reading about the 540's and doing a side by side with the Kinco 2M880N (that was top of my list...)

I don't know what "microstep to full step morphing" is, or if there is any advantage of "256 microsteps", my reading list just got a bit longer!
:-)

Jonathan
19-09-2011, 11:31 PM
I don't know what "microstep to full step morphing" is, or if there is any advantage of "256 microsteps", my reading list just got a bit longer!
:-)

The morphing thing is, from memory, switching to full step mode when the motor is run at higher speed. It's a good plan as you get a bit less torque when microstepping...
I wonder if the gecko's use vector current control, like the 2M880N, bet they don't...could be wrong.

To me it's obvious - get the 2m880N as that's about 50% higher voltage than the gecko which should have a much greater affect than the rest of it.

No point in using 256 microsteps ... that high wont help with accuracy (only cheating yourself if you think the resolution is 256th of full step resolution). As long as the driver does up to about 10 microsteps that's fine.

More info on microstepping here, here and here:

http://www.micromo.com/microstepping-myths-and-realities.aspx
http://www.euclidres.com/apps/stepper_motor/stepper.html
http://reviews.ebay.com/Microstepping-Versus-Gear-Reduction_W0QQugidZ10000000002352664

Disclaimer :
Other websites are available ...
Your blood pressure can go down as well as up if you choose to read them ...

mocha
20-09-2011, 12:07 AM
Thanks Jonathan, lol, I got as far as "Magnetic backlash" and decided I need far more coffee than I've had already! I'll leave it for tomorrow! :-)

JAZZCNC
20-09-2011, 12:52 AM
I wonder if the gecko's use vector current control, like the 2M880N, bet they don't...could be wrong.

If by vector control you mean current recirculation while stood still then yes they do.



To me it's obvious - get the 2m880N as that's about 50% higher voltage than the gecko which should have a much greater affect than the rest of it.

Only really apply's if your motors are good for the extra voltage.? Most nema 23's are not when wired parallel.!! . . . . Over rating a motors voltage will give extra speed but it also creates extra heat, iron loses etc which then slowly damages the motor shortening strength and life.

Jonathan
20-09-2011, 01:09 AM
If by vector control you mean current recirculation while stood still then yes they do.

No, I mean vector control. I wont try and explain as it's a tricky one:

http://en.wikipedia.org/wiki/Vector_control_(motor)

http://www.eng-tips.com/faqs.cfm?fid=1062


Only really apply's if your motors are good for the extra voltage.? Most nema 23's are not when wired parallel.!! . . . . Over rating a motors voltage will give extra speed but it also creates extra heat, iron loses etc which then slowly damages the motor shortening strength and life.

Mocha is using the same motors as I am, or at least very similar - 3Nm Nema 23 with low inductance. I've been running mine on 75V since I got them well over a year ago with no ill effects. The highest temperature I have ever recorded was 60 celcius (so at least 25C below rated) on the case which was on a sunny day when the machine had been running for a couple of hours. Most of the time they linger around 45C. I check it regularly as I have an infra-red thermometer to hand and it's something to do whilst the machine's running...good for getting estimate of cutter temperature too.

mocha
20-09-2011, 01:11 AM
The main benefit of Gecko's is the microstep to full step morphing, plus they're small!

:wink:

Thanks, m_c, I'll face the rigours of JB's reading list in the morning! I'd seen the Homann site, it was very helpful and the ease of installation of the 540 is a bonus although sorting the electricals doesn't concern me as much as some of the other decisions! (It's just like wiring a plug, lots of plugs! )

I'll certainly keep an eye open for the sale! Thanks for your help!

JAZZCNC
20-09-2011, 01:34 AM
No, I mean vector control. I wont try and explain as it's a tricky one:

No need to explain I know all about torque vecter drives but are you sure these drives mean the same.? I don't see any referance to torque vector control but I do see current limiting (Half current).?



Mocha is using the same motors as I am, or at least very similar - 3Nm Nema 23 with low inductance.

If these are the motors with 3mh inductance I've seen specs sheets flouting around for then your running them approx 20V over spec, this will sooner or later have an affect.!!

