The Plight
Many Eflite foamy planes sold by Horizon Hobby come with SAFE® technology based on AS3X® receivers from Spektrum. While Spektrum’s AS3X receiver can be purchased separately and installed on any planes to give them 3-axis gyro stabilization, Horizon Hobby has coupled the AS3X receiver with most of their Eflite foamy planes, with additional programming, to make their planes more accessible to beginner flyers. The receiver/plane package is known as SAFE®. And the main features of SAFE® include the famed “Panic” button, as well as beginner-friendly receiver-side flight modes.
These SAFE® features annoy veteran flyers to no end, and render most of these fine aircraft useless to experienced flyers, unless the $80 AS3X receiver is replaced with a normal receiver. Take the NIGHT VisionAire that I can’t stop flying, for instance. This is an exceptional 3D plane that delivers great value for the price. But its built-in receiver forces the pilot to choose either the Precision flight mode with intermediate gyro gains and ridiculously low throw rates, or the 3D flight mode with very high gyro gains, and 100% control surface throws. The gyro stabilization can never be turned off.
Perhaps Horizon Hobby can’t fathom why anyone would want to fly their VisionAire with low/zero gyro gains and very high throw rates, or high gyro gains and low throw rates. The end result is that one can never fly the VisionAire at very high speed without the plane swimming in the air like a dolphin. And one can’t have a relaxed cruising experience under strong winds.
Sarcasm aside, I do understand why gyro gains are coupled with expo and throw rates in these receiver-side flight modes. Often beginner pilots have nothing more than the free DX5e that comes with their plane. So Horizon Hobby must make it such that pilots with a dumb radio can still fly these sophisticated planes. Receiver-side flight mode is one way to achieve this goal.
The Seldom-mentioned Solution
But it turns out that most of these planes actually come with an extremely capable $80 Spektrum AR636A Sport receiver, and it can be reprogrammed using just a smartphone and a special programming cable. You can change gyro rate gains, as well as heading gains. You can completely turn off AS3X stabilization in any of the three receiver-side flight modes, if you want to fly your plane without gyro stabilization.
The fact is, Horizon Hobby does not go out of its way to advertise that these supposedly locked-down “AR636A Sport” receivers can be reprogrammed without losing SAFE® features. There isn’t a lot of information online talking about repurposing the AR636A receiver, except on rcgroups.com and some YouTube videos, and only if one knows what exactly to look for.
Updated March 2019: I’ve finally spent time understanding the AS3X firmware, SAFE and SRM (Spektrum Receiver Model). I have now written a much longer and more comprehensive article which you may want to visit, in addition to this one. Go to: What on earth is SAFE® or: How I hacked AR636 from V900 to fly the Freewing Mirage 2000, with SAFE and AS3X









