Y axis stalling / missing steps
Question for you. How do you know when a stepper motor is bad? I have been having a horrible time with my Y axis losing its zero reference while cutting a project. I spent quite a bit of time trying to isolate the problem and thought I had it narrowed down to Mach3 and/or my computer. I replaced my computer, reinstalled Mach3, and spent several days tweaking the motor tuning to what the Mach3 tech support staff told me to do and I am still having the problem.
There are a lot of things that can cause this. I suggest you read the FAQ Missing steps – motor not behaving properly. There are many diagnostic steps you can take.
I have also noticed that when I am moving the Y axis from front to back it freezes on me in several locations when moving it at 100ipm. However, it runs fine from back to front at that same speed. I have never had a problem with this in the past. I have also taken the machine apart and checked that there was no mechanical binding the entire range of the Y axis in both directions.
Slow down the Z axis to 50IPM (or 20 or 10). Slow down the acceleration. Run some tests. If OK at slower speeds – start bumping up the speed. Is your power supply doing it’s job?
If you think the problem is a stepper motor I will be happy to buy some replacement units from you.
I’m happy to sell you one, but I’m not convinced it’s the motor.
How Do I Fix It?
The spouse has taken the kids for an afternoon getaway with the inlaws. The dog is fast asleep on the couch and your boss has promised not to bother you for the weekend. Here it is, that once in a blue moon opportunity to finally fire up that Multi-Function CNC machine and start creating! You can hardly contain your excitement as you run to the garage, USB in hand ready to change the world with your new design! The Z-Axis sings its sweet song as it moves for the first time in ages, followed swiftly by the X and Y. The clamps are tightened and anxiously awaiting the buzz of the spindle on the freshly planed baltic birch. This is it! The sun gleams through the window and a rainbow suddenly shoots across the room as you do it! "Cycle Start". Birds are singing and you can just about see a coconut drink on its way. Then ... it happens. Somewhere, someway, somehow your machine has decided that it wanted to cut an inch and a half to the left of where it was instructed. Ecstasy shattered. Your machine has experienced the dreaded ... loss of steps.
My name is Greg and as the Support Manager here at Stepcraft, I know firsthand how frustrating and debilitating it can be to exprience losing steps on your CNC machine. That is why I am here to tell you ... DON'T PANIC! In this article I will share with you the reasons you may be losing steps and the keys to getting back up in running in no time!
What is Losing Steps?
Most modern day CNC machines are powered on each axis by Stepper Motors. In the most basic of terms, these are very powerful motors that constantly "count" the steps they take as they turn. Step 1, Step 2, Step 3, Step 4, etc. The important thing to note is that there are no feedback loops on these motors, or anything that tells the motor what is actually happening vs. what is was told to do. If the motor was instructed to go to position X, which may be 6 steps, it will travel until it has counted 6 steps. Because there is no active feedback, if something happens along the way that physically stops the motor from moving, the software is still counting Step 5, Step 6, when in reality it may be PHYSICALLY STUCK on Step 3. Now, the software "thinks" it has reached Step 6, or Position X when in reality it is still back on Step 3, never having reached Position X. Because the software "thinks" it is at one position, it will carry out the G Code from that position, never "knowing" that it is actually at another position. This is what is called Losing Steps and it stinks. The major signs that you have lost steps are ...
Shift in Project Position
Your project may appear to have shifted to the left, right, up or down
Z-Axis Cutting Too Deep
The Z-Axis is cutting deeper than instructed
Small Lips or Ridges
Noticible ridges around the outline of vectors
Deep Cut Directly Across Project
Related to the Z-Axis, if too low during rapid transits it may leave a gauge across your project
Not Cutting All the Way Through
Depth of cuts not even close to what was instructed
Project Running out of Bounds
Running into limit switches or out of the bounds of your project
When we experience losing steps, especially for the first time, our minds tend to take a trip down panic lane as they spin with the "whys" and "what ifs". When we break it down, there are really only two main reasons why our machines lose steps ...
Electromagnetic Interference (EMI)
Rare in comparison, but can be even more frustrating. This can be the silent killer as you can not see and hear this like you can when there is a mechanical impediment. This can occur when a machine is 100% free to travel with no mechanical impediments and still appears to lose steps. One of the major signs of this is the randomness of occurances. Any machine controller, such as the UC100 on a STEPCRAFT machine, can be susceptible to EMI from power sources such as power supplies and shop vacuums.
