I have had what I would describe as a major failure with the new Powerbox Cockpit SRS (Serial Bus) unit fitted to my Carf Tucano. I had installed the cockpit as per instructions with the following layout.<p class="MsoNormal"><o
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>2 x Futaba 6108SB receivers<o
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></p><p class="MsoNormal">2 x Aileron servo’s Futaba S9156<o
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></p><p class="MsoNormal">2 x Flap servo’s Futaba S9156<o
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></p><p class="MsoNormal">2 x Elevator Servo’s Futaba S9156<o
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></p><p class="MsoNormal">1 x Rudder servo Futaba S9157<o
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></p><p class="MsoNormal">1 x Steering Servo Futaba S3305<o
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></p><p class="MsoNormal">3 x Jetronic dual air valves (doors & gear)<o
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></p><p class="MsoNormal">1 x Jetronic proportional valve (brakes)<o
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></p><p class="MsoNormal">1 x ECU throttle<o
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></p><p class="MsoNormal">1 x ECU Auxiliary<o
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></p><p class="MsoNormal">1 x Jetcat Smoke pump channel<o
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></p><p class="MsoNormal">1 x Relay kill switch<o
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></p><p class="MsoNormal">2 x 2 cell, 2200 Mah Lipo’s (original Jetcat batteries)<o
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></p><p class="MsoNormal">The receivers are plugged into RX1 & RX4 via the supplied 3 core wires, as they are serial bus design, these are the only wires connected from rx's to the Cockpit unit much like spectrum satellite rx's.<o
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></p><p class="MsoNormal">Based on the instructions, I powered up the unit and proceeded to set up Futaba as the receivers being used. I then powered down and connected both receivers and then powered up again. Both receivers were then bound to the radio and all basic functions (flight controls) were tested.<o
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></p><p class="MsoNormal">At this point I started to work on the gear sequencer programming and after approximately 10 minutes I noticed that the green status lights on both receivers had gone out, I then found I no longer had a radio link to the plane.<o
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></p><p class="MsoNormal">After some testing of the receivers with a separate battery pack, I concluded that the power supply from the Powerbox S-Bus lead had failed. After some additional testing, I concluded that I could run a “patch” lead to each receiver Batt port from a spare servo output port on the Powerbox and the receivers would work fine, as a precaution I slipped the positive pin out of the S-Bus lead at the receiver end to ensure there was no potential for back feed in case the receiver power supply had pulled down to zero.<o
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></p><p class="MsoNormal">Both receivers functioned as per normal during the rest of the set up and ground runs at home. These patch leads were left in place (and still are) during the maiden flight and subsequent flights.<o
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></p><p class="MsoNormal">Whilst this system and my plane are actually working (very well), I am at a loss to understand how the Powerbox Cockpit SRS with the “advertised” redundancy can have such a simple failure that would have led to absolute destruction of my aircraft and very much potential damage to persons and/or property. Having a patch lead from a spare servo port to the receiver at least gives me the confidence that I have some form of power redundancy, as if I now lose power to the receivers I must also be losing power to the servo’s.<o
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></p><p class="MsoNormal">From my observation, there is no redundancy for the receivers, this is very disappointing based on the advertised specs and price, I also use the standard Cockpit unit in my F14 and the Royal unit in my A10 although I am now curious if the power for the receivers on those has a redundancy???
An email to the Powerbox Company resulted in a replay that I "must" have plugged the S-bus lead across the line of zero volt terminals on the Futaba reciever's thus shorting out the mosfet? when it was pointed out that the recievers were supplied power from the Cockpit during the binding and setup time which was well over 10 mins, they answered that the Mosfet could take a short for a few milliseconds and die later?? They pointed out the the 2 x 6108SB rx's only require 0.1 amps and the Mosfet is rated to 10 amps. When I then asked how the tiny s-bus lead (about 28 gauge) could withstand a 10 amp hit without even discouloring the plastic wire covering, they replied that the thin wire can take 10 amps for some milliseconds and "this is the time it takes to destroy a mosfet" so one email says that the mosfet can "take a hit and die some time later" and another that says that "it only takes milliseconds to destroy the mosfet". I still have the emails if anybody wants a laugh.
I then went back into the programming side of the Cockpit and selected Spectrum as the radio system (you can select Spectrum, Futaba, Multiplex or Jeti, the Spectrum must have 3.3 volts all the others are rated to 5.9 volts), low & behold I now had power coming from the S bus lead, if I then select any of the other 3 I get nothing, nada, zilch..
I asked Powerbox to comment but I guess they lost the email address.
I know I can get a replacement unit from my distributor no problems, Powerbox had offered to fix it free of charge if I pay shipping!! But even if I had a new one I could not trust it as I know ABSOLUTELY that the S bus leads were connected correctly, I had done the binding process and I had operated all the surfaces, it was after all this that the power failed to the rx's. If I fitted a new unit I would still run a patch lead from the servo ports to power the rx's and I would advise EVERBODY else to do the same, as there is what I believe is a software issue (if they only use one set of mosfet outputs) or a swtchover issue (if they use 2 outputs 3.3 & 5.9).
PLEASE PLEASE PLEASE BE CAREFUL IF YOU ARE USING A POWERBOX COCKPIT SRS POWER DISTRIBUTION SYSTEM!!!!!!!!!
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