Constant Velocity

[Fromtheworkshop]

Hello all,

Having used UCCNC for some time now on a number of different setups, I would like to ask about an issue I have with CV. It has been said that a switch from Mach3 to UCCNC should result in the same or better CV performance using the same settings. However I am struggling at the moment to get the smooth motion that I have with Mach3 on many programmes. Often my code will be made up of many polylines, such as when engraving maps with a laser or perhaps doing a 3D profile. I have gotten into the habit of switching to Mach3 when carrying out these kind of jobs because it seems to blend the movements better and my machine runs nice and smooth. It copes with a trunk load of lines of code buzzing past and produces nice motion. With UCCNC unfortunately I get a lot of rough motion and also the speed slows right down on many parts where there are a lot of lines to process at a time.

I understand CV and I have worked with both programmes for a few years now. However on my particular setup I don't seem to be able to get the motion smooth on these programmes, no matter what I change the settings to. I guess what I'm saying is, are there any other factors that would affect this for example, the performance of the computer? Are there any known problems that are being ironed out at the moment?

I have attached screenshots of my settings and also an example gcode file with a waterline finish on a 3D shape.

Example 3D.nc.zip

(125.75 KiB) Downloaded 769 times

[cncdrive]

I think I should start with how the CV description works in Mach3 and how in the UCCNC to let you understand a few things:

In Mach3 the CV planning is kind of unpredictable, because you can't define how much error Mach3 will make on the path, the path error in G64 mode depends on the acceleration parameter with Mach3, the higher the acceleration the less it will run off the path the less it will round corners etc.
In the UCCNC you can exactly define your job tolerances, you can define the corners error in lenght Units and you can exactly define how much you want to allow the software to run off the path, in other words you can define how much path error you want to allow for the UCCNC to make.
In general the higher the path error you allow the faster the job will be done.
Tight defined tolerances can cause more slowdown where the UCCNC will have to and will obey your settings and will have to take the law of physics into account while Mach3 has nothing to obey, it will run as it thinks it will be OK with undefined tolerances, unpredictable path errors.

The other thing is that the CV planner in Mach3 is broken in a way that it often over accelerates and deccelerates the settings you set for the acceleration parameter.
This is usual upto 2x value, but we've managed to measure out over accelerations and deccelerations upto 8x the defined value.
This issue in the CV planner will make Mach3 to finish faster with the jobs than with any other softwares, but the same time this involves a risk of lost steps when the overacceleration/decceleration happens.
The UCCNC plays safe with keeping your settings in mind and always obeying them.

And this also means that you can safely set the acceleration parameter value 2 times you setup in Mach3, because Mach3 overrides it sometimes upto at least 2 times anyways,
so what you have once setup for Mach3 as a safe acceleration value is the half the value your machine could really do.
So, I advice you to try to higher the acceleration of the axis with the UCCNC, because that will make the jobs to run faster, less slowdowns etc.

I've also noticed that Linear addition length and unify lenght is set to relatively low values, you could try to set them much higher to allow the UCCNC to unify longer vectors to a longer overal length,
this is especially adviced when the job is a high speed machining made from lots of miniature vectors.

[Fromtheworkshop]

Thank you for your detailed reply. I will try some of the changes you have suggested. Also I have closed loop steppers so there wouldn't be an issue with losing steps if I increase the acceleration - funnily enough my approach previously was to REDUCE the acceleration as my thinking was that would force the CV planner to smooth things out!

[cncdrive]

Ok, no problem.
Yes, with closed loop steppers your machine will really not loose steps, the worst thing what could happen is that the servo faults with a too high following error.
The thing is that when the machine is running on complex paths the axes have to accelerate and deccelerate many times, so the acceleration parameter will play a big rule in how the axes can maintain the feedrate. The UCCNC will always obey your settings, so if higher than the setup accelerations are required to follow that path with the set feedrate then the feedrate will have to slow down.
The higher the acceleration parameter is the faster the axes can slow down and accelerate up, so the easier they can maintain the set feedrate.