First impressions of FY-21AP stabilization and RTL unit

As part of my ongoing research project to buy every autopilot out there and see how they work (an expensive hobby!), I just got a FY-21AP, which is a $250 stabilization and RTL box (basically an autopilot with most of the usual features taken out).  (I bought it from HobbyKing for $195, but as Hooks warned us that didn't last long. It's no longer available from HobbyKing.) You can read Hook's introduction to it (and links to reviews) here, but I just wanted to point out some cool things that caught my eye in a quick unboxing.


First, it comes with a really neat vibration isolation "hammock", which is the little platform in the picture above with rubber bands on all four corners. That's a great way to dampen vibration; we should make and sell one of those for APM, too.


Second, here is the usual warrenty-breaking opening of the box:

It's got the same ST ARM chip and ST sensors as all the other FeiYu boards, with a barometric pressure sensor in the bottom right of the board at the top. A neat, simple design. It uses a Locosys 10Hz GPS with a small ceramic patch antenna.


There is no provision for a ground station or any desktop setup software (although you can hook up an optional OSD and see data in the video stream).  All adjustment for your airframe must be made via the little trim pots. It can handle elevons with a jumper, but not V-tails (you need to use an external mixer for that).


There are three modes: stabilized (optionally with fixed altitude), return-to-launch (RTL) or circle-in-place. They are selected with two toggle switches on your transmitter.


Throttle is not controlled, and altitude is only controlled with the elevator, so the manual warns you to keep your throttle pretty high to avoid stalls in auto mode.


The documentation is much improved from the previous FeiYu Tech manuals (which were partly in Chinese) and comes on one big double-sided sheet of paper:



I haven't flown it yet, but I'm guessing it a does a pretty good job on most aircraft. If you don't need a full autopilot with programmable waypoints and ground stations, etc, this seems like a fine choice. In particular, it seems really well suited for FPV fliers to protect against getting disoriented and having trouble making it back home.

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Comment by Russell B. Sutton on July 7, 2011 at 10:31am

Which plane r u going to try it with? 


3D Robotics
Comment by Chris Anderson on July 7, 2011 at 10:38am
I'll probably start with a Skyfun delta-wing. It's a good test, since it's fast and hard to fly for mere mortals (APM flies it great, right out of the box)
Comment by Teejay on July 7, 2011 at 11:31am
@Chris - You can use the FY-21AP + XBee 900's and use the HKGCS. Just change the baud rate to 19200 with X-CTU and connect it to the UART port you're all set. :) Although I've only tried telemetry (downstream) data.

Comment by John Arne Birkeland on July 7, 2011 at 12:11pm
I use the 21AP + 117AP (OSD) in my pure FPV Skywalker. Works great for easy RTH, Loitering, altitude hold and flight stabilization. Probably one of the best "plug and play" solution available at a reasonable prize. No problem doing hand launches with the 21AP in any mode you want. I just put mine in RTH mode and set the throttle to about 80% before I throw it. And then let the plane gain altitude and start circling home position by itself, while I put on the video goggles and get ready.

Comment by Robert Krogh (hooks) on July 7, 2011 at 1:04pm

@Teejay yes you can use the new FY GCS to have point to point navigation. But but.. the PID settings are not tuned for specific platform/aircraft means it will not navigate in fine lines.

It's perfect for wing aircraft and the lazy Skywalker.


FY21AP is a great system. I love it and it got me home a few times. When people got problems with this it's because of bad installation (not using the anti vibration mount) and noisy power from ESC.


Use Gain minimum 80%.


Next generation of the FY21AP is the FY31AP.

This will have software so you can tune PID settings / upgradeable.

  • V tail supported.
  • Tilt and role for camera mount.
  • Better and improved code for stabilization/navigation
  • Alu case
  • Etc.
Comment by Kirill on July 7, 2011 at 1:39pm

FY-21AP system is very popular among Russian FPV pilots. It's a little difficult for me to undertand why, but it's so loved here (all other systems are in the shadow of this one). I guess because of its simplicity, many owners said it's very easy to setup and learn the basics of usage. Only few people had difficulties whyle setting up. However, the price of the whole KIT is almost the same as the price of APM. But APM has much more functions than FY-21, it's obvious.

I think, if you just want to fly not getting in details of how it all works, the FY-21 is a good choice. But it doesn't provide a DIY opportunity, so you can't upgrade it or add something new - just set it up and "use as is".

Comment by Matthias Badaire on July 7, 2011 at 4:47pm
I like the altitude hold. Correct me if i am wrong but we do not have that and fbw does not do it.

3D Robotics
Comment by Chris Anderson on July 7, 2011 at 5:00pm
Matthias: altitude hold is in all the APM auto modes. It's also one of the ArduCopter manual flight modes. If anybody wants it in an APM manual flight mode, it's easy to add.
Comment by Teejay on July 7, 2011 at 7:57pm
@Hooks - The FYGCS-based 'point-and-click' navigation great for something that's plug-and-play. And yes - the flight path to the selected waypoint is 'curly' on the GCS screen.
Comment by Simon Wunderlin on July 8, 2011 at 2:29pm
Interesting. What are the dimensions of the vibration isolation (roughly), could it be used with APM, can it be ordered as separate part?


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