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cakeslob wrote:

alright, awesome thank you!

question, your previous images had the rt already installed, is there some limitation to why they arent this time, or is it so you can hit update before loading the kernel?

I chose this procedure because it allows you to choose the best Raspbian configuration (user, password, ssh, wifi, locales, etc..), to update an already existing version, to install the version of LinuxCNC of your choice and other alternatives.

However, for those who don't want to, in these links there are the ready-to-user images with LinuxCNC 2.9.2
(user:pi  pwd:raspberry)

OS: Linux raspberrypi 6.6.32-rpi999-rpi-v8 #1 SMP PREEMPT_RT Mon Jun 24 15:56:31 CEST 2024 aarch64
( image_lcnc_pi4.zip )

OS: Linux raspberrypi 6.6.32-rpi999-rpi-2712 #2 SMP PREEMPT_RT Sun Jun  9 10:10:54 CEST 2024 aarch64
( image_lcnc_pi5.zip )
 

you can see a couple of example trajectories here -  rotary toolpath .
simpleTP with parabolic blending and 1 line look ahead and there is a reason for slow velocity - it never reaches target speed on them...

No problem with large motions(x0a0 -> x100a100) - all the problem is that any multi-axis trajectory = polyline of many microscopic motions(I attached two examples with screenshots at the link). Simple parabolic blending on each of line is not enough, you need global blending with tolerance... (what Rob Ellenberg's planner does for XYZ axes).

Of course.

Well that is simple yet complex to explain. First, is the following error in the drive a match to the one derived in LCNC. The TP is in the drive so LCNC is not the ideal place to see the true FE.

In position mode, the controller should only need to send position commands as needed. It does not need to even know whether the following error exists given the actual position is dynamically controlled locally in the drive. Now, there are considerations in excess error. Time delay of the cyclic updates. Properly sized servo motors for the load(this is vital to ensure you have a 125% power to load ratio - see final note below), and the FF forward parameters which will ensure enough torque is available to maintain P/T or velocity until the loop position becomes zero. The position control loop receives a command to move 1" at 10 IPM. It will then take that 1" and use the Delta to start positioning the servo via the position FB loop to drive the motor from 1" to zero. The error is calculated within the Delta. The job of the Position loop is to make it to zero in the T requested. If it sees that the T is being stretched it will request more torque to compensate and if to early it will remove torque to comp that. The issue can be in many cases that the LI or load inertia is too great in both ACC/DEC states and continuous travel.

Most higher level drives have several params that adjust the servo response time, power levels, and FF(Aka Loop Gain). These drives also have dynamic auto tuning and if the input calcs for your inertial loads are accurately calculated will allow the auto tuner to account for the calculated load while tuning for you. But, that is the caveat. You must ensure that you have properly calculated the true inertial load of your axis.

Final Note -

The axis has a load characteristic before it actually starts cutting. Cutting requires additional torque to ensure the loop is maintained else you may have a perfectly tuned machine and fined out later while milling a slot that the error is pretty wide and may even see issues with blending or ovular interpolations. It is key to ensure that you know the static load(unloaded machine not cutting) and the dynamic load(machine moving the static while cutting adding a variable load). The math can be a bit much but there are many calcs out there in the ether to help. Once you know that value of what is specifically required, as a rule engineers like myself add 10-25% additional motor KW to ensure that the motion can maintain P/T and make targets without under shoot or overshoot and minimize oscillations at idle.

So if my calc says I need .75kw to handle S and D loads, then I install a 1kw servo. Keep my FF low, and use minor filter adjustments to cancel out ACC/DEC response at higher V.

Following error is more a measure of the servo response not the command response of the controller if in ECAT mode. ECAT can be used in closed loop of course, but that is redundant and increases chances of issues of imbalance of power. ECAT wants to separate concerns. Controller decides where the servo should go, tells the servo go here, the servo does it's job and next. If the servo has an issue, it has its' own ability to stop before disaster. Like I said, ECAT is better at point and shoot than have a controller try to manage everything. That would be like racing a Ferrari while hooked to a tow truck. It works, but the tow truck(controller) is never going to be a Ferrari(servo).

Hope that helps.

PS - Closed loop stepper drives and motors are not Ferrari's. More like a Lota. Lol. But, you can put a spoiler on a Lota and it looks pretty cool.

Thanks for thorough explanation. Drive tuning is no big deal. So if I understand correctly, the position mode is way to go. Now we only have to sort out the excessive following error within linuxcnc in position mode. Can anybody explain, why?

Just to add, I've been hovering over the lathe and unpausing it very quickly while the motor is still running. This works fine, so I think that rules out the VFD sensing any issue.

