| | |
How literally can I take Keling's ratings?
I was looking through the stepper specs and most are showing torque curves under 10K pps. Then this one:
http://www.kelinginc.net/KL23H284-35-4BT.pdf
Says 80k pps??
Is that a typo?
Same price as the 425 oz-in, but that one is like 1/10th the speed by comparison.
Torque curves are not really ratings. And you need to be careful when you look at them. They are generated with a specific drive, at a specific voltage. If you use a different drive and a different voltage, the published torque curve may be nothing like the results you may get.
Gerry
Mach3 2010 Screenset
http://home.comcast.net/~cncwoodworker/2010.html
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
That's what I wondered about.
I'm needing a stepper for 4th axis and it's becoming apparent that this stepper's speed is the one ultimately setting the speed that the program can run at during mill-turn. So speed will be good.
I've got a G540 so that limits my current to 3.5A. 48v power supply.
Any recommendations?
Using a stepper as a conventional motor for lathe operations is not a good solution, you would be much better off using a servo.
Jeff...
Last edited by jalessi; 03-09-2009 at 05:01 PM. Reason: Mistake
Patience and perseverance have a magical effect before which difficulties disappear and obstacles vanish.
Uhh, I think you forgot there are 60 seconds in a minute Jeff.Originally Posted by jalessi
Not that the 387 can run at 24K RPM though. That 80K PPS must be a mistake.
CR.
IIRC, you want to turn foam and are running the motor 1/1. You shouldn't need much torque, and this $33 185 oz KL23H256-21-8B motor will run about as fast as you can get with 3A and 50V (Crank up the PSU a little)
CR.
Ah know what? They're using the unit "pulses" not "steps", and the description in the middle mentions microstepping. So with 10x microstepping driver the chart would be scaled by 10x!
Well the foam turning was one operation. The stepper works dandy and I don't need another drive! Actually the stepper already goes fast enough for that op, the ablation rate of the cutter is the limiting factor. Run it too fast and the foam smudges up. I don't seem to suffer from lack of torque with the 282 oz-in.
The other operation involved the Sherline rotary, which already has a 282 oz-in. That one can stall when run at "high speed" (>2400 steps/sec) though I think it's due to pulse train issues from the parallel port. Due to the gearing of the Sherline, "high speed" is already really slow and in plastics or wood it's not capable of running anywhere near as fast as the material can take.
I figured if I was gonna get a motor I might just get a higher torque one and see about higher speeds. Or maybe put it on the heavy Z-axis, whatever. It's only like $10 more so it's not a big deal, not unless the bigger motors are actually slower at high speeds due to inductance or whatever.
Bigger is ALWAYS slower.
Is that the Keling 282?
what driver/PSU are you running that with?
CR.
Well just a follow-up.
I got the KL23H284-35-4B 387 oz-in and swapped it for the existing 282 oz-in on the Z-axis, figuring it could use the power. I set the G540 to 3.3A instead of 3.5A because that's a standard resistor size.
With the G540 and SmoothStepper, I was getting insane speeds with either stepper actually. Like 120ipm, at which speed the ATF lubricant will sling off the leadscrew. 150ipm would cause a stall. I set it to 70ipm for a fast but slightly less crazy speed. And leaning on the headstock it still lifts fine.
I'm just saying there's no speed limitation showing up with the higher torque motor. In fact, the inductance is MUCH less than the 282, 2.8mH as opposed to 8.8mH. Inductance has a lot of influence on high speed torque.
The rotor inertia part I didn't notice the first time, 840 vs 480 gcm^2. Wow, that's heavy. I don't know how that factors into the big picture in regards to acceleration capability since the inertia of the leadscrew and table or headstock all get lumped together for that. If the rotor's inertia is not very large in relation to these then doubling the rotor's inertia might not affect the total inertial load substantially.
One benefit that I think the bigger ones may have to offer is being able to turn down the current and still be able to meet or exceed the power needs. This means a cooler motor. Motor temp is simply (I^2*R)/case dissipation. The case is slightly larger here, which is a bit more dissipation. If lowered to 2.55A, the 387 has the same holding torque as the 282. But that's 6.5W of head for the 387 as opposed to 8.11W for the 282.
Lower motor temp should increase bearing life (not like anyone's reported a failure that I've seen). It'll also somewhat increase the power output over that projected by the current since the magnetic properties are higher at lower temps. Mainly I'm just tired of getting slightly charred by these steppers in a hot garage. The G540 is already nice though since it turns down the current if the motor's not moving, but if it's been running they're pretty toasty.
Well introducing the smooth stepper into the equation causes an apples to oranges effect. You have probably gone from max 25K PPS to 245K PPS. That will get you some insane speeds alright.
I'm not sure why you are using the SS if you are not running more than 4 Axes. Are you running with a laptop? Might have been less costly to buy another computer.
Anyway, I'm glad to hear that all is working well for you.
CR.
Why? If anything, it would make the comparison more accurate, because it removes any irregularities that may exist in the PC's pulse stream.
The biggest difference is that the 282 oz motor was wired bipolar series, while the 387 is a 4 wire motor, which is more like bipolar parallel.
Your previous statement, that bigger is always slower, is not always true. Maybe when all other things are equal, but a larger motor with lower inductance may very well be faster.
Also, you don't need a Smoothstepper to run more than 4 axis. A $15 PCI card to add a second parallel port is all you need.
Many people report much better performance from a Smoothstepper, though, due to the smoother, more consistent steps.
Gerry
Mach3 2010 Screenset
http://home.comcast.net/~cncwoodworker/2010.html
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Yeah. I should have said All other things being equal. But it's still Apples to Oranges because only with a Smooth Stepper would a series wired motor even begin to match a parallel wired motor in speed.
CR.
Posting Permissions
| | |
LinkBack URL
About LinkBacks
