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Old Jul 14, 2012, 07:44 PM
kaz1104 is offline
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Australia, TAS, Memana
Joined Aug 2004
2,222 Posts
Originally Posted by HappySundays View Post
Hi people,

I have been working clodely with the KK2 while writing new software for OpenAero and I have just come across something that I need some help with wrapping my head around...

From the manual, "With many servos, for example airplane stabilization, there may be necessary with an extra BEC. Do not use multiple switched BECs."

The reason is this:
For the motor outputs, the +5V signal of M2 to M8 are connected together, but not to anything else. M1 is connected to the +5V of the five RC inputs. This all then goes through a simple filter to power the board.

Now, for a model with ESCs and motors, you'd likely have ESCs plugged into M1 to M4 which would mean that all ESCs, the board, and the RX would have power.

But what about designs with NO ESCs? Designs with all servos?
This includes most aeroplane stabilising types (motor goes direct from RX) and all camera stabilisation designs.

The problem is this:
If you power the board via a battery or BESC etc from the RX side, only M1 will have power.
If you power the board via M1, the same thing happens of course and...
If you power the board via M2 to M8, neither board, RX or M1 will have power.

It's very messy. Is there any reason we can't just short M1 and M2 +5V underneath the board so all input and output +5V are connected?
It's a shame as some might find that difficult.

I just can't think of a neat way of wiring this up that doesn't involve multiple BESCs... surely that's a bit crazy?
If using CPPM mode you could put a cable between an unused RX input and an unused servo output but with PWM all inputs are used and you may wish to use all outputs meaning you'd need a custom linking cable. Again messy and confusing for the noobs.

Any elegant solutions out there?
Would it be logical to use full leads from receiver the flight board. UBEC could then power the receiver through an unused channel, or into a Y lead into any channel. The flight board could then be powered through all channels into the FC by the one UBec.
CPPM is a little more tricky ... or as you say between an unused Rx channel and an unused servo output on the FC .
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