Location: London, UK
Flying since: March 2011
Helicopters: 2x Synergy E7 with prototype lowered head
E7-1: HV2BEC Alu / Vbar Silverline / JR 8917HV Cyclic Servos / Align BL750H HV Tail Servo / Scorpion 4525-520 Ultimate / YGE 160HV-K ESC / Edge 693 main blades / Edge 105 tail blades
E7-2: HV2BEC mini / Vbar Silverline / Align BL700H HV Cyclic Servos / Align BL750H HV Tail Servo / Scorpion 4525-520 Ultimate / YGE 160HV-K ESC / Edge 693 main blades / Edge 105 tail blades
Other setup details: +/- 11.7 degrees collective pitch. 1.5 mm head shim per side. Vbar governor at 2200 rpm, 9.67 gear ratio, 12S 4500 mAh 65C Scorpion Lipo, 4 minute flight timer.
Sponsors: Align-trex.co.uk, Climbout-uk, R2prototyping, Scorpion Power Systems, Synergy Helicopters
Testing the performance of various power supplies
In search of a quality power supply for my helicopters i tested the performance of three BECs and a 2S lipo in my E7: WR Hercules Super BEC, Quasar 7075LMT BEC, HV2BEC and ThunderPower 2700 mAh G6 Lipo. I performed these tests as an independent pilot long before i became affiliated with R2 Prototyping (having paid full retail price for each component ).
In these tests, the blades are removed from the helicopter and the swash is moved rapidly from full negative to full positive position. This single vertical movement of the swashplate produces a collective pitch change of -12 to +12 degrees. The voltage of the power supply and the position of the swashplate are measured simultaneously using a 50 kHz D/A converter and a laser displacement transducer. The graphed results show how the voltage output of the power supply varies during the servo movement. The helicopter setup is as detailed above, with the exception of increasing the Vbar pitch pump setting to 50.
I first came across the HV2BEC whilst reading through Mikado’s power supply test data: http://www.vstabi.info/en/node/1327. I had been flying the WR and Quasar BECs for about 1 year, and did not know that there was an alternative high performance BEC to choose from. I was interested in Mikado’s data because I had been extremely disappointed with the performance of these ‘standard’ 12S BECs, both of which exhibited dangerously large voltage sags during servo movement. For example, the graph below shows a preliminary measurement of the output voltage of a WR Hercules Super BEC during a full pitch swash pump. You can clearly see two large voltage sags which coincide with the servo motion. Superimposed on these sags are high frequency fluctuations which combine to bring the voltage down to at low as 3.5V. The duration of the voltage transient is significant.
Upon reading about the HV2BEC I immediately ordered one. My intention was to conduct a series of thorough comparison tests which simultaneously measured the servo position and BEC voltage. I also decided to include measurements with a high performance 2S lipo. The results are shown in the figure below:
In this graph, the swasplate position is represented by the dashed black line. It shows that during the test, the swashplate is moved vertically through ~20 mm by the three cyclic servos. The measured voltage output of each power supply is shown by a coloured solid line. These data therefore illustrate how the voltage output varies as the servos move. The performance of the Quasar 7075LMT BEC (blue line) is very poor. In the middle of the servo movement its output voltage drops to just 3.5v and does not recover to 8.4V until the servos stop moving. The 2S lipo performs better, sustaining a voltage drop of roughly 1V over a similar length of time. The HV2BEC (green line) is the clear winner, with a rock solid output voltage that exhibits negligible change during the servo movement. This test shows conclusively that the HV2 is the only BEC with sufficient power to running HV servos at a true continuous 8.4V
It is shocking to think that a standard BEC’s output voltage can drop to as low as 3.5V during a single swash movement. Furthermore, this test is not even performed with the additional load on the servos that is experienced in flight. I have used my DX8 telemetry logger to confirm that voltage transients of a similar size occur repeatedly during 3D flight on the WR and Quasar BECs.
Many people do not even realise this is happening because the voltage monitor on the Vbar or other measurement devices is buffered. You need sufficiently fast measurements to observe these voltage fluctuations. Whilst the performance of standard BECs is usually sufficient to prevent RX brownouts, they do not provide enough power to maximise the potential performance of high speed / high torque HV servos.
The difference between the HV2BEC and other BEC’s is definitely noticeable in flight on my setup. Stops are sharper and in general the heli feels like it responds better during 3D manoeuvres. This is hard to quantify but i can say that it is similar to what i’ve experienced when upgrading to faster servos with more torque. I believe that as servo performance improves the performance benefit when running the HV2BEC will only become larger.
I recently installed the new Align brushless BL700H HV cyclic servos on my E7-2. These provide a massive 20 kg/cm and 0.065 s/60 speed at 7.4V. These servos are based on Savox 2271sg internals and although the are extremely high performance, they require alot of power. There are many examples of these causing brownouts on standard BECs:
http://www.helifreak.com/showthread.php?t=398142. I have performed my bench test on these servos and found that the HV2BEC performs identically to the data shown above. In back to back flight tests between my E7-1 and E7-2 I can feel a significant improvement over the JR 8717HV’s!
After I saw the quality of the HV2BEC and had a chance to experience its performance for myself, i decided i wanted to help Linus bring this great product to other pilots. If you have any questions or would like to try this BEC for yourself before purchasing, i’d be happy to loan out one of my units. Just send me a message
Build and Installation Photos: