Optimising a Magnetic Launcher 

It’s all fun and games at the Nerf match until Tom shows up with a handheld version of this with an automatic trigger and backpack mounted battery

Honestly, your channel is such a gold mine. This is one of the best demonstrations of the engineering process at work: you find the issue, you think of a solution, and then you tinker and optimize until you've achieved what you've set out for. You demonstrate this whole process so eloquently in your videos that it's inspiring

Wow the slow-mo of that glider taking off was glorious. And the release mechanism working exactly as intended!

Calculate how long it takes for the coil to reach maximum magnetic power, use this to determine how far the triggering hall effect sensor needs to be to optimize energizing the coils as the velocity increases. Also, when you lower the winding count, increase the wire size. Remember, wind count has an effect on the speed at which the magnetic field builds to maximum. I was involved in the original development of the brushless motors in today's electric planes and drones.

That slow motion shot of the launch sled falling away from the glider looked fantastically elegant, awesome project!

I built a mass driver as a science fair project back in the '80's, I got around the curve flattening by progressively spacing the driver coils further apart as they went down the track. My reasoning was like a transmission in a car the impulses then match the speed of the projectile as it accelerates.

I love watching the progression by tweaking certain factors. I also learned a lot as you walked us through the process. Keep up the great work!

You can improve even more replacin alluminium rod with plastic, a magnet sliding on metal tends to reduce the speed because of the inducted current generated by the movement.

I love how this channel started as modelling planes and various flying ... things (some of them is hard to describe) but then evolved into trebuchets and now its about building a coilgun.

A way to know which reason is the most limiting would have been to make a regression, it the curve is close to an exponential it's mostly a back EMF reason, if the curve is close to a square root, it's mostly due to kinetic energy (harder and harder to increase for a given power).

Excellent video, Tom. Very interesting and clearly presented data that you've provided. Keep up the great work. Slow-mo was amazing.

Brilliant video Tom. Even when I cannot quite follow all the info you are giving. You still make it all clear enough to make it really interesting. Thank you.....

A few ideas: - You don't have to reverse polarity to also push the sled. You can just use a second Hall sensor located after the coil, and a second winding on the coil wired up in inverted polarity, so when the second Hall sensor turns on the second coil, it will push. With the position of the sensors, I think it can be timed perfectly. Yes it is 2X the components (and thus cost and power draw), but also roughly 2x the force at each magnet, resulting in a speed increase. - With a lubricated sled (and the plastic part of it shaped aerodynamically), most of the drag on the sled would be eliminated. - I've also noticed on the high-speed footage that the coils lean in a bit when active. This is expected as per Newton's third law, but the coild might need to be mounted more sturdily.

The air gap is still ~40mm long. The other side of the electromagnet is open, so the magnetic flux has to flow to the next electromagnet via air. The overall reluctance is still quite high and can be greatly reduced by tying backs of electromagnets with an iron bar and using a magnet that partially overlaps 2 electromagnets.

Totally excellent. Especially the slo-mo videography of the glider launches at the conclusion. Thanks!

I love listening to the audio on the slow mo of the plane launch at the end. You can hear each individual pull or push of the magnet on the sled.

cool project! I've always been a fan of linear induction motors!

I feel like randomly seeing someone using a trebuchet in England wouldn't look that out of place 🤣🙏👍

Just gorgeous work!! The story is beautifully told; the video is just stunningly shot and expertly edited; and you convey the science so accessibly. Mate, pretty good for a ginger. 😋😋😁😁 Also, the glider sled drop-away - the money shot!

I wish I could have liked this video more than one time. So glad that I am a patron - I get joy from supporting Tom, I learn something from each video, and hopefully help these videos reach more and more people to increase our collective knowledge.

Tom is a young man who gives me a positive feeling toward the future. We need to support people like him.

For those still confused about the difference between railguns and coilguns: Railguns use two rails and lots of electricity to launch a projectile with the Lorentz force. Coilguns have a projectile that goes through the center of a group of coils stacked like donuts, with the ones in front of the projectile attracting it and pulling it forward, and ideally, the ones behind it repelling it and pushing it forward. The magnetic launcher in the video uses the same principals as a coilgun, but with the way the coils are oriented, calling it a magnetic launcher would be more accurate since its primary purpose and design is for it to launch stuff from the sled rather than simply using the sled itself as a projectile like a standard coilgun would.

Really enjoyed the curiosity and detail - thanks Tom

What a glorious feeling it must have been when you first saw a successful launch! Very impressive, looking forward to more!

