Unexpected Dynamics in SimMechanics Model

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Jonathan
Jonathan on 5 Mar 2016
Commented: Rajeeb Barma on 11 Jun 2016
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.

Answers (1)

Rajeeb Barma
Rajeeb Barma on 11 Jun 2016
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
  1 Comment
Rajeeb Barma
Rajeeb Barma on 11 Jun 2016
Please reply if you get any answer! I have an urgent requirement.

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