Uploaded May 2026 | Updated September 2026, 1 hour ago
Because the Schaublin 125-CNC lathe spindle control is based on the manual 125, it is rather overcomplicated. I am trying to create software control of the VFD, CVT and backgear automatically, and it is difficult.
Here is the LinuxCNC forum post on this...
forum.linuxcnc.org/26-turning/41498-schaublin-125-cnc-retrofit?start=670#346453
__________________
18 MAY 26
Before I add a sensor which Schaublin didn't need when they designed this system in the first place, I am thinking of taking one last swing a software solution. My original idea, which I have not yet tried. How accurate does a lathes spindle speed control really need to be?
- divide the CVT range into 5 "fixed ratios", one second apart.
- survey the whole range, generate a look up table of CVT "fixed ratio", and VFD Hz.
- Command the CVT in one second bumps (gear changes).
- largely open loop with VFD frequency interpolated between LUT values.
- Maybe switch to closed loop to fine tune speed (but I am hoping not to need to)
-- if closed loop needed, add PI gains to the LUT.
-- I already have VFD "motor on speed" wired in, and had not thought to use that to gate and freeze the ratio calculation when it would be garbage.
-- when there is steady state operation, use the calculated ratio just to cross check and maybe correct for CVT drift after multiple shifts. In practice, I expect it to be on limits quite often, which is a natural drift reset.
If I can't get that working, and really need a sensor, there are a number of ideas:
1/ pull the motor fan, and use the shaft stud to drive an encoder, and then mount an electric cooling fan on the shround for the motor.
++ Seems most robust solution.
++ covers entire drive train with single unit.
++ high resolution, low noise
++ encoder in and encoder out, the gear ratio would be rock steady and real time.
++ be done without pulling the entire drive unit.
2/ Make a little amplifier to scale that 0-10V motor speed output to 0-36V
++ Simplest solution
-- I am not strong in electronics.
-- less resolution than motor encoder
3/ use an optical or hall sensor to count motor fan fins, or CVT features.
++ Slightly simpler that adding an encoder... or not,
-- as it would need the entire drive pulled.
-- less resolution then encoder
-- doesn't sense gearbox ratio.
4/ Add an encoder to the CVT linkage, or to the CVT lead screw, or an AS5600 sensor to the joint
-- better options above
-- need to pull drive unit.
-- non-linear relationship to ratio
-- needs LUT or algorythm to convert to approx ratio.
-- less resolution than motor encoder
-- doesn't sense gearbox ratio.
5/ Replace the CVT motor with a stepper or servo
-- more work than the better options above
-- better options above
-- need to pull drive unit.
-- non-linear relationship to ratio
-- needs LUT or algorythm to convert to approx ratio.
-- less resolution than motor encoder
-- doesn't sense gearbox ratio.
6/ Use a laser range finder on the CVT belt with a look up table to estimate ratio.
-- dirty environment, optics will likely be unreliable over time.
-- better options above
-- non-linear relationship to ratio
-- needs LUT or algorythm to convert to approx ratio.
-- less resolution than motor encoder
-- doesn't sense gearbox ratio.
7/ Using a sensor to detect backgear lever position .
-- dont think there is an external lever, it is internally, pneumatically actuated with no external moving parts.
-- Since it is only shifted stationary, this is the easiest to infer. I can log last position, and cross check it using overall ratio, so this seems unnecessary.
8/ add a prox sensor to measure gear teeth in the gearbox
-- lot of work to pull, strip, modify the gearbox.
-- less resolution than a motor encoder.
better solutions above.
Seems to me that the motor encoder would to be the most likely to simply work, and work best. It covers the entire drive train in a single component, offers the highest resolution, and provides (with the spindle encoder) the most direct measurement of overall reduction ratio without noise, interpolation, LUTs etc.
___________________
If you enjoy my content and would like to support my channel... I'd really appreciate it.
Please join me on Patreon and help build this community.
patreon.com/RotarySMP
or sign up for youtube memberships using the "JOIN" button above.
or please just buy me a coffee...
tinyurl.com/5cv2yscb
____________________
00:00 - Intro
00:55 - Why the complicated drive system?
04:07 - The CVT
04:43 - The system architecture
05:56 - Control inputs
06:22 - VFD control
07:53 - Why not simplify the drive system?
08:07 - Gearbox control
09:08 - The dynamic change in inertia makes it challenging
11:16 - What does the software need to do?
14:09 - How to infer the overall reduction ratio?
17:32 - Test cuts with Chat GPT's software
23:16 - Complex model from Claude AI.
