Hi everyone. I’ve got some questions about differences in flight performance between different size drones. Let me set the stage with some data points.
- Drone 1: 550 mm hexacopter weighing 7.6 lbs fully loaded
- Drone 2: 960 mm hexacopter weighing 18.8 lbs fully loaded
- The 960 has retractable landing legs; the 550 has fixed legs.
- Both drones running PX4 v1.13.3
- All PIDs are default.
When flying, there is a noticeable difference in their stability (I’ll use a non- scientific term - smoothness). When the 550 comes to a waypoint, it yaws smoothly on its axis while doing a slight roll as it turns. It then heads directly towards the next waypoint without changing heading, i.e., there is no overshoot.
The 960 on the other hand, when it comes to a waypoint, has a more jerky motion. As it yaws and rolls, it overshoots heading and then brings it slowly back to correct heading. This motion is very noticeable from the ground. This happens whether the landing legs are down or retracted.
So here are my questions. How does the size and weight affect flight dynamics? Do heavier drones with larger moments of inertia behave differently than lighter drones? Does this have anything to do with the power-to-weight ratio? Does propeller diameter and rpm have any affect? Is there any theoretical work that’s been done to explain this phenomena?
Clearly, from my experience, the larger drone flies much poorer than its smaller brother. I’ve tried adjusting some PIDs without much success. I’m interested in knowing if there is some way to make the larger drone fly smoother. Or am I barking up a tree because the physics are what they are.
Sorry for the long dissertation. If you got this far, thanks for reading!
Thanks
Joe