A whole lot of questions about the PandaPi, because it sounds awesome:
Looking at the images, I only see 2 hot-end thermistor and heater connectors. So it's OK for e.g. a Diamond 3-into-1 hotend, but not for 3 separate hot-ends?
What stepper drivers can I use? Obviously A4988, TMC2208, TMC2209. But what about DRV8825 (which I have several spare)?
Can the bed heater output switch 240VAC? Or would I need an external SSR?
You have Marlin 2.0 running as a Real Time task on the Pi CPU itself, right? So the only function of the STM32 CPU is to extend the number of IO ports? Seems overkill for a 32-bit CPU! Could you not connect to those devices (heaters, fans, thermistors) directly from the RPi via I2C or SPI? Especially since they are all slow speed and not particularly realtime-critical.
20A is a lot of current... the power connector doesn't look beefy enough. Is it rated for 20A?
Can I plug another RPi shield (e.g. watchdog timer, UPS) into the RPi?
Why not flash your MCU firmware from the RPi itself, rather than needing a micro-USB connector and UART?
Any issues with the RPi and/or stepper drivers overheating? I see you have big heatsinks on the drivers in one of your photos.
What are all the heater outputs rated at? I assume only the bed is 15A? Typically hotends are 40W, so 4A@12V or 2A@24V.
If I have a heated bed at 15A, and 2 hotends at 4A, that's more than the 20A you say the input is rated at.
Is there any need for an LCD and knob, with Marlin running on the Pi? Can't everything be controlled via the Octoprint website? Perhaps running on a full-size HDMI screen?
On the PandaPi3d.com website, I can't look at my cart with "View Cart" in either Firefox or Chrome, so I can't buy a board here. :(
Frank
That's depends on users. there is one advantage of LCD and knob, you can stop print immediately with knob,but can not with octoprint because it sends gcode command to stop,and the printer will wait all the cached gcode fininished and then stop.
that's strange, because I use firefox and chrome too.and I will feedback to the site supplier. Sometimes it’s because the site is slow.
that's big heatsinks are for the TMC2208 which I ordered, different company have different heatsinks for their driver modules. if the temperature of the TMC2208 is higher than about 90°C it will reboot.
the output rate depends on the mosfet. and all the heater mosfets are the same,it is PSMN1R0-30YLC, 30V/100A/1.15mO,I have tested with 30cm bed about 360w,because of the 1.15mO ,the self heat temperature is very low.
that's right! but I found the common used thermistors and fans are not I2C or SPI. actually, the 32bit CPU connect to RPI via I2C, so you can consider this 32 bit CPU is just a I2C devices(heaters,fans,thermistors) connect to RPi directly.
The connector for the power and heater is KF129 5.08mm,that can load 25A 300V
you can plug another RPI shield, but there are nearly no free GPIO left.
the MCU connector to the RPi via I2C,and I have tried to writing a bootloader for flash MCU firmware from RPi, but unstable,so I will try to that when I have time.
they are very good questions!
That's right, there are 2 hot-end thermistor and 2 heater, so not for 3 separate hot-ends.
like many other control board,the driver connector support not only a4988,TMC2208/2209, also LV8729、DRV8825.
the bed heater output is within 24V, can not be connected to 240VAC directly,but it's OK for relay of 240VAC,or external SSR.