Heavy Duty Switch

[Gary Manuel]

Here's a thread that I posted on our local forum some time ago. I need to reference it again as part of my Thunder Tiger 35% Extra 260 Build Blog so I thought it might be useful to someone here.

I've recently been having problems with my ignition and receiver switches.
A fault on the ignition switch took some finding but both faults turned out to be the same problem - intermittent open circuit on the slider switch.
Just touching the switch or the wiring in the rear of the switch caused the receiver to brown out / ignition to cut. Not good as the sole means of supplying power to your pride and joy.

These are the type of switches I'm talking about. They are RCExl branded ones but other similar looking generic ones have the same problem. They are simply not up to the job in my opinion, relying on slider switches originally designed for selecting wave-band on old transistor radios. This is not a pop at any particular manufacturer. I just think these are rubbish and will not be using them again.

I came up with a modification that is now tried and tested. It involves a fair bit of work, but it's fairly easy and satisfying to do and results in a very nice switch. At the end of this post, I'll suggest an alternative off-the-shelf switch that I think is up to the job.

Case removed:

Anyone who's ever opened an old radio up will recognise this type of switch.

Only the positive (red) wire is switched - note that each red wire connection bridges the two banks of slider switches, providing switch redundancy. The black wire is needed only to allow the charge socket to work.

This is the type of switch I think they should be - much more robust.

I got 2 of them from Maplins for just over £5.

This switch could be used as it is but I wanted to recess it into the switch housing to prevent accidental operation. I also wanted to retain the charging socket. Read on to see how I converted the RCExl switch to the Maplin ones.

Switch de-soldered / removed and circuit board cleaned up.

Charge sockets left in situ.

Track cut on the rear to isolate the negative solder pad.

The positive pad is already isolated on this side by de-soldering the switch but .....

..... the positive track needs to be cut on the front side.

Large hole cut for the switch body and small hole cut for the tab on the outside edge of the special washer.

The tab on the inside edge engages in a slot on the switch body.

This is to prevent the switch body from spinning round in use.

[Gary Manuel]

New switch assembled.

 

Original cover put back on (not fastened / glued on yet)

 

Switch head just sticks out through the hole by enough to allow switch to be used.

 

Switch is rated at 5A, which should be enough for my needs.

I decided to use a Double Pole switch and wire both poles in parallel - see the copper wire soldered between the 3 pairs of terminals.

This will effectively double the current rating but more importantly, I've got two switches supplying the receiver.

If one fails, the other one is still there as a back-up.

 

Not quite finished, but this is what the inside looks like with the wiring soldered.

Note the fuel tube / fuel dot close to the switch.

 

View from the front.

 

This is the receiver switch which has been similarly modified. This shows the finished switch with wiring secured to the switch using hot glue - essential to provide stress relief to prevent the wire vibrating off.

 

I can still use the charge socket for charging.

Switches are still working well after many flights, but time will tell.....

A bit time consuming but not as difficult as it looks.

I said at the start of this post that I would suggest alternative off-the-shelf switches. I have used these on other models and can vouch for their quality. They are a bit expensive, but I'm not going to risk losing my models by using cheap-tatty switches.

They are NOT available as a simple single switch with charging socket, but they are available as DOUBLE switches.

They are also available as SINGLE or DOUBLE switches with FUEL DOTS. All available in a selection of colours.

 

 

 

 

 

Edited By Gary Manuel on 01/02/2017 16:45:14

[Rich too]

Interesting thread Gary, and I do use those types of switches. I am impressed with your work but it is not something I would be prepared to do. I think I may look at the pin type switches in future. I do always use two switches so that I have some redundancy.

[Adrian Smith 1]

Gary, I admire your ingenuity I really do.

However, as one who likes to use an off the shelf remedy that has proved reliable I always use the Rcexl Opto Kill Switch unit inside all my gasser aircraft. The main reasons are that it is a simple job to programme a switch on my TX to any appropriate RX channel using a separate power source for the ignition on board. This means all control of the ignition is done completely away from the aircraft. Any failure of that particular circuit will just lead me to remember how to do a decent dead stick, as the main power source to the RX is served by my Powerbox and 2 other batteries, allowing a controlled landing. Lastly, I don't consider £18 or so as too big a price to pay to avoid another switch on the side of the plane. That said it's all down to personal preference and me being lazy. No one way is wrong!

[Gary Manuel]

Rich,

I bought the branded "Heavy Duty" switches with confidence and was surprised when they failed after 1 or 2 outings. Surprise turned to disgust once I saw how poor quality the physical slider switch was. I'll not use them again even if they are duplicated. After all, how do you know that the second switch you turn on or the first one you turn off is actually doing anything?

Having said this, I have an ancient Glenns Cap with Zenoah 62. This has a single switch of similar design on the receiver and has never missed a beat (Ignition is Magneto). Other club members fly petrols with similar switches and haven't had problems. Maybe I've just been unlucky with the recent ones, but once you lose confidence .....

