Originally Posted by 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. |
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.
Originally Posted by noisillator 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.