Jonathan
20-09-2011, 01:36 AM
I'll compare with PM752 driver as that's what I have. Copied from Gecko site:

3.5A 50VDC maximum PM752, 75V & greater current
Digitally filtered STEP, DIRECTION and DISABLE inputs same
3.3V and 5V logic compatible inputs Same I think, can go higher with resistor. Also if you accidently pop one with 75V it's easy to replace the optoisolator :naughty:
300 kHz maximum step pulse frequency same, but who needs more than about 50kHz anyway
Top settable Adjust trimpot None
Power LED indicator same
No user settable jumpers PM752 has internal jumpers for motor direction and something else I can't remember ... not much use really
20 kHz switching frequency I'm pretty sure PM752 is much higher, will check it with scope tomorrow
Mid-band resonance compensated Probably none
Microstep to full step morphing at higher speeds Probably none
Small size Nobody cares
Four layer PCB That just means they weren't good enough to make it 2-layer
Discrete all N-channel MOSFET full bridge design same
14A rated power MOSFETs PM752 mosfets are 33A and 100V, so will almost certainly have lower Rds and therefore power dissipation.
3.5mm 12 position connector with screw type terminal Pluggable, which in my opinion is better
Recirculate mode while the motor is stopped, reducing motor heating Probably none
70% current when stationary 50% on PM752 so possibly lower power dissipation - possibly not due to the above, can be changed with a bit of effort

Maybe I should have compared with a different Gecko, but you get the idea.

One more for your reading list:

http://www.scribd.com/doc/29405701/Closed-Loop-Control-of-Stepper-Motor-without-Position-Sensor

Looks like vector control is one up from resonance damping.

Jonathan
20-09-2011, 01:46 AM
No need to explain I know all about torque vecter drives but are you sure these drives mean the same.? I don't see any referance to torque vector control but I do see current limiting (Half current).?

http://www.zappautomation.co.uk/product_info.php?products_id=20&osCsid=af9a458a4de2bf810aec77476e499bf4

'The application of advanced vector control algorithm greatly reduces noise and vibration of the motors during operation, '

The link I gave in my previous post explains it better. In particular this is interesting:

'The motor operates in continuous mode rather than conventional stepping mode.The audible
noise and resonance effects associated with conventional stepping mode are effectively
eliminated.'

That sounds alike to the Gecko - although it's not full stepping at higher speeds it's applying a sine wave to each phase, so operating it like a 'normal' motor not stepper motor. Bound to be quieter and more efficient for obvious reasons.

I'm intending to implement vector control on the stepper driver I'm designing/prototyping.


If these are the motors with 3mh inductance I've seen specs sheets flouting around for then your running them approx 20V over spec, this will sooner or later have an affect.!!

Well it's been 16 months. I'll let you know if they break!
The formula you are probably using to say they are 20V over-spec (32*sqrt(L)) is almost certainly an oversimplification / guideline. I think the fact my real life experience with these motors shows the temperature is fine at 75V says it all.

JAZZCNC
20-09-2011, 01:53 AM
Maybe I should have compared with a different Gecko, but you get the idea.


Yes maybe you should have because I have 3 PM752's sat on a shelf that where taken off my machine and replaced by 203v's and I can tell you again from experience the Gecko's knock the spots offf them in every department. . . . . I wouldn't swop you one of my 203V's for 10 PM752's. . . . But hey if your happy with them that's all that matters.!

mocha
20-09-2011, 01:56 AM
ah, looks like this might be a duplicate... I'll put it in here as I'll never find it again otherwise! :)

Breakthrough 1: Total improvement of performance
2M880N adopts high performance DSP motor control chip, current control will be more precise if combined with space vector current control technique. Low frequency vibration of stepper motor will be much improved.
2M880N optimize motor power drive circuit, so even the drive current is raised 2A higher than 2M860, the temperature of drive stays almost the same, meanwhile the working noise is lower.
Subdivision accuracy is 3 times higher than 2M860, the maximum pulse input frequency is 400 KHz.

Breakthrough 2: 5 functions are newly added, easy to use
The five newly added functions such as alarm output, single/double pulse, motor parameter adaptation, phase memory and trial operation will bring wholly new use's experience.
The motor adaptation function could detect the motor it drives and allocate the most appropriate parameter to make sure the motor run in the best condition. Open collector alarm output, the output port could adapt with the most of PLCs. Host computer could monitor the drive working condition at any time which improves controllability of the whole equipment. Phase memory could assure stepper motor won't vibrate after power-off restart. Clients don't have to worry about unplanned outages anymore.

Features:
Motor parameter adaptation
Drive trial operation
Phase memory
Single/double control pulse input
Automatic semi-current
Optocoupler isolation ERR fault signal output, the maximum current is 20 mA
16 mirco-step. Maxium is 256
Overvoltage, undervoltage, overheat, overcurrent alarm


All of this is well over my head so I'm greatful for the discussion about it.

