Centroid Community CNC Support Forum

Deadstart generally applies when one axis has to start, stop, or reverse while another axes continues moving (e.g. at the quadrant points of an arc). It is the maximum instantaneous jump in speed that this axis can be forced to make, to or from a stop.

DeltaVMax generally applies when an axis continues moving in the same direction, but is required to make an instantaneous jump in speed.

At the lowest level, all moves that the control makes -- even during circular arcs -- are a series of straight line segments. It is not possible to turn a corner from one straight line to another, going in a different direction, without either (1) bringing all axes to a full stop, or (2) requiring one or more axes to instantaneously change speed. Obviously, the smaller the angle between the two lines, the smaller the jump in speed, and the smoother the transition.

My guess is that, with your X axis DeltaVMax set to 10mm/min (ca. 0.4 in/min), X is forcing all axes to slow down in corners and arcs. It is this deceleration/acceleration that is leading to the banging. We usually set DeltaVMax to 3 or 5 in/min (75 - 125 mm/min); and sometimes higher when contouring at high feedrates is a priority.

cncsnw wrote: ↑Sun Aug 29, 2021 2:51 pm Try increasing Deadstart and DeltaVMax on all axes to around 120 mm/min, then running the same toolpath, at 100%, with smoothing off.

Thanks. I will give it a try. I thought bigger numbers meant more 'banging', Do you know what these number actually do? My understanding is dead start is the speed it will slow to before changing direction so the less it slows the more abrupt the direction change. Delta vmax suggest some speed change limit but I dont know about that one!

ashesman wrote:Do you know what these number actually do?

Deadstart generally applies when one axis has to start, stop, or reverse while another axes continues moving (e.g. at the quadrant points of an arc). It is the maximum instantaneous jump in speed that this axis can be forced to make, to or from a stop.

DeltaVMax generally applies when an axis continues moving in the same direction, but is required to make an instantaneous jump in speed.

Imagine driving a car around a polygon. At each corner, you have a choice: maintain speed and make a very abrupt turn; or brake to a lower speed; make a more gentle turn; then accelerate back to speed.

Setting higher Deadstart and DeltaVMax numbers means the control can maintain speed, but if the values are too high there may be some lateral banging as it tries to turn corners without slowing down.

Setting lower Deadstart and DeltaVMax numbers means the control has to slow down for any significant direction change, then can resume speed after the corner. If the numbers are too low, then you get shaking as the control decelerates into, and accelerates out of, every little corner. That is magnified at higher feedrates, and especially if you have aggressive acceleration rates.

Thanks for clarifying that. I have tried numbers from 10 to 75 but not higher. I will have another play and see how it goes.

This problem is still plaguing me. It is the only thing stopping me from being able to make some decent parts.

I really don't know how to fix what is going on. I am 90% sure it is the DMM drives causing the motors to oscillate but hard to confirm. It seems OK when I enable smoothing and use tool paths that have no square corners. But it is tedious having to check every tool path and sometimes there are little short square moves that I miss. I am getting more confident now with higher feed rates (1500-2000 mm/min, 60-80 inch/min) so this issue has reared its head again.

The banging is accompanied by oscillation. To my knowledge the Oak is open loop control when in precision mode so cannot be the cause of such oscillation. Assuming the Oak sends the correct position pulse count and rate to the drive, only the drive (or some mechanical issue) could oscillation at the cutting head. The oscillation does not occur when entering a cut from a radius, and cut finish is perfect once the oscillation dies out.
You can see that at on entry into this chamfer (in the X direction), the tool overshoots, then continues to oscillate (in X) as it travels in the Y direction. The chamfer goes all the way around the part and back to the start, the last cut it makes is nice as entry to the cut was a radius so no sharp X acceleration.

The problem only happens on the X and Y axis (worst on X) but seems good on the Z axis. The Z axis is under load all the time as has no counter weight. The X and Y axis present very little resistance to the motors, you can turn the ball screws by hand super easily.

Talk me through sorting this out. I have tried fiddling with every setting in the drives and the Oak!

Oak in position mode is closed loop, its just not doing the PID.

Reset drives to factory settings.
reset drive parameters for use with oak.
retune the drives with the DMM software
run position mode tuning in CNC12

cnckeith wrote: ↑Thu Jan 20, 2022 3:51 pm Oak in position mode is closed loop, its just not doing the PID.

Reset drives to factory settings.
reset drive parameters for use with oak.
retune the drives with the DMM software
run position mode tuning in CNC12

Thanks.

Could you elaborate on how the closed loop works without a control algorithm? Is it just monitoring for excessive position error or is it actually driving the output to correct the input. The reason I ask is that I am trying to determine if the Oak is causing oscillation or the drives.

I have twice now done a complete reset of the drives and tuned them again. And the oak dwell time tuning. Each time I get the same values.

yes cnc12/oak will monitors position all the time to make sure the drive actually makes it to the target time and place.
the PID control (motor motion control) is handled by the drive when in position mode. works amazingly well with yaskawa and delta.

i would re install cnc12 to set to factory defaults parameters and then set up again to make sure you didn't dig yourself a hole by changing things.

ashesman,
I do not remember,
Are you using the DMM Servos as well now?
I think Keith makes a good suggestion. Take screen shots of all your pertinent screens. Run a fresh report. Rename the CNCM directory to something like CNCM -old.
Do a fresh install, hand key in your machine settings
Try and retune the axis with DMMDRV (Screen shots before you do for reference)
Run the position mode tuning.

See if the problem persists.
Marty

martyscncgarage wrote: ↑Thu Jan 20, 2022 8:41 pm ashesman,
I do not remember,
Are you using the DMM Servos as well now?
I think Keith makes a good suggestion. Take screen shots of all your pertinent screens. Run a fresh report. Rename the CNCM directory to something like CNCM -old.
Do a fresh install, hand key in your machine settings
Try and retune the axis with DMMDRV (Screen shots before you do for reference)
Run the position mode tuning.

See if the problem persists.
Marty

Yes, using the DMM 11A servo motors. Using the entire off the shelf DMM kit now including cabling to the Oak.

To be honest I am not super keen on a re-install. There are only a handful of parameters that affect motion control and most are on their default values. I am.worried re-install could result in something not getting setup correctly. I have custom machine parameters and all sorts.

I have some things I want to try this weekend if I get some time so will give those a go before a re-install.

I had been recommended to try running in one of the analog control modes but I dont think DMM does analog control on the firmware I have.