Stepper motors for the McWire

Hi

I've read that a 1.8 degrees stepper motor will make the McWire too slow to use as a bootstrapper for the Mendel, if so I can see three solutions:

1) Get stepper motors with 7.5 or 15 degrees, but that raises the question, where (in Europe) can I get some of those?

2) Convert the McWire to a pulley system, can it be done?, I'm especially worried about clearance for the stepper motor and pulley system for the X plane

3) going for liniear stepper motors, but they appear to be hugely expensive :-(

Is this something I should worry about, if so, what has others done to fix this?

/anton

I think the speed issue isn't so much the number of steps per rev, but getting the rods moving fast enough in the first place without thread friction and/or whip becoming a major issue. If you want it fast, get higher torque motors rather than ones with larger steps, and ball leadscrew (or whatever it's called) rather than threaded rod.

The McWire was designed to do both FDM and light milling, so the speed and torque were compromises vs each other. Remember- mathematically, speed * torque = power.

A repstrap is anything that does the job- innovate using whatever's available to you. I have access to a woodwork shop and (literal) tons of scrap, so mine is being made from wood

I'm not that well versed in mechanics, I did math and CS !

My question is based on this topic in the forum, specifically this statement:

Quote
Forrest Higgs
when you specify a 1.8 degree step stepper motor you are going to have the devil's own time getting it to turn fast enough to do any printing in a reasonable amount of time. Figure that you have 200 steps per revolution and 1 mm pitch on your threaded rod. That means that one step moves you 0.005 mm. If you do 1,000 steps/sec you are going to be moving your axis 5 mm/sec. Getting a stepper motor to do 1000 steps/sec is hard work. Ask Zach or nophead or anybody who's worked with them.

Also, when you are running at 1000 steps/second and more your available torque drops like a stone, so that big holding torque value and all that power isn't getting you very much at speeds high enough to get some printing done in reasonable time frames.

That made me go on a search for a 15 degrees stepper motor, but the only ones I could find didn't have sufficient torque.

Yes, mcWire does take along time to print.

I am using 1/4"-20 rods for the X and Y axis and it barely goes fast enough for minimum extrusion speed. I've had some good prints but it actually needs to go a bit faster than the extrusion speed to stretch the melted extruded plastic as it comes out. I'm switching my X and Y axis to 1/2"-13 in order to achieve this.

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B^2 : [replibot.blogspot.com]

~~ We Are The Factory ~~

Sir,

We have stepping motor type 103H7523-8053 lot no 08904 of Sanyo-Denki.
This motor is burn. We already search on google for windding instruction and we aslo wind this motor but we can not make 5 phase particullar order. Please how make 5 pashe cannetion from winding.

Thanks

Randhir Singh

Isuzu Garments
Tonk (rajasthan)
India

Mobile No. 09887410216

Sir,

We have stepping motor type 103H7523-8053 lot no 08904 of Sanyo-Denki.
This motor is burn. We already search on google for windding instruction and we aslo wind this motor but we can not make 5 phase particullar order. Please how make 5 pashe cannetion from winding.

Thanks

Randhir Singh

Isuzu Garments
Tonk (rajasthan)
India

Mobile No. 09887410216

hey guys. you need to think outside the box.


the reason a stepper can not push a higher speed is from torque required to overcome binding.

place 3 or 4 larger washers on the end of the threading, and bolt them in place. this will act as a fly wheel that maintains speed, and the mass to overcome some bindings. you will more than double your speed!

keep in mind that adding mass of a fly wheel requires acceleration and deceleration as well. also try to use a good controller.

i have a mendel prototype design that is pushing 120mm/s using my own advice.....


take care!

I am just about to start building my McWire. I think I have all the parts in house. I have heard the complaints about the design being slow, and I will experiment with using inexpensive steel wire cable instead of 1/4-20 threaded rod/studding.

The earlier comments are correct. The basic NEMA 17 stepper motors (there are variations, including the depth of the motor, so watch carefully when you buy!) steps at 1.8 degrees per step, 200 full steps per one rotation. Using the 1/4-20 threaded rod (I am guessing this is around M6 studding with 1.0mm pitch) each full revolution of the motor, every 200 steps, advances the extruder 0.05 inches (1.0mm). I found one listing on Google that puts the top speed of the stepper motor at 80 rps, which means that absolute fastest you could go is 80*0.05 4 inches per second. This would mean 4 seconds to move from on end of the build bed to the other!

