Nerf Gun Platform - PiWars 2024

      In a team, items come along all the time and if you're writing the blog then either you leave a mountain of things to add, or just publish them there and then. 

     Some things just get decided as the obvious way to go so building a platform for aiming and firing a Nerf gun just seemed the sensible thing to do for the Zombie Apocalypse challenge, though there'll be a blog analysis of it along soon.

Mounted on the rear lid of the chassis, the arm is rather overkill to support a Nerf gun, but it has it's origins in one cooked earlier for a drawing robot arm, so easier than developing a whole new arm. The servos are AX12 serial servos controlled via the official Dynamixel USB controller by a Pi Zero, which can be just seen mounted under the arm, with camera for aiming. The gun connector is a Picatinny rail, Nerf fans will appreciate that.

The heart of the arm is this bearing. It weighs 220gms just on its own without the rest of the arm, but gives superb glitch-free smooth rotation with any weight, even unbalanced.

The whole truck now weighs 2Kg, but it still drives OK

The Nerf gun we are intending to use is a Nerf Stryfe which may not be available in shops any longer, but we have one because we like playing with things. NOTE: this is different to many of the newer versions of the electric Nerf guns in that it is screwed together and so can be disassembled easily, some of  the newer ones are glued together so much more easily damaged when being taken apart, possibly a job for a Dremel if using one.

The following pictures are of the gun mechanism.

Electric motors spin up flywheels just before the barrel of the gun and after the Nerf dart magazine. 

Once the flywheels are up to speed, the trigger is pulled and a mechanism pushes a dart forwards from the magazine, see the arrow in the picture above, until it is caught by the spinning flywheels which catch hold of it and accelerate the dart out of the gun barrel. The flywheel motors are designed to be run by four 1.5V alkaline batteries (about 15Wh) and are normally expected to not last long, but powering them from the vehicle batteries (31Wh) is expected to be ok for the challenge. 

A test cradle has been designed to hold the active portion of the Nerf gun and dart magazine to facilitate fitting to the aiming mechanism.

Out of the box, these foam dart guns have a surprising range and accurate over short distances so are worth the effort to modify. In the unmodified versions, the flywheels are only powered when a trigger switch is pulled, connecting the batteries, so are unlikely to be operated for long periods of time, this is an area which needs to be understood in order to ensure the reliability of the mechanism and prevent overheating. Of course, if the mechanism is going to be modded, increasing the voltage, and thus the speed of the flywheels, might increase the accuracy, something to experiment with. The mechanism also has a variety of interlocks to prevent operation when the gun is not complete, all of which will need to be removed or bypassed.

So, on with the fun, though it might be a bit longer before the next blog post!!!!