Reliable Switches?

[GordonTarling]

I'm building a large electric model and plan to use two receiver batteries for safety. What would people consider to be the most reliable switch to use for the receiver wiring harness? At the moment, it's a toss-up between a relatively cheap double-pole slide switch or a miniature double-pole toggle switch with a locking toggle. Anyone got any better ideas?

[Ollie]

Why use switches at all? Just plug two cables together to complete the circuit and pull them apart to open the circuit. This increases reliability, saves weight and only adds minor inconvenience by having to open a hatch to access the plug and connector.

[vintage1]

Slide switches are better than toggle due to a better self cleaning action, but I am with Ollie on this.

[AndyOne]

Gordon,

I once read a review of switch types in an RC mag. back in the 1970s. The conclusion was that toggle switches rely on a single point contact which could easily be perturbed by vibration and so could the Nobel type which has a sliding balls, the best type for reliability is the sliding clasp type as used in all good quality radio gear these days.

Connecting nicads in parallel, which it sounds like you are about to do, is not a good idea because if one has less charge than the other very large currents can flow between them. You would be advised to use diodes so they can't charge each other. Diodes, however they drop about 0.6V so you may want to use 5 cell batteries. Separate charging inlets for each battery will be required.

Given the above, why not use two standard single way Futaba switches, I have never known one to fail.

Andy.

[Viper Pilot]

Check this switch out (http://www.maxxprod.com/mpi/mpi-28.html)

[vintage1]

Originally posted by AndyOne
Gordon,

I once read a review of switch types in an RC mag. back in the 1970s. The conclusion was that toggle switches rely on a single point contact which could easily be perturbed by vibration and so could the Nobel type which has a sliding balls, the best type for reliability is the sliding clasp type as used in all good quality radio gear these days.

Connecting nicads in parallel, which it sounds like you are about to do, is not a good idea because if one has less charge than the other very large currents can flow between them. You would be advised to use diodes so they can't charge each other. Diodes, however they drop about 0.6V so you may want to use 5 cell batteries. Separate charging inlets for each battery will be required.

Given the above, why not use two standard single way Futaba switches, I have never known one to fail.

Andy.

Actually not, apparently. Red Schofeld (Reds Battery Clinic - http://www.rcbatteryclinic.com/) has the theory - something to do with needing to drive a cell much higher voltage in order to charge it than its discharge voltage.

Worth a read. He makes some good points.

You are probably correct on charging - see his article.

[vintage1]

Oh, I remembered a big thread I read on resilience and reliability somewhere...dual receivers? Different makes, separate packs, split elevator servos, rudder and one aileron one one, t'other aileron and throttle on t'other..analysis of MTBF and monte carlo analysis of failure modes...

Lots of ideas were presented. Probably in the google news archives somewhere...

...my own take from years in electronics - things either fail immediately, or after a short time, when dodgy joints become apparent, then they work well for a long time until age takes its toll and bits begin to drop of. Repalce all switches packs and potential wires every year, and test thoroughly under vibration before committing to flight?

[GordonTarling]

Thanks for the heaps of advice guys!

Ollie - access to the inner depths of the model will be tricky, so I'd prefer just to have switches which I can locate in an inconspicuous place.

AndyOne - I'll take your advice about slide switches being better. However, battery packs CAN be connected in parallel - as Vintage1 says - read Red Scholefield's articles. However, I don't plan on following his advice on this model.

Viperpilot - I've seen a similar electronic switch being sold by a German company - sorry, I wouldn't trust it 100%.

Vintage1 - I'm sure you're right about failure modes etc. I've evolved my own philosophy over the years which hasn't let me down yet. However, this model is large and heavy, so I plan to take additional precautions.

I'll be using a battery backer device which is made by a German company - yes, I know I don't NEED one but I haven't finished yet! :) This battery backer has individual voltage displays for each battery as well as two warning LEDs which can be situated remotely. I shall be feeding one input of this backer unit from 4 x RC2400 cells and the other input from a Universal BEC device. This way, I think (hope?) that I've got most eventualities covered.
The inputs to the battery backer will have slide switches which I shall hard wire in. Anyone see any flaws in this plan?

[AndyOne]

COLOR=royalblue] A simple ESE preflight test would detect a pack with a shorted cell.[/COLOR]

What if you forgot! There's an awfull lot about battery fires in the E Zone.

Gordon,

I have also considered using two batteries on a large, valuable model but I opted instead for the highest quality high capacity Sanyo cells and constructed the battery myself so I could be sure of the quality of the welds and solder joints. I decided this on the basis that the more components in the circuit, the more there was to go wrong. It has't let me down (yet).
K.I.S.S.

