Optimising a Magnetic Launcher

this video is sponsored by ren more on them later in my previous video i built a launcher that used electromagnets to accelerate paper planes up to about 26 miles per hour which is quite fast for a paper plane but i want to make it faster with a purely mechanical launcher such as my trebuchet i can simply increase the size of the counterweight or with my flywheel trebuchet i can just spin it faster but increasing the speed of this launcher isn't so straightforward an obvious suggestion would be to just increase the input power but there's one issue electrical power is calculated by multiplying the voltage by the current so increasing either of these will increase the power output however the on and off switching of the coils are precisely timed using a number of electronic components all of which have a voltage and current limit which the launcher is currently operating at it seemed there was some confusion from the comments on my last video that i had built one of these [Music] which works by shorting a metal projectile between two high power rails creating a very strong magnetic field and launching the projectile so as long as the projectile or the rails don't melt the power can be increased for higher launch speeds but with my launcher i need to take a different approach between each coil is a magnetic hall effect sensor that detects when the magnetic sled passes it which is then used to time the activation of the coils however we can also use this sensor data to measure the speed of the sled by timing how long it takes to travel between each coil and as they're all equally spaced we can divide the distance by the time to get a speed measurement at 20 intervals along the rail which also allows us to plot a graph of velocity versus distance each dot on the graph represents a coil on the launcher and you can see the speed gained by the first few coils is huge and starts to flatten out as the sled gets faster now i had a theory as to why this was happening but as of editing this video i now think i was wrong in short the rpm of a dc electric motor is limited by its input voltage and because my launcher is essentially a linear motor i thought the same thing was occurring the theory is that the magnet's part in a coil will generate a current in the coil and once this generated current is equal to the input current the projectile won't accelerate any faster the only way to get it going faster is either increase the input voltage or decrease the voltage generated by the magnets passing the coils which can only be done by reducing the number of turns of wire per coil and seeing as i can't increase the input voltage i decided to replace all the coils starting with the original 80 turns of wire in the first set of coils and reducing down to 30 tons of wire in the last pair of coils so this is the first test of the new rewound coils as you can see got the super capacitors plugged in got the computer ready to do the data logging so i'm gonna press the launch button and wait five seconds four three two one that look pretty fast the data logging says 15.79 meters per second that's uh that's what over 30 increase in speed not bad so if replacing all of the coils resulted in a 35 speed increase why do i now think my original theory was wrong well if we open up an excel spreadsheet we can create a column for the distance which is the distance that the projectile travels down the rail we can also create a column for the acceleration and we can create a column for the velocity in the distance i'm going to put 0 and then i'm going to do it in meters because i know each of the coil coils are spaced by 4.2 centimeters so if we drag that all the way down to there that should cover all 20 coils for the acceleration i know the acceleration is roughly 90 meters per second squared so i can type that in there and then for the velocity we need to use an equation which if you've studied physics or maths mechanics before you've probably heard of the suvat equations they're essentially a set of equations that describe the motion of an object for this instance we want to calculate the velocity using the distance and acceleration so we're going to use the equation v squared equals u squared plus 2 a s so if i enter that into this box solving for the velocity we put the square root of the initial velocity squared plus two multiplied by the acceleration multiplied by the distance between the coils because we want to calculate this thing for every instance uh along the rail and i can drag that down and we get an end velocity of 12.29 meters per second now what's interesting is if we plot these values as a graph with the velocity on the y-axis and the distance on the x-axis we get a very familiar looking graph in fact it looks a little too familiar so let's copy and paste over the actual velocity data and paste it in this column actual velocity now if we import this into the graph wait for it it looks almost too good to be true we have the blue line which is the simulated velocity using that suvat equation and then we have the orange line which is the actual velocity which was measured by the magnetic sensors on the launcher and they almost perfectly line up and this makes sense for the previous coils as they all have the same number of windings so produce the same magnetic forces and therefore the acceleration is constant but to be totally honest i think i was lucky that the new coils were faster this is because reducing the number of turns of wire would in general reduce the strength of the electromagnet but fortunately reducing the number of windings also reduces the resistance of the coil allowing more current to flow which produces a stronger magnetic field not only that but after some research i found that reducing the length of the coil also results in a stronger magnetic field and if i calculate the relative magnetic field strength of each individual coil based on their length i can multiply this by the known acceleration of the previous coils resulting in another very familiar looking graph for reference here is the actual data gathered from the new coils but there is one side effect of these lower resistance coils and that's the current load it puts on the power source in this case i'm using super capacitors which are designed to handle high discharge rates and i actually use these same super capacitors on my four kilowatt e-bike so they should handle a small paper plane launcher with these fortunately i can log the input voltage to the launcher using the main control board and during the launch we can see how much the voltage of the super capacitors drop under load here you can see they are initially charged to 16.5 volts and immediately drop to about 13 volts when the first coils turn on and there's a very clear spike in the voltage between each coil switching on and off which i thought was quite interesting as each spike gets closer and closer together as the sled gets faster but what does this data show in terms of performance well power is equal to the voltage squared over the resistance which i know these first coils have a resistance of 0.16 ohms so if the voltage stayed at 16.5 volts we should be getting 1700 watts of power but instead at 13 volts we're only getting just over a thousand watts i then thought i should test my lithium batteries that i use for my electric bike and just from the sound i could tell the sled was faster they were charged to the exact same voltage as the super capacitors but on average provided 20 percent higher voltage which is a huge difference and it's even clear from this graph that it was faster because the final coil switched off earlier meaning the sled reached a higher velocity of 16.42 meters per second at the end of my last video i mentioned that i want to have the coils not only pull the magnets along but also push them the only issue is that the electronics required to flip the polarity of the coils will massively increase the complexity of the system so my cheat solution was to make a sled that has two sets of magnets where one is a north pole that will be attracted to the coil and the other is a south pole that will be repelled by the coil effectively doubling the forward's force without requiring any more power from the coils however by doing this we also double the mass of the sled so even if the forward's force is increased the acceleration is still the same and the end velocity isn't any faster but whilst designing this double sled i noticed the magnets on the original sled were slightly higher than the center of the coils which could affect the strength of the magnetic attraction and it could also be pulling the sled downwards and potentially increasing friction so i redesigned the sled with the magnets at the perfect height and adjusted some of the dimensions so it didn't wobble so much on the rail allowing for the sled to be one millimeter wider so the magnets can sit closer to the coils which i think should help as electric motors always have really small gaps between the magnets and the coils this resulted in a top speed of 18 meters per second so after changing all the coils using a better power source and redesigning the sled we've increased the speed from 26 miles per hour to now launching over 40 which is definitely too fast for a paper plane so i designed a mini 3d printable glider that attaches to a sled using these mounting arms which only allow the sled to pivot off with this direction of rotation so even if the plane wants to take off before reaching the end of the launcher like the paper planes did it will be held down until the sled falls away [Music] thank you very much for watching this video whether it's uh useful to you or not i hope you found it interesting and uh be great if you could leave a thumbs up down below if you did find it interesting thanks to all of my supporters on patreon.com for making these projects possible i couldn't do this work without your support so thank you very much i guess i'll see you in the next video goodbye

Channel: Tom Stanton

Views: 2,883,697

Keywords: electromagnet, magnet, coil, electronics, physics, rail, launcher, catapult, aircraft, paper plane, glider, acceleration, 3D printing, electromagnetic, how to make an electromagnet, electromagnetism

Id: g2p4P36VtQE

Length: 11min 25sec (685 seconds)

Published: Fri Nov 26 2021