I'm non the wiser, but I am much better informed! :-)

Jonathan
20-09-2011, 02:02 AM
Yes maybe you should have because I have 3 PM752's sat on a shelf that where taken off my machine and replaced by 203v's and I can tell you again from experience the Gecko's knock the spots offf them in every department. . . . .

Were you operating the PM752 on 75V, or very close to? If not then it's a pretty meaningless comparison.
The 203's should be better than the PM752 as the PM752 does not use vector current control. Compare 203's to 2M880N and the latter will be better as Vector control > resonance damping

Edit: should have checked the 203's rating. They're quite similar, except the price!

JAZZCNC
20-09-2011, 02:19 AM
Were you operating the PM752 on 75V, or very close to?

Yes and actually on the very transormer and with same size caps I gave to James/Luke.

Lets just leave it that I Know what I know regards Gecko's V's Pm752's and I'll reserve judgement on the 2m880N untill I've had actual hands on experience. . . Which I'm sure will happen at some point in the not too distant future.?

m_c
20-09-2011, 11:37 AM
There is a new range of gecko drives on the way with all sorts of goodies, including vector drives. Marriss has just posted details about the first one over on the zone, which is a pretty conventional drive but with standalone functionality.
I'm more interested in the closed loop stepper driver, which is part of the new drive range.

mocha
20-09-2011, 05:06 PM
Thanks m_c, just had a read through that post from marriss, seems like there might well be another g540 in the pipeline? If I'm right that the G540 has 4x g250 or G251 in it(?) the New G215 might just drop in! I noted too that there is at least two versions of it;

"recent mods to the sense lines and the new trim pot location"

either way, if the new ones come out at the end of September, it might drop the price of the "old stock"enough to get me in the game!

Not sure how most of it affects my type of home brew machine. I can't think of a way I could use it other than Arduinocnc??? lol

Here's the post in question for those with an interest;
quote

First off, in our future new products we leaving CPLDs behind and be will using FPGAs instead. For the non-technical types, CPLDs and FPGAs are programmable ICs that replace a boatload of discrete logic such as gates, counters, decoders and such which are necessary to build motor drives.

The difference between CPLDs and FPGAs is the size of the 'boatload'. A CPLD replaces about 20 discrete 7400 logic series ICs while an FPGA replaces over 200. Think of it as moving from a 500 square-foot studio apartment to a 5,000 square-foot luxury home.

That's what it feels like to an engineer; all the stuff that wouldn't fit in the apartment now fits in the home plus lot more things you'd always wanted to get. It's like you died and went to heaven.

The G215 is a step motor drive. It's like the G203 (lot's of protection circuitry), like the G201X (DIP-switch settable features) and like a G901X (a can't be fooled step pulse multiplier). All the goodness of the best of our drives all rolled into one.

That uses up only 1/3 of an FPGA.

The G215 has a MODE switch on it's internal 10-position DIP switch. When 'OFF', it's an ordinary step motor drive. When switched 'ON', it changes personality.

It becomes a motion controller with its own built-in step pulse generator. The STEP input becomes a CW limit switch input and the DIRECTION input becomes a CCW limit switch. Two trimpots set independent CW and CCW motor speeds. The DISABLE input becomes a RUN/STOP command. Another trimpot sets the accelerate/decelerate rate. It now performs the most common industrial applications for step motors; run between two limit switches at two different digitally set speeds with the option of stopping and restarting motor motion between the limit switches. The FAULT output indicates when the motor actually stops after deceleration. All motion is digitally generated with digital accuracy.

This uses up another 1/3 of the FPGA.

The remaining 1/3 of the FPGA is used for several purposes:

1) In a perfect world, step motors would be perfect and need only sine and cosine currents to move them. In the real world, step motors have non-linear characteristics which requires a compensating distortion of the sine and cosine currents that drive them.

You may have noticed this if you use step motors optimized for high holding torque. They have pronounced vibration at low speeds even when driven with perfect sine-cosine drives.

These motors need to be driven with a drive that has a compensating distortion of its current profile.

Now imagine a drive that has a family of 8 current profiles stored in it ranging from undistorted to significantly distorted. The profiles are arranged in FLASH memory in the G215 in order. The best profile for your motor is selected by turning a trimpot; you turn the trimpot until your motor vibration goes away. Again, all digital. The trimpot goes to an Analog to Digital converter that selects the best profile of your choice.

2) There is a whole bunch of reasons why a drive might not work.

A miss-wired motor, a motor winding that isn't connected, a short circuit, bad STEP and DIRECTION input signal quality or polarity, insufficient or excessive power supply voltage, drive overheating, etc and etc.

Our existing protected drives light up a FAULT indicator for some of these problems or give no indication at all for others.

