Unexpected Dynamics in SimMechanics Model

Hi community,

I am in the process of learning Simulink, SimMechanics, and SimElectronics. I am leveraging these tools to model a quadcopter system ( see attached ). So far I have used SolidWorks to create an assembly representation of a DJI F450 frame and brushless DC motor quadcopter system. I used SimMechanics Link to generate a SimMechanics 2nd Generation model of the system for Simulink. At this point I am having trouble with the dynamics of the system when I apply a torque to the motors. If I apply a positive torque to arms 1 and 4 and an equal but opposite torque to arms 2 and 3, then the quadcopter spins out of control. However, I would expect the quadcopter system to maintain stable upward thrust.

Any insight as to why this is happening would be much appreciated! I have not been able to figure out why it is doing this. I have verified that all of the arms, motors, and body have identical parameters. I have also verified the dimensions of the various components are symmetrical, so there should not be any discrepancies due to lack of symmetry.

Answer 1

[Rajeeb Barma]

i have the same problem with altitude. I have given thrust to all the four rotors through a single ramp input. My quadcopter gains and overshoots normally for some time. Then at around 12-13 secs, it gets imbalanced and pitches/rolls arbitrarily. It happens faster (i.e starts pitching at around 2-3 secs) if the weight is decreased. PS: I have checked that the dimensions of the quad are identical

[Rajeeb Barma]

Please reply if you get any answer! I have an urgent requirement.