Flight path not following waypoints accurately

This is my first post here, and I am still getting oriented to Ardupilot and Mission Planner. In the past I have used QGroundControl and PX4. Most of my drone flying involves missions that move thru geometric patterns, like circles, rectangles, and other more complex shapes, like a star. When flying these missions using Ardupilot, the drone does not follow the waypoints accurately. I find that it sometimes curves around a waypoint instead of stopping right on it. When it flies a circle it really can’t stay on course. I also had a recent mission that had an altitude error of one to two meters.

I have flown all of these missions with PX4/QGC before, and they give very accurate representations of the waypoint path. So I am wondering if anyone else has experienced this issue? I know that most people fly drones with cameras, and they are not too picky about how accurate the path follows the waypoints as long as the pictures come out great.
But in my case I am not flying a camera. My requirement is to position the drone fairly accurately in order for our tests to go well.

I am thinking that perhaps there are some parameters that need to be tuned to make the position responsiveness tighter and more crisp. Maybe it needs to accelerate and decelerate more rapidly. Not sure. But if there are any possible solutions or approaches to this, I would like to hear from this group.


Your question is a bit universal, accuracy of flight and position.
There are many factors that are going to affect the repeatability of the flights and accuracy to the given flight path.

1: GPS - There are many discussions on GPS (used generically here) accuracy. And there are many ways to improve the results. Most hinge around dollars spent. A search will reveal the discussions.

2: Copter design and tune - As you have given no details about your copter I will leave this in general terms.
Weight/Power/Tightness of Tune/Weather and a myriad of other smaller factors are going to have an impact on the accuracy of flight.

3: Mission commands - There are many types of waypoints and mixtures thereof. For example, adding a small pause at a waypoint will assist in making it more defined instead of curving around it.

So that is just food for thought for starters.
This is a vaster topic than you might first think.

Mike, some of what you say is what I am trying to get my arms around. For example, how similar are the default parameters in PX4 and Ardupilot? If they are significantly different then I expect different results. My problem is I don’t know where to start looking. When the same drone performs differently with two different flight stacks, my assumption is that its not the drone, but the differences in the flight stacks. What are these differences? How do I go about finding them, and then what parameters need to be changed?

The copter is a DJI F550 Flamewheel with all DJI motors / ESCs, and the Pixhawk 1 controller. Without changing any of the components of the system, all I did was install Ardupilot in place of PX4 and fly the same missions.

I can try the small pauses at waypoints, but that won’t help the situation where it doesn’t go to the waypoint but curves away from it to point to the next one. Then there is the wavy line, where instead of moving on a straight line to the next waypoint, it weaves back and forth.

If its a parameter issue, which ones are causing these behaviors?

Thanks for any help you can make available.