Project not dead!
I have been really distracted with my CNC hot wire cutter and have been waiting on a few parts. I decided to make a bungee launcher as this will make a much shorter takeoff that i can use in more areas.
This is a version of what i have seen online that lots of others have made. My contribution is that instead of it having back legs it has a ground plate that will have ground screws. I feel this is a pretty large improvement over the other designs i have seen. In the other designs, when the sled "hits" the front or is stopped by a rope connected to the back, the effect is the same. All that force slams the entire unit forward. To stop the machine from jumping forward and collapsing there are usually some pins in the front to stop the legs from rotating. This is a lot of repeated force applied to two small areas of thin tubing. In my version the front legs have nothing stopping them from rotating. The back plate will be locked into the ground with 4 long screws, like the ones used for large dogs. The rope to stop the forward motion will be attached to this plate. So all force will be applied to the bottom plate and 4 screws.
The length of travel is 77 inches. I made up 2 bungees that have 12 inches of material in between the rings. When stretched to 77 inches (6 times there length as recommended by hobbyking) they each have a pull of 15lbs. So for the f-100 i will have 4 of them for 60lbs of pull throwing a 10lb plane. Of course before doing this i will be using a 10lb dummy weight and seeing what the thrown trajectory is like. At the moment i feel like the front end should be higher. This is easily accomplished by getting some wooden dowels or some kind of rods that can just insert into the legs.
All parts are rated at least 200lbs and usually are in the thousands of pound ratings.
I just received my snap shackle (last picture) that will be the release mechanism. It means i will be standing off to the side in case anything releases prematurely. It will also have an emergency lock that needs to be removed before the shackle will release.
The trolley is going to be setup so that different top plates can be attached depending on the size/type of plane being launched so i can use it for other stuff in the future.
Here is a playlist made on youtube of different launchers:
https://www.youtube.com/playlist?list=PLMieSP4Ym7qq3Nz1NjVfsoLUlxXVbRltJ