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Lost radio contact

Possibly due to dodgy/worn battery contacts

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GrahamWh08/04/2019 21:06:50
356 forum posts
53 photos

I was flying a Flair Fokker D7 last weekend using a Spektrum Dx6i radio and lost control of the model which happily headed off in a straight line over the boundary fence of the field and out of view as I played frantically with the sticks trying to get control back.

Fortunately the failsafe was set to idle (ic power rather than electric) and the model descended into the ground in the next field. Quite a bit of damage but repairable.

The RX battery was still on and showing good voltage (6.56 volts with a 2s LiFe) and when I got it all back to our pits area we did a range check and all was well on all the controls.

The Rx will not be used again just in case it was that, but when I got home I decided to change the Tx batteries as although they were still at 5.1v a fresh set might be better. When I put the new ones in the set would not power on. I fiddled with the battery compartment, resetting the contacts to improve their tension, and cleaned them with alcohol and got the set to come on, but it kept going off and on again if I touched the batteries.

I think the battery connectors in the battery box might have got too worn or slightly corroded and possibly a momentary loss of contact may have caused the loss of radio control of the model.

Any one else noticed this with their Dx6i or other Tx with dry cell battery box?

Any way, I have soldered a servo lead connector to the battery box contacts and plugged in a LiFe battery to the Tx with the battery connected to the rear of it with tie clips.


Some plastic cornering protects the soft edges of the battery from the tension of the tie clips to prevent damage and a bit of double sided tape helps prevent slippage behind the battery.


I must admit it was pretty frightening to see the plane fly off to who knows where - whenever I have crashed before it had I think been my own fault for stalling or something like that.

Is this why more modern sets use battery packs rather than single cells and do you think there is anything else I should check? ( The Rx and its satellite will be replaced).

Edited By GrahamWh on 08/04/2019 21:08:25

SIMON CRAGG08/04/2019 21:30:41
521 forum posts
15 photos

I think you were very could of ended in tears. After 40+ years of model flying I would NEVER EVER use or recommend the use of fitting loose AA cells in a TX. As you have found, even with a fairly new set, it can still go pear shaped. As long as your LifePo4 pack is hardwired, you should be bullet proof in the future. Good luck.

Denis Watkins08/04/2019 21:44:43
4045 forum posts
75 photos

Lads, I have to give a balanced comment to radio gear designed for cell use and replacement.

Have always used Duracell dry cells in these radios since the advent of this Tx, years ago

Never ever had a clip or tension problem to date, and a set of cells lasts a flying season

The manufacturer chose this form of power too

We fly with what we are comfortable with, and modification to our choice

And the working failsafe meant the RX did its job

Paul C.08/04/2019 21:46:54
609 forum posts
150 photos

Hi Graham, check out youtube dx6i battery pack conversion it's a bit of a fiddle but looks to do the job ok. I found it by Google spektrum dx6i battery pack, worth taking a look. By the way I don't think that there is anything wrong with your RX , if it range checks ok you should be ok.

Cheers, Paul.

Paul Marsh08/04/2019 21:47:06
3808 forum posts
1097 photos

Always use a welded pack in both the aircraft and transmitter.

Simon Chaddock09/04/2019 00:15:17
5564 forum posts
2930 photos

I have two DX6i (they were second hand when I got them!) and only use alkaline cells - as recommended by Spektrum.

It perhaps worth noting that alkaline are a particularly tight fit compared to regular AA cells. .

They are replaced when the voltage drops to 5.9 V but otherwise they stay in the Tx.

Over 3 years I have never had a moments trouble with the either as far as batteries are concerned.

Just saying.

gangster09/04/2019 07:08:20
985 forum posts
17 photos

Although the thought of loose cells terrifies  me and I would never use them I must admit that I know a lot of people who use this radio with them and over many years don’t appear to have had a moments problem with them so seems a good system

Edited By gangster on 09/04/2019 07:08:53

Old Geezer09/04/2019 09:29:11
657 forum posts

I too suffer from a gentle touch of the heebies about the loose cells in my spare/reserve dx6i - but have never actually had a problem. Apart from checking the voltage when it emerges blinking into the daylight after a period of disuse, I take the battery cover off and roll the cells ( Duracells ) with my thumb to "freshen" the contacts. Don't know if it does any good because I have ( so far ) never had a problem - but it makes me feel better!

David Ashby - Moderator09/04/2019 09:47:59
10932 forum posts
1681 photos
613 articles

Is that sellotape holding your Tx aerial together Graham?

Exposed wires, sellotape fixes? I've got to be honest, it's not a Tx that inspires confidence. smile

J D 809/04/2019 09:59:48
1353 forum posts
78 photos

Watching a flyer trying desperately to put the loose cell's back in his TX as his glider heads off into the distance is both funnylaughand concerningcrying

SIMON CRAGG09/04/2019 10:17:21
521 forum posts
15 photos

Its each to thier own of course, but its just another thing that can go wrong IMHO. In these days of "where there is blaim there is a claim" etc. I would never trust this type of set up, especially when it is easily hard wired. How many times have the batteries in the TV remote need to be "rolled to work" or those outside solar lights etc. I think its a recepe for disaster!.

Cuban809/04/2019 10:22:53
2827 forum posts
1 photos
Posted by SIMON CRAGG on 08/04/2019 21:30:41:

I think you were very could of ended in tears. After 40+ years of model flying I would NEVER EVER use or recommend the use of fitting loose AA cells in a TX. As you have found, even with a fairly new set, it can still go pear shaped. As long as your LifePo4 pack is hardwired, you should be bullet proof in the future. Good luck.