Adrian,

You've raised a couple of interesting points here.

Firstly, I too always use RcExl Opto Kill Switches on my petrol engines. Rightly or wrongly, I only use the kill switch for cutting the engine to stop it once running. I also wire in a physical switch (battery to physical switch to kill switch). Maybe I don't need to, but it's worth discussing. I would appreciate your thoughts on it, because life would be easier without a physical ignition switch. My logic for using a physical switch goes like this:

1. With I/C models, I believe that the safest failsafe is a nice slow tickover, rather than engine cut. I set my failsafe up to achieve tickover on the throttle servo. My failsafe does not kill the engine via the kill switch but I can cut it at any time via a tranny switch. This means that my ignition is always live (even with transmitter off) unless I switch it off. I use the physical switch when priming the engine (on full throttle) to give piece of mind that it is isolated. Then switch it on to start the engine. Do you set your failsafe to cut the engine?
2. The kill switch will have some current drain, so the battery will go flat if left too long. A physical switch stops all current drain.

Secondly, I agree that £18 should not be considered as excessive. I have used the AGM switches before and have said that I will use nothing else in future. Pity they don't make one with just a single switch without the fuel dot, which is what I'm after. The other thing is that when I tried to order a single one with fuel dot from AGM, they are out of stock in the UK at the moment.

[Bob Cotsford]

I do the same as you with regards to ignition switches and failsafes Gary. I've used a similar switch to the AGM one supplied by HK, both with and without the fuel dot. As for those HD slide switches with the built in charge sockets, I'm pretty sure that was what did for my Jabberwok. It certainly showed all the signs of a total power loss.

[Gary Manuel]

Do you mean THESE Bob?

Not seen these before. Any good?

[Bob Cotsford]

I don't see the AGM style one listed any more but I've also used this medium duty one on 20cc models with no issues to date. I might even have one on the Acrowot XL but I'd have to go out to the garage to check!

[MattyB]

I've never really trusted switches full stop - as you note most of the ones sold for RC use as really aren't up to much. Your method though, whilst effective, does seem like rather a lot of work compared to wiring up a decent quality high current connector (XT60, EC3 or 5) as an arming plug in the +ve rail. The plug can be modded to be held captive within the model to prevent it being lost. Extremely reliable, quick, simple and guaranteed to work through thousands of cycles if done right.

If you don't like the inconvenience of having to plug in the connector each time whilst testing the RC, simply fit a cheapie switch in parallel and mark it for ground use only. Alternatively if you worry about flying with only the switch in place wire one in series between the two contacts of a spare arming plug and mark it for ground use only. Simples!

[Frank Skilbeck]

After having problems with mechanical switches, I've gone over to the FET type switches in larger applications.

[Peter Miller]

While I fly smaller models with glow engines I have had problems with the cheap slide switches.

Now I use Futaba Heavy Duty switches and have had no problems with them.

**LINK**

[Adrian Smith 1]

Ok Gary let's address your discussion points.

Taking the Fail Safe issue, In answer to your question I do use that facility on my Futaba 14SG TX, however the way it is done is more detailed. The programme allows you to set each channel at a fail safe position you choose. So all working services I set at neutral (they don't have to be) with this displayed as a %. Mind you if the glitch occurs in a dive I am not sure how that helps. The throttle is set at tick over. In this programme you can also set the RX battery at a selected fail safe level. I don't use that mode as that is really what I want the PowerBox to do. By the way you can assign a spare switch on the TX to override the battery Fail Safe temporarily.

I don't use a physical switch on the plane largely because if I need to cut power to the ignition while in the air I can do this from the TX using the Kill Switch. I appreciate that you can use a trim switch to cut the throttle, but I don't set my gassers any lower than tick over on the TX. I just find it easier setting it up like that. Two observations that worry me slightly is you say the ignition is live even with the TX off. Is that wise? The ignition batteries I use are 2200 mAh at 6v and I think I would have to go some to flatten that in a session.

The other worrying thing for me is the idea of a fuel dot within the external switch panel. Petrol & switches near each other? Not sure about that either.

MattyB, I accept that the switching requirement for electrics and IC might be different, but with IC (petrol) simplicity is what I go for. Indeed I have taken your good advice given in another thread on switching for electrics. For I/C the Opto Kill switch fulfils that simplicity with a minimum of connections and safely. I am open to persuasion though!

 

Edited By Adrian Smith 1 on 02/02/2017 09:13:39

[Gary Manuel]

Thanks for your opinions chaps. Lots of food for thought here. I'm going to chew on it for a while.

Frank - Do you have any info / links on FET type switches?

[MattyB]

Posted by Adrian Smith 1 on 02/02/2017 09:12:38:

MattyB, I accept that the switching requirement for electrics and IC might be different, but with IC (petrol) simplicity is what I go for. Indeed I have taken your good advice given in another thread on switching for electrics. For I/C the Opto Kill switch fulfils that simplicity with a minimum of connections and safely. I am open to persuasion though!