I used to wind and assemble r/c brushless motors. As far as I can tell, they are pretty much identical to your linear motor. The fewer the winds (w/heavier wire) the faster the motor, but the lower the torque. What would happen if you had progressively fewer winds as the carrier went down the track? It would start off at low speed w/high torque, then go progressively to high speed with low torque. Much like gears in a car. The last few coils could be only a few winds (with heavy wire OR multiple strands in parallel) and this would really kick up the speed. Also, work to get the air gap between the coils and the magnet as small as possible. The magnetic attraction (reluctance) drops off as a square of the distance. In motor construction, this is the easiest way to increase efficiency. This is hard to do in mass production, but with a DIY project the effort really pays off. Reduce the gap by a power of two and get four times the output power!

As others have pointed out, you need to either increase coil spacing with distance, or increase your control speed, which means hitting the coils harder down the line. One way to do that is to distribute the capacitor bank down the length of the gun, adding caps as you approach the end. Your existing system is running out of power as the projectile advances, when you want to be increasing power as it advances in a system with constant spacing. One way to advance the design is to simulate the system. There are SPICE models for coils and moving magnets that can help simulate this whole thing. There are also tricks to shunting flyback into the next coil…

I'm amazed by the perfect separation of sled and printed plane. Were there more iterations of it before it worked like this?

The slow motion video of the glider launch and the magnet(s) dropping away - excellent!

The way the sled detached from the glider was amazing!

Twinkle Twinkle Little Star Power Equals I Squared R I'll remember it forever because of this.

I really enjoyed watching this and it brought back some of my interest again in DIY electrical fun. Good Job! Thanks.

Wonderful stuff, can't stop watching your videos ! Thanks!

2 thoughts: Instead of velocity vs distance graph, try using an energy/time graph. Kinetic energy is equal to velocity squared, so if energy increase is constant, then a velocity/time graph would look like sqrt(t). Using distance instead of time also skews things, and you switch to using time instead of distance for the battery graphs. My guess is that a good curve to have in energy/time graph is a straight line. I love your constant attempts to use super capacitors only to find out batteries work better. Definitely a consistent theme of the channel. I think we both just think super capacitors are so cool and want to find uses for them :) I wonder - capacitors definitely have faster response times than batteries when load changes, while batteries can sustain the load better. Their strengths and weaknesses compliment each other. Did you try connecting both the capacitors and the batteries in parallel?

4:30 I did physics this year and used these a lot, but I've never heard them be called "SUVAT" I assume some call it that because those are the variables it takes? I think we just called them "equations for constant acceleration"

You're an absolute lad of a gentleman for making a video even better than the last one! I put off watching this because I didn't want to be disappointed as the first one was so well done imo

I've always wanted to work on a rail coil launcher and your videos are a 100% my inspiration !

Love how the spreadsheet graph matches your test data. You might try flipping the sensors so they tell you when the sled is leaving the coil. Then play with successively larger distances between coils as many have commented. The spreadsheet will help maximize acceleration per coil prior to a rebuild. A fixed distance between coils locks in a maximum speed since pulse timing is critical as speed increases.

Tom, you're my hero! With strong affinity for the mechanical/physical realm, and unfortunately now quadriplegic, I live vicariously through your videos! So now I'm back in school for computer science/software engineering. You're a huge inspiration and I look forward to all your videos Please don't stop uploading.

I love your in depth explanation of your excel formulas

Wow, that's a fantastic project! Nice work sir!

Well done . . . includes formulas and concepts I've forgotten over the past 70 years. It would be interesting to see how the system described here scales up to the General Atomics EMALS system now in use on the USS Gerald R. Ford Carrier. EMALS has had an extended development period as the issues and weak points are now being explored in use on a ship. One significant difference between the system described here is that it uses uses capacitors and/or batteries for energy storage while the EMALS system uses flywheels. [Based on my career I would have thought EMALS would have used capacitors.] So far EMALS seems to be beating the steam catapults in use now although problems are still being discovered.

I do love projects like this and have a multi-stage coil gun that I've built myself to explore this fascinating area of physics. I do find your design to be quite interesting in general with having the idea of "un-rolling" a standard electric motor to make a linear motor. The way I had managed to maximize my projectile velocity was to move away from super capacitors and move towards high voltage caps with a much lower capacitance. Since P = IV or I^2*R, and capacitor potential energy is a function of both the capacitance and the voltage squared I found that operating with more voltage and a capacitor that drained very quickly with P also being equal to J/s I managed very high speeds with far less coils. Perhaps moving towards high voltage and lower capacitance could yield an even higher end velocity with your design. Oh and I found it quite interesting on how many people thought that your device was a "rail gun". While both your device and a rail gun are both linear motors, you system is far more similar to a coil gun since rail guns operate on quite different systems. I guess this may be a result of people hearing a term tossed around online without understanding what that device is. I hope to see more wonderful projects from you in the future.

