R_Lefebvre
Arducopter Developer
Just throwing this out there as a courtesy to the folks on this forum who might not otherwise see it.
I started flying an octocopter with APM2.5 a few weeks ago, and discovered that it has a fairly significant performance issue. We have long been concerned about the processor loading on the 8-bit AVR, and as seems to be all too common, I'm the canary in the coal mine. I guess nobody else has been flying octocopters on AC 3.0 up until now? I was flying helicopters all summer and they do not exhibit the problem. I finally started flying my Octocopter on 3.0 and realized the problem.
Basically, quads and helis fly great on 3.0. And I guess Hexas are OK. But Octo's really start to bog down the processor in Loiter mode. Stab mode is fine. Alt_Hold is OK. But Loiter and Auto start to exhibit performance deficiencies that result in unacceptable behaviour. Basically just sloppy control from Alt Hold and Loiter, though stabilization is still good. However, if you use Simple mode, it really goes to hell. The extra couple trig calculations for Simple mode really kill it. And, if you have camera mount code running, the situation is critical and could result in a crash.
It's not a software bug, or a hardware design problem. It's just, the extra calculations, from those extra two motors, and simple mode, push it over the edge to where the process breaks down. In testing, I had repeatable crashes due to the issue.
So, my recommendation is, don't do it. Don't use an APM for Octocopters unless you only want to use Stabilize and Alt Hold mode. Avoid Loiter in combination with Simple mode. Waypoint flying could be bad too.
I started flying an octocopter with APM2.5 a few weeks ago, and discovered that it has a fairly significant performance issue. We have long been concerned about the processor loading on the 8-bit AVR, and as seems to be all too common, I'm the canary in the coal mine. I guess nobody else has been flying octocopters on AC 3.0 up until now? I was flying helicopters all summer and they do not exhibit the problem. I finally started flying my Octocopter on 3.0 and realized the problem.
Basically, quads and helis fly great on 3.0. And I guess Hexas are OK. But Octo's really start to bog down the processor in Loiter mode. Stab mode is fine. Alt_Hold is OK. But Loiter and Auto start to exhibit performance deficiencies that result in unacceptable behaviour. Basically just sloppy control from Alt Hold and Loiter, though stabilization is still good. However, if you use Simple mode, it really goes to hell. The extra couple trig calculations for Simple mode really kill it. And, if you have camera mount code running, the situation is critical and could result in a crash.
It's not a software bug, or a hardware design problem. It's just, the extra calculations, from those extra two motors, and simple mode, push it over the edge to where the process breaks down. In testing, I had repeatable crashes due to the issue.
So, my recommendation is, don't do it. Don't use an APM for Octocopters unless you only want to use Stabilize and Alt Hold mode. Avoid Loiter in combination with Simple mode. Waypoint flying could be bad too.