PCutSpeedCTRL

PCutSpeedCTRL Constant Speed Controller

• It provides constant speed operation and remote control of single phase AC motor suitable for operation with 220 vac 50hz.
• When produced with BTA41 triac switching element, it provides usage up to 40 Ampere. In my initial tests I used a 1.2kW AC motor.
• The first version component cost was calculated as $3,075.
• Suitable for use with standard hand milling motors that are easily available on the world market.
• The mentioned milling motors are suitable for use in CNC machines.
• Any CNC controller can be connected directly and in isolation with a standard PWM output.
• This resource contains design and production files for hardware and firmware.
• PC Software used in the development process; KICAD 9 for Hardware, MOUNRIVER 2.1 IDE and C programming language were used for Firmware. OCTAVE was used to create look up tables for some mathematical equations.
• Test Video Youtube Link

HARDWARE Detail:

Schematic Detail:

Panelize Detail:

• We use the Kikit plugin for PCB paneling.
• We can panelize the PCB design by running the panelize_multiple.py file located in the "/HW/Panelize/" file path.
• Phase cut topology used.
• In panelized form, a new kicad project is created automatically.

Mechanic Detail:

• When the AC motor top cover is opened, 4 screw holes can be seen.
• When the top cover of the spindle motor is first opened, there will be no hole in the middle
• A metric 5 diameter hole should be drilled along the shaft, coinciding with the center.
• While designing the PCB, compatibility was ensured by using the Mac Allister manufacturer MSR1200 model AC motor.

When the rotor is turned to different angles, it should be confirmed that the magnet rotates together.

Firmware Detail:

• MOUNRIVER 2.1 IDE and C programming language were used for Firmware.
• The HYB cooperative operating system was used for the MCU resource management organization.
• Since the cooperative real-time operating system we use is very lightweight, it can easily adapt to the Microcontroller despite its weak memory.
• With this project, I am also sharing the cooperative operating system that I have been developing over the years as open source.
• I also added some libraries to the firmware that are not actively in use but could enable developments that fit the structure of the project.
• NTC temperature sensor data interpretation, ADC reading, moving average filter, some of them.

About the main routine:

• Using 2 different input capture modules, PWM input data was taken with IC1 and the magnetic sensor digital output frequency value was measured with IC2.
• Speed ​​change commands have been smoothed to create a ramp between the PWM data and the target speed information.
• Zero Cross detection was performed using the external interrupt module. Triac triggering and PID routines were run with each ZC detection.
• For linearization of the system, the source signal is assumed to be a sinusoidal signal. The equation used is the integral of the half sine signal.
• For system linearization, PID output information was applied to the linearization function using the look up table interpolation created with the Octave PC application.
• Thus, a more stable closed-loop system was obtained with fixed PID coefficients.
• Duty data was evaluated as time data to convert it into TRIAC switch signal.
• In addition to the look up table, a firmware setting option has been added to enable linearization by measurement method.
• The firmware can be made to work with different features with a set of predefined settings.
• The mentioned settings can be seen in the image below, as well as in the main.c file.

Firmware Managment Settings 1

Firmware Managment Settings 2

Octave Equations Plot and Print :

• The linearization table created with Octave PC software can be examined graphically and can be evaluated by copying and pasting directly into the C code.
• Similarly, the linearization table output from the MCU serial port output at boot up time can be directly copied and pasted into the Octave software and visually inspected.

Some Tests:

• As can be watched in the video link shared above, we performed some aluminum sheet and PCB drilling tests.
• When we apply sudden strain and sudden release tests, overshooting values ​​of up to 800 rpm occur.
• The spindle motor we tested has a 30k rpm feature at full power.
• As is known, keeping a constant speed at low rotational speeds can be a very challenging goal.
• Its ability to remain at low overshoot values ​​while at 1k rmp target speed is at a satisfactory level.
• We could observe that it does not work so stably unless linearization is applied.
• We made it possible to observe the result by disabling a single predefined setting via the firmware.

PCB Milling and Edge Cut Test Front

PCB Milling and Edge Cut Test Rear

Production:

• Gcode files created for PCB production with DIY techniques can be found in the HW/Panelize/Plot_diy folder.
• The bom list, along with supply links and unit prices, can be viewed in the "HW/bom" file path.
• For PCB fabrication files, files in the "HW/Plot" or "HW/Panelize/Plot" file path can be compressed and shared directly with the PCB manufacturer.