Electromagnetic Launcher Prototype

Welcome! The Electromagnetic Launcher Team consists of two members: Eric Kwan and West Liang, Mechanical Engineering students in the Masters Program at San Jose State University. 

The project is a creation of a rail system launcher that uses the interaction between magnets and electromagnetic field generated from solenoids. Specifically, timed using analog method with hall effect sensor to activate electromagnetic field (EMF) at a specific interval to propel the cart forward.

In this Instructable, we will provide an overview on the design, what components are used, and steps in how we assembled our prototype version of the Electromagnetic Launcher. 

All components are designed through Fusion 360 and digitally fabricated with 3D printing.

Prior to assembling, there are equipment, tools and miscellaneous parts required for the project in which most can be easily purchased or obtained through local hardware and electronic supply stores. Some can be easily purchased online if not obtainable through local stores depending where you are located.

For fasteners, we kept these in metric but because in-house designed components are 3D printed, the parts can be easily modified or dimensions can be easily tweaked to fit what is available locally.

The following list below provide details on the equipment, tools, and parts for this project:

Equipment and Tools

• Solder Iron
• Car Battery or Super Capacitor (12V, capable to carry high current)
• Screwdrivers and Allen Wrenches
• Tapping Set (Optional. Can use the screw to self-thread the holes)
• Heat Gun (Optional, Use with Heat Shrink Sleeves)
• Wire Crimps

Electrical Components

• (1.5 m) Enameled Copper Wires 
• (10x) Hall Effect Sensors
• (10x) N-Channel Power MOSFETs
• (10x) MOSFET Heatsinks
• (10x) High Speed Power MOSFET Drivers
• (20x) 1k~10k Resistors
• (1x) Momentary Switch
• (2x) Power Distribution Bus Bars (Optional)
• Wire Connectors (Optional)
• Heat Shrink Sleeves (Optional)

Hardware and Fasteners

• (1x) Aluminum Extrusion Bar (or similar)
• (40x) 8mm or 10 mm T-Nuts for M4 Screws
• (40x) M4 x 20 mm Socket Head Cap Screws
• (40x) M4 Flat Washers
• (20x) M2 x 6 mm Socket Head Cap Screws
• (20x) M6 x 20 mm Socket Button (round) Head Screws, Stainless Steel
• (20x) M6 Nut, Stainless Steel

The project is inspired by the recent release of Top Gun Maverick and the exhilarating adrenaline we get when the aircrafts launches off the carriers (image from the Aviationist). As such, we began our research and came across many references, specifically one produced by Tom Stanton. The idea of utilizing electromagnetic fields and magnetism to propel an object is not a new concept. It is actually being used to help fighter jets reach the speed to generate lift quickly due to the short runway of a carrier as shown in the movie.

Thus, what more fun would it be to be able to launch various objects such as paper airplanes, RC airplanes, or any other fun objects we can think of for the summer.

There are a few terms used and items that are used require some basic description prior to talking about them and understanding the general concept of the project. A Hall Effect sensor is a type of sensor that detects the presence and magnitude when a magnet is present. A solenoid is a coil of copper wires wound to a certain number of turns and diameter. When energy, specifically electrical current, was to travel through the coils, it induces a field known as an electromagnetic field, EMF, that can interact with ferrous material or magnets. However, a coil itself is not enough, it requires a metal, ferrous core to strengthen and concentrate the electromagnetic field. A MOSFET is a transistor, or chip, main purpose is to act like a switch. If it receives a signal, it will close the circuit similar to as if someone were to press a button to close a circuit and allow energy to pass through.

The mechanism behind the circuitry is simple. A Hall Effect sensor is mounted in the upstream direction of the solenoid. When the cart moves closer to the sensor, it sends a signal turning on the MOSFET, which drives the solenoid and creates an electromagnetic force to pull the cart forward. When the cart goes past the center of the coil, the Hall Effect sensor is no longer triggered, the MOSFET is turned off. This is to avoid the generated electromagnetic force pulling the cart backward after it passed the coil. Thus, allowing the cart to continue traveling forward. The attached image referenced demonstrates how this portion of the system works.

By repeating the procedure using multiple pairs of solenoids, the cart can be accelerated along the rail.

