M2 RevE Z stepper steps per mm

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airscapes
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M2 RevE Z stepper steps per mm

Post by airscapes » Tue Nov 30, 2021 12:42 am

So I am trying to get my M2 changed over to a Duet 32 bit main board. I am not going to call this an upgrade because it has been a real pain in the butt so far.
Does anyone know the number of steps per mm for the Z stepper motor and the pitch of the lead screw.
The wiki has the following info
The Z motor is a standard, 1.8°/step stepper motor, with an integral, four start 8mm pitch leadscrew with a metric trapezoidal thread. Four start means that there are four individual threads along the length of the leadscrew; 8mm pitch means that the center to center distance of the thread is 8mm (or, in our application, that a nut mounted on the leadscrew will be driven 8mm for one full rotation of the leadscrew). So 200 full steps = 3200 microsteps = 8mm. The firmware uses values of [micro]steps/mm, so the firmware value is 3200 / 8 = 400 steps/mm.

Which does NOT match what is in the firmware
#define DEFAULT_AXIS_STEPS_PER_UNIT {88.88,88.88,1007.7,471.5} // default steps per unit for Ultimaker //v000 9/24/2015

When I use 400 in the Reprap config the z axis only travels about half way up from home. I assume the black Z motor has a different number of steps per revolution?

1007.7 seems like a very odd number and using it the bed still comes up short at 200mm

Any help is greatly appreciated
..

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ednisley
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Re: M2 RevE Z stepper steps per mm

Post by ednisley » Tue Nov 30, 2021 1:55 pm

airscapes wrote:
Tue Nov 30, 2021 12:42 am
1007.7 seems like a very odd number
Because it comes from a hard-inch leadscrew:

https://forum.makergear.com/viewtopic.p ... 7.7#p37559

Comments in source code rarely match the actual code after many fingers have messed with the details, so even this may no longer be correct:

// default steps per unit for Ultimaker //v000 9/24/2015

Bonus: that (almost certainly) isn't the source code corresponding to the Marlin firmware in your RAMBo.

A bit of rummaging turns up MG's "legacy firmware" page:

http://makergear.wikidot.com/m2-firmware

Wherein it is written:

All printers shipped after 02/08/2013 have RAMBo boards with 1/16th microstepping. The steps/mm values for 1/16th microstepping are: [88.88,88.88,400.00,471.50]

To be absolutely certain, you should download the source code and verify the actual value.

As a rule of thumb, one careful measurement of a physical constant outweighs a thousand expert opinions, particularly when software is involved.
not going to call this an upgrade
You're also upgrading your knowledge of how this stuff works, which can only be done the hard way …

airscapes
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Re: M2 RevE Z stepper steps per mm

Post by airscapes » Tue Nov 30, 2021 2:26 pm

Ed, the 1007.7 is what is in the stock firmware for the RevE as found on the old firmware page which is where I got it originally.
So what exactly are you suggesting I measure on the lead screw. Was trying to measure the space between the theads, and came up with 1/16 can't get hold of a thread with my caliper to get a measurement of that.

I hate when I fix shit that ain't broke! :oops:

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ednisley
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Re: M2 RevE Z stepper steps per mm

Post by ednisley » Tue Nov 30, 2021 5:04 pm

airscapes wrote:
Tue Nov 30, 2021 2:26 pm
measure the space between the theads,
Use the caliper's internal jaws (the pointy ones opposite the external jaws) for this.

Count off and mark four threads (= one rotation of the leadscrew, assuming [0] it has four starts), eyeballometrically [1] center one pointy jaw's point atop each marked thread, and you have the lead. Divide by four to get the pitch, although you probably don't care about it.

Divide the number of microsteps per rotation by the lead to get steps / mm.

If the quotient comes out close to a nice number like 200 or 400, use the nice number.

If you get some weird-ass value like 1007.7, then remeasure with the caliper set to inches and the lead will work out to a nice decimal fraction of an inch. Do the conversion from lead-in-inches to steps / mm by hand.
as found on the old firmware page
Or somebody put the wrong file in the wrong place. shrug

Always always always measure physical properties!

[0] Hell hath no fury like that of an unjustified assumption. Use a Sharpie to mark one of the threads as mentioned earlier; one turn will verify the startedness.

[1] Just line up the point of each internal jaw with the center or edge of the thread crest. If you want more accuracy, measure two or three or four turns to get multiples of the lead, then divide by the number of turns; the average will be Good Enough™.

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