wiring for twin mustang with two batteries

[john davidson 1]

I have built a rwin mustang and want a battery in both fuselages for balance,connected individually to each esc, and with a y lead fron the receiver to each esc with the red lead cut in one branch... this does not appear to work, both escs do not energise but if i remove the y lead and connect an esc it works and if I disconnect then plug in the other it works.

I have built twins and fours with one battery and cut the red ,I expected two batteries to work but I must be missing some thing obvious

[pete taylor]

Hi John,

have you tried disconnecting the red wire from both esc's (no need to cut, just remove the little gold connector from the plug housing) and powering them up with a separate receiver battery?

That will rule out any peculiar bec issues and is my preferred method with any model capable of carrying a rx pack.

If both esc's are working when plugged in individually and with a separate battery, then try another y lead. I used to assume that there was nothing to go wrong with extension leads, but in the past year have had 2 issues that were resolved by replacing leads, so that's another thing not to assume!

Let us know how you get on.

[Denis Watkins]

Ditto Pete

Y leads are a weak point even if new

I checked a box full of new at a show, and meter tested 12 before 2 were found to have continuity

Somehow they are selling cheaper and cheaper makes

Conversely, a good Y lead will last a long long time

[john davidson 1]

First thing I did was to put a meter on to test both branches of the y for continuity , both ok

[john davidson 1]

What I really want to know is the theory of using two lipos individually to each motor sound? and how to wire them up as the method i tried seems to be flawed (cutting one red lead to an esc.)

[john davidson 1]

one motor connected individually works but when the other is plugged in none work , is there interference via the white signal lead? this does not happen when using one lipo with the red les cut

[Geoff S]

When both escs are connected but neither motor runs, do the other controls work ie is the receiver powered as normal?

Your method of using separate batteries for each motor/esc combination would seem to be perfectly reasonable. You could try disconnecting both red leads (ie dispense with the BEC) and powering the receiver separately and see if that works. I don't see why it shouldn't because, provided there's a common (black) and the signal (white?) to both escs and the centre (red?) BEC o/p is disconnected then the escs don't 'know' there's another esc connected to the throttle signal.

Geoff

[pete taylor]

That's all very odd John.

First thing I'd do is to check the y lead for continuity across the servo/esc ends - there shouldn't be any, but that would explain what's going on.

Secondly, my normal practice for multi-engined electric models is much the same as yours appears to be, ie independent systems with a common link at the receiver (albeit using a separate NiMh rx pack) which I've found to be problem free apart from the 2 dodgy y leads. I have done a couple using shared flight packs and these were without issues too.

The one other suggestion I can offer is to try putting each esc into its own rx channel - shouldn't make a blind bit of difference though!

[Bob Cotsford]

One remote possibility is that the escs are sinking too much current from the signal line and preventing that channel generating enough of a voltage swing, unlikely but possible. Alternately could they be putting too much noise on the signal line when Y'd together? Do you have a spare output on the receiver that could be slaved to the throttle channel to give each esc it's own receiver output?

[john davidson 1]

cracked it! plugged the second esc into channel 5 and slaved it to throttle at -100% works perfect, .this was before i saw Petes reply above, it does make a blind difference but how is another matter

[pete taylor]

Posted by john davidson 1 on 13/03/2018 14:15:17:

cracked it! plugged the second esc into channel 5 and slaved it to throttle at -100% works perfect, .this was before i saw Petes reply above, it does make a blind difference but how is another matter

Nice one John, there's always another way of doing things. I'll have to get the grey matter working as to why this should be though. Did you check there wasn't a short anywhere in the y lead?

You've now also got the facility to have differential throttle mixed with the rudders!

[Simon Chaddock]

john d

What you were doing should certainly work. It is exactly the set up I use on my Bombardier Q400 which has a battery and ESC in each nacelle.

The Y lead still sounds suspicious as your new set up is working without it!

If you are using ESCs with 'switched' BECs you must disconnect the red wire from one ESC but remember this means everything is being powered by one BEC.

