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Idea for more reliable switch

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Old 08-25-2003, 05:46 PM
  #1  
greenboot
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Default Idea for more reliable switch

Here is an idea that can make the receiver switch virtually 100% reliable. It uses a standard switch, but changes the way the wires are attached to it.

First, remove the black wires from the switch and just solder them all together. There is no reason to switch the black wire. Having them soldered together cuts the failure rate in half immediately.

Next add a jumper across each of the three pairs of switch contacts. This allows both poles of the switch to provide a current path for the red wire. If either pole fails, the other one can provide a perfectly good circuit. The switch continues to operate normally, switching only the red wire.

Haven't tried this yet, but one of our engineers suggested it. I believe it can eliminate the threat of switch failure for those who choose to use a single battery/receiver.

Tom
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Old 08-25-2003, 06:04 PM
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Phil Cole
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Default Idea for more reliable switch

Yes, the total failure rate of the switch will be lower.

You do need some way to know when one of the switch poles has failed. When that happens the switch failure rate would be the same as the original switch.
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Old 08-25-2003, 06:18 PM
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greenboot
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Default Idea for more reliable switch

Yes, I agree, it won't be apparent if half the switch failed. But even if that happened, it would still be twice as reliable since the black side of the circuit always has 0% chance of failure.

Carrying this modification one step further...

Rather than jumper the two switch poles, you could add independant battery and receiver leads. One for each pole. You could plug both receiver leads into a single receiver use two receivers. This would allow you to test each pole separately as well as provide redundant wire connections. Again all the black wires are soldered together and not switched.

Tom
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Old 08-25-2003, 10:33 PM
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Lynx
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Default Idea for more reliable switch

Not 0 percent, solder joints still break, in fact they're just as likely to break as the soldering connection to the switch itself. Keep in mind there is no such thing as 100% Only disconnecting the negative terminal to the battery isn't a good idea, it makes a short easier to occur because there's one wire that's already connected. If you want to decrease your chance of failure, simply wire two switches, that way you have to use them both. If one fails you'll recognize it when you go to turn it on and can replace it. It's not 100% but the chances of two switches failing at the same time are so remote as to be negligible.
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Old 08-26-2003, 01:09 AM
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Default Idea for more reliable switch

Lynx,
I guess I went a little overboard when I said 100% reliable. That's always bound to draw criticism.

I do know that just about anything can break. But I didn't realize every solder joint was as likely to fail as the switch. In fact, I notice quite a few posts that mention switch failures being a problem.

Actually, I think you failed to see the theory of using one TWO pole switch in place of TWO switches which does the same job. I get the impression you have just discounted the idea and have invented a bunch of "faults" that don't really exist.

You do have a point that leaving the black wire always connected is electrically differant. But house and automotive wiring has been done this way for many years and it's sort of a proven method.

Tom
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Old 08-26-2003, 02:02 PM
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RJChip
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Default Idea for more reliable switch

Excellent idea for an improvement!

I deal quite a lot with redundant systems and their failure rates in industrial control systems, and I agree that redundancy in the switch wiring can be helpful. We may want to carry this idea a little further and also consider some of the practical aspects as well. I would like to add the following comments for consideration if you plan to try this:

First, of course it is always dangerous to use statistics like 0% and 100%. Naturaly, this always arguable. I am 100% certain of that.

Tieing the ground wires all together should not hurt anything - AS LONG AS, (also pointed out by Lynx,) you don't increase you're chances of shorting out the other lead. How you go about the wiring can affect that. If done properly, there will not be a significant increase in the probablility of the positive side shorting out. If there is a higher prob. of shorting out, at least this will be a risk on the ground, more than in the air. I would want to minimize the risk in the air, and worry less about any shorting occurring on the ground. (The assumption I make here is that shorting occurs when it is being handled. If all wiring is done with good practices, nothing will short out all by itself while flying.)

Using both poles of the switch to carry the load on the positive leg is fine, but, as pointed out, there is a bit of a headache factor in assuring that one of the poles has not failed at any given time. Using the dual connectors would probably be good, but it is a bit fussy, and the more you handle those connectors, the more likely it is that one of the connections/solder joints will break.

