[jim_stoll]

I have just replaced my venerable (but recently deceased) Xylotex with a G540, and even just based on my axis jogging and calibration tests thus far, am very pleased with the G540! (faster, smoother, steppers not getting hot, etc)

I have a mish-mash of steppers on my Taig - a 1.16A on the Y, a 1.75A on the X, and a 2.8A on the Z. (All bipolar series, 1.8 deg/step, 1500rpm, 65v - the Z is 425 oz-in, the X and Y are in the neighborhood of 116 oz-in, if memory serves me correctly). They are currently running off of a 24v power supply. With the new G540, I can drive the X and Y reliably at 42 ipm. (they can go at 48 ipm, the max that the emc2 stepconf wizard would allow, but they sound a bit harsh at 48 ipm, so I stepped back down to 42). The Z axis, on the other hand, cannot be driven faster than 6 ipm. Even going at 6.6 (1.1 in/sec, in the emc2 config file) causes a stall and/or missed steps (and it just sounds rough - very 'chunky' or 'grindy' sounding). I also needed to back the acceleration off quite a bit on Z, compared to the X and Y (not a big deal to me).

I am planning to replace my 24v supply with a 48v supply, since the G540 can handle that. I frankly don't need to really go any faster on the X and Y, though I'm open to doing so if it works well. :-) Its the Z that I'm really interested in trying to improve. (I don't need 42 ipm on the Z, but at least 10+ would be a real improvement.)

I've been told that something like the Taig doesn't need a big motor on the Z, but I went with the 425 oz-in motor, as a smaller (200? 270? somewhere in that range) motor I'd previously tried on Z was stalling on me semi-frequently (with the Xylotex - I haven't tried the original 200-some-odd motor with the G540) just in regular use at slow speed (4-5 ipm). BTW, I got the same max Z speed on the Xylotex that I've thus far been able to get on the G540 - 6 ipm.)

So, the question is (there is a question in here :-), is there a recommended motor for use on the Taig Z axis, driven by a G540 at 48v? (And, I guess, just as a sanity check, does it make sense to go to 48v overall?) Finally, since I've sucked up this much of your time and attention, are there any particular recommendations for different motors for the X and Y, again, considering Taig, G540 and 48v. I'm of course looking for an economical solution, but something that would give me good bang for the buck. (and I'd spend a little extra buck if there was significant extra bang to come along with it...)

Thanks!

[awerby]

If you do change out the power supply for the 48v model, you should see a significant speed improvement on all axes. But I'm not sure that 425 oz/in motor is the right one for your Z axis. The Taig has plenty of mechanical advantage in its 20 pitch screws, so ultimate torque really isn't the issue (although 116 oz-in might be a bit low). Especially if you're doing 3D work and need quick response from the Z-axis motor, it might be better achieved by the ~200 oz-in motor, which probably has a lot less inductance. When you do upgrade the PS, try both motors and see which performs better while running a program, then write back in this thread and tell us, okay?

Andrew Werby
www.computersculpture.com

[doorknob]

I'm wondering whether rewiring the current 425 oz-in z-axis motor for bipolar parallel might help (the driver current setting would need to be adjusted as appropriate), by substantially reducing the winding inductance.

[Mariss Freimanis]

Rewiring your 1.75A in series motor to 3.5A in parallel will be the same as doubling your supply voltage from 24VDC to 48VDC. If you do go to 48VDC as well, performance will double again. Doing both (re-wire to parallel and go from 24VDC t0 48VDC) will quadruple performance. You will be able to 4 times as fast if you mechanism permits such speeds.

Mariss

[jim_stoll]

Just an update - I got a 48v supply and the Z axis speed has improved dramatically (something around 4-fold, without any rewiring - still running bipolar series). My X and Y are pegged at what EMC will support given my computer's latency numbers (somewhere around 45 ipm - anything higher, and I start getting 'joint following errors'). Z is now running at that same speed, though I've got the acceleration on Z set at about 1/2 that of X/Y, as it was stalling occasionally on the start of Z motion.

