My problem is that when i hold my sensors (MPU9150) so that +y axis is downward, and y axis is on the horizontal plane, i expect that pitch = 90 degree, and roll = 0 degree, but actually pitch = 90 degree, and roll = 160 degree. However, when roll = 90 degree and pitch = 0 degree (That is what i expect). Do you know what cause my problem? Thanks


For the most common definition of roll, pitch, yaw used in UAVs, when pitch=90deg you encounter what's called gimbal Lock. Basically, when pitch=90deg you have infinite combinations of roll and yaw that will give you the same physical result.

  • $\begingroup$ Okie, Recently, i knew the reason like you said. Thanks anyway $\endgroup$ Oct 31 '14 at 13:06
  • $\begingroup$ @TuyenVoQuang ...which is why the MPU 9150 can also output quaternions. $\endgroup$ Nov 2 '14 at 5:40
  • $\begingroup$ Yes, i can know that, but how can we use quaternions to control the quadcopter is difficult so i choose Eulers. $\endgroup$ Nov 3 '14 at 6:48

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