The G215 will use a 16 error 'blink code' to identify why your motor isn't running. The G215 has two LEDs; a red and a green one. If everything is OK, the green LED will be a solid green.

If there is a problem like motor winding 'A' not connected, the LEDs will blink 'RED, RED, RED, GREEN, pause, RED, RED, RED, GREEN' pause, and so on. The code for that sequence will be listed in the manual as "Winding 'A' not connected". This will make trouble-shooting much easier.

The G215 will become available in late September. It will be the first of our new line of FPGA drives. Many other new products will follow in the next 6 moths based on this switch to FPGA logic drives.

Cost? Equal to or less than our current drives. Why? because so much functionality now moves inside the FPGA and no longer requires external analog circuitry.
end quote

Jonathan
20-09-2011, 05:32 PM
To save everyone finding the relevant thread:
http://www.cnczone.com/forums/gecko_drives/135952-g215_drive.html

Interesting that he makes using an FPGA sound like it's something special/unique to use, or at least that's how it reads to me. PM752, and no doubt many others in the range, also use FPGAs as it's just easier. I'd use one if I thought I had a chance of soldering BGA's!

The original comparison was 540 vs 2M880N - there the latter surely wins due to the better control algorithm and ratings. 2M880N vs 203V is less clear cut ... until I see a fair test done between the two I would go for the 2M880N as it seems to still have the better control algorithm, and it's cheaper? (Correct me if I'm wrong, not sure how much the 203V is?). I'd happily do the comparison properly, i.e. at different feedrates and accelaration with a few different motors plus record waveforms with oscilloscope, but currently I own neither drive.


Yes maybe you should have because I have 3 PM752's sat on a shelf

Are they for sale :naughty:?

JAZZCNC
20-09-2011, 05:32 PM
You have to admire Marriss for the both way he's so transparent and gives clear no bull shit information and how he runs his business.
How meny large company directors would take the time to post and directly chat on a forum.? . . Not too meny mi thinks.!!

The warranty and service Gecko gives is unrivelled in my experience, even if it's your own stupid fault you've fry'd the drive (Which it often is) I've seen them replace units FOC. . . . Now thats service.!! . . . .Try that with a chinese manufacturer or even UK distributor and watch them :lol: you out the door.:exclaim:

JAZZCNC
20-09-2011, 05:45 PM
Interesting that he makes using an FPGA sound like it's something special/unique to use, or at least that's how it reads to me. PM752, and no doubt many others in the range, also use FPGAs as it's just easier.

First Jonathan I wouldn't even start down the road of trying to discredit what Marriss fremarnis say's, you'll make your self look pritty silly.! . . He's probably forgot more than you'll ever know lad.!



Are they for sale :naughty:?

Nope I use them for testing motors and setting up machines.!

Jonathan
20-09-2011, 06:04 PM
First Jonathan I wouldn't even start down the road of trying to discredit what Marriss fremarnis say's, you'll make your self look pritty silly.! . .

I wasn't intending to discredit him - only point out that I didn't like the style of the first part of that post. Can't fault the content.


He's probably forgot more than you'll ever know lad.!

When I'm his age hopefully that won't be true...

m_c
20-09-2011, 07:22 PM
I've got to admit, one of the reasons why I like Gecko stuff, is how open Marriss is, and his willingness to discuss things on forums. Alot of other companies would do everything they could to prevent alot of that info making it into the public domain. Plus they're one free replacement if you blow it up, is an added bonus.

I know JohnS on here had issues with earlier drives, so they're not perfect, but it's very rare to hear of anybody having problems now.

As for the new G540, there is a GM540 in the works, but I don't think it adds anything in the terms of drivers, just that it has a built in motion generator, and has a RS485 interface. Details are on the gecko forum at http://geckodrive.com/forums/showthread.php?93-(GM)-Product-Line-Feature-Request



Jonathon, if you want to try a G203V, I've got one sitting here that I've never used, and won't be needing to use for a while that you could borrow to try.

JAZZCNC
20-09-2011, 07:26 PM
When I'm his age hopefully that won't be true...