I've not jumped into the code to check this yet... but what flow control is the on the HAL -> user module signals? It appears to me that you could end up sending multiple commands to the user module, but are they buffered in any way? What happens if the user module is already dealing with a previous command?

Back in the day before the current chips used, the data for position mode was at times difficult to handle and had to be buffered on both ends to avoid stalls in motion because the drive had to process how to handle the coordination in the drive. In most cases Velocity mode was avoided because it forced the controller to do nano second position adjustments and if not tuned perfectly would cause runaway events leaving steps and tool marks in the drive.

In the industrial world the use of either position mode or torque mode are chosen. It reduces internal overhead allowing for faster feeds and more granular accuracy of motion. That said, torque mode requires additional tuning as well. The caveat in torque or velocity mode is that you machine MUST be very stiff mechanically. Otherwise you will forever be retuning the coordinated motion as all axis must be tuned to each other.

In position mode, the controller need only look at the FB compared to the actual and make minor adjustments in realtime on each cyclic data stream as needed. The drives of today have their own internal motion controller and active tuning while in position mode. This cuts out the middleman issue and allows for extremely accurate and fast position updates.

It is my express opinion that using V or T mode while possible, these are very impractical and overkill for hobby or light industrial as the cost of the required measuring equipment to tune the machine as tightly as position mode will pretty much do for you is very high. Ball bars and laser measurement is required and costs nearly $30k. And then there is the know how aspect. If you have tolerances of volumetric accuracy of .0005" or .01mm position mode is more than enough. Even for 5 axis work. Below that, and you must also include temperature compensation in the mix to maintain a true net accuracy below .01mm.

The best practice in position mode is encoder counts, encoder counts, encoder counts. 23bit absolute multi turn encoders area ideal. This gives the TP(Trajectory Planner) internal to the drive more than enough information to do nano second position loop adjustments and control servo error to sub micron accuracy. If you have a loose machine mechanically, this will help tighten the gap but never eliminate it. The second best practice is near zero backlash on all axis.

Hope that helps keep you from running down the rabbit hole of chasing tune.

Hmm, what about a Nakanishi AIr Spindle? No frequency required and obscene speeds.
Yes I'm in .AU here. Puts us close to China if you must deal with them.

hehehe

i am looking for 2 "guinea pig" buyers... nudge nudge.

The spindle i have no is DECI brand, although i am working with jianken on the the one we will use for the final machine. I need to order 5 or more to do modifications though beyond the simple winding change to 36k. They do an iso10 variant, its a few hundred dollars extra.

Your in aus right? you can buy 1000hz drives there still, but they couldn't be sent here and even if i "smuggled" one in, i could not then resell the machine with it anyway. So annoying.

There seems to be a possible exemption on PMSM spindle "kits" like a jaeger because the drive is only usable with that spindle, and not generic (so you couldn't run a centrifuge with it.

So annoying, but i think the smartest thing to do here for customers is to restrict it to 36k. 36krpm is still pretty amazing for micro cutting.

I've been thinking of a similar design. What  brand is your spindle? Maybe you should send it to me down under and I can source a 1000 Hz VFD
Did you look at ISO-10 spindles?

I’m talking both. How to make the whole setup accurate and reliable. Tuning a servo drive is a necessity.

Hi,

If i run this in a 9 axis config, it blends the corner, and therm condition=2. Wich means TC_TERM_COND_PARABOLIC.
It has a 4th axis a.



Maybe i need a sample file where the motion stops each segment.

Thanks

My spindle has caused a big issue. I wanted my 60000rpm spindle for micro milling etc. But it turns out the drives above 599hz are basically banned now.

So now i have to either get the same spindle custom wound to 36000rpm, or alternatively go to a larger 30000rpm iso20 spindle which has a lot of plusses but is really kinda too big for the machine.

 

Hmmmm

On the bright side I did get the existing spindle behaving since the steel cutting video. It doesn't bog down anymore. Gonna do another nifty video cutting 0-1 steel next week. Waiting on cutters.
 

Very cool machine.

# Module loaded in main hal.
loadusr mitsub_vfd --baud 19200 --port /dev/ttyUSB0 mitsub=01

# custom_postgui.hal Connections for mitsub as it is a user module.
net estop-out mitsub.estop
net spindle-vel-cmd-rpm-abs => mitsub.motor-cmd
net spindle-enable          => mitsub.run
net spindle-cw             => mitsub.fwd
setp mitsub.scale-cmd .084175
 

Are you talking about the tuning on the servo drive? I have already turned it off. I have only adjusted the stiffness setting on the servo drive, but it seems to be useless. I adjusted the stiffness using the p item in the pid