Soldering. Big issue here. The solder joints on connectors, especially those little lugs on the switches, and when using small guage wire, do have a high failure rate. However, good solder joints can last years and be VERY reliable. If the solder joints are done on the switch, you may indeed introduce a higher failure rate than what you are protecting against. If the solder joints are done as splices to wires, done properly, and protected both electrically and mechanically, they will not be an adverse risk.

The factory solder joints on the switches are just what they are, possibly prone to defects, but it is best not to open the switch and possibly weaken a joint. Given that a switch may have defects, or be prone to breaking contact due to vibration, etc., it is somewhat likely that both poles may be equally at risk! Therefore, the solution suggested by Lynx of using two switches is probably better. The switches must be wired in parallel, of course. You can then turn on each switch one at a time to verify that both are always working. Turning them both on gives you a redundant circuit.

Now, the sum total of the reduction of risk depends more on how this is all implemented than on the reliability of the switch all by itself. Whether you use one or two switches, be sure to produce good quality solder joints by splicing wires (unless you are using larger switches with heavy duty lugs.) Try to minimize the number of connectors used. They are part of the potential failure, also. The common ground should probably NOT be made by twisting all of the black wires together and soldering! (This is known as a single point of failure.) It will be much more reliable if individual splices are made into the wires attached to the battery, for example.

Again, if using only one switch, make all of the connections by splicing the wires coming out of the switch, not by opening it and jumpering the lugs.
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Old 08-26-2003, 02:19 PM
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Default Idea for more reliable switch

Would another consideration for this excellect thread be for the use of a better switch as well. Maybe one thats got military approval. Can we source one thats used on the space shuttle? I not sure if we could find one thats nice and light though. I'm pretty sure the switches we buy from JR, Futaba, etc. are pretty common "run-of-the-mill" varity. I've opened many, and they appear very, very cheap!
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Old 08-26-2003, 03:02 PM
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RJChip
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Default Idea for more reliable switch

Absolutely, a better switch would certainly be worthwhile.

Keep in mind, that even cheap switches would be plenty reliable IF you implement the power system with redundancy where the likely failure points are.

Having said that, I would suggest a quality automobile 12v instrument switch is a good choice. They are designed for use in an environment rich in vibration, temperature, and humidity extremes. Not only that, they have huge lugs that you can solder to!

Alternatively, there are plenty of very small, lightweight switches available from industrial suppliers, that are quite reliable.

I would think the best choices will be toggle switches with strong springs = longer levers = mounting internally and rigging a pushrod or something for switching from outside the model.
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Old 08-26-2003, 03:50 PM
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Default switch

Years ago Logictrol had the switch wired as suggested in this thread. I guess we have not learned anything in 30 years.
BTW a simple cheap slide switch is more reliable when used under our conditions than any toggle switch be it MIL SPEC or otherwise. Toggle switches don't like vibration.
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Old 08-26-2003, 04:34 PM
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Default Idea for more reliable switch

Ok. I'll buy that about the toggle switches not standing up to vibration. I've never looked into specs on them. I've used hundreds of toggle switches without problems before. I have had some of the RC switches come apart in my hand, though. That's what scares me the most about them.

I still stand behind the concepts of redundancy, so long as the design takes into account the whole circuit, and all the likely points of failure.

I now question the mode of failure that people are seeing in these switches. Does anyone know if there is a typical failure mode of the standard RC slide switch?

It just seems too likely that a single defect in the plastic can too easily cause both poles to fail. And yes, the same can happen to a toggle switch. Just that, once the decision to use an aftermarket switch is made, it should be easy to make a quantum step up in the durability of the device.
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Old 08-26-2003, 04:35 PM
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Default Idea for more reliable switch

Why don't toggle switches like vibration?
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Old 08-26-2003, 08:38 PM
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Default Idea for more reliable switch

Originally posted by greenboot
Actually, I think you failed to see the theory of using one TWO pole switch in place of TWO switches which does the same job. I get the impression you have just discounted the idea and have invented a bunch of "faults" that don't really exist.
I don't think he misunderstood or discounted the idea, I think the point is that if one pole fails, the other will will do the job, but you're now flying on only one pole. You have no way of knowing that "half" your switch is dead.