Yes and I wouldn't bet against it Jonathan but unfortunatly today and for a good while yet you don't so I wouldn't go there.!! . . . . . Now give me a hug and lets play nice. .:rofl:

mocha
21-09-2011, 03:06 AM
more updates!
G540, GM540, 2m880n decision pending on Gecko sale / price info.
supported rail to 25mm all round... maybe! or if funds allow, at least profiled rails on Z :)

Also toying with the idea of putting some isolation rubber bobbins between the frame and the surface, but as I have some 50mm rubber horse mat (don't ask!) that might work better than ny previous idea of bolting / bonding it to the floor.. absorb any vibrations / resonance rather than ignore them(?)
:)

Rogue
21-09-2011, 10:36 AM
Also toying with the idea of putting some isolation rubber bobbins between the frame and the surface, but as I have some 50mm rubber horse mat (don't ask!) that might work better than ny previous idea of bolting / bonding it to the floor.. absorb any vibrations / resonance rather than ignore them(?)
:)

You have mats for a rubber horse? Awesome :lol:

The mats are designed to give all that energy somewhere to go, so as to protect the horse's legs. They sound like they would be an excellent idea though it would be worth trying to find out how they react to any chemicals they might be exposed to in the workshop. While they should be able to handle a variety of things - they are designed for stables, after all - I am not sure how "non-natural" products might affect them.

Best way to find out is to try it - and that way we can learn from your experience as well!

mocha
21-09-2011, 04:45 PM
BOOM BOOM! :rofl:

I imagine that they should be hardwearing enough.. but it'll be interesting to see how they deal with the various types of swarf. I might try pads of it under the frame first before I start dragging sheets of it around. It's very heavy and one of the most akward things I've ever tried to move.

I've got one down in the workshop and that's been fine with garage use, oil, petrol and most types of abuse I've thrown at it, oh and apparently they can be used for horses to stand on too!

:lol:

mocha
01-10-2011, 10:27 AM
Streuth! Only 25 days to go!

As mentioned elsewhere, trying to get precise measurements for items I don't yet have in my hands has been frustrating! The details are slowly filling themselves in... Instead of building to "My ideal" of 650 x 650, I'll build it around ready made sizes all the other bits will be off the shelf standard stuff too.

I'll put pulleys into it at some point, after getting it working, dust extraction system, acoustic cabinet and other items are ahead in that list.

In searching out info I came across a guy who had reported favourably about using the rubber underneath idea,although he used anti vibration feet http://www.5bears.com/cnc01.htm , near the bottom of the page. Nice build story too.

Rummaging in a draw, I found an old combined 16 key and mouse controller called an N52te which might get do the job as a pendant...

Swarfing
01-10-2011, 01:22 PM
I have a Nostromo (N52) too and there is a thread somewhere on the net with a configuration tool to use it under EMC2.

mocha
01-10-2011, 03:33 PM
thanks, just found it. I'd done a quick search on Mach3 and n52 but found nothing. Looks like it might work?

JAZZCNC
01-10-2011, 04:45 PM
Let me have it and I'll getting working for you.!. . . Thou I may lose your return address if I like it. .:naughty:

Post the link to the info or anything about the pendent and I'll have a look to see I figure making it work with Mach. . . It will probably just need a plug-in or script writing/altering.


I would Put a post on the mach forum and pritty sure someone will know about it.

mocha
01-10-2011, 07:31 PM
lol, it's designed for left handed use...but it comes with some programming software which doesn't get in the way of game software.. just sends keypresses to the PC.. I'm assuming here that mach 3 has shortcut keys?

here's some pics;
46574658

mocha
01-10-2011, 07:42 PM
here's a better one; there's three switchable keyboard maps and macros too.
4659

Swarfing
01-10-2011, 10:01 PM
Heres the link to the thread i was thinking of and the software you are looking for is called PYSTROMO

http://www.linuxcnc.org/component/option,com_kunena/Itemid,20/func,view/catid,18/id,4573/lang,german/

mocha
02-10-2011, 01:20 PM
Bookmarked! Thanks for that. Another subject to explore. :-)

mocha
03-10-2011, 01:13 AM
Z axis question... I've read that minimising the distance from the spindle to the Y axis is a good thing to prevent flexing. Is that it or are there other reasons to do this??

What I suppose I'm asking is does getting it wrong affect the load that the spindle can handle or is there more to it?

thanks

JAZZCNC
03-10-2011, 01:49 AM
Z axis question... I've read that minimising the distance from the spindle to the Y axis is a good thing to prevent flexing. Is that it or are there other reasons to do this??

What I suppose I'm asking is does getting it wrong affect the load that the spindle can handle or is there more to it?

thanks

Well it don't really minimise flex as so much as it doesn't waste cutting area.! But another, better reason IMO, to minimise offset is to help with balance and reduce un-even loadings on both Y and X Axis bearings.

There are far more important areas on a Z axis that affect flex. . . Front Plate thickness and design combined with bearing/rail placement have far more impact than offset from Y axis.
A lot will depend on material and rail/bearing type in which is the best way to go about designing a Z axis with minimum flex.! . . . . You don't always have to use thick expensive material either and thinner material can be used with the right design.

