Wires and wherefores

While most of the conducting paths use PCB tracks, power at any significant number of amps usually has to come down cables and even where it doesn't, there are usually wires to the battery contacts. As more and more functionality tends to be put inside pieces or equipment, the enclosures become smaller and more fiddly - and there seem to be more and more wires. The wires have to be kept free of being trapped when the enclosure lid or back is put back on, whether this happens during assembly, when some repair has to be made or merely to change a battery. Trapping a wire between lid and enclosure can result in a cut wire, rendering the device inoperable, or worse, reduce the number of functioning conductors adjacent to plastic that can start a fire when full current is passed. The Challenge The challenge this month is to come up with a simple means of ensuring that cables carrying power inside a piece of equipment can in no way become caught between the enclosure body and the back or front lid when it is put on. There are engineers who carefully bundle cables together with cable ties, but it is still possible to trap individual cables between the ties, as the tie ends can also get trapped in the gap and anything that requires extra labour adds to cost. What is really needed is some small creature inside that is willing to hold the cables together when the lid is put on, but even if such an animal could be found and trained, how would it get out? The solution we will offer is simplicity itself and the cost is trivial. Once you see it, you will consider it obvious, except that we have not seen it before. The solution and its application will be described fully next month. See if you can come up with anything better. Solution The solution to last month's Coffee Time Challenge - to come up with a mechanism for opening jars - came from MAS Design proprietor Mark Saunders. He uses an epicyclic gearbox as a differential. If the gear ratios are chosen such that balancing is equal, you end up with two balancing forces. The product, called Cascade, starts gripping the body, then starts to tighten its grip and twist. But building a 2500:1 gearbox using the minimum number of components is not easy, which is why the product has massive gears with tiny pinions. Other solutions were offered by readers, including one from Alan Horsell involving fingers moving radially and along the axis. He said: "Clearly I stole the idea from the human hand, just added a little more muscle." Another, rather more low-tech solution came from Denis Sharp who suggested the simple teaspoon, "The main problem is that low pressure inside the jar holds the lid on and increases the friction between the lid and the jar, and presses the handle towards the jar. The leverage distorts the side of the lid and breaks the seal, letting air into the jar." But perhaps the most ingenious solution of all came from Liquid Levers, which is a vee shaped plastic moulding which is screwed underneath a kitchen cupboard. You just slide the jar cap into the vee until it grips, and then turn the jar to undo the cap.