Are there any reasons to chose one over the other? I know that the props turn in opposite directions relative to each other but what actual difference does it make? We are flying a coax octo that is longer length wise than width so H seems the more appropriate but I have no idea how this would really effect frame choice rather than just having slightly different PID values when tuning. Thoughts?
The difference has more to do with the arm geometry to the frame. Compare the illustrations on the motor order page between X&H.
An answer to an old post by a Developer.
H frame works better for frames
that are somewhat flexible in the “waist” area. I.e. frames that can
twist a bit in the middle.
The H frame doesn’t help with frames that
are not symmetrical. I don’t think a non-symmetrical frame will have
too many problems using a regular X frame.
This has been my experience after building all manner of quad geometry. Different case but even some that look like V’s worked better on X than V.
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I had a use-case where “H” type seemed to make sense. If you’re into the race/freestyle quad hobby, they usually refer to this as reverse-yaw. Some of the freestylers that fly around trees a lot prefer reverse-yaw as the props tend to bounce the quad off of branches that you accidentally run into, where as normal-yaw tends to grab branches getting your quad stuck in trees more often.
I know that in the copter setup documents, they indicate that somehow the arm geometry is different, but in the end, with regard to controls, the only real difference is that all the motors spin the other way. There is no place to enter any parameters relevant to arm geometry.
My use case was on a larger (15"), lightly loaded quad where yaw authority was weak. I ended up angling all the motors to directly augment yaw through a small thrust vector. It just takes a few degrees to do this. This has worked well, and works the same with both “X” and “H” setup.
That particular copter also has a very low CG. The low CG puts the bulk of the lift burden on the rear motors in cruise flight. All copters that I have ever flown suffer from biased aft loading in high speed flight, but the low CG made it even worse.
The rationale for switching to “H” came about from the modified motor thrust lines for augmented yaw. In the “X” configuration the front motors are angled slightly back, and the aft motors are angled slightly forward. Therefore in cruise flight, the aft motors had a steeper pitch angle than the front motors, making it harder for them to support the vehicle weight. The theory was that by switching to the “H” configuration the aft motors would be closer to level in cruise flight, making it easier for them to support the vehicle weight.
In real flight experiments I have not been able to measure a difference in motor loads between “X” and “H” though. If there is a difference, it is subtle and lost in the noise of flight in real world conditions.
I suspect on an octocopter the difference would be more subtle, and on an X8 (coax-oct), I can’t imagine that there is any difference at all, from a performance perspective.