The CoilGun MK.III Project

Chris, Mon Oct 16 2023 • Electronics Electromagnetism Esp32 Programming

CoilGun MK.III prototype

After few years from the MK.II I decided to start a new coilgun. As you can see the model itself doesn't differ much from the MK.II but a few major changes were made:

Instead of using an Arduino Nano as the MCU I switched to the more powerful Esp32
The IR led and receiver were replaced with an easier to use CNY70 IR sensor
The old boost converter was trashed and replaced with a much more efficient and powerful ZVS Driver

In the end I decided to scrap this design beacuse I wanted something more modular and easier to assemble. So all of these changes where channeled in the final MK.III design.

Coilgun MK.III

Everything changed.

This is the best design I've come up with in the last 2 years. All the experience gathered in the span of 10 years is inside this design, from the electronic circuit to the 3D model itself.

Let's start!

Breakdown

Unlike the MK.II, this iteration is fully modular, meaning that stages can be added/removed by simply modifing a couple of lines of code. Here's the list of features that'll be broken down:

Plug and Play modular stages
Esp32 custom PCB
OLED interface
Safety
CNY70 IR sensor custom PCB
Separeted SCRs firing circuit PCB
SCR custom PCB
Capacitors banks auto-charge
ZVS Drivers as the capacitors banks chargers
Capacitor Charge Feedback Circuit (CCFC) PCB
Code explanation

1.Modular stages

The main goal of this coilgun was the modularity so that there's the possibility to build a user defined number of stage coilgun. For example the MK.III is a 4 stage coilgun that can be expanded in a 5, 6 or even 8 stages without problems.

Creating a modular stage wasn't hard at all, it's a pin based design as you can see here:

The model is quite simple:

holes are present on both stage ends to insert the pins that will link the other stages togheter
in the middle the solenoid is wound and incapsulated within the stage
at the end of the stage there's the socket for the CNY70 IR sensor
on top there're holes to attach the firing circuit
on the bottom there're holes to attach the stage to the base of the coilgun

One of the most important changes it's the positioning of the firing circuit directly on top of the stage itself, this way the wires coming from the coil are shorter that the previous versions, ensuring less energy dissipation from wire resistance.

2.Esp32 Custom Board

To control the MK.III I went with an Esp32-WROOM-32 DEVKITC board, widely available and quite powerful. The custom PCB is just a breakout board with all the needed connectors for the coilgun:

5x 3p male headers, for the CNY70 IR sensors of which 4 for the stages and 1 for the bullet sensor
4x 2p male headers, for the CCFB input
1x 5p male header, for the SCRs driver circuit
1x 4p male header, for the OLED display
1x 2p male header, for the safety
1x 2p male header, for the trigger
1x 2p male header, for the Esp32 5V power input
1x 2p male header, for the debug toggle
2x 2p screw terminals, for the ZVS Drivers

There're also 2 leds:

1x red 5mm led, for power checking
1x yellow 5mm led, for debugging

On the board are also present 2 N-Channel mosfets, IRLZ44N, for the auto-charge feature.

By shorting togheter the debug toggle pins the debug mode is activated, meaning that through the serial monitor we can check the CNY70 sensors values and see if they're working correctly.

Here's the schematic:

And here's the PCB:

3.OLED interface

I wanted some kind of visual feedback but not just simple leds, so I went with an OLED display. At first I used a simple 0.96in model but I later found out that bigger models are available, such as a 1.3in one. The size is the same, 128x64 px, but the screen is wider and the driver is different, SSD12306 for the 0.96in and SH1106 for the 1.3in one. The displays are available both as I2C or SPI, but I prefer using the I2C one.