Flywheel Trebuchet

three two one this video is sponsored by simply safe more about them later a trebuchet stores energy by raising a counterweight which when released converts its gravitational potential energy into kinetic energy but what if there was a way to store this energy as kinetic energy before release in something like a flywheel let's make a flywheel trebuchet unfortunately my old trebuchet hasn't aged very well and the plywood sections are falling apart so i've decided to make this new trebuchet completely from aluminium the frame will be built using these extrusions which have a track built into them allowing these nuts to slot in and clamp down giving lots of flexibility for mounting positions the frame design will be an equilateral triangle for maximum strength which means cutting custom 60 degree angle plates to join the sections together once the two frame halves were assembled the cross joint extrusions could be attached with the 90 degree bracket and it's already starting to look like a trebuchet it's probably a bit overkill for this project but with the extrusions being so adjustable it can be reused for future trebuchet experiments the arms are made from 25 by 50 millimeter rectangular tube section as these need to be strong to survive the huge amount of force accelerating a tennis ball so fast the official world's fastest tennis serve was 157 miles per hour and to put that into perspective this is my old trebuchet topping out at 124 miles per hour so to beat the record speed the 60 gram ball will undergo a centripetal acceleration of at least 265 g's which is equivalent of hanging a 27 kilogram weight from the end of the arm which according to my stress analysis can bend this arm by four millimeters at the tip i then added bearings to the arms which allowed the whole assembly to be mounted to the axle with a small push everything seemed to run smooth but it needs some balancing instead of mounting another long arm to the opposite end i decided to use a counterweight because at high speed i expect the arm to produce quite a lot of drag so having only one arm will reduce the amount of energy required to spin it the balance isn't perfect but it's far better and i'll balance it properly once the flywheel is mounted there's just one problem i need a method of spinning it faster so i 3d printed a pulley which mounts to the arm then a timing belt can be used to drive it from an external source and i mounted a secondary axle and larger pulley to the frame and using the slot nuts the belt could be correctly tensioned i can then attach a crank handle to the end of the secondary shaft and wind it up to speed but first let's build the flywheel the flywheel was cut from six millimeter thick aluminium and it will have a diameter of 800 millimeters but because that's too large to fit on my cnc router i've decided to cut it in four pieces each section can then be bolted to the arms to produce a large flywheel ring and the unsuspecting opposition has yet to recognize the potential of this machine so tomorrow we can attach the projectile slinging components and get on with the testing unlike traditional trebuchets the projectile will be constantly moving with the arm so it needs to be held in position until a trigger is pulled this nylon strap is sprung loaded to clamp the ball in position and is attached to a small hook near the axle to trigger this latch to release i built this contraption that moves into the path of the hook as the flywheel rotates so the trigger can be pulled at any point during the flywheel's rotation and the ball will always release at just the right time and this release contraption can also be advanced or delayed by sliding it up and down on the frame to get the most optimal release angle i then place the ball in the sling and attach the sling strings to the end of the arm a trebuchet sling has two attachment points one is fixed to the end of the main arm and the other is loose but is hooked over this pin then as a projectile swings around the loop slides off the end of the pin and releases the projectile time for a first test albeit a slow test as i haven't made the crank handle yet and oh i should probably pin this to the ground it seems like all the weight of the flywheel pushed onto this pulley and has destroyed it but nothing else seems to be broken so we could probably give this another test by hand in three two one that actually went pretty far after the first test being so slow right so i now have the crank handle on here and also i've fixed the pulley which is now half aluminium half 3d printed so we should be able to get up to some pretty high rpm this slow-mo was filmed at 1 500 frames per second and has been slowed down 60 times using the length of the arm as a reference we can measure that the ball traveled 1.44 meters in 22 milliseconds so by dividing the distance by the time we get a calculated speed of 65.5 meters per second or 146 miles per hour which is 22 miles per hour faster than my old trebuchet but it's still 11 miles per hour slower than the world's fastest tennis set the fact that a human can hit a tennis ball faster than this is just insane so today