'Linear BEC ESCs can have both connected (there are on my Q400) but it is likely one will be doing most of the work.

[john davidson 1]

I didnt have a y so made one from two extensions and first suspected a dry joint but put a meter on it for continuity and was ok so thought for another answer. I am usinng two donkeys from HK with soldered on escs (£12each) so wondered if the cheap escs being built down to price is a factor. I had used another donkey in a depron Hurricane tankbuster (40 mm cannon) and it was perfectly ok

[Simon Chaddock]

john

I would be surprised if the ESCs are to blame but I suspect the only way you could get to the bottom of this is with some bench testing.

To avoid using extension leads I prefer to extend the ESC (and the servo) wires (solder and heat shrink) as required and also solder the wires to the socket inserts rather than crimping. Tedious but less connectors equals less points of potential failure.

[Chris Walby]

Worth just checking the fail safe and throttle hold (if you use it) on both channels as I had a bit of grief getting the latter to work the way I wanted it.

[Gordon Tarling]

The problem is the combination of ESC and receiver. The receiver can't supply enough current on the signal line to drive both ESCs at the same time. You have already found one answer, though I believe that there is some sort of signal amplifier available from somewhere which will also solve the problem.

FWIW, I wouldn't set the model up as you have described - I would use one battery per motor, as you have, but connect the batteries in parallel also. Disable the ESC's built in BECs and use a separate BEC unit that's man enough for the job - a safer setup in my opinion.

[Nik Harrison]

John,

I had problem very like yours with a set up I had using a quad ESC on my A400. It would not work if all four throttle signals were joined up. It would work on any 2 but not four. Lack of current drive was the problem. Solved by building a unity gain amp which then ensured correct drive. Details were discussed in forum

Design & Build FW 200 Condor / Syndicato if you want further details.

Cheers

Nik

[Geoff S]

Glad you solved the problem.

It seems the esc throttle inputs impose a higher load than (say) a conventional servo does. After all it's common practice to drive 2 servos from a single receiver output via a Y lead (that's what they're for) It's not something I've ever considered before but I'll bear it mind in future.

What receiver and esc combination are you using?

Geoff

[john davidson 1]

I can see the sense in joining the batteries in parallel, the downside is taking a heavy lead across to the other fuse. The twin mustang is quite small-1.3metres , a larger plane would justify the extra wiring . I would hesitate to disable the bec as I have had no trouble using up to 5cells ( with advice from 4MAX using a quality power train)

The receiver is Spektrum which I use in all planes except small 2 to 3 cell . As I said above the motor/esc is the donkey combo from HK quite good performance for £12 each!

[Chris Bott - Moderator]

John, many Spektrum receivers have a different failsafe action on the throttle channel, to all other channels.

Please do check failsafe operation by starting both motors to say a tickover, then switch off the Tx.

(Props off first, of course)

This is particularly important on a twin as you really want both motors to do the same thing (stop) if signal is lost.

[john davidson 1]

Thanks for that point, I hadn't appreciated there could be a difference between the channels. Presently at the stage of tidying the wiring and situating the batteries for balance so tomorrow I will include that in my run up checks.

Appreciate everyones comments and help,the forum is great help in expanding ones experience even afer many years flying

[Gordon Tarling]

John,

The balance lead between the two batteries doesn't need to be as heavy duty as the normal battery leads - you can use something a bit thinner, as it's not carrying full motor current for most of the time. The problem with the ESC built in BECs is that an ESC can suffer a burnout at any time - if that happens the the ESC whose BEC is supplying receiver power, you can guess what happens to the model. I've seen this happen on several occasions. If you use a separate BEC, then an ESC burnout won't normally affect the receiver supply.

[Geoff S]

Certainly an esc can fail any time but so can a separate BEC (for that matter, I guess, so can a receiver or servo). The only esc failures I've witnessed concerns the high current output to the motor which on neither occasion affected the low voltage output of the BEC. Modern esc seem to be pretty reliable provided they're operated well within their current ratings.

Geoff