Stepper Power to Resolution Ratio

I wanna pick some very sharp brains here, on Stepper Power to Resolution Ratio.
The kit i sell utilizes:
Tr8*8-2p (4 starts)
Lead Screw Diameter ∅ 8 (mm)
Pitch: 2mm
Lead: 8mm
So i have been using 1/4 stepping at 200spmm, and have had almost no issues unless i crank the speed too high.
Settings i use:
$100=99.178 (x, step/mm)
$101=99.011 (y, step/mm)
$102=98.961 (z, step/mm)
$110=4000.000 (x max rate, mm/min)
$111=4000.000 (y max rate, mm/min)
$112=4000.000 (z max rate, mm/min)
$120=200.000 (x accel, mm/sec^2)
$121=200.000 (y accel, mm/sec^2)
$122=200.000 (z accel, mm/sec^2)
$130=790.000 (x max travel, mm)
$131=800.000 (y max travel, mm)
$132=165.000 (z max travel, mm)

Question is as follows, at what point on the lead screw does acceleration and power trade off for loss of resolution. Math and electricity is not my strongest subjects so at full stepping and low acceleration (i believe from what i read is the most powerful settings for a stepper) what is the theoretical maximum resolution? And what is the trade off for 1/2 or 1/4 stepping in the ratio?
@PhilJohnson @JustinBusby @LarryM @EliasPolitis

Using a standard 1.8 deg stepper motor, you get 200 steps per revolution.

1 revolution moves linearly 8mm on your screws.

Theoretical resolution (mm/step) = 8 / 200 = 0.04 mm per step.

That’s at 1X microstepping. For 4X, that changes to 0.01 (divide by four). 2X would be 0.02 mm.

For comparison, the standard belt has a resolution of 0.025 at 8X microstepping. Or said another way, a full step moves 0.2mm. The screws give a nice improvement over that.

Incremental torque drops pretty rapidly as you increase microstepping. 71% at 2X, 38% at 4X (http://www.machinedesign.com/archive/microstepping-myths).

So what does it all mean?

Microstepping will do much more than just give better resolution. It’ll smooth out your motion, less mechanical wear and tear, less noise from resonance. Your acceleration is also going to be limited based on the microstepping value. The best way to figure out what works best is to just test it.

Did you test to get the 200 accel values?
What’s your max feed rate before stalling?

5000 max feed for me, but im an experienced installer. Some newbs may not get perfect alignment on their first try.
I Pushed 9000 with 500 acceleration but during cutting it stalled on one side.
im looking for the right tradeoff. 4000mm/m is fast enough for 150ipm cut speeds. and higher acceleration is better, but resolution is important too. as for wear and tear most people wont care as its not an expensive machine and replacement parts are quite affordable.

Just adding to what you mentioned already:
Microstepping will on paper give better resolution but the smaller steps the harder it is for the stepper to be exactly at that position. Since torque drop off at higher exact position become equally harder to achieve.

Ideally you should use 1/1 step of resolution, if it is within intended resolution, and use the least amount of micro stepping, only enough to smooth your machine.

Whats the right amount on paper? i need to start somewhere.

So is 0.0016" a good enough resolution for a hobby machine?

The power transmission method is one of a few factors that contribute to machine resolution. The more you can minimize one area of resolution, the better but there could be other factors that then become the “long pole in the tent”.

In my opinion, the only way to on paper figure it out is you have to know the loading of the machine and then it’ll change when cutting walnut vs. oak vs. plywood vs. mdf…etc etc. Each stepper motor and wiring could also provide a different torque curve, etc.

So essentially, trial and error is how you’ll truly figure it out. Understanding what you are changing and changing things one at a time to see how it changes things and when you’ve gone too far. When you find your max, back off around 10-20% to allow for extra loading and wear over time and use that.

I just don’t think there is an easy way to calculate what you’re asking for.

