Redundant Switches and Switch Age

A British model magazine distributor once asked me why I called my switches “Redundant”. I explained they could suffer multiple dirty contacts or failures inside yet still continue to conduct as they had duplicated current paths inside. They’re much safer than a single contact switch. She explained in “British English”, “redundant means extra or garbage or not needed. If your laid off from work, your made redundant.”

Let me be clear, having a layer of redundancy to me means you’ve got a backup system. One thing can fail, the system continues to function. As our models become larger, heavier, faster or just plain more important to us we start to realize the need for system redundancy. Battery and switch failures are some of the most common pilot error crashes that can be avoided. I say boldly “Pilot Error” because in most cases such failures could have been avoided by proper selection of switch and mostly by not using them till they don’t work anymore. Likewise, failing to properly select, properly charge or periodically test a battery leads to many crashes that could have been avoided. Not doing what you ought to do and having an accident is one way the pilot errors.

A conspiracy of connections: Think of your battery, switch harness and all the parts that make it up as a “chain”, as long as all the links are connected, you’ve got power. A 4.8V battery and switch harness has 26 separate connections in the chain from the negative trace on the receiver through the connectors, switch harness, battery wire, tabs and solder joints/ spot welds on cells, back through the red wire, through connectors, through switch harness, back to connector pin on RX. Any one of these 26 connections fails or opens up, your model is in the dirt.

First thing to watch out for:

The switch can be a big culprit of failures if you’re not careful. All our receiver switches (All standard size and up at Radical RC) are double throw double pole knife. This means your red wire is being switched with two switches simultaneously. Each of these switches is a kind of double switch since they are double sided themselves. It could be argued there are 4 parallel switches working together. If you’ve got an old switch, tear it apart and study how it works. Each of the switches inside is made up of a pair of blades. There is a slider that contacts the flat surfaces of each side of each blade, when you move the switch, the slider bridges the two blades making the connection. The slider contacts the pair of blades on each side. So, if one side of one blade (or slider) gets dirty, it’s still contacting on the other side of that same blade. In a high quality switch there are two such assemblies, 2 pairs of blades, two sliders that connect the pairs. There are 4 independent current paths. 4 specific places need to get dirty or corrode before the switch can fail to pass current. Your switch is subject to this corrosion from dust, dirt, oil (which makes it attract dirt), water, just plain age (oxidation) and wear from use. All switch failure crashes (98% anyway) are PILOT error for failing to keep this item in a high state of maintenance.

What you should do:

Replace the switch when you replace the battery pack. I am presuming you’re dating your packs and not using any of them beyond 3 years. Certainly, most of your switches will last much longer than 3 years. However, who among us is willing to keep using one to see how long it will last? ;-) It’s a pretty low cost item that adds a great deal to your models electronic integrity and reliability. When your confidence is increased in your model’s integrity and reliability, you’re free to concentrate more fully and will become a better pilot.

Dave Thacker

Radical RC