I got "Prearm Board (6.6V) out of range 4.3-5.8V" when powering up servo rail with 8.4V without a Zenor diode

ArduCopter Traditional Helicopter
21

@steveross1234 hi Steve I’ll answer here if that’s ok (others might find it helpful) .
They recommend 3s because the BEC can provide power for up to 7.4V, so a 2s battery (considering voltage ripple) wouldn’t be enough. You could probably run on 2s if the BEC was set at 6V or default 5V, but I would recommend a 3S setup anyway.
As an example, on my gasser (equipped with h743wing) I could run on a 3s setup (3s 2700 battery- cheap) for 4 consecutive flights ( say about 15-20 mins each), powering both servos and ignition unit.
The other question, yes S1 output can be used regularly, despite the weird layout on the board (it provides Vx from the BEC).

22

Hi Ferruccio,

Thanks for the answers. I have another question. The max Vx voltage is 7.2V, if I use 3S LiPo, is there any way to modified the H743-Wing so that the Vx can output 8.4V instead (so that the HV servos will get higher torque and speed)?

Thanks.

23

Moved to next message

24

I got an answer from Matek about increasing Vx in H743-Wing to beyond 7.2V as follows.

Vx= 8V

thumbnail_Catch(04-14-12-24-43)

When I ask it again from Matek to make sure (because I never see any Matek documents said so), I got another answer.

It said:

If you don’t trust me, just forget it.

Let me re-answer this question.
" if I use 3S LiPo, is there any way to modified the H743-Wing so that the Vx can output 8.4V instead"
No way

25

Hi Dave and Ferruccio,

I previously used a **Pixhawk 2.4.8, it has a socket to plug in a 3-pin safety switch (with a red light), which is used before the arming. I cannot find any info on which pins to install the safety switch for Matek H743-Wing. Or there is no safety switch for newer FC? How did these newer FCs arm without safety switch?

Could you please help me on this?

Thanks.

26

Hi Steve, there is no safety switch pin on these boards.

27

Hi Ferruccio,

Should these boards be armed or disarmed by the usual ways (throttle down rudder right/left in Tx) without the steps of enable/disable safety switch?

Thanks.

28

Hi Steve, correct, either arming with usual rudder procedure or you can use an auxiliary switch.

29

Hi Ferruccio,

Do you think the 1st answer I got from Matek is credible?

30

I wouldn’t question the manufacturer answer you got. But I have not tested this myself so I can’t really tell if any side effects might come along with this “hack” (here considering the servos might be hammering hard on the BEC-especially during fast movements).
The real question in my opinion is why you need to run them at 8V? Nominal rating for HV model servos is 7.4V, to my knowledge even the really high end ones (Futaba HPS) are rated for 7.4V. I’m aware some guys run Hv servos directly off a 2S lipo (with OptiGuard device) but I believe that is an overkill even for 3D flight range of loads.

31

Hi Ferruccio,

Thanks for your answers. I tried to get the best options before I start the soldering process. I have not yet have any camera in any of my heli. But the Matek H743-Wing have several voltage options on Vsw (5V or 9V), also 9V raise to 12V, what are the best options on these to commit so that I won’t regret in the future?

Thanks.

32

If you plan going digital, set it at 9V.