On what components is the maximum speed of stepper motors dependend on?

Hey guys,

I am currently designing my third 3rd 3D printer - after having owned a Powerwas Evo and now printing on a prusa i3 aluminum -
i want both - something bigger and something more rigid.

it is going to be a machine with a frame consisting of Aluminum Extrusion Profiles in either 30x30 or 40x40mm - depended on the size and several calculations and of course motor-decisions - which i plan to
base upon reply to this thread.

Currently my i3 uses m5 - 0.8mm per turn for Z-Axis, and GT2 pulleys with 2 teeth on x and Y-axis.

While th z-axis i sobviously extreeemly slow (I can`t test the real speed, since the m5 threaded rod wasn`t made for linear movement and therefore has a lot of the motor`s torque eaten up by the movement alone and the friction the darn m5 nut is eating up.

With the X and Y-Axis I see them being 20 teeth - 2mms apart - coming out towards 40mm per rotation.
So for 40mm/s the motor would have to have 40rpm and so on.
being 1/16 micro stepping - it requires 3200 Steps per Rotation - ergo 40mm, which equals out to 80 steps per milimeter - which is nice, since it is 1) evenly dividable 2) quite a good resolution while maintaining enough speed.

which the controller should be easily up to.
I have seen videos of people driving their axis with more then 200mm/s
so let us assume, even 5x my speed with same configuration (currently RAMPS 1.4 - Mega 2560) is still doable.
That would be 5x 3200steps per second - coming towards 16000 Pulses per second.

but if I used 1/128 microstepping - which is 8x as much, as I am using now -
i am sure, the RAMPS 1.4 could not hold up.

This would need 128.000 Pulses/s to the motors.

but since I plan on using either ballscrews or trapezoidal leadscrews at about 5mm slope (is that a good value?!) that would come out at even 8 times less movement per full rotation of the stepper motor....

So I would or could easily need the motor do to 1600rpm...
I think I read somewhere the motors hard-limits for nema 17 or nema 23 sized motors is somwhere between 3500-4500rpms - so still room ahead.

but would the controller (RADDS Board) be fast enough to do 1.024.000 pulses/s ?!
I highly doubt it... what is the "hard-limit" here?
100khz? 400khz? Is there such a limit?

How are huge CNC machines moving so fast - are they relying solely on the PC´s processing power - certainly not huh?!


As I am opting for both - an increase in microstepping (at least 1/64 maybe even 1/128 microstepping) for ultrasmooth linear motion - see this link:

[www.dr-henschke.de]

and this Video: [www.youtube.com]

where He tests different stepper drivers and finds out, only the ones with 1764 or 1/128 microstepping are allowing for a really smooth movement of slow moves and that Decay musst be selectable via a trim-poti.

- I am unsure about which speeds I will be able to reach!

I am not sure that with the size of printer i am planning (bed 30x40cm) and it`s inherent need for rigidity and thus weight, nema 17 motors will be enough, I might go for Nema 23, also when doing 1/128 microstepping I am afraid I will not be able to reach higher speeds aany more - even with a RADDS Board and it`s faster processor.

With a GT2 pulley system it would be surely achievable, but I am opting for ball-screw driven system on all axis/at least on some axis.

So What kind of slope would I need to choose, to be able to run all of my axis at about 200mm/s.

Do you think, 5mm of a slope on ACME screws or ball-screws would be enough?

reason for screw-driven axis is that i want to be able to attach some sort of light spindle - like 800Watt Kress Spindle - to do some light milling in Wood, Carbon and Soft Alloy Metals.

I just don`t think, a belt/pulley system would be a good choice for a hybrid machine.

i know, it`ll be a compromise -
for sure, but with th desin I have in mind (no gantry system, but rather a moving Y-table) and the Z- and x-axiis combined, It will be allright and rigidity of the frame will most certainly not be a problem.
it will use either 12 or 16mm supported rails on all axis, so should rund both - smoothly and very stable with minimal play.

I just don`t know which component will limit me the most.

the electronics? How many hertz will the Allow for a signal?

I thought I once read somewhere, that it is the electronics capping the machine`s movement at XXXXXX instructions/pulses a second thus setting a hard limit for linear motion sped.

I want to reach at least 150 or 200mm/s for prints.
For milling such fast speeds would not be required, but for travel moves it would still be a nice bonus.

So which slope would the ball-screws or trapezoidal screws need to have minimum/maximum for the machine to still allow for 200mm/s with 1/128 microstepping
on a RADDS Board?

Don`t worry about the stepper drivers. I may use aftermarket drivers which are rated up to 4A - So I can crank up the power to the motors quite a bit when neccessary.

thanks in advance for any help on this,
as I am kind of lost, which system to use to drive the bed with it`s weight at my wanted speeds.

Alex

Edited 1 time(s). Last edit at 11/09/2014 04:45PM by Alexander1984.

Wow! Too many variables. For firmware speed caps I would post a separate question to the firmware forum of your choice. Make it simple.

For a leadscrew system I'm not sure you gain much going from 16X to 128X microstepping. It wouldn't really make any difference if the smallest real step is say 0.1mm and 16X stepping does it in 4 steps while 128X does it in 32. Also if you are looking for speed, the faster you go the less those microsteps are going to matter.

Just to add to the confusion, power supply voltage will affect top speed as well. Higher drive voltages increase the speed at which back EMF equals drive voltage.