Andy.

[Greg McFadden]

here is a good one, been using it on my helicopter for a while now. Scroll to non-regulated realswitch
http://www.fromeco.org/Reliaswitches.htm

here is the whole product tree
http://www.fromeco.org/Fromeco%20product%20tree.htm

Upsides are that they fail in the on position.

Downside, draw current all the time.
Upside: off current draw is between 5-50 micro amps.... almost nothing at all, I could leave my heli with the switch off for a year and not have a drained pack.


Whole reason I started using these was a rash of switch failure caused crashes or jsut switch failure caused good luck (the heli's survived) in the group of people I fly with. One guy went through something like 3-4 switches in one month!. I think it has to do with a combination of our high frequency vibration environment and our continuous servo draw of 2-2.5 amps, spike being a whole heck of a lot greater than that.

[Christer Lagerstedt]

Hello Gordon

Middle Wallop was great. The AN-2 is repaired now.

When I started with proportional radio gear, most gear used the very high quality NOBLE 4-pole slide switch. I still use the ones I have and have also managed to find new 4-pole slide switches. I usually switch both plus and minus on two contacts each but one can chose to use all of the connections for the minus cable.

A couple of years ago I used another 2-battery setup. I cut the minus rail in the reciever between the battery connector and the servo connectors and used two batteries. One for the electronics in the reciever and another bigger one for the servos. The idea was that the reciever should not be effected by sinking voltage from hard working servos. Of course I used high quality switches for both batteries.

Christer

[GordonTarling]

AndyOne - If you read Red Scholfield's treatise on this subject, you'll see that cell internal shorts are VERY rare. Most shorts that I have seen have been caused by shorts outside of the cells.

Greg - Sorry - just don't have 100% faith in those electronic switches for some reason. I can see why they would be good to use in an I.C. helicopter though.

Christer - Glad that you enjoyed Middle Wallop and that the AN2 is now fully repaired - it's a lovely model. Can't seem to find those Noble switches these days, so I'll use a double-pole slide switch with the poles connected in parallel. The servo load on this model is relatively light, so I don't also need a split supply for receiver and servos.

[Dylwad]

Red Schoefeild knows what hes talking about, and ill trust him over any self proclaimed battery experts. ive found the futaba digital switch is a very nice piece of equipment, although pricey at $20. i use 2 RX packs on my larger glow planes, both plugged in to the rx, no diodes or other silly nonsense to fail and heat up/drop voltage. i usually use 1 digital switch and one standard switch, and switch them on opposite each other every time to check they are both up to snuff.

I have had a futaba switch fail. took out a scalemasters winning plane. never again will i use a single RX battery and cheap switch on anything big.

Dylan

[opualuan]

remember. receiver headers/plugs are adopted from the computer industry (pc 0.1" header pins). read the specs. these pins and sockets are not meant for multiple connect/disconnect cycles. they will loosen, possibly abrade inside each connection cycle.

also, the crimped wires have no strain relief once exiting the header shell... any flex of the wires at the base when connecting/disconnecting can lead too flaky connections/fraying wires under their insulation. I've had two of these problems happen in one glider, lucky it's foam.

no matter what mechanical means, maintenance is key. also helps to eliminate as many points of failure as possible...

[Dylwad]

Originally posted by opualuan
remember. receiver headers/plugs are adopted from the computer industry (pc 0.1" header pins). read the specs. these pins and sockets are not meant for multiple connect/disconnect cycles. they will loosen, possibly abrade inside each connection cycle.



Molex states 25 cycles for tin plated and 50 cycles for gold plated. kind of scary eh?

[GordonTarling]

These last two posts give the reasons that I don't like to just plug in the battery rather than use a switch.

[AndyOne]

why not use two standard single way Futaba switches, I have never known one to fail.

I was discussing this contention recently and the fellow I was talking to said "they're rubbish I had one that just fell to bits inside". After some questioning to find out just what had happened it transpired that he had been using said switch for 15 years.

There are some components that should be regarded as replacement items, not permanent fixtures. Tx antennas are a case in point, they gather muck (and grease if you're an IC flyer) and the joints go high resistance and there is no way of satisfactorily getting it out without destroying it.

Back on the switch reliability issue, there was a case of a glitching radio at the flying field the other day. It turned out that the switch which was mounted through the side of the fuz and the hole hadn't been cut large enough to allow it to fully slide to the on position. It wasn't making it past the detent and the vibration from the engine was causing it to lose contact. The problem was obscured by the exterior bezel. I wonder how many models have been lost through this simple error.

Andy.