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Switch failure

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Old 09-05-2010, 09:05 PM
  #1
mogyd
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Default Switch failure

Iam highly suspicious aFutaba switch harness with about three flights on it from the factory package, malfunctioned and caused the crash ofa newGreat PlanesEscape today. Ihave two questions:

1. Isit possible totest this switchto confirm my suspicion?

2.Is there a brand / model switch someone might recommend asa dependable replacement?

I read in "Model Avation" that switch failure was the#2 cause ofcrash ...following pilot error. I had no idea this was such a significant problem. Before Iattempt to get back in the air, I'd like to ensure Ihave done all that canbe done to prevent bringing home another bag of broken balsa.

Thanks.
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Old 09-05-2010, 09:28 PM
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Default RE: Switch failure

Yep, it is indeed a common problem, along with connection issues on the power source. I made a connector to hook the switch output to a hobbico load testing volt meter, so I could watch the voltage when the power was on. I can also hook the volt meter to an open channel on the RX.

I generally use heavy duty switches for all my planes, the big JR heavy duty or MPI brand switch is what I use. Also, if using glow power, be sure the power switch is on the opposite side of the plane that the muffler is on.


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Old 09-05-2010, 09:44 PM
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Default RE: Switch failure

First experienced this a month or so back.

I was flying my battle worn, tried and trusted 60 size Ultrastick. Taxied back to the pits. Killed the engine and nothing happened. Gave the sticks a wiggle. Nothing.

Odd.

Had to kill the engine by pinching the fuel line.

Turned the plane off, nothing, on, nothing.

Dead switch. Go figure. 60 seconds or so earlier and I would be down a plane...
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Old 09-05-2010, 10:23 PM
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Default RE: Switch failure

Futaba switches have never failed to me.

Still a failure due to vibration or high Amps is possible.

The way to verify the condition is by measuring the Ohms with a meter while the engine is running and while turning it back and forth.

Switches are necessary evils:

http://www.rcuniverse.com/forum/m_45...tm.htm#4507366

A silly question: was the switch installed to be on while pointing towards the tail? (preventing that something hits the switch in flight or taxing)
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Old 09-05-2010, 11:06 PM
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Default RE: Switch failure

I've never had a Futaba switch fail. I do have a couple EMS switches (sold under various names : Cemark, Smart-fly, etc) that are more robust and also double pole so you have half as much chance of a failure. You can also use dual switches (and batteries) if you're really paranoid.

The test is whether the switch works now after the crash. If it does: it probably wasn't the cause. They don't "get better" after a failure.
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Old 09-06-2010, 12:25 AM
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Default RE: Switch failure

It is also worth noting that most of the switch failures I have seen, the switch was intermittent, I have only seen one switch fail completely, it was a single pole 2 wire. (I don't remember the brand).
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Old 09-06-2010, 12:45 AM
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Default RE: Switch failure




Quote:
ORIGINAL: mogyd Iam highly suspicious aFutaba switch harness with about three flights on it from the factory package, malfunctioned and caused the crash ofa newGreat PlanesEscape today. Ihave two questions:
1. Isit possible totest this switchto confirm my suspicion?
2.Is there a brand / model switch someone might recommend asa dependable replacement?
I read in "Model Avation" that switch failure was the#2 cause ofcrash ...following pilot error. I had no idea this was such a significant problem. Before Iattempt to get back in the air, I'd like to ensure Ihave done all that canbe done to prevent bringing home another bag of broken balsa.
Thanks.
Switch failure happens to all brands, especially where brands offer,micro, standard amd heavy duty switches andthe wrong switch is selected for the application.
Micro for small EP&Parkflyers, standard for sports upto say .60 and use HD for all GP Heli and any Acro model with say above .60 size engine.
Use two switch harness & batteries for petrol powered aircraft which are subject to much more vibration and failure is common where wires vibrate and break at the switchsolder joints.
- This from both servicing RCsystems and experience, hence now use:
Dual (Parallel) Battery Operation = Reliability & More Flight Time - for all petrol models
also common: Black Wire Corrosion within switches when models stored even for short periods and batteries not removed.

See also sub Section "Glitches & Jitter in Receiver, Servo & ESC - causes and cures " under
"Radio Systems, Accessories, Alterations and FAQ." at:
Alan's Hobby, Model & RC FAQ Web Links



Regards
Alan T.

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Old 09-06-2010, 05:52 AM
  #8
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Default RE: Switch failure


Quote:
ORIGINAL: andboy

First experienced this a month or so back.

I was flying my battle worn, tried and trusted 60 size Ultrastick. Taxied back to the pits. Killed the engine and nothing happened. Gave the sticks a wiggle. Nothing.

Odd.

Had to kill the engine by pinching the fuel line.

Turned the plane off, nothing, on, nothing.

Dead switch. Go figure. 60 seconds or so earlier and I would be down a plane...
If it had happened in the air, a lot of fliers would have posted the following:
MY (***) RADIO RECEIVER FAILED IN FLIGHT
*** Pick one, Futaba, Hitec, JR, Spektrum
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Old 09-06-2010, 06:23 AM
  #9
mogyd
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Default RE: Switch failure

Alan,

Thanks for the response and the great link detailing dual battery operation. I was curious on how that was done.

All the best!

Curt
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Old 09-06-2010, 07:18 AM
  #10
mogyd
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Default RE: Switch failure



Being relatively new to this hobby, mistakes in judgement, assumptions and conclusions can come at a high price - financially, emotionally and physically. Regrettably, I've experienced all three ... but I'm learning with every mistake!

Theswitch was "on" toward the frontof the plane, and wassubject toan inadvertantbump. Future installs will be reversed.

Some additional info surrounding the event:

1. During the pre-flight and run up, all seemed normal until we did the engine run up and attitute check. When Iput the plane back on the ground for taxi, the engine wouldn't return to idle. The first assumption was a loose throttle linkage, so Ipinched the fuelline to kill the engine, and prepared to repair the throttle.I turned off theswitch (note still in on position) and removed the canopy. Once Iverified everything wasconnected,theswitch was activated and we were back in business. My conclusion: I must have inadvertantly opened theswitch while holding the model during start and run up. It never dawned on me that the switch wasfailing intermittantly.

2. We put the plane into the air for a seven to tenminuteflight until afew rolls turned into adeath spiral. Onthe ground,all theservos ... including the throttle worked flawlessly.Field post mortum:radio interference or piloterror. Later reflection: suspicion on switch failure.

What always seems so obvious in hind sight rarely surfaces during thatmental check list leading up tofull throttle!

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Old 09-06-2010, 09:01 AM
  #11
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Default RE: Switch failure

In some 50 years of flying RC, I have experienced several switch failures, most if not all of intermittent nature. It is very hard to detect a bad or partially failed switch. Most of the ones used in RC are knife type (a contact bar sliding over contact points) which tend to be self cleaning and probably the most reliable type you can get in such a small package but dirt and grime can work their way into the mechanism and cause a high impedance or failure. Also, most of them are double contact or dual contacts (the ground side is usually not switched and only the positive line is doubled up so you have two paths to minimize failures). Do not use toggle switches in this application as they are more prone to failure.
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