Components are separated into in-house and external components that are modeled or imported into Fusion 360. The in-house components include the solenoid and sensor mounting brackets, launching cart, stabilizing feet, covers, and control board enclosure. The control board was designed and purchased through JLCPCB and obtained a 3D model that was imported into Fusion 360.

Most of the in-house components are designed around the extrusion’s bar dimensions as they will be mounted to it. The focused approach is simple but practical to keep cost down, ease of manufacturability and assembly.

External components that were measured and modeled, or imported, were the extrusion bar, car battery, Hall Effect sensor, MOSFETs, fasteners, momentary switch and magnets. The fasteners, such as screws and washers, were obtained and imported from Mcmaster Carr.

Prior to designing the in-house components, a CAD model of the external components is needed in referencing and determining any possible interference with any of the other components. Therefore, this step is to obtain or measure and model all the external components.

The fasteners and momentary switch models are obtained from Mcmaster Carr while the MOSFET is obtained from online sources such as GrabCAD. These were imported into Fusion 360 workspace. Because these are available online and free, we decided to still provide it in the list so anyone can easily reference to what was used.

The Hall Effect sensor, car battery, grounding bar and extrusion bar, obtained from previous projects, were carefully measured and modeled in Fusion 360 workspace to be used in the assembly.

The mounting bracket for the solenoid incorporate cutouts to reduce filament usage, cost, and uses M4 clearance holes which are holes sized to 4.5 millimeter. The design incorporates ridges to help guide during the coiling process and allow 1/4 -20 sized ferrous screw to fit through the center. To note, after preliminary test mounting and clearance checks with the cart using a 1/4 - 20 button head screw, there were interference with the cart. Therefore, added additional flat spacer pieces set to 2 millimeters in thickness.

The sensor bracket is designed separately with a slot to allow adjustability in determining the placement of the Hall Effect sensor found during testing phase of the prototype.

After determining the sensor position to be 25 millimeter center-to-center distance between the sensor to the solenoid, the brackets were improved into a one piece design as intended. As improvements, the 1/4-20 ferrous screw was changed to M6 stainless steel screw as its core as testing shown to improve the performance. Further, the cutouts found to weaken of the 3D printed part and the amount of cost saved through less filament usage was insignificant. Further, incorporated the spacer block 3 millimeter thick into the design.

The optimized solenoid mounting brackets have two types that are noted as LEFT and RIGHT; one type of bracket allows mounting of the hall effect sensors. The main goal of the bracket is a simple but practical approach with ridges to help guide the coiling process, a center hole to fit an M6 stainless steel screw as the coil’s core, and two M4 clearance holes for mounting to the extrusion bar. The bracket also is designed with a built-in spacer to avoid interference with the cart. Fillet command is used to reinforce areas of the design that may easily fail as well as to make the design more aesthetically pleasing.

The bracket with the hall effect sensor is designed with built-in stand-offs, with a 1.90 millimeter through-hole, to avoid any interference when mounting the sensor’s board. There is a square cutout set to be a bit larger than the sensor with recessed and fillet features to allow the sensor to sit further in to detect the magnet.

The cart uses the T-slot of the extrusion bar’s channel to guide and slide along its surface. Modeling of the cart follows the simple but practical approach as well. Most of its design is a square design with 3 millimeter, 45 degree chamfers on four edges. The cart can be printed with various designs to launch various objects. Additional aesthetic feature is implementing letterings to the front and rear surface of the cart to indicate the projectile the cart uses. This was created using the text command in sketch, then using extruding cut command up to 2 millimeters. A recessed area on either side of the cart with 2 millimeter hole is to mount the magnet used for this project. To note, during the testing, the screw mounting the magnet had some negative effect on the performance. Thus, it was removed and double sided tape was instead used.

The stabilizing feet helps in potential roll movement of the extrusion bar. The model uses a combination of line and spline commands along with a counterbored M4 clearance through-hole for the M4 screw and T-nut.

The extrusion bar cover is another simple but practical piece for better aesthetics for the extrusion bar. It is a 80 millimeter by 40 millimeter rectangular shape with fillet features. The protruding inserts allow ease of assembly onto the extrusion bar. This can be easily modified in the CAD model to fit any types of extrusion bar one were to have on hand. The text command is used here again cut to 2 millimeters to mainly help in distinguishing front and rear side of the extrusion bar to avoid misplacing of the cart.

