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CNC V3.2.2 - SIMATIC IOT2020 and bipolar stepper motors

Electronic components of CNC v3.2.2

Short video about CNC v3.2.2

Carving lenses with CNC v3.2.2

About CNC v3.2.2

Mechanics of CNC router v3.2.2
Figure 1:
The development of CNC v3.2.2 is sponsored by Siemens and RS Components. The machine was displayed on the Maker Faire on May 25-27, 2018 in Berlin at the stand of Siemens.
The frame of CNC v3.2.2 is mostly composed of 19mm chipboard as an option to the steel frame of CNC v3.2.1. The wooden frame is cheaper and simpler to build.
The motors I am using are bipolar stepper motors to get an option for the electronics as well. The central brain is a SIMATIC IOT2020. I am running the "Apache" webserver on the IOT2020 to control the machine through a graphical user interface and an adopted version of grbl to implement G code functionality.

Parts list (not complete, yet)

This CNC originates from a cooperation with RS-Components which is why links in the table point to their online shop.

Part Pieces RS Components Remark
SIMATIC IOT2020 1 124-4037  
Siemens SITOP PSU100S 1 776-7738 12V 14A output
RS Pro Hybrid stepper motor 2.8A at 2.8V 1 535-0423  
Chipboard ca. 4m2   Plan will be published, soon.
Aluminum square tubes 20x20x1000mm, 2mm wall thickness 18   Steel square tubes are an option.
Parts motor drivers
Part Pieces RS Components Remark
IC motor driver LV8772-E 2.5A 3 821-3068 Pin distance 1.78mm
Axial Wirewound Resistor, 220mΩ 3W 6 485-1414 Current sensors
Single Sided Matrix Board 3 206-8648  
Ceramic Capacitor 180pF 3 133-5673  
Ceramic Capacitor 0.1μF 12 133-5719  
Electrolytic Capacitor 470μF 3 365-4313  
Trimmer Resistor 10kΩ 3 473-473  
Fixed Resistor 47kΩ 12 707-8369  
Fixed Resistor 10kΩ 3 132-731  
Fixed Resistor 2kΩ 3 132-567 Optional for green status LED
BS170 N-channel MOSFET 3 671-4736 Optional for green status LED
LED 5mm green 3 228-6004 Optional for green status LED
Heatsink 8.5K/W, 50mm x 21.45mm x 19mm 3 674-4715  


Electronics of CNC router v3.2.2
Figure 2:
I am using ICs type LV8772 as motor drivers, all soldered on prototyping boards. The chips are manufactured with a distance of 1.78mm between the pins, but the boards I have in stock have a 2.54mm grid. In prototyping there is: What doesn't fit will be made to fit. By bending the pins and using pieces of copper wire, I managed to build the circuit on my boards.
Only a few external components are needed to make the motor driver work, such as 6 capacitors, one is a large electrolytical type to smoothen the input voltage, two 220 milliohms 3 Watts resistors operating as current sensors and finally six 0.25 Watts resistors and a potentiometer. The green LED used to indicate the function of the IC is an extra I have implemented.
Cooling power ICs is always a good idea, I am using aluminum heat sinks.
The phase current is adjusted with the potentiometer on the board. The maximum phase current of the IC is 2.5A which is below the limit of the motor, however 1.3A are definitely enough to move the axes of the CNC with sufficient torque and speed. Avoid going to the limits to get a long life-time of your electronics.

Electronics of CNC router v3.2.2
Figure 3:
Circuit layout motor drivers:
3 boards in total are needed vor this CNC.
This machine is under construction. The documentation will grow as the machine does - stay tuned!

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