I am having some trouble with an external IMU on my VESC build. I am using a flipsky 75100 pro alu with a mpu9250 IMU. The issue is that the IMU will work for a little bit but after the board is running for 20-30 seconds the IMU just stops working entirely. The board will just output some wild reading then freeze up. Does this seem like a communication error between the IMU and the controller? In the refloat config I have set the app use to no app. Does anyone know what could cause this? If it helps I am using the SDA and SCL pins on the board to connect. I also moved the IMU as far as I could from the controller and phase wires to reduce noise.
Try putting pullup resistors to SDA and SCL pins. I had similar problems, I think I put pullup (not sure exactly, mybe even pulldown, could check in a few days) and it worked. However, I am using 75200 Pro V2.0, and still after powering off the board I need to manually search for IMU at startup. But when found, it never loses signal to the IMU and works flawlessly. I bought 3 different IMUs to try to get rid of that problem however.
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I got the IMU to stop losing connection by changing my app setting from uart to none. I think I had a port designation issue with that. Also using the 6 axis IMU instead of the 9 axis one helped reduce noise. Im using a bmi160 now. I also twisted my wires to help reduce interference.