Here's one that use's 9.5mm Ali and would be very strong.

Jonathan
03-10-2011, 11:46 AM
Deleted...
[Duplicate post, not sure how I managed that given the time restraint]

Jonathan
03-10-2011, 11:47 AM
Z axis question... I've read that minimising the distance from the spindle to the Y axis is a good thing to prevent flexing. Is that it or are there other reasons to do this??

Increasing that distance clearly increases the turning moment which results in the magnitude of the forces on the Y-axis bearings being greater. Also, for the same reason, if the Y axis ballnut is not directly between the Y-axis linear bearings then, for forces parallel to Y, you will get a lot of deflection as the parts in between don't have to flex much at all - it just 'rotates' about the ballnut since the ballnut is essentially the only support in that direction.

mocha
03-10-2011, 02:22 PM
Thanks chaps! Jazz, that's alloy porn! LOL, Very pretty. Is it in use / used or planned for the next one?

The location of the supported rails on their side is unusual isn't it? Most of the ones I've seen seem to be in the Z; up/down axis usually one facing up and one facing down. Any reason for doing it that way?

I've attached a few shots of something I was playing with to help me understand what I am trying to do... It's not to scale! more of a schematic block diagram sketch to see if it could be done, but comments are most welcome.

I've left out some of the elements so it can be seen easily. (like the colums parralell to the Z ballscrew joining the upper and lower Y axis motion, joining the upper and lower blue box sections etc.) and I've shown as bars things that could be plate etc. The purple areas are the supported rail, any other questions just shout. If you want to play with the Sketchup file PM me and I'll send it over as Google wont let me upload it, they must have standards! lol.

As I said it's not to scale and not an opimised design, putting the ball screw mount under the 3rd Y axis support, moving the Z ball screw closer to the spindle, etc. could all help to reduce the overall footprint - although the overall size should be spindle + ballnut + Y axis support? could drop it in the region of under 200mm??

I'm wondering if the ideal position for a high sided frame design be putting the whole of the Z axis UNDER the Y axis? (but I might have OD'd on the coffee this morning LOL)

46754676467746784679468046814682

JAZZCNC
03-10-2011, 03:55 PM
Thanks chaps! Jazz, that's alloy porn! LOL, Very pretty Is it in use or planned for the next one?

No not in use, Like a lot of stuff I do and make it was designed to make best use of cheap available materials, in this case the machine was going to be for a guy who had bought some really cheap 150x9.5mm Ali and was on a real tight budget.
It actually never happened due him losing his job scraping the project, I ened up buying the Ali off him which luckly for him was is only outlay upto that date.




The location of the supported rails on their side is unusual isn't it? Most of the ones I've seen seem to be in the up/down axis usually one facing up and one facing down. Any reason for doing it that way?

If you mean the Y axis rails then No they where just drawn that way, they could go either way round. The back plate and rail was just put there for affect really and this was just quick mock up drawing really not actually a finished design in any way. . . . . . Only posted to give some idea how thinner material could be used put still give a stiff Z axis.!!

Regards your design I'm slightly struggling fully under stand the layout but my first initial reponse would be "WHY".??? . . . . Why all the complexity when you won't really gain any extra support over a conventional Z axis.

The way you have it drawn you are still relaying on just 2 rails/bearings and if the bit with rail on top thats jutting out from the Y axis with rails top n bot is not directly mounted to the gantry sides or X axis bearings plate then your in big trouble.!

If Z axis was supported on 4 sides with rails/bearings then yes I could see the bennifit but can't see any how you have it now. . Plus still the jutting out bit would need attention.

If you have the length and done right then the wide gantry with central Z axis (Ala Mech mate) can be very strong it just cost's MORE, more expense, more real estate, more work.! . . . trick is working out if it's worth that much MORE.:question:

Swarfing
03-10-2011, 05:06 PM
So what you have there is a copy of the MECHMATE? that is the type of arrangement they use.

mocha
03-10-2011, 05:13 PM
470347044687
[edit: added pics 2 and 3, x axis in yellow! that might be clearer and make more sense!!]

Apologies for poor quality drawings!!!:redface:

Thanks Jazz!

Yes, the image probably doesn't make too much sense as it is, LOL, this might be clearer, although not necessarily better! :-)

In answer to your points;
Why? I'm thinking that the closer to the spindle that the supported rails of the Z are, the less leverage that can be applied to them, so the spindle mount is also the supported rail bearing mount.... This of course assumes that fitting the rails to the spindle is a good idea! lol



The way you have it drawn you are still relaying on just 2 rails/bearings and if the bit with rail on top thats jutting out from the Y axis with rails top n bot is not directly mounted to the gantry sides or X axis bearings plate then your in big trouble.!yep, ammended pic above


central Z axis (Ala Mech mate) Not familiar with that design, will go find it.


