#1
Posted 20 September 2017 - 02:55 PM
I have not been here in a while because of summer school and stuff that my mom made me do but I wanted to let you guys know of a new project I'm working on.
The launch is not finalized, but the idea is that a water bottle connected to a sting is dropped of a balcony. Chain is tied to the string. The car is attached to the chain. Scince gravity goes speeds up a falling object increasingly as time goes by, the car speeds up and launches. I think the launch can launch a two car train about 5 feet, which is pretty good in my opinion. The reliability of this launch is really good and I like how easy it is to reset the launch (pull back chain, hook it on something.
#3
Posted 21 September 2017 - 08:49 AM
Do you have any reduction between the launch cable and the weight? It looks like it is hitting the ground with a lot of excess energy. With no reduction your acceleration is capped at 9.81m/s due to inertia of the weight - almost all the available energy goes into accelerating the weight and not the train.
I use a reduction of 5:1 - Schwarzkopf used 3:1. It's a trade-off because with a higher reduction you need more weight to develop the same force, so to get the best acceleration for a given mass you want reduction equal to the square root of the ratio between the train mass and the counterweight mass (if my calculations are correct).
#4
Posted 21 September 2017 - 11:46 AM
#5
Posted 21 September 2017 - 01:30 PM
A pulley system is the approach I took (also what Schwarzkopf used IRL)... it's very simple and low friction. Since you already have to route a cable through pulleys, it's just a matter of doing it more than once. You don't have to be bang on the optimium ratio - you'll never achieve optimal performance anyway due to friction.
Another advantage of adding some reduction even if you don't need any more acceleration is that it reduces the height of the tower you need to drop the weight from. This makes the whole system more compact (though it's still very bulky compared to almost any other launch technology), and is especially important if your design calls for the train to clear that tower.