If you would like to build your own for a science or engineering project, lets start with the basics and talk about the operating principle and how this thing works. Here i have a wire coil wrapped around a hollow tube and a cylindrical piece of steel that i cut from a steel rod. Im going to connect this wire coil to a series of three batteries that are connected in series forming an electromagnet when electrical current flows through this coil, it is going to generate a magnetic field with a shape very similar to that of a bar, magnet that magnetic Field will attract the ferromagnetic steel projectile if it is placed in the tube so, for example, im going to place the piece of steel in the tube, so it is off center, not directly centered in the coil im going to take my final alligator clip here and Close the circuit to my battery and we see the piece of steel gets pulled in and if we watch that again in slow motion, we will see that it actually got sucked through the coil. But then, once it went through the coil, it got pulled back towards the center, so it oscillated a bit and eventually settled right there in the middle of the coil. So if i slide the piece of steel out of it and do that again again, we see that it overshoots the coil a little bit but then gets pulled back to the middle.

So that means that if i want to launch this projectile its not simply a matter of connecting power and leaving this coil on, ideally, i would like this projectile to keep traveling down the tube after it has passed through this coil. So what i want to do is have it start going through the coil and then once its gone through. I dont want to keep the coil on because then thats going to suck the projectile back towards the middle just once it is past the center. I want to turn this coil off, so the projectile can keep going down the tube and you can sort of do that manually if youre really really quick. If i take my alligator clip here and just touch it to the battery terminal, youll see how that kept. Going down the tube, but i obviously timing that manually is going to be pretty difficult. You, especially if you have multiple stages which well talk about later, so that is where a microcontroller and sensors are going to come in. So we can properly time turn this coil on and off and then add more stages to accelerate our projectile even further, so here ill show you that one more time as i try to do it manually, if i just very quickly touch the contacts together and then Release them thats, going to energize the coil suck the projectile in, but then once it has started to pass through current through the coil stops and the projectile will keep going.

So that was the basic idea behind the operation of a single stage mass driver. What i have here is a three stage mass driver with three different coils, again, the idea being that each successive coil will further accelerate the mass down the tubes. So if you had a very, very long mass driver on the surface of a planet, for example, you could reach very high speeds and even reach escape velocity to launch something into orbit, and in this case ideally, i would work out the timing such that, if i Load, the projectile into this end of the tube. The first coil will energize sucking the projectile. In the moment it reaches the center of that coil. I turn the first coil off it keeps going and i turn the second coil on which again is going to attract it, accelerate it even more. Once i reach the center of the second coil, i switch that coil off and turn the third coil on and then again finally repeat that process, where im ready to exit the tube and just past the center of that last coil. I turn the third coil off and the projectile is launched out the tube. That raises the question of okay. Well, how do you know when and where the projectile is in the tube, and that is where the hall effect sensors come in? These are magnetic sensors that can detect a magnetic field. So in theory you could try to do this open loop.

You could do calculations to figure out exactly how fast this projectile is going to be moving and then figure out exactly what time it should be at each one of these coils, but that is going to be very difficult and its not really going to account for Variability and friction, or things like how far you load the projectile into the tube initially so its much better to do this closed loop and have some sort of feedback or sensors placed along the length of the tube that are going to tell you when this projectile Has reached a certain point in the tube, so you cant really see them because theyre all wrapped up in tape, but there are three of these hall effect sensors placed just at the exit of each one of the coils. Now there are two different types of hall effect: sensors. There are analog sensors that will output a continuous voltage proportional to the strength of the magnetic field, and there are digital sensors that will simply output a higher low voltage. Once the magnetic field has passed a certain threshold, so in this case, im just using digital sensors because they allow use of the digital read function with the arduino, which is faster than analog read. Since we really just want to know as soon as possible, when this projectile has gone through the coil, so we can switch that coil off and switch the next coil on. So the electronics are the next piece of the puzzle.

Here we have the arduino, which is the brains of the operation, running a program to take those sensor, readings and use that information to control. When the electromagnets turn on and off, we have a breadboard that largely serves as the interface between the sensors and the arduino. With some extra parts in there again like the pull up, resistors and connections to power and ground, and then finally, we have the driver board, which takes the low power signal from the arduinos. I o pins and uses that to control the high power signal to the electromagnets. So if you have worked with arduino before youve, probably done something like plug leds directly into the arduinos, i o pins, and that is fine, because leds are very low. Current the arduino operates at 5 volts and can only provide about 20 milliamps per pin, whereas large electromagnets like this, require much much more current than that. So you cannot power a big electromagnet or a large motor directly from the arduinos i o pins. That is where a driver board like this comes in, so this board has two sides: it has input pins on the left that take your low power signal from your microcontroller, like your arduino, and it safely isolates those but uses them to control the high power signal From an external power supply, which in this case, was my bank of lantern batteries and uses those high power signals to control your load like your electromagnet.

