I have an idea. It could be a good one, and it could be a useful one. It could even be a money-spinning one, but I want to spread it instead of earn from it.What I'm thinking of was inspried by potato cannons:Imagine a combustion chamber of reasonable size, say a gallon volume. Cylindrical, it is domed at one end t withstand internal pressure, but the other end tapers to a narrow outlet.The idea is that an explosive mixture in the chamber (anything handy, but gasoline/air, ethanol/air and butane/air are the most likely) is ignited by a spark, just like a potato cannon. There is no ammunition, though.The tapered pipe (I hope) concentrates the blast to release a "bullet" of rapidly-moving gases.The whole cannon points down at the ground, the muzzle only a few inches from the ground. The detonation is triggered via a long cable (metres long). The "gas bullet" hits the ground with a large enough force to simulate the step of a human or animal, or the passing of a tyre. This triggers the landmine left months ago under the soil.My idea is, in effect, a low-tech device, capable of being built and repaired by semi-skilled locals, from scavanged materials, in war-torn areas. With a bit of training, a small team could use one to safely pound a mine-field hard enough to trigger the mines and make the area safe to live in. The cannon would be damaged by explosions, but not so badly that it would need repaired after every use, and it could be easily fixed with scrap from the nearest wrecked landrover.Would this work? Or would they need solid ammunition, say lumps of timber or rocks wrapped in rags to make a seal? That would need a staight (not tapered) barrel, but it's the same idea.I don't have the space or equipment to make one myself, and land-mine charities won't tell me how much force is required to trigger a mine, but most of you reading this are in the US, and it seems you have an easier time finding this kind of thing out.Run with the idea, chaps. Build one if you can, and ship it to somebody who needs it, or come up with better plans than my rough idea, and post them to those who need them.