FPV-Community Reviews

The FY-21AP with RTH (return to home) is the extended version of FY-20A RC stabilization system, which we tested in our last review.
This time we got it directly from the manufacture Feiyutech.
We tested this product for the community to see if the additional functions work well for every day use.

Technical data main module (manufacture data)

Type: extended version FY-21AP gyro 3-axes stabilization with RTH
Input voltage: 4.0 to 6.0V
Current draw: 52mA @ 5,0V
Size: 55× 33 x 20mm
Weight: 20g
Temperature range: -25°C – +70°C
Maximum rate of rotation: < 1200 °/s

Application: normal plane with and without aileron, v-tail with and without rudder, and planes with delta mix

Compatible remote control systems: Robbe-Futaba PPM / PCM 1024 / PCM G3 Mode Graupner JR PPM 8, PPM 12, SPCM Mode Multiplex PPM 8, PPM 12 with UNI Mode 1,5ms

Technical data GPS module (manufacture data)

GPS Data refresh rate: 10Hz
Interface features: TTL Level
Baud rate: 38000 baud
Data Bits: 8
Stop Bits: 1
Parity: None

Packaging and content

The package arrived well packed in an air cushion. The accessories were extensive. The module itself is about the same as the FY-20A, except for the 2 additional connections for the second switching channel and the GPS module. It is 55mm x 33mm x 20mm and weighs only 19g. Unlike many similar products, the module is not covered with heat shrink. The housing is robust and can be unscrewed.
With the circuit board removed it only weighs 9.5g.

Also included are five 18.5cm JR- servo connectors, one plastic shock mount, two pieces of Velcro tape and an illustrated English manual.

Functional principle and installation

Like the FY-20A, the FY-21AP offers, stabilization on three axes (elevator, rudder and ailerons). It’s even possible to control models with v-tail or delta mix. The model type is selected via plug contact. Three gyro sensors and a microprocessor provide the stabilization.

In contrast to the basic version FY-20A, the FY-21AP offers additional functions like RTH (return to home). This feature provides a semi-autonomous return to home function. For this the GPS module has to be connected to the FY-21AP main module. Flying circles with only the autopilot is also possible. So you can enjoy the landscape and let the autopilot do the work.

Unfortunately the system needs a y-cable for the second aileron. So it’s not possible to set an aileron differential via the transmitter. If the servos are running in the same direction, it’s possible to buy a y-cable with switchable inverting.
In the test we tried to misuse the rudder axes for the second aileron, but failed. Using only one aileron for stabilization made the RTH function too difficult.

The installation is done in a few steps. You should install it in a position with good airflow, to have a constant temperature. Otherwise the gyros will drift too much. The manufacturer suggests resetting the module before the flight if the temperature differential is above 30 °C. The same should be done after a longer break. Possible problems of the gyro drift are explained in the Flight Test chapter.
The FY-21AP calibrates itself after powering up. Once adjusted, you are ready to fly.
The module is mounted with Velcro tape onto the shock mount. The printed arrow on the module must be in the flight direction.

The FY-21AP must be connected with the following channels from the receiver: aileron, elevator, rudder, switch in 1, switch in 2 and throttle. For use without the optional FY-606 data radio module, the throttle channel cannot be connected because it has no function. Here we use the five provided servo cables. The two switch channels are user defined switches of the transmitter, like a three position switch. They are used to toggle the different modes:

Flight modes

- Switch IN 1 – mode 1: Deactivated – normal RC control – no stabilization

- Switch IN 1 – mode 2: Auto balance mode – aircraft will enter horizontal level flight, when the transmitter’s control sticks are centred. Deflections are limited and the FY21-AP will not allow any acrobatic flights.

- Switch IN 1 – mode 3: Auto balance mode with fixed altitude – aircraft will enter horizontal level flight and stay at the current altitude, when the transmitter’s control sticks are centred. Deflections are limited and the FY21-AP will not allow any acrobatic flights. Attention: throttle position has to be set manually, because it won’t be controlled by the module. It is possible to set a fixed throttle position, but this can cause problems with non self stable air crafts. Especially if the down thrust is not correctly adjusted. You have to test this yourself how the plane reacts. Alternative you can use the Eagle Tree OSD Pro in combination with the FY-21AP. This OSD can control the throttle for the right level flight. For example to use the throttle channel separate with the OSD Pro without use of the rudder function of the OSD.

Autopilot modes

- Switch IN – mode 1: RTH (Return to home) – The model flies independent and stabilized back to the pilot. At arrival the model flies circles with a diameter of around 200 meters. Attention: throttle position has to be set manually, because it won’t be controlled by the module. Alternatively you can use the Eagle Tree OSD Pro in combination with the FY-21AP. This OSD can control the throttle for the right level flight. For example to use the throttle channel separate with the OSD Pro without use of the rudder function of the OSD.

- Switch IN 2 – mode 2: autopilot deactivated

- Switch IN 2 – mode 3: ACM (auto circling mode) – The model flies independent and stabilized circles with a diameter of around 200 meters. Circle position is position of activation, independent of the home position for RTH. Attention: throttle position has to be set manually, because it won’t be controlled by the module. Alternative you can use the Eagle Tree OSD Pro in combination with the FY-21AP. This OSD can control the throttle for the right level flight. For example to use the throttle channel separate with the OSD Pro without use of the rudder function of the OSD.