So when the input over here on the left goes high, that will switch the corresponding output on the load side. Over here high, this particular board has four channels, so i can use it to switch up to four electromagnets. The design of a board like this is an interesting electrical engineering project in its own right. So i bought this four channel board that would have allowed me to build a mass driver with up to four stages. You can also buy smaller individual boards, designed to drive a single, electromagnet or load and then buy multiple of these. Depending on how many stages you have, you can also decide to try and design and build something like this yourself just be careful, because if you use a breadboard which youre probably used to working with, if youve done arduino projects before, as i learned, you can pretty Easily melt a breadboard, i dont know if the camera will focus enough, youll be able to see this, but when you start pushing several amps of current through these plastic breadboards that are common for arduino projects, that is actually more than enough to melt the breadboard. So i have fused a couple transistors to the breadboard here. So if youre going to kind of go to, do it yourself route and try to build your own drive circuit, you really need to take heat dissipation and thermal management into account. Maybe get some heatsinks for your mosfets or attach these to some big metal block or something thats going to do a better job dissipating the heat, because the plastic breadboard on its own really cannot handle the amount of heat and current that these coils are going to Want so again, you can go the route of buying something like this and dont worry about this big messy circuit diagram.

Here again, if you go to the description of this video, we have a link to all the materials individual items in a much neater circuit diagram. You can follow to build this circuit, but there are different options for the power electronics. Again, you can buy a board. You can try to do it yourself, but ultimately, your goal is to use that low power signal from the arduino to control the high power load of your electromagnets. So now that ive, given you the tour of that system, lets go through again and talk about how this works. What i do is load my projectile into the front of the tube. I press the reset button on the arduino. That starts the program which you can download again from the written instructions linked in the description of this video. That starts the program energizes the first coil, which is then going to suck the projectile. In the moment the projectile gets through that coil. The signal on this hall effect sensor is going to go low. It is pulled high by default. That signal goes low. It is read by a digital input on the arduino theres, not an if statement in the code that says if that signal goes low turn coil. 1 off turn, coil 2 on and the same process repeats. The projectile gets pulled in here, theres, another digital read for this pin another. If statement that says, if this signal goes low, turn this coil off turn the next one on then do the same thing for the final coil.

We turn all the coils off once the projectile has ended. We also have a timer with kind of a safety measure. It says if the program has been running longer than two seconds just shut everything off. Maybe my projectile is stuck in the middle or maybe one of the sensors didnt fire properly or something. Because again these coils draw a lot of current. They will get hot. So you dont want to just leave these on indefinitely or you risk burning or melting something, so that is sort of the crash course overview in how one of these works and again you can find the materials list circuit, diagram and working example. Code on our website, which are linked in the description of this video, what you can think about now is: if you want to do this, for a science and engineering project, what can you improve or what variables can you change to improve the performance of your mass Drivers, so you probably figured out, as you were, watching this video well, there are a ton of different variables. I didnt talk about here like what about the wire gauge for the coils, the length and diameter of the coils, the spacing between the coils, the number of stages, the diameter of the tube itself and the length and diameter of the projectile. I can use a permanent cylindrical magnet instead of just a steel rod for the projectile and then thats on the physical side of the tube and coils themselves and then theres the entire electronics side to this.

So i have a battery bank here, but you could do a super capacitor bank. You could use a dc wall adapter instead of batteries, so theres the power supply. You can experiment with, even if its just adding more batteries in series or in parallel. If you stick with the batteries and then again, theres also the drive electronics side, so i have a off the shelf driver board. I bought here, but you could experiment with building your own drive electronics, because you really want to be able to turn the current onto these coils very quickly and ramp that current and that magnetic field up as quickly as possible. So there are a lot of different variables you can play with. It makes for a great science in our engineering project but again to get started check out the link to our website. In the description of this video for thousands of other fun, science and engineering projects visit us online at www.

https://www.youtube.com/watch?v=GFJSwrSvlN4