parralell port voltage.

[crossleymarko]

No it doesn't quite work like that with steppers but it's far too late for me to get into it too much now.
Steppers get there speed/torque from voltage/amps. So if your drives or PSU limit you below the motors ideal operating voltage/amps then you'll get far less speed/torque before the motors ideal corner speed is reached and torque drops away and stalls the motor.
So say at with 48V they will only reach approx 650-700rpm when motor stalls.
With 65v this changes to approx 1000-1100rpm. These figures are lose figures but you get the drift it could be 25-30% less performance than what the motors are capable of giving with correct size drives/psu.

Look around and some where on here Irving did a spread sheet that shows you the differences at different voltages.

All I'll say is your a braver man than me "Gunga Din" if you try to run these drives any were near them voltages. Give them 65V put the kettle on and see how long they last.? Bet you £10 the drives boil before the Kettle.!!

i get it, motors will outperform the drivers,,, or drivers cant feed enough to the motors,, i was told these drivers would be adequet... what motor would you recomend..

so in my head i have it this motor would work as well as a motor running at the ful voltage .

[Jonathan]

I'd bet more than £10 on that!

i get it, motors will outperform the drivers,,, or drivers cant feed enough to the motors,, i was told these drivers would be adequet... what motor would you recomend..

The drivers are adequate yet, but not ideal. Ideally the 3Nm motors should be run from at least 60V, which means you'd have to use m752 (which is what I use), or any 70-80V driver. The corner speed, which is the motor rpm at which the torque starts dropping off rapidly, is proportional to the supply voltage and inversely proportional to the inductance. Incidentally, this is why it's best to wire the motors in bipolar parallel since that's the lowest inductance and therefore highest torque configuration. Anyway, since the corner speed is proportional to the applied voltage running the motors from 48V instead of 70V will result in (approximately) 1-48/70=31% reduction in speed...as Jazz said.

For a fuller explanation see my post here:
http://www.mycncuk.com/forums/showth...ll=1#post25191

However you've got to consider that although you may find motors with a lower inductance, if their torque rating is much less you'll still have less torque at the corner speed.
Lets look at Zapp's offering:
http://www.zappautomation.co.uk/sy57...cPath=9_159_42

The 1.85Nm motor inductance in Bipolar parallel is 1.6mH (compared with 3.2mH for the 3Nm). The corner speed can be approximated by 191*V/(IL), so on 48V that's 191*48/(4*1.6)=1432rpm and similarly 682rpm for the 3Nm motors.
Now we want to know which motor has the highest torque at the corner speed of the 1.85Nm motor, i.e. 1432rpm. This is a bit more difficult...

When operating at or below the corner speed the motor output torque is approximately the rated torque divided by square root of 2, so for the 1.85Nm motors it's 1.85/1.41=1.31Nm.
When operating above the corner speed the torque is calculated from the motor's rated power, which is calculated from; P=[torque at or below corner speed]*[corner speed]/9.55, so for the 3Nm motor the torque below corner speed is 3/1.41=2.12Nm. Substitute that into the formula for motor power and you get, P=2.12*682/9.55=151.5W. Now we can find the torque at 1432rpm, which is given by 9.55*P/rpm=9.55*151.5/1432=1.01Nm.

So at the corner speed for the 1.85Nm motor you will get about 30% more torque from the 1.85Nm motor than the 1Nm motor, however below 1100rpm the 3Nm motor will develop more toque than the 1.85Nm motor.

This demonstrates why it's a bad idea to just go and buy the biggest motor you can find, especially with Nema 34 motors, since the bigger motor may well actually be worse. But...

Thing to do now is do the calculation again, but this time take into account having pulleys to change the ratio since I'm confident you will find the 3Nm motors on 48V will perform better than the 1.85Nm on the same voltage if you gear them up - larger pulley on motor.

(This is essentially the same method of calculation as Irving's spreadsheet. I've just explained it step by step to hopefully make how the system interacts clearer.)

Oh and if you want to know the recommended minimum voltage for a stepper motor it's 32*L^0.5, where L is the inductance. So for the 3Nm it's 32*3.2*2^0.5=57V, and similarly 40V for the 1.85Nm motors.

If I were you I'd wait until you've got much further with the design and know what ballscrews (silly to use anything other that ballscrews since most of the motor power is lost via friction with single start leadscrews or threaded rod) you'll be using and the mass of the gantry etc.