Missing Steps Poss TB6600 Fault

[neilricketts]

Hi, i am new here and i am hoping you may be able to help me. I have built my own cnc router and it is working but i am losing steps on all of my axis. I have tried changing and making various designs of anti backlash nuts. I have also tried adjusting amp settings and step settings from 1/8 to 1/2 steps. It is more pronounced on z axis. when doing a project of a v carving i can end up being as much as 3.4mm above the work piece at the end. I am now beginning to suspect that my tb6600 drivers are at fault because when the machine is running the alarm light is continously flickering during the machine is running. I am wondering if this could be resulting in the loss of signal which is then resulting in lost steps. My machine is

4x Nema 23 stepper Motors bought second hand. (ebay)
4x TB6600 stepper drivers (ebay)
M10 x 1.5 Leadscrews
24v 10a DC PSU
5 axis breakout board (ebay)
Mach3 version 3.042
Dell Laptop with power management turned off running xp
Chinese Quiet 400w DC Spindle.

Cheers Neil

[Clive S]

Hi Neil Welcome to the forum.

First a picture would paint a 1000 words. You are never going to get an accurate machine with the stuff you have built it with, however, can you up your PS to about 30V as the drivers can accept about 42V that would help a bit.

Are you driving the motors direct to the end of the lead screw or with a pulley and belt to give you an increase in torque.

[neilricketts]

Hi, i can't up the voltage and my leadscrews are directly driven. What i am unsure on is the calarm light on the drivers when the machine is running are flickering on and off continously during use. This is making me suspect faulty drivers that are losing signal. I will try and make a video to show what is happening when i finish work tonight

cheers neil

[Clive S]

Hi, i can't up the voltage and my leadscrews are directly driven. What i am unsure on is the calarm light on the drivers when the machine is running are flickering on and off continously during use. This is making me suspect faulty drivers that are losing signal. I will try and make a video to show what is happening when i finish work tonight

cheers neil

Are you using shielded cable between the drives and the motors as it could also be electrical noise causing that.
Upping the Voltage will give you more power

[neilricketts]

to be honest i am using 2 core lamp wire for connecting the motor to the driver which is all i have had available. The missing steps is worse on the z axis which is the one that takes the punishment with up down movements when doing 3d projects.

cheers neil

[Clive S]

to be honest i am using 2 core lamp wire for connecting the motor to the driver which is all i have had available. The missing steps is worse on the z axis which is the one that takes the punishment with up down movements when doing 3d projects.

cheers neil

Yes don't blame the drivers if you not have done the correct use of cabling as you have to get rid of noise etc. Remember you are not using ball screws so upping the voltage WILL help.

[neilricketts]

what cable would you recommend. also any idea on this as a possible replacement 4 Axis Stepper Motor Driver Card 4.0A NV8727T4V4 100Khz CNC MACH3 Control Board http://www.ebay.co.uk/itm/4-Axis-Ste...3D252493649303

cheers Neil

[Neale]

I've just been through a similar exercise on my own machine which has only just reached the point where I can start using it. First cuts doing some simple profiling were fine, but a bit of vigorous 3D V-carving left the cutter a couple of mm down on its starting point. I fixed mine, but your problem is very slightly different.

First - you end up high rather than low in Z. Typically, the error is the other way (as it was with mine) as the big load on Z is when you are raising the spindle as you don't just have inertia but also the deadweight of the spindle plus Z platform. Missing steps, slipping coupler, will generally have effect when the spindle is on the way up. In my case, I had stupidly forgotten to put a flat on the end of the Z ballscrew and the pulley was slipping. Easy fix.

Secondly, you have an error light flashing. Don't know what that means on your drivers, but it doesn't sound right! Do you have any kind of manual that says what it might mean?

Thirdly, you are using a laptop. Turning off power management is a small step in the right direction but I wouldn't trust a laptop to deliver reliable real-time pulses. Processors for mobile (basically, battery) systems can do some odd things where the processor just goes off and does some internal housekeeping. Doesn't affect normal use but it's a bit of a killer to realtime operation. That's why Mach3 is not officially supported on laptops. You might expect this to give random axis movement, though, and you are reporting a consistent change in one direction, so maybe that's not too big a problem in your case.

Lastly, and my best guess at the problem, is that you have the step signal inverted. It's not always obvious how to wire the BOB to stepper driver, and it is possible to get the signal wires the wrong way round (red face at my end - I wired mine very carefully but obviously not carefully enough). Mach3 wants the driver to operate on a rising edge of a pulse but if the signal is inverted, it's triggering on the falling edge instead. The quick fix is to go into "ports and pins" in Mach3 and swap the step signal for the Z axis to active low. What happens in practice is that on every direction change, you lose a step. On my machine I could check this by using my Z height-setting touchplate; I just repeated the height setting operation many times and (looking at machine coordinates, not work coordinates) saw that each time, the spindle had gone down about 4-6 microsteps (based on Mach3 DRO readings). Swapped signal polarity and now get repeatability within a couple of microsteps time after time. You are either going to need a height touchplate to do this, though, or use a dial gauge to measure actual height after multiple up and down movements.

Or it could be electrical noise...

Good luck!

[neilricketts]

Thanks for your reply Neale. I have had issues with my couplers in the past but i have since made solid couplers and ground the threaded bar with a angled slot to prevent it dropping out. I have also made new spring loaded anti backlash nuts. as soon as i can get me another pc i will try that but i do not think that is causing the problem. I have tried the active low in mach 3 which just causes the z axis to go in opposite direction. For example press up it goes down, press down it goes up. I am looking for a reasonable priced shielded cable to redo the wiring. I am however still leaning towards faulty tb6600 drivers considering the alarm light flickering on and off when that axis is changing direction.

cheers neil

[john swift]

are you sure its an alarm and not an activity light ???

a link to the advert or photo of the TB6600 driver would help to find the data for your driders

John