The control board enclosure is made to fit just the control board itself to protect user from electrical hazards. It is designed to use either sheet metal, 3D printed material, or clear acrylic glass. It is designed to be external due to its size. Built-in standoffs allow to raise the PCB board from touching surfaces as well as mounting points for M4 x 6 mm socket head screws. The lid is currently designed to be pressed-fit.

The enclosure's lid has a cutout for a momentary switch that is used for the last step to launching the cart. The entire enclosure also have cutouts for the power and sensor connections that can be easily accessed without affecting safety of the user.

For aesthetics, hazard labels can be made and added to the design. In this project, we added them to the CAD model for now.

All in-house components are 3D printed with an Ender 3 Pro with a 220 millimeter by 220 millimeter sized heated print bed. The only components that require support are the solenoid mounting brackets and carts.

Details of the printing parameters used for this project used for the prototype are summarized below:

• Material: PLA+
• Nozzle Temperature: 200 oC
• Bed Temperature: 70 oC
• Wall Thickness: 3 Layers
• Layer Thickness: 0.15 mm
• Support: Grid, 5%, everywhere (if applicable)
• Infill: Cubic, 80%
• Build Plate Adhesion: Skirt, 1 Line Count, 10 mm Distance

Filament Information For Each Components (g = grams)

• Front and Rear Covers: 44 g
• Stabilizing Feet (x2): 40 g
• Solenoid Mounting Bracket with Sensor: 8 g (total for 10 is 80 g)
• Solenoid Mounting Bracket without Sensor: 7 g (total for 10 is 70 g)

Total Filament Needed: 234 g

Program Used: Fusion 360 and Ultimaker Cura

With the information we gathered from Tom Stanton’s video, combined with the mechatronics knowledge we learned from the program, we are able to replicate a circuit with similar functionality. 

The main part of the circuit contains a hall effect sensor (A3144 or equivalent), which is used to detect the magnet approaching the solenoid. A high speed power MOSFET driver (TC4428A) to enable quick switching of the solenoid. And a power MOSFET (IPP026N10NF2SAKM) that allows us to handle large currents with a lower current control signal. 

The hall effect sensor will output a reversed signal (output LOW when the sensor is triggered by a magnet), therefore the output needs to be patch into the channel A of the driver, which inverts the output signal and sends it to the power MOSFET.

The power MOSFET is placed at the low-side of the solenoid, which means one side of the solenoid is connected to the power, and the other side of the solenoid is connected to the drain pin of the power MOSFET. The source pin of the power MOSFET is connected to the negative terminal of the power source. Pull down resistors (1k-10k ohms) are required on all signal lines to preserve signal integrity.

When the MOSFET is activated, the drain and source pin becomes shorted, which means the power source is shorted. The process generates a lot of heat and current, even with the MOSFET of our choice will be damaged if placed in such a load for a sustained period of time. Therefore a momentary switch is added to the circuit to make sure in the event of an accident, we can disconnect the power source quickly to prevent damage to the components and danger to the operator.

Overall, the assembly utilizes ten solenoids with Hall Effect sensors mounted on the left side of the extrusion bar while ten solenoids without Hall Effect sensors are mounted on the right of the extrusion bar. Below is a prototype setup for the testing and another setup of the final prototype.

Externally, and can be mounted to the extrusion bar, is the control enclosure containing the main control board (MCB) that uses TC4428 high speed driver MOSFET chips, an optional centralized bus bar with one being for the main power source for the solenoids and one for the ground. The ten 025N10NS MOSFET and ten heat sinks for the solenoids can be made to mount near by the solenoids but for the prototype, they were mounted separately and externally for testing purposes.

A summarized video demonstration of how some of the components are assembled is shown below.

For the solenoid mounting bracket with sensor: obtain one bracket, one hall effect sensor with board, two M2 x 6 mm socket head screws, two M4 x 20 mm socket head screws with flat washers, two T-nuts, one M6 x 20 mm button head screw, and one M6 nut. 

