First, in what I'm about to say, I am not trying, or wanting, to put Hobbywing down...I'm trying to help. Also, I won't post all the technical jargon, partly because I can't remember it all, and partly because I didn't exactly understand all of it. Anyways, here's the "condensed" version of what I was told:
Bluetooth 5.0 BLE can handle approximately twice the data, and to approximately twice the distance, as Bluetooth 4.2...when it's implemented properly...and therein is the problem that several companies are having problems with. In the API, you should be targeting at least Level 21...anything lower/older, and your, essentially, causing a limitation. Additionally, while Bluetooth 4.0-4.2 is backwards-compatible with older versions, Bluetooth 5.0 is not...a BT5 device can only connect with another BT5 device. Some manufacturers have tried to create "hybrid" chips, but all have (supposedly) been proven to be problematic...if they work at all.
Another problem is radio interference. Having too many "devices" (a chipset, in the circumstance being received, can be considered a "device), too close together, operating on similar frequencies, will problems. BT operates on the 2.4GHz band, as do RC receivers. Electronic devices, such as ESCs, can "create" frequencies...and those are usually in the 2.4GHz range. When he mentioned this, I thought to all the times I've been wearing me BT headset in the kitchen, and the interference that's been caused when the microwave is on (which also emits frequencies in the 2.4GHz range.
Finally, as I mentioned in an earlier post, the chipset, itself, can also cause this type of problem. Cheaply designed and/or manufactured chips can lead to problems, but even chips from well-known/high-quality manufacturers can have problems. When he mentioned that last point, it reminded me of my Samsung Galaxy S5. Instead of using their own BT chipset, they went work a 3rd-party design. Little did they know, but it had connectivity problems, to the point that other BT devices (headsets, speakers, etc) would randomly disconnect/reconnect with the phone. Continuing on that point, where iOS is concerned, since all iPhones are built under the complete control of Apple, Apple controls (essentially) all the variables, including the BT chipset, thus not as much testing by other manufacturers (including Hobbywing) is required. Unfortunately, there are not only dozens of Android device manufacturers, but each manufacturer can easily have a dozen...or a few dozen...different models, and there's no way any "accessory" manufacturer can possibly test their product with every Android device.
What this all boils down to is this: neither Android, or the API library, is "at fault" for causing the distance problem being experienced with the AXE ESC. There are numerous factors which can cause, or lead to, "distance-draining". As you mentioned, yourself, the max distance is shortened when dealing with surface vehicles, as opposed to air vehicles, which makes sense, and ground (ie. the Earth) provides the greatest insulation. If you've heard of SLAC (Stanford Linear Accelerator), then you'd understand why the actual accelerator is 25ft below ground.
~ More peace, love, laughter & kindness would make the world a MUCH better place
