HobbyCNC for Taig?

[noisillator]

OK, it seems there's not much reason to use separate drivers from Gecko (as opposed to the G540). By the time everything is done, the cost is nearly the same. Despite its performance, I personally feel the G540 is overpriced. It has features I don't need, and I gather that the price of this board was increased significantly earlier this year.

After searching for other products, I've come across the HobbyCNC kit:

http://www.hobbycnc.com/products/hob...oard-packages/

This is considerably less expensive, looks to be well supported, and on the surface at least, seems to have the features and performance needed to run a Taig CNC mill. I'm wondering if anyone here has used this product with their Taig, and whether there are any significant "cons" compared to more expensive drivers.

[DeusExMachina]

I run my Taig with a Hobby CNC, 36v psu and 270 oz-in motors. Rapids at 45-50ipm depending on how wells the ways are oiled...

The major con of the HobbyCNC controller is you have to assemble it yourself...Hope you're handy with a soldering iron. I personally didn't have any problems but I've heard of several damaging the chips because they waited too long on the via... The controller is a little hard on the steppers at low speed (they make a lot of noise, this'd be the midband resonance that the gecko's get rid of). The board isn't opto-isolated either so its possible, but rare that you may get a voltage spike back through the board and possibly damage the parallel port on your machine.

The HobbyCNC is limited to 42v input, so about the best you can do is a 36v power supply, this will severely limit your performance, for instance my motors to would like 48v to run at optimal power, so I'm losing 25% of my steppers top end performance right there. Most mid range nema 23 steppers except for the extremely small ones will want around 50v.

Personally, it may sound strange, and actually more expensive, but if you have the money, get 3 of the Gecko 203s and an opto-isolated breakout board. It may be years from now, but you will want a bigger machine, and when it comes time to convert it, you will already have the necessary drives to do so.

[jalessi]

Noisillator,

The HobbyCNC driver will work with the Taig mill however it may run a bit slower and have a little less torque.

A unipolar driver is not as efficient as a bipolar driver.

The second drawback is mid band resonance, Gecko's don't have that issue.

You may need to add harmonic dampers to your steppers to obtain the performance you are looking for.

Jeff...

[noisillator]

Thanks for sharing your first-hand experience with this DeusExMachina. Here are my comments on the points you made. Feel free to correct me anywhere you see an error in judgement.

I run my Taig with a Hobby CNC, 36v psu and 270 oz-in motors. Rapids at 45-50ipm depending on how wells the ways are oiled...

The major con of the HobbyCNC controller is you have to assemble it yourself...Hope you're handy with a soldering iron.

That's the least of my worries. I built my first vacuum tube radio kit shortly after the Beatles first came to America. My workbench at home includes a temp-controlled iron and all the other things needed to assemble PCBs. I also have access to SMT equipment at work, but these boards won't need that.

The controller is a little hard on the steppers at low speed (they make a lot of noise, this'd be the midband resonance that the gecko's get rid of).

Any idea how the Geckos eliminate this effect? Stepper drive circuitry is a little out of my field. Does the resonance affect low speed accuracy?

The board isn't opto-isolated either so its possible, but rare that you
may get a voltage spike back through the board and possibly damage the parallel port on your machine.

That shouldn't be an issue. I'll be using a desktop, and plug-in LPT cards are probably less than $5 now. I'd probably worry more about the cost to repair or replace the driver board.

The HobbyCNC is limited to 42v input, so about the best you can do is a 36v power supply, this will severely limit your performance, for instance my motors to would like 48v to run at optimal power, so I'm losing 25% of my steppers top end performance right there. Most mid range nema 23 steppers except for the extremely small ones will want around 50v.

Are you using the unregulated supply suggested by HobbyCNC? A full wave bridge with a 24V transformer will produce about 34VDC, but that's only with no load. The output voltage of an unregulated supply can drop quite a bit depending on the current draw, filter capacitance and transformer sag. Worst case, it might be pulled all the way down to 24V or less. I'm thinking I'll want to power this project with either a regulated linear supply or a switcher rated 36-40V. Maybe that's what you're doing (?)