By far the most common reason for losing steps. This occurs when something (which we will discuss below) physically stops or prevents the axis from moving forward. The subcatagories for this can be vast, but just remember the reason you are losing steps is because the axis can not travel without impediment. Factors that contribute to mechanical impediment can include alignment, dirt and grime, grease, obstructions and feeds and speeds.
The Only Part You (Probably) Care About
Stay Away From the UC100
The UC100 is the grey dongle that plugs into the back of your Stepcraft and runs to your computer VIA USB. This is what interprets and runs the G-Code on your machine and is vulnerable to to EMI. Make sure anything that is electrically charged is as far away from the UC100 as possible (usually 5-10 feet is safe). The major things to consider include power supplies, shop vacs, dust collection systems, and anything else that can throw off static electricity.
Use That Green Cable
Every Stepcraft machine comes with a green grounding cable that can be attached anywhere on the machine, but normally goes on one of the two screws holding the bottom plate on. Make sure your machine is grounded using this cable that plugs into the wall or your power strip. This can help the buildup of static electricity and discharge
Consider Using Ferrites
Ferrites are non-conductive insulators that help to prevent electrical noise from entering equiptment. In this case, these are the "beads" you see on laptop and other electrical cables. Available from Stepcraft or online, these low cost snap on devices can be applied to the USB cord going from the UC100 to your computer and can help prevent stubborn EMI issues.
100% Jog Speed, 100% Travel
The very first thing to check after losing steps would be your machines mechanical alignment. The goal is to jog your machine at 100% jog speed the full length of each axis. Even if your machine was working perfectly, you may find it binds up towards the ends and needs readjustment. The following videos will walk you through the adjustment process.
Y-Axis Alignment -https://youtu.be/KDuogPSI5tw
Z-Axis Alignment - https://youtu.be/kUG12Z-Lndo
Clean and Re-Grease the Axis
Regular cleaning should be done every 20 hours or so, depending on the material and dust colletion system you are using. If you notice the machine binding in the same spot, this may be a hint that it is time to clean each axis and apply a small amount of re-grease. The following maintenance video will walk you through this process.
Maintenance - https://youtu.be/IIYcZ9M20nU
When All Else Fails ...
When you purchased your STEPCRAFT machine, you also received a lifetime membership to the best support community in the business! Feel free to reach out to other owners VIA the STEPCRAFT Crafters club on Facebook, give us a call at (203) 556 -1856 or email us at [email protected] Our team here at STEPCRAFT has experienced it all and are more than happy to help you through the frustration of losing steps.
Leo, I am saying it is missing steps because I don't know what else if anything it could be. I set the machine to the corner of the workpiece & zero all 3 axis, I then raise the z axis by 10mm & zero the z axis again. Run the job & on completion the machine will be sitting at x zero, y zero z at the safe height above material. Lower the z to zero plus the 10mm I initially raised it should give me my original starting position.
Leo wrote:You are missing steps while cutting air?
That certainly sounds like there is resistance in that one particular slide.
Just the machine motion is skipping steps.
I still do not know how you are determining that you are loosing steps.
x & z axis are fine but the y axis has moved from it's original zero position. Faster I run the machine the further away from this position it gets but no matter how much I slow things down I can't seem to get it to the original zero point.
With no power on the machine I can move the spindle left & right along the gantry with no problem at all so don't think it is binding at all. With power on the machine I couldn't move it so thought the holding torque was ok, although I must admit I didn't try to move it to hard.
Mach3 missing steps
Steps mach3 missing
I have no more ideas for my problem ... PLEASE HELP !!!
What I want to eliminate .... When I moving Y axis by JOG ... after 10 - 20 or 30 cm of movement ... and when I hold the stepper motor by hand .. I fill strange, fast, single motor stall for very small period of time . This is as losing steps ..... When add dial indicator to the axe after some movements .... I lose 0.1 mm linear accuracy ... for 1-2 and more hours will be about 5 mm .... maybe
The sound is like a little, fast "knock" ....
What I did to eliminate the problem, noise .. losing steps ...
I tried many combinations
- 2 PC with Mach3 + LPT to the drivers. ( Acer 2 GB, 3 GHz.... Win XP .. ) and Cel 2.4 GHz, 256 MB ... Win XP
- 2 types of drivers - DQ860MA + Purelogic driver PLD8220-G2
- 2 power supplies ...