we are going to beat the world record tennis serve i reckon the most optimal release point is when the sling is in line with the arm because then it's at the largest radius from the main axle so what i've done is i've set the trigger to release the ball earlier dropped from the arm earlier and then the sling to open up later so should have the same trajectory but just hopefully slightly faster [Applause] i didn't even see where that went managed to snap the sling though i hope that went forwards wow let's check the high speed footage then i need to rebuild that sling right so according to the high speed footage the ball traveled 0.82 meters in 10 frames so that's a hundredth of a second that means it went 82 meters per second in miles per hour that's 184 miles i think we need to redo that test and this time i'm going to make sure that my hand is completely off of the crank handle before the tennis ball is released just to prove that it's purely the inertia of the flywheel at the point my hand stops applying power the flywheel is spinning at 263 rpm and i know from my cad model that its moment of inertia is 1.1 kilogram meters squared from this we can calculate the flywheel has a stored energy of 419 joules that's equivalent to raising a 39 kilogram counterweight to the height of the axle but this flywheel only weighs about 18 percent of that at seven kilograms once the ball is released it leaves a sling with a kinetic energy of 132 joules meaning the usable energy efficiency is just 31 percent however the flywheel is still spinning with an energy of 79 joules and i reckon if we increase the mass of the projectile we can extract that last remaining amount of energy that went high doesn't quite stop it so we need to increase the weight a bit more but it's getting close right so this is now 180 gram tennis ball which is about three times the weight of a standard tennis ball that's so weird to watch at the point of trigger release the flywheel slows to almost a dead stop in a sixth of a second losing 99.5 percent of its energy what's interesting about this is the flywheel on the left has twice the stored energy to begin with but the projectiles leave the sling with almost the same kinetic energy so the heavier projectile on the right is traveling quite a bit slower but still launches about 20 further due to it being affected less by air resistance seeing as this flywheel trebuchet likes projectiles a little heavier than a tennis ball maybe i need to get some baseballs and stick a motor on this thing but for now i'm very happy with the performance back in the days of trebuchets this device would be used to protect my home from intruders but nowadays there is a more effective solution from simplisafe home security is made easy with their wireless devices such as doorbell cameras security cameras motion sensors entry sensors and so many more i personally use their camera on my shed as there is a lot of equipment and tools inside in fact their cameras are so easy to set up as i even use one to monitor my 3d printer when i'm not around with the sensors being wireless they're so easy to install like this one i put on my garage door was literally installed in seconds the monitoring center can then call the police if alerted or simply remind you that you've left the window open all these devices can be ordered online or over the phone and you can choose from their wide range of products to meet your security requirements simply safe is award winning home security that keeps your home safe around the clock it's reliable easy to use and there are no contracts so if you want to upgrade your home security system without having to build one of these then check out simply safe at simply safe dot com forward slash tom stanton i would like to thank simply say for sponsoring this video and i'd like to thank you very much for watching this video if you enjoyed the video it'd be great if you could leave a thumbs up down below if you're new to my channel and want to see other projects similar to this then please click subscribe down below and a massive thank you to all of my supporters over on patreon.com for making these projects possible i honestly couldn't build them without your support so thanks once again thanks once again for watching and i'll see you in the next video goodbye

Channel: Tom Stanton

Views: 2,192,728

Rating: 4.9422107 out of 5

Keywords: trebuchet, catapult, physics, engineering, tennis, projectile, flywheel, machining, engineer, 3D printer, 3D printed, CAD, design, fast, speed, power, sling, launcher, CNC, router, aluminium, metal, spinner, energy, kinetic, gravity, mechanics, 3d printed, homemade, DIY, trebuchet design, how to build a trebuchet

Id: RVT5i4nhIGs

Length: 10min 16sec (616 seconds)

Published: Thu Sep 24 2020

Reddit Comments

[u/gonegib]

He needs to put a drill where the crank is

[u/eatlego]

That was very interesting.

[u/pws3rd]

It just came up in my feed. Guess you beat me to pusting a link here 😂

[u/Y0V0]

Can someone help me get dimensions of this incredible machine? Would like to yeet some apples in a field.

[u/vociferant-votarist]

Really, that’s just remarkable. Good work!