Personally, it may sound strange, and actually more expensive, but if you have the money, get 3 of the Gecko 203s and an opto-isolated breakout board. It may be years from now, but you will want a bigger machine, and when it comes time to convert it, you will already have the necessary drives to do so.

To be honest, I doubt there's a larger machine in my future. The purpose for buying the Taig mill (and lathe) is to build several pieces of electronics equipment that I've been planning for some time. Once those projects are done, I'll probably sell this equipment. I'm not really into machining for its own sake, and I don't think I can stand anymore hobbies at this point in my life. Simple is better, if ya know what I mean.

[noisillator]

Noisillator,

The HobbyCNC driver will work with the Taig mill however it may run a bit slower and have a little less torque.

A unipolar driver is not as efficient as a bipolar driver.

Jeff, I read somewhere that the Taig mills can't really take advantage of motors larger than 140-160 oz/in. On that basis, I was thinking about buying the 205s from HobbyCNC. Is this really likely to pose a problem compared to other motors or systems? I should add that the projects I'm planning will require cutting a few radiused holes in 0.5" (13mm) aluminum plates, probably 2-3" (50-75mm) diameter.

The second drawback is mid band resonance, Gecko's don't have that issue.

You may need to add harmonic dampers to your steppers to obtain the performance you are looking for.

Jeff...

I'm not familiar with those. Is the dampener a digital device that works with the pulse timing/width, or some sort of resonant LC circuit? Do you have additional info about this (maybe schematics)?

[DeusExMachina]

Are you using the unregulated supply suggested by HobbyCNC? A full wave bridge with a 24V transformer will produce about 34VDC, but that's only with no load. The output voltage of an unregulated supply can drop quite a bit depending on the current draw, filter capacitance and transformer sag. Worst case, it might be pulled all the way down to 24V or less. I'm thinking I'll want to power this project with either a regulated linear supply or a switcher rated 36-40V. Maybe that's what you're doing (?)

Yes I'm using a regulated 36v power supply, if you can find a 40v, go for it

As far as the harmonics issue, there are two ways to get rid of it one is a mechanical dampener which is basically a disk thats built a lot like an old steam engine governor. Typically they seem to have 2-3 weights that move outward as the stepper spins up. Basically they're just added dampening mass.

It can also be dampened electronically. Basically (...I think...) as the rotor in the steppers start to speed up the phases in the mid band range end up being 180 degrees out of sync, so the flux ends up building at a certain harmonic, this can in fact knock the entire rotor out of sync, or at the very least reduce its over all torque. I'm not entirely sure how its dampened, but I'd imagine the gecko's do it by watching the EMI off the windings, when theres a condition for resonance it may temporarily increase the current to the current driving windings to give it the extra power it needs to overcome the resonance but I have no idea honestly.

Once the rotor is moving fast enough, there is enough stored inertia in the rotor to overcome the resonance and at extremely slow speeds the flux has time to dissipate before effecting anything.

This is kind of a problem with the hobby cnc's, for instance my machine gets extremely rough around 3-5ipm and its very easy to stall. It stays rough up until about 12ipm where the steppers start sounding smooth again. 1-2IPM is also very rough, but theres a lot of torque.

[jalessi]

"http://www.youtube.com/watch?v=EXdvgIG-lwk"]YouTube - Stepper Motor Anti-Resonance Control In Action

"http://www.youtube.com/watch?v=8Am69_F93yA&feature=channel_page"]YouTube - 65 ipm

I would use the 305 ounce steppers from Hobby CNC they are a good match for the HobbyCNC driver.

[MechanoMan]

OK, it seems there's not much reason to use separate drivers from Gecko (as opposed to the G540). By the time everything is done, the cost is nearly the same. Despite its performance, I personally feel the G540 is overpriced. It has features I don't need, and I gather that the price of this board was increased significantly earlier this year.