No persuasion necessary - if I flew gassers I would always fit one of those opto switches on the ignition circuit (my Dad has one in his NGH 38cc Spit).

My comments on using an arming plug were still in the context of large IC powered aircraft like Gary's Extra though; I was suggesting it as an alternative method of switching the power on and off to the the RX and servos. Using a single servo wire with bog standard servo connectors is ok in smaller models, but on something like a 30% gasser I'd feel much happier knowing all the power to those big digital servos is coming across wires and connectors designed for the job. Whether you use a arming plug in series on the +ve rail or simply connect the battery direct to a flylead with a decent high current connector on the end is personal preference, but the key thing is not to rely on the friction fit and current carrying capacity of a single servo lead for all your RC gear!

PS - With a model like Gary's I personally wouldn't let my servos take power off the RX power rail; there is no way it can be rated to supply the kinds of currents all those big digital servos could pull simultaneously during 3D flight (I've read in some XPS documentation that 10A is the max most RXs can handle). I suppose that is the reason most of these big models use Powerboxes, though there are now power and RX redundancy products from FrSky (the RB-10 and Redundancy Bus) and my personal favourite from XPS, the X10+. These products mean RX and power resiliency can be added in medium sized club sized models for a very reasonable price. Worth investigating if you want to add additional redundancy and peace of mind for your pride and joy.

Edited By MattyB on 02/02/2017 11:58:32

[Gary Manuel]

Matt.

I agree. Wouldn't dream of using a receiver with standard connectors and bus for anything with more than standard servo arrangement.

I'm using a JR 922 Powersafe receiver, which is designed for the job - see photos on first page of my thread - with high current connectors / bus and duplicated battery supplies. It uses a fail-safe electronic switch so there's no issue with the receiver side. It's just the ignition supply I'm considering at the moment.

Like you, I replace the servo type power leads (don't know what they're called) in the battery supply with XT60s. I therefore already have a disconnection / isolation point that I could use anyway. Still thinking whether I need a switch in the ignition or whether I can isolate the ignition during priming without one.

Edited By Gary Manuel on 02/02/2017 12:15:20

[Peter Christy]

I was warned off those switches with a built-in charging socket many years ago, by a friend who ran a model shop! Doesn't matter which manufacturer, apparently they all suffered similar failures.

The best "off-the-shelf" heavy duty switches I've come across are the JR ones that have a separate charge lead, though I'm told the Futaba equivalents are good too. But NEVER one with a built in charge socket!

I've still got a small hoard of Japanese Noble switches - probably the best ever for our application, but sadly long out of production.

--

Pete

[Cuban8]

The only switches that I trust are genuine Futaba heavy duty ones. The large ones that are sold sealed in a plastic bag with a green Futaba packaging label. Anything sold as a genuine Futaba item that is not packaged as described, I would be wary of.

[Frank Skilbeck]

Posted by Gary Manuel on 02/02/2017 09:42:19:

Thanks for your opinions chaps. Lots of food for thought here. I'm going to chew on it for a while.

Frank - Do you have any info / links on FET type switches?

Gary, I've used the ones from Multiplex (6amp and also the 12amp) and also from Hobbyking (only used the Hobbyking one in a regular sized glider so far). Powerbox and Jeti also do similar units

[Gary Manuel]

Thanks Frank.

I like the look of those.

[Frank Skilbeck]

I use them in my larger models, the 12 amp version has two power feeds to the Rx as the standard servo plug is limited to around 6amp with a high power connector to the battery. The only thing to watch is that the switch does draw a small residual current even when off, so if you forget to disconnect it after a days flying then over the next few days your battery will gradually discharge.

[MattyB]

Another option are magnetic switches; they are available from T9 (and other suppliers I am sure) in single and dual battery configs. 20A capable too; quite an elegant solution.

Edited By MattyB on 02/02/2017 16:25:35

[Martin McIntosh]

I must be lucky, but have never had a switch failure other than on the bench.

I do, however, try to use genuine JR heavy duty ones which are far superior to the others on the market.

For petrol I use a toggle switch combined with a receiver operated switch for safety and so that I can kill the motor from the Tx.

I am now changing to the HK failover type with two LiFe packs. If either fails in any way the other will save the day.

[Rich too]

I use the Tech Aero IBEC which uses the receiver for power, and two batteries and switches for receiver. Redundancy for both the radio and ign. I use the tx failsafe and can also kill the ignition from a channel on the tx.

Pin switches seem to be favoured on the FG forum. Like this... http://www.boomarc.com/en/hidden-balance-switch-with-pin-flag

I'll try one on my next model.

Edited By Rich2 on 02/02/2017 19:39:25

Edited By Rich2 on 02/02/2017 19:40:12

Edited By Rich2 on 02/02/2017 19:42:52