The modes are switchable during the flight. You will need two 3 position switches at the transmitter. If you have only a 2 position switch, you can only choose between mode 1 and 2 or between mode 1 and 3.
The ailerons are connected through a y-cable with the FY-21AP. Rudder and elevator are also directly connected to the module. We had no problems with the connections during our test. All plug connections were stable and their connections secure.

During the first start-up you have to check the correct rotation directions of the servos and the rudder effect in the stabilization mode. With the help of the three rotation potentiometers you can set the maximum deflections and the correct rotating direction. We suggest using as much as possible small deflections to get the right feeling during flying. Too big deflections can cause the loss of the model, if you are not fast enough to deactivate the stabilization during the flight.
Close Attention is required and the maxim “Less is more” is valid here.

Flight tests

Chapter 1 – stabilization

For the maiden flight we chose the Bormatec Maja. We did a test flight with and without the shock absorber during low and high wind conditions. We flew the Maja without stabilization to a secure flying level and switched to mode 2.   In this mode the FY-21AP fully controls the model. We watched amazed how stable the Maja was, even with its weight of around 3kg. Even stronger gusts of wind had no negative effects. This is one of the main advantages of this system. We could not control the Maja that accurately while the wind was blowing so much. There was no noticeable deviation in the flight path. The Maja flew stable and smooth.
Controlling during mode 2 is a little unfamiliar. It is like having 100% expo on all channels, but we quickly got used to it. The model was still very controllable and we felt secure knowing the FY-21AP would take over if we needed it to.

You need watch the flight speed during autonomous flight; especially with non-self-stable models, as it could result in a stall.
The FY-21AP does not like vibrations. That’s why the shock absorber is very important. We made test flights without this absorber and the FY-21AP reacted with uncontrolled deflections. Tests with gas driven aircrafts showed that the FY-21AP will work with reasonable damping of the module, like foam or cotton wool. During our longer tests in different weather situations we noticed a little drift because of temperature fluctuation. We could fix that really fast and easy with a manual calibration. That’s not a big problem and conforms to standards.

For comparison, The FY-21AP was tested in a Multiplex Cularis. Except for the much tighter fit, the system performed as described above. Only the fixed altitude mode worked, because the self-stableness of the Cularis is more precise.
The FY-21AP has consequently no problems with electro sailing planes or even motor planes.

Chapter 2 – ACM mode, autopilot and fixed altitude

ACM mode

ACM stands for: auto circling mode. We powered up our plane and waited until the FY21-AP gets its home position via satellite link. The led signals shows the actual state, which is described in the manual.  After that we did a short pre flight check and started the plane. As stated in the manual, the ACM mode centre is the actual model position where you activate the mode. We flew away with the plane and activated the ACM mode. Immediately the plane started a constant turn, sometimes a right, sometimes a left turn. The radius was about 120 meters. We noticed that the plane banked a little too much, because of the relatively tight circle. This can be a problem at slower speeds, where the plane looses altitude during the circles. Generally the ACM mode worked reliably and the model was never out of control.
As an important side note: You can take back the control of the model immediately and at anytime in any mode.

Autopilot – RTH mode

We started our model again and flew away, then activated the RTH mode. The autopilot initiated a turn immediately and the plane flew straight back to its home position. Upon arrival the FY21-AP switched automatically to the ACM mode and flew circles until we took back control. After this successful test we did the same with transmitter turned off. We programmed the fail-safe and tested it. As above the autopilot flew the plane without problems back home.

We would have liked the FY-21AP to control for flight altitude, but alas no. If you activate the RTH at a 600m altitude, the plane will come back and circle at 600m. So you would probably need binoculars to find your plane in the sky, if you lost the video signal. You have to find the right throttle position to hold the altitude in the RTH mode. Just manually switch on RTH and play with the throttle stick to find the right value.

Fixed altitude

This mode is to hold the plane at a fixed altitude. Our tests showed that this mode is only useful if the plane does not climb or sink very much during different throttle positions. The FY-21AP is not able to control the throttle so; too much push from the motor can override the deflections of the FY-21AP, which can cause problems.  A mechanical correction of the throttle is necessary. Unfortunately this is not possible with all planes, so a correction of angle can help here.

Conclusion

The FY-21AP is a much better solution compared to the basic version. With the optional OSD you can get a fully graphical flight system with auto pilot. The different functions do their jobs reliably. The small enervations do not diminish the use of this product.
Especially for the price of the FY-21AP, you get a very good package.

Scoring

Pro

+++ versatile additional functions compared to the basic version
+++ reliable operation
+++ very lightweight
+++ small size
+++ uncomplicated and easy assembling
+++ modes switch able during flight
++ extensive accessories inclusive

Con

— throttle is not controlled by autopilot
— no second aileron connection
– little gyro drift in the case of intense temperature fluctuation

Further information about this product

• FY21AP Review (German)
• FY21AP – Discussion and Support Thread
• FeiyuTech Homepage
  
• FY21AP Manual
• Antenna tracking with FY21AP (Video)
  
• MAJA as platform for FY21AP review (English)
• MAJA as platform for FY21AP review (German)

Tags: autopilot, Borjet, Borjet Maja, Bormatec MAJA, FPV, FY20A, FY21AP, Maja, RC, return to home, RTH, UAV

This entry was posted on Saturday, December 4th, 2010 at 1:59 pm and is filed under Reviews. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.