...can be very strong it just cost's MORE, more expense, more real estate, more work.! . . .

Yep, the real estate is going to be my main issue on an 800 x 800 table,



trick is working out if it's worth that much MORE.

LOL, and therein lies the answer! I'm guessing that if it was worth it, evolution would have saved it and it would have been done by now!

Interesting exercise in getting my head around some of the things that I've only read about so far.

mocha
03-10-2011, 05:26 PM
So what you have there is a copy of the MECHMATE? that is the type of arrangement they use.

Thanks, will go have a look at it!

:-)

JAZZCNC
03-10-2011, 05:40 PM
4687Thanks Jazz!

Yes, the image probably doesn't make too much sense as it is, LOL, this might be clearer, although not necessarily better! :-)


Nope certainly wouldn't go with that layout.! . . . .Just think of all that weight levering on the Y & X axis bearings.? . . . Bad idea.:thumbdown:

Go check the Mechmate out and you'll see how it could be done, thou it will make short work of your 800mm.!!

mocha
03-10-2011, 06:21 PM
I can't pretend I understand the reasons, but I do agree with the conclusion! I'll stick with using a "traditional" Z axis if only because of time and cost restraints. :-)

Apart from the length of the Z ball screws, 400? 450?? I don't think I need to worry about the Z just yet. Still got other areas to sort in the next three weeks!

JAZZCNC
03-10-2011, 08:58 PM
Mocha sorry didn't see this before but Doing it this way means the X axis is unsupported from under neath and could flex.?

I would still do it with this configuration but lift the whole thing up and sit it on the X axis bearings, basicly making a rectangle box section frame.
Like I say Spindel supported on four sides would be better but I see why you have done it this way to keep the width down, thou I think the extra strength would be worth the width loss.!

Swarfing
03-10-2011, 09:22 PM
Mocha take a look at Rogers build, this is similar to what you want to do, he told me he would have taken a more traditional approach if he were to do it again.

http://www.mycncuk.com/forums/showthread.php/1160-5-Years-in%21

mocha
04-10-2011, 05:06 PM
there's some serious work gone into that! He mentions some sort of design flaw??

JAZZCNC
04-10-2011, 05:55 PM
there's some serious work gone into that! He mentions some sort of design flaw??

Ye I big design flaw.??. . . . He used springy unsupported round rail.!

Jonathan
04-10-2011, 06:20 PM
The location of the supported rails on their side is unusual isn't it? Most of the ones I've seen seem to be in the Z; up/down axis usually one facing up and one facing down. Any reason for doing it that way?

Putting one up and one down evens up the load ratings. Clearly the supported rail bearings are weaker in one direction as that portion of the bearing is 'missing'. Sure I've mentioned this before, but nevermind. I calculated it once by measuring the angular position of each of the rows of bearings in a SBR25 block and from that calculated the relative force rating. The figures I ened up with for the SBR25 blocks was 980N (from datasheet) and -340N (calculated). So clearly if both rails are the same way you get 1960N in one X direction and only 680N in the other, however if they are opposite it's 1320N for both up and down, and even for X directions.

But... there's more to it than that. The round rails are connected to the aluminium support by a series of bolts into the rail from underneath. This connection isn't actually that strong (though clearly it's a whole lot better than nothing), so the rail will slill bend on the support with a force (if the beraings are mounted facing) parallel to X, or if the bearings are mounted on the same side they'll deflect with forces parallel to Z.
So it's debatable which is best...the force ratings above are a lot greater than what you will actually encounter, so perhaps deflection is more important because as the force increases the deflection will be greater. One day maybe I'll measure it.


Mocha take a look at Rogers build, this is similar to what you want to do, he told me he would have taken a more traditional approach if he were to do it again.

http://www.mycncuk.com/forums/showthread.php/1160-5-Years-in%21

Interesting that he used a worm drive...

This is similar to what was thinking of doing, and may still do, for my machine. The difference is I also considered having two ballscrews on Y:

http://www.mycncuk.com/forums/showthread.php/3700-Two-ballscrews-on-both-X-and-Y-axis

Adding a third rail would help, but when the two rails are profile rails I don't think it will make much difference, as long as what the rails are mounted on is strong, as they are rated for an equal load in all directions.

mocha
05-10-2011, 01:46 AM
No, I think he said something about it binding somewhere?? and having to "ease it" with a hammer (?I think...)

