Motor System Identification using asctec MAV frame work
I am trying to do motor system identification of pelican using MAV frame work. I'm giving one of the motor of the pelican a step input and trying to record the motor speed by reading the ROS topic "/fcu/motor_speed". I'm doing ros bag record to save the data on the onboard computer of the pelican. The response of the system is not like a first order response, rather the output is just a delayed version of the input. In other words, when I give a desired speed of 100 starting from 0, I expect "/fcu/motor_speed" to give me values like 01,3,5,7,9,14,24,33,39,45,...99,100,100,100... (like an exponential function tracking a unit step input). However the response I get is 0,0,...0,0,100,100,100....
Clearly, this is wrong. I'm getting the commanded motor speeds after some delay! Has someone performed pelican motor's system ID before? Am I doing any thing wrong in recording the data?
Re: Motor System Identification using asctec MAV frame work
How did you set the IMU-packet rate? That's the rate at which motor speeds are sent as well. The default is 50 Hz, and the time constant for a Hummingbird motor is 1/80s and 1/40s for spinning up/down  (I'm assuming it's somewhat similar to the pelican, maybe a bit slower), so that might explain the behaviour.
If you need accurate results, you should probably record the measurements on the HLP and then send them to the onboard computer.
 Wang, J., Bierling, T., & Höcht, L. (2011). Novel Dynamic Inversion Architecture Design for Quadrocopter Control. Advances in Aerospace Guidance, Navigation and Control.