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Dear Evil Engineer: Could I build an arm cannon for my ‘armless’ henchman?

Image credit: Dreamstime

Modern prosthestics could bring a whole new meaning to ‘firearms’...

Illustration of arm handgun

E&T Magazine

Image credit: E&T Magazine

Dear Evil Engineer,

I breed and train crocodiles, which I sell to villains in want of exotic pets. My most senior henchman recently got into an altercation with my prized crocodilian stud, and he unfortunately lost his lower left arm to the beast.

While I have done my best to demonstrate my sympathy (I offered to remove the lower left arm of the rest of my employees so he would not need to suffer this alone) he remains aggrieved and has refused to return to work or respond to my voicemails. I want to turn this uncomfortable situation around; perhaps if I build my henchman a prosthetic arm with some impressive villainous functions, he may be persuaded to continue in my services. I hope you could advise me on the feasibility of building an arm cannon; would this be a practical and desirable tool?


A resourceful villain


Dear villain,

I am sorry to hear about this incident. While nobody can take full blame for the loss of your henchman’s arm, you are taking the right path by trying to make amends.

You will be glad to hear that there are several options available when it comes to building a high-tech weaponised prosthetic. Technological advances over the past few decades mean that the days of hook hands and wooden legs are mostly behind us, and it is entirely possible to build a weaponised prosthetic which can be operated without the remaining hand.

Myoelectric prostheses respond to the electrical signals associated with muscle contractions, picked up by electrodes in contact with the wearer’s skin. These signals are sent to a controller, which subsequently passes on the appropriate intention commands to actuators in the prosthesis, such as to grasp or relax the hand. While there are some alternative approaches – such as by surgically rerouting motor nerves to another part of the body, or connecting the prosthetic to a brain-computer interface – all these work on the principle of converting electrical signals from the wearer into commands.

Prostheses are not required to mimic biological limbs if the wearer prefers to deviate from nature; consider the running blades worn by some athletes, for instance. Myoelectric-triggered commands relayed to these prostheses need not imitate conventional movements either; the child-focused IKO Creative Prosthetic System allows for different Lego attachments to be added to the end of a prosthetic arm (including digger, blender, and torch) while French tattoo artist JC Sheitan Tenet sometimes wears a modified prosthesis incorporating a fully functional tattoo gun controlled with his shoulder.

From a technological perspective, then, it is perfectly possible to create a myoelectric prosthesis incorporating a firearm which is triggered by a controller when certain muscles contract, such as those associated with grasping.

However, there are some practical obstacles to building your fantasy arm cannon. Arm cannons are depicted unrealistically in popular media, often with bottomless magazines and carried with as much ease as a biological arm. In reality, it is impractical to wear and wield a large firearm (let alone a true cannon) with a centre of gravity near the end of the arm, and many firearms cannot be used one-handed on account of their forceful recoil.

Taking all this into account, your henchman would be much more comfortable wearing a prosthesis incorporating a lighter, handgun-style weapon which does not require extra support, such as a machine pistol.

You could go further still and design a bionic arm capable of shapeshifting into a gun when your henchman anticipates combat. The firearm could be stored inside the shell of the arm where the bones would sit, and extend from the arm like a pop-out USB when needed, while the hand folds and recedes back into the wrist. While in ‘assault’ mode, the controller would use myoelectric signals to trigger the weapon rather than to move the hand. You would be limited by the space left available inside the arm, but this should not cause an insurmountable problem, as you do not need to stick with the traditional shape of a firearm, built to be held in and operated with a hand.

All you need is a barrel, magazine, and mechanism. I would suggest taking inspiration from existing non-standard firearms, such as the ‘pen gun’, and designing and 3D-printing a lightweight firearm which perfectly fits the prosthesis.

So, in answer to your question: yes, it is it is entirely possible to build a weaponised prosthetic for your henchman which can be fired without the aid of his remaining hand, although the classic hefty ‘arm cannon’ is out of the question.

Despite the feasibility of building a weaponised prosthetic, you must still ask yourself two important questions. First: is the ‘wow!’ factor of the weapon worth the effort when you could more easily offer your henchman a commercially-available bionic arm and weapon of his choice? Secondly: is this the best way to retain his loyalty?

Given that you previously offered to amputate all his colleagues’ lower arms in order to improve his mood during this difficult time – which he did not consider as comforting as you hoped – I suspect that you may be somewhat misestimating his needs. Once your henchman is receptive to communication, try to initiate an open conversation about how the loss of his lower left arm has affected his feelings about continuing work on your crocodile farm. He may be delighted with the offer of a bespoke arm cannon, but he may prefer to leave your services and enter a different field of villainy (such as piracy).


The Evil Engineer

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