This for me helps to solves the problem for electric powered flight, and so it is interesting to see you take up this method. I have seen gliders use this method on take off using a pulley line, which on reaching a certain height drops away, or aircraft carriers that use steam and magnetic rails.

Interesting and entertaining all rolled up in one video, I love what you do, please keep doing it...

I would like to say that you did an excellent job with clarity in this video. Your slow, even tone and stating things planely made it very easy to follow. Also, NOT throwing lots of numbers out. Many presenters think they need to say every number of the screen for clarity when this does the opposite. Stay with m/s or km/hr. Convert the number but leave them on the screen.

You could also try launching steel, while it won’t have as much of a generated magnetic field, I feel as if it may give you a acceleration advantage because it’s not canceling itself out therefore allowing more coils(and unlimited amount of coils) throughout the launcher Also you can try dry graphite on your launcher which will make the friction very minimal on your sled(trick used from pinewood derby cars)

In weapon terminology what you made is a coil gun. Lots of people confuse rail guns and coil guns despite coil guns being significantly more complicated (due to the need for rapid switching as you are clearly aware)

Currently taking physics 2 as a senior in high school. Gotta say, after doing an entire magnetism and electromagnetism unit and learning everything theoretically, it’s really cool to see these concepts be implemented in such an easily understandable real-world example!

That take off was amazing. Looked like a real hi tech launching system.

As others have mentioned, kinetic energy goes up with the square of the velocity. Another way to increase power is to add a flux return path for the magnetic fields. There might be a solution in chaining linearly but, especially for this setup, I think just a chunk of iron in like a "C" shape, oriented Up, around the track, would get you ~3x improved magnetic performance. You'd wrap the iron with your coils and trigger it the same way. Iron is good for these low frequencies but higher frequencies need different core materials. It also makes the steel the "force carrier", as in what actually gets pushed on. It can be a lot easier to hold onto steel than to coils. Notice the individual wire of the foreground coil moving at 10:01 in the video. Eventually that wire will fail as copper fatigues/work hardens quickly...

I really enjoy it when you improve your projects, how an engineer thinks and solves problems.

Genius! Good work. Really enjoyed this.

From what i know, the coils need some time to energize fully, so it might be worth to put the activation sensor further back the rail, and then use software delay so you can adjust timing, and find sweet spot. This might be especially important for the last few coils because when the projectile is travelling with high speed, the coils might not have enough time to energize properly.

What about the inductance of the coils? Current flowing through a coil can't ramp up infinitely fast. The more windings, the higher the inductance and the slower is the ramp up. This may be an additional or even the main reason why less turns give you a higher end velocity. At the end of the track the sled may be already too fast to allow the current through the coils to ramp up to maximum before the sled has passed the coil. So I'd suggest to measure the inductance and tune it by adjusting the number of windings in order to better match the current ramp up to the position and velocity of the sled.

That's a hell of a project my friend. Well done 👍.

Amazing stuff Tom, keep up the good work :D

You're one of the few RU-vidrs who I'll totally interrupt whatever I'm watching when I see you've posted.

I’d love to see the flipped polarity. Even if it does take some time to perfect, I’d be amazing to see you make that in the next video.

Those slow-mo outdoor shots are Bellissimo!

Great video, it was interesting to see the velocity over time

use a prediction time for actuating a coil: use a estimated time of actuation of the coil instead of the sensor, use every sensor reading to adjust the prediction for the next coil, like an advance for a piston engine, if you tweak the activation time maybe you can squeeze a little more performace.

The electrical genius of this guy is deeply underappreciated.

I could watch your videos for days. Kudos!

The elegance of that little release mechanism was a thing of beauty.

I absolutelly love your optimization videos ! Not only are they very entertaining, they are also extremely informative, giving both information regarding the topic and insight into the mind of an engineer

I like how all of your videos have to do with science and are getting people excited abought the science behind magnets. Great job on the video and keep up the great work.

This is an absolutely amazing exhibition of engineering talent, fantastic job Tom!

Awesome video Tom I would have like to see more of the glider testing though.

Very cool!! The switching topology can also make a big difference to linear accelerator performance. The rise & fall time of the magnetic field also affects performance, so on & off time have to be adjusted, the faster the projectile travels. Later stages benefit from less turns to decrease inductive reactance. 😊😊

Great design! I think having the plane have its wings deployed while being shot down the track might be contributing heavily to a performance hit. Having some sort of retaining mechanism on the wings or even a mechanism that tilts them from 0 lift/negligible drag to take off position with some sort of trigger on the end of the track or attached to the the sled dropping away might massively improve flight performance

900k subscribers I don’t understand half of the stuff you showed but intrigued on your presentation!!!

