With the amount of equipment in my X8 is on the increase, so is the weight. Its becoming very difficult and somewhat dangerous to hand launch.
Iv decided to build a catapult. I dont like the idea of a bungee launcher because of the amount of flat space required. some places I fly dont have this.(eg: off a cliff =) ) I really wanted something self-contained and foldable.
The APM flies the X8 really well BTW =)
If anyone wants to build one I have posted all the info and pics here
Comments
Who will be willing to build one like this catapult for me?
Thank's Brett and the other ideas, I'm going to try to make my catapult for a Skywalker plane and post at catapult group if I can do it
Just knew Aeromao has released an UAV launcher http://www.aeromao.com/uav_launcher .
It seems the mechanism they adopted is very similar to this design.
Rivets dont work well, screws are more work butt better.
10mm surgical tubing in two loops as the original but I'm going to add a pulley at the top and make it double length for a longer pull, the system works better with with the cord brake to stop the trolley and the support for the plane needs to have as little friction as possible so the plane slides off it easily. fibre sticky pads from Home depot work well.
The clips are from Home depot 7$ and work well as long as the screw position is worked out OK.
I used 2 pieces for the 3/4 square tube inside the 2 x 2 tube as the original design but I made mine longer at 6 inches so I could fix it more securely, 2 and 1/2 inches stick out to support the joint. I also found a problem in that the 3/4 tube had square corners outside but the 2 x2 tube had round corners inside. I made 1 corner of each insert piece rounded to match and this then they fitted much better. If you look at the first picture you will see 2 black lines that I added before I cut the tube so that angles would be the same when I assembled the tube. mine is also a bit longer at 9 feet. The front legs of the ramp are also modified to reduce the angle between them from 90' to 60'
Hi Guys
Here are my modifications to the original , they are designed to make the carriage stiffer ans so there are no exposed threaded parts to hold the bearings the top plate is 1/8 Aluminium and the square tubing is 3/4 x3/4 x 1/8 inch, total length 12 inches. note that the top hoops to support the plane are missing in the pictures ,
note that the assembly is easier as the small screws in the plate are fixed first to allow precise adjustment of the fixing distances to get the bearings in the correct place before the other through bolts are fitted. This keeps everything solid. Testing at the weekend if the snow stops.
Hi Rich
I am also build my version of this catapult, First I thank Brett for a great design. My capatult is complete and ready for testing as soon as the tubing arrives.
I think that I see the problem with the catapult of Rich as I went down the same route and it did not work. When the elastic is under tension and then released with the aircraft in place the aircraft has a considerable inertia which is a long way above the carriage., this then acts s a lever and forces the rear of the carriage down and this forces the bearing support bolts to bend and open, this also adds a lot of drag to the trolley slowing it down.
The original design had a much longer trolley which then reduces the lever effect and so reduces the drag. I have also made my new carriage longer at 12 inches long and stiffer (details tomorrow as I am at work) It does not open even with a heavy load and a high tension and is a bit lighter. The bearings will last longer as well !! I have also added a cord STOP to the system so that the carriage does not hit the end stops and cause damage, the cord simply stretches a bit after its set to a correct length and is attached to the trigger end of the ramp and the carriage.
What bungee cord are you using. I used latex tubing from a local medical supplier. It is capable of storing a lot more energy than standard bungee. The Force you measure while the bungee is stretched is NOT a reading of the stored energy. Bungee cord is designed to absorb energy and not store energy. For that reason,I recommend you use latex tubing.
I believe that is main problem with your launcher Richard otherwise it looks well made.
Did you sort out the issue of the carriage coming off the rail?
@brett can you please make list of all materials you bought and how you used them? That would be really helpful.
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