Introduction: Mk4 Coil Gun 6-Stage 3D Printed
The Mk4 is a 6-Stage Opticially triggered coil gun capable of firing upto 780 round per minute. (900 if tweaked and pushed).
The gun operates directly from batteries so there is no lengthy charge time between shots, This does however, limit the max power to some extent.
Operating voltage: 66.6V DC (Lithium Polymer batteries)
Coil resistance: 2 Ohm +/- 0.1 Ohm
Peak current per coil: 33.3A
Peak power per coil: 2.22Kw
Muzzle velocity: 15.41m/s (Average from 100 shots)
Muzzle energy: 0.85 Joules (calculated from muzzle velocity)
Ammo: Post 1992 2 pence coins (british currency). Weighing in at 7.12g, 25.9mm diameter and 2.03mm in depth.
Pre september 1992 coins are made from bronze and do not work in this gun and may result in catastrophic failure if used! You have been warned! (I will mention this a few more times during this instructable)
Control circuitry and reloading motor operates at 14.8V DC with a dedicated battery
Max fire rate is approx 900 Rounds per minute, but starts to jam at such high reloading rate.Max reliable fire rate is around 780 Round per minute.
Instructable is a work in progress" - STL files and schematic have already been uploaded if you wish to attempt this without full instructions.
Step 1: Things You WIll Need
3D Printer + 2KG of Filament
Lots of Enamelled copper wire (0.80mm Diameter) - Can be changed but must be suitable for power supply and Mosfets.
1x Arduino Uno
1x Nema 17 Stepper motor
1x A4988 Ramps Stepper motor driver
6x 5mm IR LED's
6x 5mm Matched IR Photo-diodes
6x N-channel Mosfets (IRFP250) - or better
2x LM324N Quad Op-Amp + optional sockets
6x 100k ohm preset potentiometers
6x10k ohm 0.25w resistors (may need changing depending on IR Photo-diodes used
6x560 ohm 0.25w resistors (may need changing depending on IR L.E.D's used
1x L7805CV (5v Regulator)
1x 0.1uF capacitor 16v+
Various sizes of heatshrink
6x FR607 Diodes (or better)
1x IN4007 Diode (Optional for reverse polarity protection for control circuit)
1x 500mA Fast Fuse + Carrier (both optional - Overcurrent protection for control circuit)
3x 6S Li-Po batteries with a good 80A+ discharge rating
1x 4S Li-Po battery for the control gear and reloading motor
connectors suitable for the batteries you have: 3x females for the large batteries and 1 female for the control battery
1 Meter of 12 gauge red+black silicone insulated wire
A few meters of stranded alarm cable or other similar wire
A couple meters of 1.5mm CSA solid copper wire (such as 1.5mm T+E)
A couple meters of 2.5mm CSA solid copper wire (Such as 2.5mm T+E) (you could just strip 2.5mm T+E and use the C.P.C. in the middle for the 1.5mm but you'd have to strip more)
2x acrylic sheet 48x500x1mm (barrel top and bottom) must be 2 continuous 500mm lengths.
4x 600mm lengths of M6 Threaded rod plus 8 locking nuts
Box of various size springs
25mm M4 button head screws
12mm M4 button head screws
M3 button head screws
4mm Drill bit (for plastic)
"Full List And Details To Come"
Step 2: 3D Files
Download the file and (unzip if required).
I've included an STL of the entire Mk4, This should not be printed as is. I included this only as a guide to help you with assembly.
The file is named "Mk4 Demonstration Model Only - Do Not Print".
Load it up into your preferred 3d software and you can rotate, zoom in etc. so should be quite helpful for reference.
Each .STL file has a number at the end, This is how many times you will need to print that same part. e.g.
"Mk4 Adjustable Opto Isolator Bracket x8" needs printing 8 times... you get the picture.
There are 20 Unique printed parts and around 70 parts to print in total.
2Kg of ABS was enough to print the whole thing.
At this point it might be worth me mentioning a feature which i allowed for but never used... Low ammo detection! I imagine some of you are going to want to increase magazine capacity. If you do, an indicator for low ammo could be a nice touch. On the magazine receiver there are 2 cutouts opposite each other, these are ready for installation of IR L.E.D & Photo-diode pair.
The holes carry on through the magazine also. You can use one of the spare LM324N channels and even the same schematic as the optical trigger to detect when coins are running out. All you need to do is swap the + and - input pins on the LM324N. This way you will have an output that goes high when ammo is low and not the other way round. The output could drive a simple L.E.D. or even another input on the arduino to do something more impressive with... Something else i'll leave up to you!
Step 3: Schematics
The schematic i used for the Mk4 is Coil Gun Optical Trigger. I removed the IR LED and IR Photodiode from the 12v as it is in the schematic and put them to the regulated 5v output from the arduino, this results in a substantial increase in stability over the old design BUT, the poor little regulator on the arduino gets very warm and a small heatsink had to be mounted to it to keep it slightly cooler.
As a result i redesigned this into the Coil Gun Optical Trigger v2 which i started to experiment with in the Mk5.
I'd go with using the V2 as it alot more stable but requires a couple extra components for the 5v regulator, i'll leave the choice to you. "note that i have removed the optional resistors in V2"
The wiring for the A4988 stepper driver can vary from make to make so double check the pinout of your driver before powering up.
The stepper position switch is responsible for ensuring that the reloading motor is always at the correct rotation for proper operation. The arduino will pull the reloading tab back until it hits the switch and then stop, ready to shoot the next coin.
Step 4: Arduino Code
The easiest step...
Download the .INO file and upload the program to your Arduino Uno. Carry on to the next step!
The code isn't very elegant but it works! feel free to improve it. Sorry for lack of commenting!
If you are not sure on how to upload a program to your Arduino Uno, There are bundles of tutorials on how to get started online. Here is a good place to start: https://www.arduino.cc/en/Guide/HomePage
Step 5: Assembly - Part 1
In this video we will get the barrel assembled and the magazine receiver mounted
Step 6: Assembly Part 2
Power Rails, MOSFET's, IR LED's, IR Photodiodes & Coil connections all in this video
There will be a delay in me making the next step, Working away from home til christmas. Assembly part 3 should be done mid january.