Using the easy driver stepper motor controllers from Sparkun, they default to 8 micro steps. At first I thought this meant 8 micro steps per cycle, but now that I have the data sheet, I can see that it is 8 micro steps per step. So the total number of micro steps in one revolution is 200*4*8 = 6,400. to get 0.001 precision with a direct drive, instead of turning a threaded rod, you want the drive pulley circumference divided by micro steps to equal minimum movement, or 0.001 inch = c/6400. This means that a 6.4 inch circumference, or 2.037 inches in diameter. For metric, 0.025mm accuracy gives 160mm circumference, 50.9 mm diameter pulley.

Mike

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Team Open Air
Blog Team Open Air
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Microstepping comes at a cost:

Quote
Electric motors and drives: fundamentals, types and applications
Mini-stepping is a technique based on two-phase-on operation which
provides for the subdivision of each full motor step into a number of
‘substeps’ of equal size. In contrast with half stepping, where the two
currents have to be kept equal, the currents are deliberately made un-
equal. By correctly choosing and controlling the relative amplitudes of the
currents, the rotor equilibrium position can be made to lie anywhere
between the step positions for each of the two separate phases.

Closed-loop current control is needed to prevent the current from
changing as a result of temperature changes in the windings, or vari-
ations in the supply voltage; and if it is necessary to ensure that the
holding torque stays constant for each ministep both currents must be
changed according to a prescribed algorithm.

Although the quote is only from an introductory level book about electric motors, it does match closely with what others have reported, so it would seem to me that the "simple" divide step precision with micro-step count, and arrive at a higher precision doesn't always match RL, in fact I'm starting to doubt if going beyond half-stepping has any merit for the purposes of reprapping. Although I'd love to get some feedback on that thought from people more knowledgeable than I.

Hi Anton,

... if microstepping with higher resolution results in really higher precision depends of the motors, the drivers and the mechanical setup.

Microstepping between the pole-positions is made with lower torque than with full-stepping, but has much lower tendency for mechanical oszillation around the step-positions and you can drive with much higer frequencies.

If your motors are near to mechanical limitations and you have high friction or dynamics, you won't receive much more accuracy ...

When your motors are 'overpowered' and/or you don't have much friction, then you can transfer the higher positioning accuracy to moving accuracy too.

I have some 1/256-microstepping drivers, where a normal 200-step/1.8deg-motor is driven until 51200 steps per rev. - here with some 2Nm-motors and a spindle-drive with 5mm per rev. i measured until 2 microns positioning accuracy below 1/16-microstepping ... my measuring equipment wasn't fine enough to detect the differences between 1/32- and 1/256-microstepping, but i could hear the mechanical 'humm' of the motors changing to a quiet 'hiss' below 1/64-microstepping ...

With some 3-phase-steppers from Berger-Lahr and corresponding drivers i can run the motors in 'normal' mode with selectable resolutions of 200, 400, 500 and 1000 steps per rev. - it's the different switching pole-gemopmetries between rotor and stator and 3 phases.

And then the drivers can be switched to 'microstepping mode' - here i'll enhance the stepping resolution tenfold, so the same motors will drive with 2000, 4000, 5000 and 10000 steps per rev.

I have to built my next mechanics first, then i can test the really achievable accuracy with milling or CNC-lathe - i have 3 2Nm-Motors with 5mm-spindles for XYZ-stages and a 4Nm-motor with a 4jaws-chuck as direct driven axis for a mini-CNC-lathe ...

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Viktor
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@VDX
Great, thanks for the explanation.

So given that most X, Y and Z axis engines of the Mendel are probably overpowered, it makes great sense to do micro-stepping. How about a McWire, which would be used for light milling, wouldn't the torque required to hold the bed in position require either higher torque motors or refraining from micro-stepping?

ps. Your motors sounds pretty cool, but it also sounds as if they are a tad out of my leage