I have changed the "bucket" to be wider for bigger "projectiles" and added a thumb wheel of easy range adjustment.
But the bigger redesign is the fulcrum. I split it into two parts to be printed easier.
Now the hole for the axle goes now through all the way, so a longer threaded is needed
As mentioned below I managed to break/wear out the spring rather quickly.
Hence I added a beefed up version. This might not be the engineering approach of Leonardo as he had presumably no access to rubber bands. I use my catapult as an office toy and am therefore not too concerned with historical accuracy.
P.S. I will need to redesign the spring and strengthen it. It suffered material fatigue due to tightening the rubber bands to much, because I wanted to increase range and power. Stay tuned!
P.P.S: Here is the original:
M4 x 25mm Cap Screws - 6
M4 Nut - 1
M4 x 15mm Cap Screws - 2
M4 x 20mm Cap Screws - 3
M4 x 35mm Cap Screws - 1
M6 x 35mm Cap Screws - 6
M6 Threaded rod 150mm long
M6 Hex Nut - 9
(M6 Nyloc Nut - 2, replace 4 regular nuts)
M6 Washers - 7
An assortment of elastic bands (smaller ones will give greater power for the arm)