I'm working on a project that involves a scale parachute. It is vital for the project to get a good measurement of the speed it has when it lands. We still haven't built the parachute, but we need a way to know the speed it has when it touches the ground. We have thought about using a cellphone as the body tied to the parachute and write an app that collects the accelerometer data, then use this data to calculate the velocity. Another option was to use two lasers very close to each other and photoresistors with arduino. Then, given that we know the distance between the lasers, the lasers would give us the time it takes the object to travel this (very small) distance and we would get an approximation of the speed at that moment. The problem here is that the parachute may move horizontally as well, and land at some point where our laser can't detect it.
We are not sure if these are good ideas or if there is any better approach. What do you suggest?
Best Answer
If you know the dimensions of the object, use a laser and detector to measure the time it takes to fall through the beam path. Distance divided by time will give you the average velocity over the period, and if your detector is close to the ground, it will give you a good approximation. The best thing to do is to use a pressure sensor and back our the velocity from the impact, but the laser option is probably cheaper.