First install the hall effect sensor with the two M2 x 6 mm screws with a 1.5 mm allen wrench. Push the sensor further forward through the cutout as needed. Screw the M6 x 20 mm screw with a 4 mm allen wrench from the flat portion of the bracket. Install the M6 nut on the other side. The holes can be taped or metal inserts can be used as a better option. However, because the components are 3D printed with PLA+, the holes can be self-tapped with the screws.

Next, insert the two M4 x 20 mm socket head screws with flat washers. Pre-install the two T-nuts. Slide the entire bracket such that the T-nuts are inserted through the extrusion bar’s channel. Slide forward or backwards until desired position is reached. Tighten the two M4 screws with M2.5 mm allen wrench. Use image as reference to the bracket position.

Only require a snug tightness when torquing all screws. Avoid over torquing.

Repeat the process for the remaining nine brackets on the left side of the extrusion bar.

For the solenoid mounting bracket without sensor: obtain one bracket, two M4 x 20 mm socket head screws with flat washers, two T-nuts, one M6 x 20 mm button head screw, and one M6 nut. 

Screw the M6 x 20 mm screw with a 4 mm allen wrench from the flat portion of the bracket. Install the M6 nut on the other side. Insert the two M4 x 20 mm socket head screws with flat washers. Pre-install the two T-nuts. Slide the entire bracket such that the T-nuts are inserted through the extrusion bar’s channel. Slide forward or backwards until aligned with the left side solenoid brackets. Tighten the two M4 screws with M2.5 mm allen wrench.

The heatsink and power MOSFET can be mounted to the coils. However, for the prototype, the design does not incorporate mounting on the solenoid mounting bracket. Depending on the heatsink of choice, the heat sink may be drilled, tapped with M3 threads then countersunk. Note: make sure to chase the threads with the tap again and test the thread with a screw. It is recommended to use dielectric thermal paste or thermal non-conductive pads on the back of the MOSFET and screw when mounting onto the heatsink as the back of the power MOSFET will be energized during operation.

In this case, the MOSFET is mounted to the heatsink with M3 x 10 mm screw with a M2 mm allen wrench.

For the stabilizing feet, insert M4 x 20 mm socket head screw without flat washer. Pre-install one T-nut onto the screw’s end. Note: may require the T-nut to be at an angle or may not insert. Side the entire assembly such the T-nut goes through the channel. Tighten with a M2.5 mm allen wrench until snug tight.

Similarly with the stabilizing feet, the optional centralized grounding bars can be installed onto the extrusion bar in the same method by pre-installing the T-nuts onto the screw, sliding it through the channel into position and then tightening the screw to snug tight. Currently, the grounding bar is optional and is not present in the final design of the prototype. 

Originally, M3 x 6 mm button head screws were used to mount the magnets. However, it interfered with the performance of the cart during testing of the prototype. Therefore, double sided tape was used.

First apply an adhesive double sided tape to the one side of the magnet with the countersink feature. Then install the magnet as shown. Take note of how the magnet is installed. The chosen side matters in how it interacts with the solenoid. Once this is done, the cart is ready to be installed onto the extrusion by simply sliding it through the channel.

See step 13 video as reference how the magnet is attached to the magnet.

The front and rear extrusion bar covers can be pressed onto the extrusion bar. Please see step 13 for reference video.

Locate the four standoffs of the enclosure. Insert one M3 x 6 mm socket head screws through the control board and then screw onto one of the standoffs with a M2 allen wrench. Leave it loose to allow ease of installing the remaining screws. Once all screws are installed, torque them all to snug tight.

The momentary switch is made up of the switch body and the locking collar that screws onto the body. First remove the collar, slide the switch body over from the top of the lid, and then loosely screw on the collar. Position the switch as desired then tighten the collar to snug tight.

Once all electrical connections are connected, the lid can be installed by placing on top of the enclosure and push down. It is designed to be pressed-fit.

The control box is now ready for its connection which is explained in section 8.

An animation of the assembly is shown below:

Schematic of the test circuit for a single pair of coils, VCC goes into the positive terminal, and the GND goes into the negative terminal of the power source.

