Thread: z axis loosing steps
Direct drive to ball screw moving the whole head.
Well ballscrews work both ways because of their efficiency.. so the inertia of the head is driving the motor and overcoming the motor torque. Its not the weight per se (although obviously the inertia is related to the mass of the head) but the overall inertia of the system - head, ballscrew and motor rotor that is the problem.
As a first indication what happens if you program some G-code to move the head down... stop for a while then move it up again... as opposed to changing direction on the fly... does it actually stop on cue, or overrun... if the latter there may be a solution in increasing the deceleration time or reducing the z-speed... which might suggest gearing the motor to the ballscrew to reduce the reflected inertia on the motor...
Not sure if overrun is a problem but the problem is more apparent if the program I wrote is just run, in step mode the error is small.
I have often wondered if the controller will allow for the steps to be carried out.
All in all I am surprised that this all works as in to get the max power from the steppers you have to step slowly and therefore max moving speed will suffer
yes, steppers lose power the faster they go, but this is countered by using higher volts. but z-motion rarely needs high speed, so can afford to gear down and get better results that way
Have you tried turning the screw and stalling the motor by hand?
That tells you what you're asking it to do and what it has to offer.
The problem may become instantly apparent :whistling:
Going to try a more powerful stepper a 3Nm one against the ones I have fitted 1.8 Nm.
Looking for others I found a nice little one on Arc euro a 3.5Nm but noticed something a bit odd in the datasheet, they are quoting 3.5Nm holding for parallel and 5Nm for series most other datasheets show the same rating for both. Is this correct or a miss print.
Finally got it to work without lost steps on the Z-axis.
Changed the motor on the Z for a 3Nm and after some adjustments to acceleration etc it now does not lose steps.
I am now not sure if I have its settings correct as it does not get as hot as the X and Y ones do.
This cnc lark is like waiding through treacle, just as you think you understand it another comment is made that makes you doubt it will ever be understood!
I have read that the normal working temp of steppers is around 80c but not sure!
bigger motor, more thermal mass, working less hard - likely to be cooler...
sorry to say but most reliable answer to this prob is to get a bigger stepping mottor for that axis
which is what Peter did. however bigger motor isnt always the solution to losing steps... could just have been too high an acceleration rate, or he could have supported the motor with a spring or pulley/mass system to balance up and down movements
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