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I am kinda asking because I have no Z axis on my machine right now and I have no way to test any cuts yet.
I do remember reading that cut settings should be set in intervals of resolution. Meaning if the resolution is .0016” then the doc should be a multiple of that. But does that apply equally to the x and y?

Ah okay, now I get what you are thinking about :slight_smile:
(Dont have the answer though…!)

If I were to think out loud:
Maximum holding torque is found at full step position only
Maximum torque while in motion is a different aspect.
Torque drop when speed increase (RPM), you trade speed for oomph.
To maintain high torque at higher RPM you need more voltage (since current is limited by the driver)
Power = Volt x Amps

Getting a single, definitive answer require a known RPM / torque value (and perhaps more) so I think what you are contemplating dont really mean much for a hobby machine. Any deviation from the “ideal” is below a hobby machine precision in the first place.

Is a 0.04mm/step resolution good enough? For sure, IMO :slight_smile:

Thanks for the response. I’ll be using full step as a baseline.

I can get that speed but it contains some risks.
And ppl with gshields cannot reach that.

Most has been already covered and indeed it’s a matter of trial and error.

I would just like to add a couple of notes.

Resolution is not one-size-fits-all. Some people and applications might be more or less sensitive to resolution. It helps if you think of resolution in relative terms as well. For example your full step resolution (0.04mm) when cutting a 750mm long skateboard will affect the outcome by 0.00533% , when carving a 2mm detail it will do so by 2% .

So, deciding on resolution is a matter of deciding on what kind (size & detail) of work you wish to feed the machine and what your acceptable error threshold (%) is.

Also, as voltage helps with RPMs, your speed and acceleration will improve with higher voltage (as long as your machine has the rigidity to accept this improvement). That is for people that do not have the X-Controller or wish to build their own controller regardless. Otherwise, low inductance motors will also help.

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Minimum :sweat_smile:
Its a simple factor to compare machines by, but how many of us use the maximum limits as actual cutting speeds? :wink:

My non-Xcarve would jolt around if I ran it at 8m/min , it is simply not firm enough :rofl:
At the moment my X rapid is a mere 2,5m/min, but it can do that on all axes.
Ideally my steppers require about 90VDC to reach their peak :wink:

As a note, The Xcontroller is only rated for 24V so you can’t just replace the PSU and go higher voltage (I checked with Inventables about that).

The Demon controller, with its separate drivers that support higher voltages, you can just replace the PSU with an appropriate sized supply and get a better (ideal) motor response with the same motors.

I was looking at one like this for a custom controller

https://www.amazon.com/dp/B01EY6HVNE

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Yes, the maximum voltage is determined by the voltage rating of the actual stepper driver circuitry, on mt TB6560´s its 36V that is max. I have a DM556 driver available that is 50V max and with 2x 24V PSU´s I can get 48V so it will be my first higher voltage test.

On a screw drive machine a 24V voltage limit is the main limiting factor when it come to all-out speed/acceleration.

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So to get moe POWAH whats the most reasonable controller to use? and can i reuse/cannibalize my gshield/xcontoller?

I had an Arduino with Adafruit g-shield. Went the same path as Phil with a “Demon” using 4 individual drivers.
If I were to do that again today, keeping the Arduino = get higher voltage drivers, they are usually powerful enough with the amps.

4x Leadshine DM856 with 80V PSU -> Just call it the “Super Demon”
Or as @EliasPolitis did go Clearpath, those eat Super Demons as snack in-between meals.
But that would probably require screws other than 8mm ACME´s :slight_smile:

Whats the total project cost?

The TB6600 can support up to 42V DC per the data sheet.

A quick Amazon search says that $35-$40 per driver to support 48VDC and about 50-60 for a psu. So $200-$250.

You can reuse an Arduino Uno but nothing with the Xcontroller unless you gut it and make your own mounting to reuse the chassis and Estop and such.

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What is your end-goal?
My TB6560’s where at about $10 each at the time, got 4.