Stepper motor capacity

[crodriguez1517]

How many pounds can a 270oz stepper motor move on a cnc with gantry sides not a moving bed(table) sorry if is a noob question I am building a cnc router for my senior project and would like to know

[ger21]

Depends what it's connected to, how fast you want it to move, how fast you want to accelerate, and how much friction there is.

With a 1/2-10 acme leadscrew, it might be able to move 500lbs very slowly, but it might not be able to move 10lbs very fast.

[crodriguez1517]

First thanks for your reply I really appreciate it and I am planing on using a lead screw and a nut and I dont care about the speed just for it to work the gantry sides would be around 10 to 15 punds

[ger21]

My gantry is about 75 lbs and I use 250oz motors, if that helps.

[crodriguez1517]

Oh ok then probably I am ok it just depends on power now I guess I use a 24V power suply that came with the motors thanks for your help I really appreciated

[crodriguez1517]

Oh ok then probably I am ok it just depends on power now I guess I use a 24V power suply that came with the motors thanks for your help I really appreciated

Is this power enough to move it

[ger21]

24V?
Yes, that's what I'm currently using.

[crodriguez1517]

24V?
Yes, that's what I'm currently using.

thanks for your help I really appreciated

[James Newton]

There is a nice little calculator at:
techref.massmind.org/techref/io/steppers.htm#Estimating
That allows you to put in the torque you need to turn the lead screw and how fast you want it to turn and it will tell you how much power (amps * volts) you need. You can estimate the power needed to move a certain weight (in US pounds, Lbs) at a given speed (in inches per minute, IPM) by the following:
Watts = IPM * Lbs / 531

For example, a 40lbs load multiplied by 1,000 IPM and divided by the magic number "531" gives you a power requirement of 75.3 Watts".

Watts = amps * volts so you need a current and voltage rating that, when multiplied, reach more than your minimal required watts. In the example above, with a 75.3 watt power output requirement, you need a 4 amp motor driven at 24 volt motor or a 3 amp motor driven at 30 volt or a 2 amp motor at 36 volts...

Given a target wattage (which is the power you need from the motor), the voltage needed to drive the motor is that wattage, divided by the rated amperage of the motor.

DriveVolts = Watts / Amps

The voltage on the motor label, is the steady state voltage, or the voltage which the motor can support when it is sitting at rest, which will be much less than the voltage used when the motor is turning. The maximum voltage that the motor can take when turning, the maximum safe drive voltage for the motor, can be estimated from the motors Inductance rating (if known) by simply multiplying it by 32.

MaxVolts ~= Inductance (in mH) * 32

In the example above, if the 4 amp motor had an inductance rating of 0.75mH or more, then we could feed its driver 24 volts and expect to get about 75 watts power out and drive our 40 lb load at 1000 IPM. That assumes a good lead screw and bearings, and no binding or other loads, of course. It also assumes 100% efficiency, which just doesn't happen, so build in an extra 20% or so as a "reality" factor.

In general, the motor needs more voltage to run at higher speeds, because the voltage pushes the current to the necessary level faster. Think of it like this: If you have a /really/ long garden hose, and you want a trickle of water out the far end, you can supply a trickle at the valve and just wait... eventually, the water will trickle out the other end. But if you want that trickle NOW, you turn the water value on full, then wait for the water to start coming out the end before you turn it down. Higher supply voltage allows faster changes to the current and field strenght in the motor coils and so faster rotation. But there is also a balance; at higher PSU voltages the motor will get hotter (because of increased wattage) and it will jerk faster from step to step, so you get more resonance and more problems with stalling. A higher voltage can actually stop the motor getting through resonance bands.

Anyway, there is more detail on the web page above.

[amishx64]

The maximum voltage that the motor can take when turning, the maximum safe drive voltage for the motor, can be estimated from the motors Inductance rating (if known) by simply multiplying it by 32.

MaxVolts ~= Inductance (in mH) * 32

I think you meant to say the square root of the inductance times 32.

At this point it is important to introduce the concept of overdrive ration. This is the ration between the power supply voltage and the motor’s rated voltage. An empirically derived maximum is 25:1, meaning the power supply voltage should never exceed 25 times the motor’s rated voltage or 32 times the square root of motor inductance.

from Gecko Support

[James Newton]

Yike! Yes, that is correct. Thanks for catching that amish!

[crodriguez1517]

Well thanks for everyone replies and help I think I am ok with the current set up they are 3 270oz stepper motors and a 24 volts power supply I think it will work well