Although I don't intend to try it, I do still wonder if mounting the rails directly onto the spindle, parallel to the Y axis has any merit, especially if they were profiled rather than supported rail... file that one under mark 2 version ideas! :confused:

However, I've been working on the work area, (bed / table element) I wanted it to be adjustable to minimise the extension of the Z axis but still have the flexibility to accommadate different work heights.

The thought of driving the table up or down was discarded as too costly, handcranking, better but too complex, but I think I've found a way that might just work. Any comments welcome!

My work area, inside the frame, is something like 850 x 900. By making the bed bolt into place inside that frame, I get the bed as in the example on the left of the pic. Undo the 4 bolts, turn the bed other way up and rotate through 90 degrees and the bed is now 70mm higher, now supported by the box section on the other sides and locked back in place with the bolts again, now on a different side. By using a couple of 70mm box section "spacers" and longer bolts, I could get another 70mm too.

I'm not expecting to be changing heights every day... do those of you with some sort of adjustment on the bed height find that there is a sweet spot where it stays most of the time, or are you constantly fiddling with the height of the bed?
4707

mocha
20-10-2011, 06:41 PM
There's been no updates for a while as I've been assimilating Jonathans reading list! LOL. Thanks to everyone who has helped, guided, suggested and corrected my understanding. I've progressed from not knowing what I don't know to knowing enough to know I don't know enough!

The design is done, I've put the crayons away, the fiddling with it over and now it's time to get some parts to fill it! So with a little luck I'll come back in a couple of weeks with some goodies and get cracking with it. Next target will be getting the frame parts machined and assembled and the unit constucted by the end of November!

JAZZCNC
20-10-2011, 06:45 PM
The design is done, I've put the crayons away, the fiddling with it over and now it's time to get some parts to fill it! So with a little luck I'll come back in a couple of weeks with some goodies and get cracking with it. Next target will be getting the frame parts machined and assembled and the unit constucted by the end of November!

Cmon then lets see the doodle's.!!

mocha
20-10-2011, 06:55 PM
lol, I'm just heading out the door right now, but I'll try and upload something later! :-)

here's an early version of the frame! :heehee::heehee:

4758

mocha
21-10-2011, 08:18 PM
4762doodle attached, front view.

mocha
06-11-2011, 08:32 PM
well that was an interesting trip! lol, she seemed to think that wandering around markets looking for engineering bits did not form a constructive part of something called a "hol-i-day-to-geth-er"... what ever that is... didn't stop her raiding the fake handbag shop for all her friends though!
I only managed to bag some Kinco drivers before I was reeled in. I do get to go again on my own and I can meander through some of the most amazing product sellers I've ever seen. Imagine everything in the RS and farnell catalogs in a 9 storey building... and someone removed the index! lol, I spent a half day there and didn't get to see all of just one floor. I did see some other stuff there too, a big wall with a roof and a bigger wall on the top of a mountain and a house with 999 rooms... and about 2 miles between each of them. other than that, an amazing place, looking forward to going there again.

mocha
17-11-2011, 01:25 AM
STILL awaiting my first delivery of bits, which are not due to arrive until the end of the month... :-(

I found a friend of a friend who fabricates for a living (and builds race cars in his spare time) and with some back scratching for a mutual 3rd friend he's agreed to look at the design from a fabbing point of view, the good news is that not only did he like what he saw, he's going to weld it for me, he can probably find me a good price for the metals too.

There's a couple of small changes he suggested to the way two of the corners are designed, in order to make it easier to weld up squarely, but otherwise it's looking good.

At the moment, I have one guy who will do the machining of the steel parts, another guy who will weld it all together, an assortment of advisors spread over 3 continents and a number of suppliers who are in the process of "supplying". One supplier who has let me down badly and one supplier who has been an absolute star and a number that are just dragging their small oriental feet!

LOL, This is turning into a international project management tutorial rather than a CNC build! :)

mocha
26-04-2012, 11:59 PM
Quick update on this slow moving build!

The good news is that the parts aquired list is getting longer! but the bad news is that the 900+ revisions of this design is not going to make it work. :-( Building a scale model exposed a major problem in the assembly phase. Which probably explains why I'd not seen others of that type of design. So, onto the mark 5.5! Nothing too ambitious this time. Fixed gantry and rotating head with 6 linear actuators to move the bed.

mocha
07-06-2012, 04:04 PM
<grin>

I'm shopping!

mocha
10-06-2012, 02:00 PM
I'm shopped!
:-)