I am pretty sure this was caused by the 3.3 upgrade. I have successfully calibrated the accelerometers many time recently and when I tried after 3.3 it times out and will not calibrate. I hooked up my trusty Iris after several attempts on my 550 and the Iris responded as normal. I then hooked up a spare pixhawk and uploaded 3.3, attempted a calibration with no results. Neither unit will calibrate now even if I revert back to 3.2.1. I took the 550 to School today and successfully calibrated 3.3 with a PC running Mission Planner. I came home this afternoon and uploaded 3.3 to my Iris and it now has joined the other two in the calibration fail pile. I am now out of tricks and could use some help.