One more thing caught my eye.
The 3 instrumentation amplifiers ( INA826 ) for the PT100 sensors are loaded too much capacitively.
The datasheet says:
Load capacitance stability: typ. 1000pF
Any amplifier with feedback is a regulating system in itself, where the bandwith and loop gain must be designed to have a sufficient phase margin at gain = 1 to avoid noise, or worse that the amplifier acts as an oscillator.
The ouput are loaded with 100ohm in series and 10nF in parallel.
10nF = 10000 pF.
Even with 100 ohms in series, the instrumental amplifier is loaded too much and challenged to keep stable.
The ADC input on the ATmega2560 has 100Mohm input resistance, so using 100ohm is not necessary.
I will suggest using 2k2 near the amplifier output and 1nF near the ADC input pin.
That will reduce the stress on the output stage in the amplifier and probably also reduce the noise on the temperature readings.
Edited by Guestspelling
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ekh 3
One more idea.
If all the linear bearings were adjustable, then we can minimize free play and get a better print quality.
It can be made as an upgrade. New bearings and plastic parts for the printhead, and replacement bearings for the buildplate.
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