That transition between project and the sponsor/ad was very smooth ngl.

Next - this, on a remote controlled aircraft carrier

Great job! Have you tried to reduce the friction of the sled using an air cushion (like it is used with air hockey) or magnets? That might boost the top speed further! I'd also suspect that the wiring of the energy supply causes some of the voltage sags due to the back EMF of the wires - try to add some caps (ceramics if you can) in close electrical proximity to the individual coils. Another idea would be to keep the coils constantly on and just turn them off when the sled passes to keep the voltage at the starting level - I suspect you may see the inverse on the voltage profile though when the coils turn off so be careful and expect some overvoltage! Also, if you do that watch out for the current/power draw in your coils and the temperature

I love it! I haven't checked your other videos yet so I don't know if there is a follow up. This would be a great opportunity for a small surface mount board with a few multiplexed H-bridges.

Fascinating stuff sir 😎 thank you!

Always amazed by your projects. I love optimization. In my own physics degree I designed something called a Zeeman Slower which basically the same thing but for atoms and does the opposite ie slows things down instead of speeding them up. I loved tweaking the design for optimum performance

You could use supercaps and lithium batteries in parallel, just for the ultimate low ESR power supply :) This is a very fun setup to watch, I'd love another episode about it!

Very interesting! It reminded me of the V1 launch footage, the way the carriage drops away.

Super fascinating video, I enjoyed and learned from it!

An intuitive way (without just plugging in kinematics) to think about why it _looks_ like each subsequent coil imparts less velocity is this: while they all accelerate by the same amount, the projectile is moving faster past later coils, and so accelerates for less time.

As always, lovely storytelling and engineering Tom. Of course you used neodymium magnets right? What about removing the slay friction? Would love to see an optimising an optimised magnetic launcher! :D

I realy do like your projects. Damn cool stuff!

Best explanation I’ve ever seen! This was written with my brain in mind.

If you do run into a back EMF limitation as you keep improving the speed, you could try advancing the timing of the later coils.

Love following your projects; super inspiring! I believe all your conclusions regarding the power delivered to the coils are in the ballpark, but the inductance of the coil will affect how the current is increasing from zero when turned on. In the end there are several trade-offs to be made when choosing number of windings, wire gauge and the geometry of your coils. Anyhow, very cool end result and a satisfying swooosh when launching :D

Your smart. Great vid man keep it up

Thank you so much for walking through your calculations, hypotheses, and conclusions.. I feel like this makes your videos so much better than others.

I think the curve flattens out because you increase not speed but kinetic energy. And as we now it has power of two. And so you get the inversed function

Greater acceleration per coil could be achieved by having steel "C" cores reduce the reluctance of each magnetic circuit. Using steel cores would increase the magnetic flux for a given current.

Fantastic work, Tom!

I felt the satisfaction from the graph lining up! 🙂

Tom, first thanks for another interesting video. I was curious (cant recall if you mentioned this) but would changing the spacing (increase the gap) as you go along the launch track given it will be going quicker would that give them more chance to pull? Would you want bigger and stronger magnetic forces too the further along to keep up with the speed increase and impart more effect? Would be interesting to see the plots for various gap deltas.

Awesome work. Your intuition that the distance between the permanent magnet and electromagnet is spot on. I used to work on the design team for a company designing motors for the robotics industry. The gap was one (if not the most) important aspect to control. You've got me wanting to make one of these now! I may have missed it but if you are not already using N52 magnets, see if you can get some of those. Don't worry about the characters following the number, such as N52H. The (H) is to do with the maximum operating temperature.

Loved watching the 3D printed glider launch, however it did remind me of archive footage of the V1 launch tests. (My mum used to work for the IWM Film Archives so she used to get copies of wartime testing footage for me to watch including the Bouncing Bomb studies)

Many, many years ago I made one of these with my physics teacher at school, I was happy when we exceeded 5m/s and that's where it ended (along with the school year!). This thing is awesome and all props but more to the point, I finally have a video to show people to explain the principle!

I was wondering Tom, what’d happen if you factor the exposure time of the each magnet on the slid. More precisely, what if you increase exponentially the distance between the magnets without increasing the number of turns of the coil windings. I expect this leading to the same results without increasing the power of the magnets.

You can try using those black powdered metal ferrite cores. Using normal steel or iron impedes with the instant flux change, but those ferrite cores are pretty fast.

That was an amazing demonstration of electromagnet propulsion.

very good work!!! excellent work Engineer!!!