Power supply

Without the flybar, power consumption will increase by a certain amount. The reason for this is simply that the servos have to do all the work to keep the blades at a determined angle, no external force (via flybar and levers) is there to help any more.

To manage the higher loads, and to get the crisp and fast pitch reactions the more and more demanding 3D maneuvers require, we need fast and powerful digital servos. If we want some power from the machine, we have to use only the good "fuel". And the digitals consume a lot more power than the analogues, especially when changing direction as fast as VBar and Ultra mode require.

When performing these direction changes, the servo motors are stopped within fractions of a second, and accelerated into the other direction, and back, and forth. Especially when using high P gains, these direction changes occur very often even when hovering, to keep the machine stable.

The battery holders and switches provided by the manufacturers of rc equipment only have some use for decorating purposes, even by normal standards. We have to get used to thinking about power supply kind of "big time", a power supply that supports safe operation of the heli in any case. You can achieve that either with a sufficiently sized BEC, LiPo controller or with a low resistance rx battery. And you will have to use switches, connectors and wirings that are up to the task, to keep voltage drop at a minimum.

The power supply on a VBar system using a 2s LiPo (7.4 volts) and a off-the-shelf power-swith can be forced to a voltage drop of below 3.5 volts (that means a drop of 4 volts!). In this case the thin wires are the bottleneck. A power supply with 4 NiCd cells of 2.4 Ah, Deans connectors, wires with a suitable wire cross section, without a switch, with two JR connectors (one into the rx, on into VBar) would even have been better than that!

By design VBar works on as little as 2 volts. The servos will lose power, of course. But the critical element is the rx. Depending on the brand and type, even a short drop of voltage can cause a cold start. The system re-binds, but that takes up 2-3 or even up to 8 seconds. Until then, the rx occasionally doesn't output valid signals to the servos, but e. g. full negative pitch. VBar accepts this signal (it's still up and running), outputs it to the servos, even corrects as a good flybar would do ... you can imagine what comes next ...

How to avoid this? By remembering the basics of electrics (aka U=R*I) and by laying out the wiring and chosing the components wisely, bearing the indicated power consumption of the servos in mind. Here is an example: it's important to use as many connectors to the rx and VBar as possible, with sufficient wire cross sections. Use every unused channel on the rx and on VBar any unused in- and output connector. If all the connectors are in use, make use of a V cable. As a recommendation, use 2, better 3 inputs to the rx and/or VBar.

Also important is to keep wires short. The resistance is directly proportional to the length of a wire. A 30 cm (12") wire with 0.5 mm^2 (0.2"^2) cross section has about the same resistance as a cable 15 cm (6") long with 0,25 mm^2 (0.01"^2).

For our helis with a higher voltage on the swash servos than on the tail servo we have another hookup diagram here:


 A check for our power supply

Knowing the high current loads on every direction reversal of our servos it is very easy to test our power supply. Therefore we had to take care that our VStabi system reacts as fast as possible collective direction changes by TX input as well on the swash servos and also on the tail servo.

In Setup menu, swashplate expert set the value for pitch pump to 100 (don't forget enter). Set also the tail torque precompensation for collective to 100 in flight menue, tail expert. Additional the I tail value to 0. This will effect the maximum response on our servos at collective stick movements.

Now do 2-3 minutes of fast pitch pumping on the bench and watch your RX voltage and complete behaviour of the Heli. Especially on 450 helis and there usual 2A BEC the limits can be exceeded within the use of digital servos very soon.