After searching for other products, I've come across the HobbyCNC kit:

http://www.hobbycnc.com/products/hob...oard-packages/

This is considerably less expensive, looks to be well supported, and on the surface at least, seems to have the features and performance needed to run a Taig CNC mill. I'm wondering if anyone here has used this product with their Taig, and whether there are any significant "cons" compared to more expensive drivers.

I am openly critical of overpriced hardware that doesn't do what it says, or is simply not competitive with alternatives.

The G540 is NOT one of those. They understood resonance issues better than anyone and the results are very, very good. The performance is vastly better than other drivers. The physical construction alone of that device is very advanced with the way the case and board are put together. These designers were experienced, I see that. This gives me much confidence that they've given excellent consideration to more subtle internal issues like capacitor ESR. A+++

And its anti-resonance features are no joke. Whether they're "simple" or complex is not the issue, they DO work as stated (have one, have verified), are of immense usefulness, and the competition does not have them.

From what I can tell, HobbyCNC uses the Allegro SLA7078 driver.
Like all Allegro products- THE MICROSTEPPING WILL NOT WORK FOR CNC. PERIOD.
Allegro used a very large minimum Ton-min time in all its products, including SLA7078. This establishes a lower limit to what the output current can be vs input voltage, as higher source voltages are used (which we need) the Iout-min goes down. At 35v some modes cannot even control the current in full-stepping. Microstepping means the target current will need to be much lower than the full-step current on the microsteps, and the Allegro drivers are simply incapable of doing this when source voltage is high and both the smoothness is gone and even the physical static (unmoving) rotor position is wrong. The max source voltage where microstepping still works may only be 6v or 12v.

Dropping to a very low source voltage will greatly lower the stepper speed though. The current will not rise fast enough to follow fast-changing steps.

Jeff, I read somewhere that the Taig mills can't really take advantage of motors larger than 140-160 oz/in.

No. Where did you hear this?? The 282 oz-in are "great", and kinda standard. They won't run out of torque at any reasonable milling speed with proper drivers. And they'll jog the headstock upwards- the heavy job- reliably at high speed. Now both the G540 and Smoothstepper will greatly increase the high-speed torque of any motor... maybe enough that a 160 might still be "acceptable", but will probably have limitations and basically a bad choice since 282's are cheap.

I take that back. I've got a 146oz-in stepper on my Sherline lathe and it's not really "pulling its weight" even with the G540 and Smoothstepper. I wouldn't put that on a mill by choice, not with $39 282 oz-in Kelings right there.

[noisillator]

Allegro used a very large minimum Ton-min time in all its products, including SLA7078.

Is that the 1.7uS spec? I assume you're not fond of the National LMD18245 either then?

Thanks for your comments on the steppers. I searched, but wasn't able to locate the exact article. I did find other mention of the "point of diminishing returns" being in the 140-160 range, but the material is dated. Maybe the one I remember was older as well.

Incidentally, I can appreciate your position regarding the engineering and performance of the Gecko drives. However, it is the purpose of engineering to solve problems. If those problems are relatively minor in terms of accomplishing the work, the additional engineering cost may not be justified. I believe that's the case regarding the Gecko controllers, at least from the perspective of a hobbyist. Searching the 'Net, I find a number of HobbyCNC users who seem entirely satisfied with their results. Also, I'm on the fence regarding resonance solutions, insofar as it may be possible to dampen it mechanically rather than electrically. Neither method is a perfect solution, but mechanical dampening appears to be an inexpensive add-on, particularly if one also has access to a lathe. In the end, this is all a matter of matching the cost to the job at hand, and to do that in a way that compliments both my DIY skills and the goals I've set for my projects.

Thanks again for your well-considered (and informative) comments on these issues.

[Jeff-Birt]

I sell 166 oz-in steppers that I recommend for the Taig. The inductance of the 270 oz-in range motors is such that you only see the increased torque at very low RPMs (unless you have a very high drive voltage.) If you are using a 36V or lower supply then the larger steppers will be a detriment. There is an article I have linked to several times here that was written by the guy that wrote the Taig lathe book, Tony Jeffrys I think. I don't have access to all my notes as I am out of town to attend a funeral. If you search you should be able to find it pretty easy. Not only does the engineering data show that the larger motors offer little or no benefit my own experience shows the same thing.