Absolutely right, in fact I'd add another NEVER to your NEVER EVER wink. Just one other thing that's worth checking with batteries that connect to the TX via a Molex connector or similar is to disconnect the connector and remate it fairly regularly. Purely a precaution but worth doing if you can get to the connector easily. Many of these connectors are not gold flashed as they used to be on older equipment (cost?) and can oxidize if kept in a humid environment. Once a year is fine, say when you're checking the battery's capacity. Seen something similar just a few weeks ago with a friend's model and a dodgy servo that turned out to be a poor connection at a servo extension lead connector with tinned crimps.

Engine Doctor09/04/2019 11:18:38
2382 forum posts
29 photos

Re OP . Its the very reason that welded packs came into fashion back in the late 60's early 70's as the spring contacts could often loose contact without warning and zinc carbon batteries of the day often leaked and damaged the contacts. Most radio gear especially low to middle range sets like the Futaba Challenger and similar were made for use with dry cell connectors fitted and were converted or ordered from the makers with welded packs by the distributors like Ripmax etc . The higher end sets back then were made for re-chargeable batteries with no evidence of connector mountings in the cases Only the cheap two channel surface use radios used for boats and cars continued to be supplied for use with dry cell batteries. Welded packs every for me . Using dry cells in the much improved radios of today is a fundamental backward step., Dry cells might be ok for small cheap rc toys but with continued use the connections will fail Converting to welded re-chargeable packs is usually a simple conversion

Paul C.09/04/2019 11:36:53
609 forum posts
150 photos
Posted by David Ashby - Moderator on 09/04/2019 09:47:59:

Is that sellotape holding your Tx aerial together Graham?

Exposed wires, sellotape fixes? I've got to be honest, it's not a Tx that inspires confidence. smile

New aerial available from wheelspin models £16 , and from there you know it will be a genuine Spektrum 👍


David Hall 909/04/2019 14:32:55
180 forum posts
9 photos

Before my "comeback" to RC flying, I too would have never considered lose pen cells in a holder for my Tx. But, as I bought some inexpensive radio gear to start with, My Flysky Tx was set up for 4 AA cells. As I had the cells, it was easy to try.

Thinking back to whatever problems I've had with this kind of arrangement, mostly it has been contact problems, largely due to slack spring fittings. My Flysky was a fairly tight fit for the rechargeable cells and to ward off the dreaded corrosion that can effect the contacts, I just coated some battery contact grease (petroleum jelly is fine) on the contacts. Three years now without any problem at all (although now it is not my main Tx).. If I ever have even the slightest doubt that it is secure, it will be changed. 

When my Q7x Tx arrived, it had a rather flimsy and very cheap looking 6 cell holder.    It seemed to be a poor holder, so for this, I fitted a welded pack...  


Edited By David Hall 9 on 09/04/2019 14:34:59

Simon Chaddock09/04/2019 14:43:25
5564 forum posts
2930 photos

A point about the reliability of wires connecting a battery pack to the Tx.

Its not the solder joint that is likely to fail but the strands next to the joint from fatigue unless considerable care is taken to ensure that the individual strands cannot move using some form of strain relief.

Even then it is important that any bending of the complete wire is not concentrated to a small area close to the joint. The drawn copper wire as used in multi strand flex is significantly work hardened so is surprisingly susceptible to fatigue failure.

ken anderson.09/04/2019 16:27:14
8516 forum posts
773 photos
Posted by David Ashby - Moderator on 09/04/2019 09:47:59:

Is that sellotape holding your Tx aerial together Graham?

Exposed wires, sellotape fixes? I've got to be honest, it's not a Tx that inspires confidence. smile


same from me graham...not worth loosing good models for the sake of a bit tlc...

ken TLC dept.

Martin Harris09/04/2019 16:35:07
9070 forum posts
224 photos

While the exposed wiring would raise my eyebrows a little if it appeared at my club, those Spektrum aerials are often damaged and a bit of tape won't do too much harm if it's just supporting the pivot joint - better than it flapping around stressing the co-ax cable...

Capt Kremen09/04/2019 17:20:17
328 forum posts
107 photos

IF it's just the (weak) plastic 'axle' pin that's broken, (as mine has done a few times!), then it's a simple matter to insert a suitable size diameter dowel/wire.

Then, 'Robert's Your Uncle', no need to shell out circa £15-00 for a pretty plastic bagged replacement.

GrahamWh09/04/2019 17:47:47
356 forum posts
53 photos

Thank you very much for all your replies and advice gentlemen.

Re the aerial I will remove the tape and redo the fix with something more substantial - perhaps fibreglass. I'll think about the wires that are outside the case too - thanks for that David and the others that commented.

I have had this Tx for nearly 7 years so am not surprised some say the system as supplied is reliable. I do not want another run away though and will not risk it this way again.

I did consider putting a smaller LiFe battery into the battery box itself, but the only one I saw on HK that would fit this 55x45x15mm space was a 700mAh job, which I thought would be a bit small. I would not consider a LiPo due to the potential damage if over discharged and the fire risk of charging in situ.

Does any one have any thoughts as to the suitability of a 700mAh LiFe - the one I fitted was 2100mAh? Again, any advice much appreciated.

Edited By GrahamWh on 09/04/2019 17:51:56

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