- 3 types of stepper motors - nema 23 - and 34 x 2...
- long shielded cables .. and short ...ones .
- Ground pipe in earth with cable to all shields .... cases ....
- tried all BIOS LPT modes EPP etc ..
- kernel mode - 25 and one level up KHz
- LPT direct cable to driver and thru BOB PCB card ....
With single G code - Y500 F500 .. after some mm I fill the same issue ...
When unattached motor is on the table ... the problem is the same ...
I have single phase 220 AC voltage ....
If someone have any ideas ... wiring drawings - please send it ... THANK YOU !!
Last edited by emilvv; 17-09-2015 at 01:14 PM.
With all the different hardware options you've tried without resolving the issue I'd guess that something may be amiss in your motor tuning, you can have problems with too fast or too slow and if acceleration is too high or too low.
I had this problem a long time ago and it was caused by running the all-in-one system3 driver/Bob board at 30V. Dropped to 27V fixed the problem.
But you are using good seperate drivers so should be ok. What Bob are you using and what voltage is going to the drivers? Is it overheating?
Also tighten all screw terminals
Problem is not resolved ... But I have one more issue to check .. this evening .... :)
My motors acts like - http://www.woodworkforums.com/showthread.php?t=167883
( only on 200 .. 300 mm of movement .. not on every rotation .. )
I have XP optimisation.txt file with step by step guide how to setup PC before Mach3 installation ... but maybe I miss this step for switching to standard PC .... and this cause this signal spikes on LPT - missing steps and stalling for small periods ...
So, I will check and if this is a problem will post the results .....
I have 2 core CPU and I hope switching to Standard PC ... will fix the problem ....
THANKS TO ALL OF YOU !!!
What voltage do you have coimng out of the PP.? This problem sounds very much like PP is low power probably 3V type. This will cause the problem you are having because there isn't enough voltage difference between HIGH/LOW.
Also one more thing that can cause this and in some way related to the above is if your Step pulse is on the wrong edge of the pulse. ie: On the down slope(falling edge) when the controller is pulsing on the up slope (rising edge). This affectively puts the timing out and you'll loose one step with every direction change.
To test this for each Axis just write some G-code which moves the axis Back n forth small amounts but 1000's of times very fast.
Copy and paste into a file to make several 100 lines. Make a Mark before starting and run the file. It should return and if it doesn't then you are on the wrong edge of the pulse.
Some drives will let you select the rising or falling edge, Some won't. To Force or change the edge just toggle the Active Low in Motor outputs. This will reverse the motor direction. So goto Homing and Limits and Click Reversed for that axis.
Try and let us know.?
Or better still do your self and machine a favor Dump the PP and get your self a external motion controller.!! . . . You won't regret it.
Last edited by JAZZCNC; 15-09-2015 at 03:51 PM.
My understanding of the operation of the drivers is that the direction pulse should overlap the step pulse at both ends, so whether direction is set one way or the other, High Low, 0v 5v whatever it should be in a settled state before the step pulse, then whether it is a positive going pulse or negative one, both the leading and trailing edges are within the direction state. I would imagine that if different protocols are used for step and direction then results would be unpredictable. As would happen when the timing of pulses is in error, then direction would not be properly set. - Hence missing steps.
JAZZ - correct me if I am being Naive
It's more to do with the Controller issuing the step pulse on the rising edge and the drive set to process it on the falling edge there becomes a timing issue so when a direction change occurs the step is in front of the Dir and a step or MS is lost on each change of direction.
Having the wires on the drive wrong way around will also cause this. So Step + being connected to Step- on BOB. Also a BOB with slow Opto's could cause this but seen has the OP tried direct to drives I reckon not.!
Last edited by JAZZCNC; 15-09-2015 at 07:13 PM.
is this happening only to the Y axis?
And I didn't see what drivers you are using.
P.S. Saw the drivers in the first post.
Last edited by Dragonfly; 15-09-2015 at 07:57 PM.
- I think that is what I said i.e direction not settled before step.Originally Posted by JAZZCNCIt's more to do with the Controller issuing the step pulse on the rising edge and the drive set to process it on the falling edge there becomes a timing issue so when a direction change occurs the step is in front of the Dir and a step or MS is lost on each change of direction.
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