BB_DF

Here are a couple of stabilization systems using the same technology as the DF. The first two pictures are a small 3-D helicopter on which I have installed the FMA Direct Co-Pilot CPD4. This was a proof-of-concept test to evaluate how well the system works. Picture #1 is the IR sensor, same as on the DF. The Falcon is a non-CCPM design and you can see in picture #2 there is a wire controlled by a separate servo that runs up the center of the main shaft, controlling collective pitch on the swashplate through a slot in the shaft. The CPD4 will work on airplanes and non-CCPM helis; FMA Direct is working on a newer system for CCPM designs, but it has not been released yet. The results - super stability for such a small heli.

Picture #3 is the Spartan-RC AP2000i controller, which works with all know swashplate mixing schemes and radio types. FMA Direct owns the patent for the leveling technology, so DFI and Spartan-RC license the designs from FMA. Notice in pic #4 the same FMA sensor is used. The AP2000i has been around for 4 or 5 years now, and the technology is pretty reliable. One nice feature is it displays the number of glitches and bad frames during a flight, and also the current and lowest Rx battery levels under load. This could give you invaluable data if you're testing a 2.4GHz downlink with your 2.4GHz Spektrum or FASST Rx, and want to see if they're interfering with each other. The AP2000i is also set up to interface with an altimeter to show highest altitude, and also 2-axis gyros for further stability.

The calibration and operation of these units is quite different. On the CPD4, you hold the heli sideways and press the cal button. When you release it, one of the servos starts to tick off a count between 1 and 10, indicating the calibration strength. I would typically get an 8. This is equivalent to the two green LEDs on the DF, but obviously more precise. Then the swashplate gyros begin to oscillate in a slow continuous motion. Then level is set similar to the DF and you're ready to go. You only need to calibrate and level once, unless the weather conditions change drastically, or you move from say, Bogota to Reykjavik.

The AP2000i is calibrated internally and doesn't have to be re-calibrated unless you feel it's needed. Then you can either calibrate the earth/sky gain, or the level, but they can be done separately. Of course there are many other adjustments that are programmable, such as response rates, etc. I fly the AP2000i on about 50% authority, switched on after it's high enough to see over the local thermal clutter. Anything above about 70% and I find it difficult to overcome the device's control. Instead of just setting the expos on the Tx, the DF would probably be well served by a %control adjustment on the spare channel, or a potentiometer on the controller. Mike Dammar said he had put a remote gain control on the DF and it was a disaster, but that's a lot different than a %control adjustment.

A practical note on flying your DF with Ti on in the wind. Sometimes it suddenly doesn't seem to have the guts to fly back to you. Turn it 90 degrees and fly it sideways, or fly it backwards towards you. A lot of times what's happening is you set the level with the nose away from you, and when you turn it around to fly back it could be bucking the Ti level. I've found that invariably it will fly better with one of the other rotors leading. This is worth practicing when conditions are favorable, so you'll feel comfortable with the maneuver when things are a bit more critical.

- Bruce