Makerbase MKS Servo42

Feb 5th 2019

As most of you are aware Makerbase knocked off the Smart Steppers and even used the firmware from the smart stepper project. 

Makerbase did not release the firmware many people have asked for the Smart Stepper firmware to support the Servo42 hardware.  Some have asked why would we do this, as we need to make money to stay in business and Makerbase's competition in the market hurts our ability to make money.   Which is all true but we also feel that creating good will in the community will pay off long term.  Also if you read about the limitations they have on the Servo42 hardware you might consider purchasing a genuine smart stepper. 

If you want to help us keep the firmware open source and thank us for porting to the Servo42, please consider donating to help us keep going, every dollar helps. 

Also if you need an LCD for your board they can be purchased  here: 


Servo42 Hardware Differences

Interesting the Servo42 is such a direct copy they even kept most of the reference designators the same, this made it much easier to reverse engineer.

There are a few differences. First off they use a different encoder the A1333 verse the AS5047D. The AS5047D has some advance processing to improve the accuracy, the A1333 is much cheaper. 

The A1333 must be powered from 5V, the diode in bottom right feeds the 5V to the encoder. Note that their are two diodes between the 5V and the A1333 which reduces the voltage on the A1333 to ~3.6V which is below the minimal operating voltage of 4.0V for the part.  MKS most likely added the second diode on bottom right as that noise on the 5V power rail was causing issues, with the operating voltage below the specifications it may still have issues. 

Their is single 22uF motor capacitor, which concerns me as that many people have had noise problem and this small motor capacitor is likely to cause more ripple on the motor voltage and thus more noise and interference. Also the small capacitor is not recommended as it will limit the inrush current to motors and hence the peak torque and speed of the motor. 

The buck converter has been removed, which means the unit must be powered from the external 5V connector or from the USB to work.  The unit will not work unless 5V is applied and 3.3V will not be enough. 

The pull ups on the Step, Dir, and Enable pins have been removed, this could cause the units to be more sensitive to noise if long wires are used to feed the step and direction pins. 

They removed the USB Transient Voltage Suppressor (TVS), as such it could be possible for ESD on USB to fry the microcontroller.

The also removed the external UART connections, so communicating with units through another processor and controlling will not be possible like on the smart steppers. 

I question some of the layout decisions on the motor driver, much less heat sink and such.

The six pin connector on bottom right in figure above is the SWD interface for factory programming, they also added J7 as a cortex debug header.

Also note the Error Pin and other connections have been removed as well as the motor and 3.3V zeners which help with ESD and noise suppression, of course they had to get cost savings from some where. 

Firmware Changes

The firmware appears to be a direct copy of the Smart Stepper firmware with exception they had to change the driver for the encoder.

The firmware and hardware are such clones plugging in a Smart Stepper LCD brought up the Smart Stepper menu system. 

The only changed in the firmware for the smart stepper to support the Servo42 was adding the A1333 encoder.  This was added in the 0.39 firmware and you can build the code and support the MKS Servo42 by making sure the following lines are uncommented in the board.h file:

#define NEMA17_SMART_STEPPER_3_21_2017

#define A1333_ENCODER


Using this firmware for the Servo42 means that you will loose the stock firmware that came with the unit.  I do not have a copy of the stock firmware for the Servo42, so please do not ask. Also if you need hardware support for the Servo42 please contact Makerbase, for support using the open source firmware please use the google groups forum for the smart steppers.!forum/smart-step...