The catch is, the Z is running H-O-T HOT - like too hot to hold my hand on for more than a second or so. I've been told that its due to the inductance and/or eddy currents of the larger 425 oz-in motor. The X/Y motors are running without any real noticeable heat buildup.

I've ordered a 270 oz-in Keling stepper for the Z, but in the mean time, I've got stuff that I need to make on the mill, and I don't want to destroy the 425 oz-in motor. It sounds like my options are to increase the size of the current limit resistor on Z, or to rewire the motor as parallel (while also setting a new current limit resistor value).

Thoughts on one vs the other? (or a different/better option altogether?) I don't think that I'm going to be able to drive the motors any faster from emc, just based on the motherboard jitter number (ie, the joint following error when I try to tell emc to go faster), and as silly as it may sound to 'real' CNC folks, I'm sort of blown away by the 45ipm rate as it is - I don't really need to do rapids any faster on my little Taig mill. :-) Additionally, I've got a total of 6" of Z travel on this mill (and less than that by the time the height of my vise is taken into account), so further increasing the rapid speed on Z isn't a big deal. Its the ability to get the Z axis moving, and being able to do so fairly quickly, that is more critical for me. I don't do 3D, but I do lots of 2.5D, so there is a whole lot of extending/retracting of the Z in short movements. (I presume this puts the emphasis on low-end torque and acceleration, vs top-end speed) My main concern at this point though, is keeping the 425 oz-in 2.8A Z stepper from immolating itself, while I wait for the 270 oz-in motor to arrive.

Incidentally, I had another 270 oz-in motor, but it turns out that it is a 35v max motor (at least, it says 'V(s) = 35v" on the motor - am I interpreting correctly that 48v would not be a good thing for that motor?), so I haven't been able to try that one out w/ the 48v supply.

Thanks for everyone's help!!

Jim

[rowbare]

Steppers can run hot, well beyond the point where you can keep your hand on them. They can run 80C or higher without damage so I wouldn't worry too much about that.

As for your 270, do you know the inductance? If you do you can calculate the voltage using Gecko's formula 32 * sqrt(induction).

bob

[jim_stoll]

Well, my curiosity was enough to cause me to run down to the hardware store and buy an IR thermometer. :-)

After being on for over 3 hours, with a good bit of use during that time, the highest temperature read on the hot stepper was 137 degrees F (approx 58 deg C). So, while hot to the touch (I still wouldn't want to hold my hand on it for long), it seems well below any danger of bursting into a fireball or such. (I do have a CPU heat sink mounted on the top, but without a fan. The heatsink itself was around 130 deg F, measured on the fins, so I'm not sure how much that might be lowering the overall temp, but still, its below frying temperature, it seems)

I'm now thinking I probably jumped the gun buying the 270 oz-in stepper to replace the 425, though by all accounts I've been given, the 425 is not a particularly good choice for the Z on my little mill.

I'll definitely update things once I get the new 270 oz-in stepper on there. (The inductance of the existing 270 oz-in motor isn't listed, but w/ the new one, I'll know for sure what I'm dealing with, so will just wait for that one to arrive - should be here by the weekend...)

Thanks Again for the help and advice!

Jim

[jim_stoll]

The 270 oz-in Keling arrived, and I've got it hooked up. Temperature is running 10-15 degrees cooler than the 425 oz-in, but still much hotter than the others. 125-130 degrees isn't particularly worrisome though. My top speed, even w/ the 425, has been limited by my computer setup. (I use emc, the top driving speed of which is dependent on hardware characteristics of the computer, and the computer I'm using isn't providing blazing speed from emc) I was, however, able to just about triple the acceleration on the Z with the new motor, and that has made a very noticeable difference in the run time for my parts requiring lots of little Z movements. So, in short, the 270 oz-in motor is running better for me than the 425 was.

I know I'm preaching to the choir, here on the Gecko section of CNCZone, but I cannot adequately describe how completely impressed and satisfied I am with my new Gecko G540 controller. My mill is running faster, smoother and quieter than ever before. My production time on parts that I make regularly has been cut by a good 25-30%. I am one very happy camper right now!