The G540 is a fantastic product. I recently sold one to a customer in Israel to replace a Mechtroncs driver. His reaction when he got it running (we were chatting over Skype) was, "Wow. Wow!". Gecko does a fantastic job on their stepper drives and they can't be beat for value for dollar spent. All the drives you will find built from commercial chipsets (except IMS and possible Lin Engineering chips) will be inferior.

[MechanoMan]

Is that the 1.7uS spec? I assume you're not fond of the National LMD18245 either then?

Thanks for your comments on the steppers. I searched, but wasn't able to locate the exact article. I did find other mention of the "point of diminishing returns" being in the 140-160 range, but the material is dated. Maybe the one I remember was older as well.

Incidentally, I can appreciate your position regarding the engineering and performance of the Gecko drives. However, it is the purpose of engineering to solve problems. If those problems are relatively minor in terms of accomplishing the work, the additional engineering cost may not be justified. I believe that's the case regarding the Gecko controllers, at least from the perspective of a hobbyist. Searching the 'Net, I find a number of HobbyCNC users who seem entirely satisfied with their results. Also, I'm on the fence regarding resonance solutions, insofar as it may be possible to dampen it mechanically rather than electrically. Neither method is a perfect solution, but mechanical dampening appears to be an inexpensive add-on, particularly if one also has access to a lathe. In the end, this is all a matter of matching the cost to the job at hand, and to do that in a way that compliments both my DIY skills and the goals I've set for my projects.

The Ton-min time versus the Toff time is the problem. To put a fullsteop across a 3v coil with a 36v source, the ratio must be 1:12. End of story. For microsteps, the destination voltage and current changes! For an 8x microstep, the 3v coil might have a target voltage of like 1v for some steps, requiring a 1:36 ratio. If the driver has a minimum Ton-Toff of 1:15, the lowest it could make even in theory is 2.4v, and that's what will come out instead of the intended voltage/current. That causes 1) failure to step smoothly, 2) the static position is wrong (dampeners will not fix this), 3) other "problems", because the voltage and current dynamics are thrown off in more complicated ways than I'm getting into here.

Mechanical dampeners might help, but I see no reason to buy into this situation. If you bought a working setup and were not prepared to gut the controller box, that's one thing. But you're assembling a setup, and can do whatever you want. $79+hours spend assembling & casing+hours spent heatsinking+possible burned out drivers+buying a power supply of a substandard low voltage is much worse than $299 for a G540.

As far as other people being "happy"... how can I say this. The standards of what it takes to "impress" amateurs varies quite a bit. Merely getting a mill to move by computer at all is amazing in itself, is it not? Things you have never seen before. But that doesn't mean the performance is actually impressive per current industry standards. In fact G540 totally changed the standards anyways.

The problem is that an inferior driver is not just "slower" at times. You must slow it down at all times because the risk of stalling can destroy your mill. The headstock stalls on lift (common), thinks its higher than it is, and next comes back down and mills through the table itself. This SUCKS. You will play a game endlessly of wondering what speed you dare to use and it may change with materials, hogging aluminum requires a lot of torque. Back when that was the way ALL drivers worked, well, people dealt with it. We don't need to anymore. If the G540 were $1000 it'd be a bigger question, but it's not.

The G540 also has a high resale value. Pretty much $299-ish! And in a few years it'll still be in demand because it does everything a driver for a mill needs to do, reliably. Much less demand for hacked-together obsolete drivers.

[amplexus]

Buy a gecko, they are in a class by themselves and represent a fantastic value for the money, 540s are cheap, 203v vampires are a bit more but still worth every penny
Amplexus Ender

Mariss does pay me, in priceless knowledge, but even if he didn't post his secrets I would still recommend geckos.