No SPI response when more than 3 Brick Pi3 boards are stacked together

For our project , we need 4 Brick Pi 3 boards stacked together. 1 or 2 boards without any problem, for 3 brick Pi boards, sometimes works well and sometimes does not. For 4 boards, we always got the error “no SPI response”.
We already updated the software on raspberry PI and firmware(1.4.6) on the Brick PI 3.
Check all the boards are stacked well and all the pins are connected well.
We need more advice on how to stack the Brick Pi 3 boards.
Thanks a lot.

I don’t believe more than 3 have been stacked and tested, so results with 4 or more are unpredictable.

Electrical signal impedance would likely be the limiting factor. The software limit is 255.

To rule out software and address configuration problems, did you follow the instructions and example here? Each BrickPi3 needs to be assigned a unique address, using it’s unique ID (or “serial number”).

In my testing, 3 BrickPi3 boards worked 100%, and using a scope, the signals were still very clean. This was specifically with a Raspberry Pi 3. I suppose a different version of Raspberry Pi board (e.g. 2 or 3B+) could have different GPIO pin characteristics.

  • What version of RPi board are you using (2, 3, 3B+, etc.)?
  • What OS are you running (Raspbian for Robots, DexterOS, Raspbian)?
  • What BrickPi3 software are you using (Python, C/C++, etc.)?
  • What is the BrickPi3 hardware version of your boards?

I’m curious, what project are you working on where you need that many sensors or motors?

Hi Matt,
Thanks for your help.
The project is for an educational lego robot which needs around 14 lego motors. They won’t work at the same time. We used one battery pack to power all the boards at the same time.
We used Raspberry P 3 Model B V1.2 board and Raspbian for robots. Our program is developed under Python. The hardware version is V3.2.3 on the board, but from the software reading, it is V3.2.1, the firmware version is V 1.4.6.
we also tried to use another Raspberry Pi board.

Do you have any further suggestion?

Just for Grins and Giggles, have you tried washing the board/pins in denatured alcohol to remove any manufacturing residue?

How did this go? I’m curious about adding additional sensors to my GoPiGo.