27:18 - Stuck in AI hell.
Because the Schaublin 125-CNC lathe spindle control is based on the manual 125, it is rather overcomplicated. I am trying to create software control of the VFD, CVT and backgear automatically, and it is difficult.
Here is the LinuxCNC forum post on this...
forum.linuxcnc.org/26-turning/41498-schaublin-125-cnc-retrofit?start=670#346453
__________________
18 MAY 26
Before I add a sensor which Schaublin didn't need when they designed this system in the first place, I am thinking of taking one last swing a software solution. My original idea, which I have not yet tried. How accurate does a lathes spindle speed control really need to be?
- divide the CVT range into 5 "fixed ratios", one second apart.
- survey the whole range, generate a look up table of CVT "fixed ratio", and VFD Hz.
- Command the CVT in one second bumps (gear changes).
- largely open loop with VFD frequency interpolated between LUT values.
- Maybe switch to closed loop to fine tune speed (but I am hoping not to need to)
-- if closed loop needed, add PI gains to the LUT.
-- I already have VFD "motor on speed" wired in, and had not thought to use that to gate and freeze the ratio calculation when it would be garbage.
-- when there is steady state operation, use the calculated ratio just to cross check and maybe correct for CVT drift after multiple shifts. In practice, I expect it to be on limits quite often, which is a natural drift reset.
If I can't get that working, and really need a sensor, there are a number of ideas:
1/ pull the motor fan, and use the shaft stud to drive an encoder, and then mount an electric cooling fan on the shround for the motor.
++ Seems most robust solution.
++ covers entire drive train with single unit.
++ high resolution, low noise
++ encoder in and encoder out, the gear ratio would be rock steady and real time.
++ be done without pulling the entire drive unit.
2/ Make a little amplifier to scale that 0-10V motor speed output to 0-36V
++ Simplest solution
-- I am not strong in electronics.
-- less resolution than motor encoder
3/ use an optical or hall sensor to count motor fan fins, or CVT features.
++ Slightly simpler that adding an encoder... or not,
-- as it would need the entire drive pulled.
-- less resolution then encoder
-- doesn't sense gearbox ratio.
4/ Add an encoder to the CVT linkage, or to the CVT lead screw, or an AS5600 sensor to the joint
-- better options above
-- need to pull drive unit.
-- non-linear relationship to ratio
-- needs LUT or algorythm to convert to approx ratio.
-- less resolution than motor encoder
-- doesn't sense gearbox ratio.
5/ Replace the CVT motor with a stepper or servo
-- more work than the better options above
-- better options above
-- need to pull drive unit.
-- non-linear relationship to ratio
-- needs LUT or algorythm to convert to approx ratio.
-- less resolution than motor encoder
-- doesn't sense gearbox ratio.
6/ Use a laser range finder on the CVT belt with a look up table to estimate ratio.
-- dirty environment, optics will likely be unreliable over time.
-- better options above
-- non-linear relationship to ratio
-- needs LUT or algorythm to convert to approx ratio.
-- less resolution than motor encoder
-- doesn't sense gearbox ratio.
7/ Using a sensor to detect backgear lever position .
-- dont think there is an external lever, it is internally, pneumatically actuated with no external moving parts.
-- Since it is only shifted stationary, this is the easiest to infer. I can log last position, and cross check it using overall ratio, so this seems unnecessary.
8/ add a prox sensor to measure gear teeth in the gearbox
-- lot of work to pull, strip, modify the gearbox.
-- less resolution than a motor encoder.
better solutions above.
Seems to me that the motor encoder would to be the most likely to simply work, and work best. It covers the entire drive train in a single component, offers the highest resolution, and provides (with the spindle encoder) the most direct measurement of overall reduction ratio without noise, interpolation, LUTs etc.
___________________
If you enjoy my content and would like to support my channel... I'd really appreciate it.
Please join me on Patreon and help build this community.
patreon.com/RotarySMP
or sign up for youtube memberships using the "JOIN" button above.
or please just buy me a coffee...
tinyurl.com/5cv2yscb
____________________
00:00 - Intro
00:55 - Why the complicated drive system?
04:07 - The CVT
04:43 - The system architecture
05:56 - Control inputs
06:22 - VFD control
07:53 - Why not simplify the drive system?
08:07 - Gearbox control
09:08 - The dynamic change in inertia makes it challenging
11:16 - What does the software need to do?
14:09 - How to infer the overall reduction ratio?
17:32 - Test cuts with Chat GPT's software
23:16 - Complex model from Claude AI.
27:18 - Stuck in AI hell.
