Gearing the bipolar motors, less RPM = better?

[Witsenburg]

Hi,

on my first build, the machine had a speed of 4mm/motor revolution, and the gantry was really, really heavy. So at higher speeds, the x axis motor stalls. (Interchanging motors and drivers between x and y axis, the problem remains on the x axis only.) Now my next build will have a lot lighter (better design, better material) gantry to move. And I read somewhere that bipolar motors have 'the most torque at the lowest RPM'. If I use belt-drive (toothed belt) with a small wheel direct on the motor axle, I get about 75mm/motor revolution. Making machining at 1500mm/min go at only 20 rpm, instead of 375. Would that be too much of a good thing, or will the motors really perform better at such low RPM? Is there a way to know (without expensive measuring equipment) in which rpm range a motor is most competent?

First build

The motors are HY 200 3438.

Cheers,

Hugo

[pminmo]

Stepper motors have more power at lower rpm's, this charactestic is true for unipolar and bipolar. Here is a sample power curve on a Vexta motor: http://pminmo.com/PMinMOwiki/index.p...e:Pk266pwr.gif

Higher voltage as is illustrated on the curve extends the power band.

[Witsenburg]

Aha, so I need to search for such a diagram. Let's google:

Found a PDF!

Now I'm not entirely sure which motor I have (0280 or 0430), but it is save to say performance would be best between 300 and 900 steps/sec, right? Since I only use 45V, let's make that 300 - 800 steps/sec. 180 steps/rev, so 100 - 266 rpm would be on the money. Hey, my 375 rpm (1125 steps/sec) would be outside the borders! I would almost think I understand it!

Let's say middle performance should be 1500mm/min, and should occour at 183 rpm. That's 8mm/rev. Great, there's my answer: double spindle speed relative to motor speed (I use 4mm/rev thread, as mentioned in the first post). At least, if this all makes sense. Does it?

Cheers,

Hugo

[ger21]

Yes, I'd shoot for somewhere between 6mm and 15mm per revolution. The downside is that you'll have lower resolution.

[pminmo]

I haven't published this link yet, as I'm not completely sure I've thought thru the mechanics correctly: http://pminmo.com/PMinMOwiki/index.p...chanical_Power
It's similar to what you are examining but rather than gearing it's comparing different pitch lead screws, their efficiency and the mechanical advantage. Then coupling those with the typical stepper power curve.