Hobbyking BEC Puzzle on J3 Cub

[Cliff 1959]

I'm trying to set up my HK J3 Cub and think I may have a problem.

The BEC beeps like it's waiting to be programmed, I've tried switching the tx on with with the throttle at max and then reducing it but the beeping continues.

I think it's because the power from the BEC is only 3v when measured on the plug, also the reading only comes from the two outer of the three wires, that is the black and yellow, I get no reading from the black and white (white's in the centre), are these the two wires to check?

[Dave Bran]

I have never in 25 years plus electric RC yet seen a ESC or UBEC with that colour scheme wiring and I have seen very very many! They are always either Black/Red/White (Futaba and many standard) or Brown/Red/Orange (JR/Spektrum "we have to be different just to confuse and be stupid".

Black or Brown is Negative to Receiver

Red is Positive to Receiver

White or Orange is signal from Rx to ESC (or nothing in the case of a UBEC)

The standard is positive centre (except really old gear like Sanwa and others which we can I think discount) so that if you reverse the plug you just earth the signal and no damage.

Does this wire end in a std Rx black plug? If not why not, its again a standard? Who messed with it?? What Receiver is in it? What Tx system are you using?

Also, there are several Cubs on HK, even more than one named "J3 Cub", so if we had a better clue....................

If you have put supply between the outer pair of three into a normal receiver, it might well not have liked it!

[Denis Watkins]

Cliff, the beeps are to warn against battery low, unlikely

Or throttle high, which is very likely.

Trim down the throttle fully negative

If this does not work, then reverse the throttle

[Cliff 1959]

Sorry my mistake the wire colours in order are black, Red and white with the standard black plug, the rx is a Graupner GR12, tx is Graupner MZ24, model is Hk the 1400mm ref Navy scheme.
There is a power takeoff from the battery that goes through a small circuit board with the usual black plug on the end which I think is intended for the optional cockpit camera for fpv, this measures 5v and will operate the rx if I plug it in to port one, of course it can't control the motor but the controls work.
Because the voltage is only 3v on the lead from the bec the rx won't power up and I get my warning of low power on the tx therefore I can't get as far as setting the bec in the first place. The battery is fully charged.

[Geoff S]

What battery are you using? Does it have more than the usual connections? ie a balance connector and 2 thick wires to the esc? The 2 thick wires can have a variety of connectors but the most common is a yellow one called an XT60. I'm puzzled by your description of a circuit board with a further power take off.

You should be able to measure about 5v (perhaps a bit more) on the connector from the ESC (ie BEC) between the centre (positive, red?) and one of the side connections (negative and black). It doesn't matter which way round you fit this connector into the receiver as regards any damage but, obviously, it will only work properly with correct orientation.

Geoff

[Bob Cotsford]

It sounds like you have a separate BEC, the little board with a receiver plug. The throttle connection from the ESC doesn't have a positive connection by the sound of it. Are your servos receiving power? If so, where from, a 5v battery? If you are only connecting the ESC then with "the BEC is only 3v when measured on the plug, also the reading only comes from the two outer of the three wires" I'm surprised that the RX is powering up.

[Bob Cotsford]

Try plugging your mystery plug into the receiver as a power source, and the ESC connection into throttle channel as usual. What happens then when you try programming the throttle range?

[Cliff 1959]

This is a close up of the 'mystery circuit' tapped off of the battery wire the black and red wires read 5v. The picture below shows the esc with the usual connector for the receiver (throttle), The black and red wire read nothing, but the black and white read 3v, this, I'm guess is not right, as the white wire should be the signal? As I said above if I plug the plug reading 5v into the receiver it powers up the servos but not the esc, so Bob, when I plug the plug from the esc into socket 1 and the 'mystery' plug into a spare receiver socket the motor now fires up as it should but am I not putting a total of 8v into the receiver?

The plane is designed to have the option of an fpv camera so I think the 'mystery' circuit powers that via the 5v plug, if I had that installed then I wouldn't be able to power the receiver on just 3v so, yes, I can fly with both plugs in but a) will it cook the receiver and b) the esc should be giving 5v surely?

[Dave Bran]

The ESC will not give any voltage to the Rx if its an OPTO type which has no BEC cct.

No, you are not putting higher voltage into the Rx.

Connect both and go fly.

[Martin Harris - Moderator]

For clarification, I believe the voltage you're seeing on those outer wires is the pulse train signal - there shouldn't be anything connected to the central pin and the red wire is superfluous. You should have the 5V from the wire marked 6 in that (or any spare) channel - failing that due to no spares, to any channel via a Y lead and the rx will send pulse information to the ESC via the white wire of the lead plugged into the throttle channel.

[Cliff 1959]

Connected both and had four good flights today, thanks for the help.