At this point all the parts should be finished printing. Starts from winding the enameled copper wire onto the 3D printer coil holder. 40 turns for each coil is a good starting point. The wire should be winded as tied as possible. It is critical to make sure that all the coils are winding in the same direction (we used counter-clockwise), and keep track of the number of turns. 

After winding all the coils, follow the schematic above to build the circuit for a pair of coils to perform a functionality test. A breadboard and jumper wires can be used except for the high current connections to the power MOSFET. Safety goggles, and insulated gloves are required. 

DO NOT CONNECT TO POWER SOURCE DURING THIS STEP.

Align the center of the car to the hall effect sensor, briefly press the momentary switch for 1 second. Release the switch as soon as possible at any abnormality. The cart should be propelled along the rail towards the coil. If the cart is being propelled in the reverse direction, reversing the polarity of the coil’s connection will fix it. 

We can now move onto a full circuitry build for after a successful functionality test. It is recommended to wire all the MOSFET drivers first, and wire the power MOSFET last after mounting them onto the MOSFET holder with heatsink. Replace all the breadboard jumper wires with appropriate size wires, and solder them to the component or using clamped connectors. Please use proper insulation (heat shrink sleeves recommended). By making 10 sets of the testing circuits, the control circuit is done. 

An alternative method is to create a PCB layout with PCB design software (e.g. Autodesk Eagle). A gerber file can be generated after the design, which contains all the information needed to make the PCB board. You can either produce the board yourself with proper equipment or send it to 3rd party manufacturers. 

The current videos attached are successful test with one pair of solenoids. This prototype setup utilized a 12V power supply as its only power source which was capable of handling all the necessary power required for the project. We obtained a reading of over 16A but due to quick triggering, it was not enough to generate sufficient heat to the solenoids and MOSFET. The cart was able to travel between 80 to 84 millimeters from the center of the Hall Effect sensor where it was initially positioned based on manual trigger. We also found we had to switch the direction of the current on the solenoid when using the Hall Effect Sensor. This is done by plugging the order of solenoid in reverse.

A key factors that plays in the role of propelling the cart forward properly is the timing of the trigger which relate to how long the Hall Effect sensor stays on.

Note: during this test, the control board did not arrive on time due to manufacturing delay from the vendor. However, when arrived, the board itself was tested successful with the high speed driver MOSFET chips to be working.

Summary

• Optimal Sensor Distance: 25 mm
• Furthest Travel Distance: 90 mm
• Average Travel Distance: 80 to 84 mm

The prototype has proven successful in terms of design and working mechanism/system. However, the project is still far from over as there are many improvements we would like to do. 

We plan to 3D print the final designed components to be installed and tested to see how far the cart will travel with all 20 solenoids in place along with the new control board; matching the final prototype design. The control board will also be assembled with the designed enclosure. We would also like to implement safety labels and aesthetic decals as shown in the CAD model on the final prototype.

A microcontroller is also in consideration to add additional safety features and feedback to the system.

We also would like to revise and improve the step-by-step instructions and have more documentation to better allow someone to safely build and enjoy the fun of launching projectiles like paper airplanes or modeled robots.

Acknowledgements

We would like to acknowledge and express much appreciation to Tyler Erwin of ASME SJSU, the entire ASME SJSU campus club and their members, SJSU's Mechanical Engineering Department, and Autodesk for coordinating and help in the process for this summer challenge, for hosting workshops for Fusion 360, and for helping us with any issues with the project.



References

• (n.d.). Retrieved July 2022, from Mcmaster Carr: https://www.mcmaster.com/

• (n.d.). Retrieved July 2022, from GrabCAD: https://grabcad.com/

• Cenciotti, D. (n.d.). This GoPro video will bring you the closest as you can get to the flight deck of a U.S. aircraft carrier during catapult launches. Retrieved July 2022, from The Aviationist: https://theaviationist.com/2014/12/31/catapult-launch-from-petty-officer-pov/

• Stanton, T. (n.d.). Electromagnetic Rail Launcher. Retrieved June 2022, from Youtube: https://www.youtube.com/watch?v=_4TGb3MsSjE

• Stanton, T. (n.d.). Optimising a Magnetic Launcher. Retrieved June 2022, from Youtube: https://www.youtube.com/watch?v=g2p4P36VtQE