By using two switches, you can turn each one on independently to verify that both are working, then turn both on and fly.

Or better yet... wire up a single switch in the manner you suggested (very elegant solution) but put an LED on each lead that comes on when you turn on. As long as you see two lights, you know both sides of the switch are active. If the time comes that you see only one light, you know you've lost half the switch and it's time for a new one.

D
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Old 08-26-2003, 09:46 PM
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Default leaving the black wires connected

I have seen a few posts that have stated that several of the multi-port chargers won't charge properly if the negative sides of multiple batteries are connected together. I presume that this is because the chargers have the positive side commoned internally and charge via the negative lead. Anyway, might be a consideration in switching both sides of the circuit.

Dave
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Old 08-26-2003, 11:00 PM
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Default toggle switches

Originally posted by Tiger
Why don't toggle switches like vibration?
The contacts are held together by a spring and have the heavy mass of the handle connected to them. Under vibration this heavy handle mass causes the spring to relax opening the switch.
Our little engines produce almost 50 G's of vibration. Mil Spec switches are usually rated to 10 G's or less.
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Old 08-26-2003, 11:04 PM
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Default Idea for more reliable switch

I know I'm dense but I don't understand this discussion! Every switch harness I have bought is wired as suggested herein. I have never seen one that switched the black wire. All mine just switch the red wire from the receiver to the test connection. Whazzup??
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Old 08-27-2003, 12:12 AM
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Default Idea for more reliable switch

I'm a bit too lazy to do it, but I'd suggest writing a battery company and mentioning the positive supply only disconnect to them. I'd imagine everyone of them would recommend against it. A battery's positive voltage is only in relation to it's negative terminal, if you allow that negative terminal to float freely you will have unknown galvanic reactions take place on the wires in your setup, because any stray positive static voltages that occur will travel through the wiring into the battery. I have no idea how bad that might be. But I know it's not good. As far as house circuits go that's perfectly fine because the ground wire is truly a ground. IE it's actually driven into the ground. I don't know how cars are wired at all so I can't even guess about that.
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Old 08-27-2003, 12:45 AM
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Default I've seen the light...

As Avinut first stated, the switch does NOT switch the black lead. So I was wrong about that. I'm not sure how this effects my original idea.

I agree using two standard switches is probably the easiest method for increased reliability, expecially if you are going to use two batteries.

For those who would want to use a high quality aftermarket switch; I would still consider a two pole double throw switch to provide a double path.

Tom
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Old 08-27-2003, 05:55 PM
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Default Idea for more reliable switch

Hi,


I use two batteries and two switches in all my big birds. I just plug into two channels of the receiver, you can use a Y harness if you need space to plug in the extra battery.

I know for a fact that this arrangement has saved my birds on more than one occasion. After landing and getting ready for the next flight on several ocassions I have found one of the systems to be non functional, either from battery failure, switch failure or lead failure. The point is the dual battery arrangement saved the bird.

My 2 cents

Jerry
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Old 08-27-2003, 08:08 PM
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Default Idea for more reliable switch

Every switch harness that I have ever dissassembled has been wired with the neg tied together, and the pos tied to both poles of the DPDTswitch. I didn't think anyone wired them any other way. I make all my own switch harnesses and always wire them this way. I do unplug the batt when storing though.
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Old 08-27-2003, 09:13 PM
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Default yes

all the standard futaba switches come with both poles breaking the positive wire only.... and yes, some chargers ( SM Services 8 output charger ) can not be used common negative or it kills something inside $100 + to fix. on my 1/3 rd scale cap i intend to not have switches but instead use 2mm corally gold connectors held in one of those "can't put together the wrong way " sheaths and just plug it together for ON. this would break both +ve and -ve to the battery and allow the use of my charger . I KNOW I CAN CHARGE ONE AT A TIME AS IS.... but with 2400 nicads that takes ages to cycle them in situ.
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