270 vs 425 oz-in stepper for X2 mill cnc

[cds333]

So I am looking at two similar motor/driver/controller kits and the only difference is that one kit has 270 oz-in motors and the other has 425 oz-in motors for only $15 more. From my reading on here I know that bigger motors might not necessarily be better as they may have less torque at certain rpms.

I really don't know what rpm they will be running at on the X2 mill however. Based on the torque curves, after converting units, it appears that the smaller motor has more torque at ~1000 rpm while the bigger motor has more at lower rpm. Of course there is also the fact that the kits are both 36V while the curves are at 48V, I don't know how that will affect the values.

Is there a definitive answer as to which is better? Or other factors which I should consider?

Thanks in advance!

https://www.automationtechnologiesin...3-axis-nema23/
https://www.automationtechnologiesin...-3-axis-kit-3/




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[109jb]

It depends on the pitch of your screws. If you are going to use something like 5mm pitch ballscrews, 1000 rpm would be 196 inches per minute feedrate. Way faster than is needed for a X2.

If you are going to keep the stock, i assume 0.1" pitch acme screws, 1000 rpm is 100 IPM. Still faster than you need on an X2, but you have screws that are much harder to turn than a ballscrew. Also, the torque curves at 48V show that the point where the torque curves cross is not at 1000 rpm, but more like 250 rpm. At 250 rpm and 5mm ballscrews you are about 50 ipm.

Really for an X2, 50 IPM is enough. An X2 has about 8 inches travel on the x axis and less on the other 2 axes, so at 50 IPM it would take only 8 seconds for full end to end travel. Most cutting on say aluminum is going to be 20 IPM or less on an X2

I'd personally go with the 425 on an X2 and the speed you get is what you get, but I would call John at Automation Tech and see what he can do for you about upgrading to a 48V power supply. The 7.3A 48V PS is the same price as the 9.7A 36V PS and 7.3A is plenty for those motors. He may just do a swap for you.

To answer your question about what voltage does, you can see it in the one plot you posted that shows 48V vs 80V. It basically shifts the curve to the right as you go up in voltage

[cds333]

But at 2.8A per motor it would equal 8.4A total, which would exceed the amperage the 48V power supply could provide, no?

Or do you ever only use X+Y axis at a time? And Z always moves alone?

[Toinvd]

The driver will draw less current at a higher input voltage. And the motors will perform better ( higher RPM )
The current in the motor coil is chopped by the driver. Peak currents in the motors are high, but average fro the power supply is far below, and capacitors make it average for the power supply.

[rodw]

But at 2.8A per motor it would equal 8.4A total, which would exceed the amperage the 48V power supply could provide, no?

Or do you ever only use X+Y axis at a time? And Z always moves alone?

You can safely go past the power supply output by about 40% (to about 10.2 amps when summing stepper amp draw.). This is explained in a Gecko tech note. A 7 amp supply will be heaps!