The Punching Machine X-26 is a non-upgradable feature of your campsite. It must be repaired in order to function.
Once the Punching Machine X-26 is repaired, it acts as a kind of automated turret. It will attack any zombie that comes within its range, dealing significant knockback (much greater than the hammer) and a small amount of damage. It works best in conjunction with a repaired and upgraded gate, as the gate will stop the zombies from advancing, and hold them in place while the X-26 winds up for a punch.
The X-26 functions much like a bow and arrow, with an automated winch of some kind serving to draw back the bowstring. However, instead of arrows, the bowstring forces a boxing glove-on-a-stick a short distance forward in a punching motion when the string is released. Once the motion is complete, the winch winds the X-26 up so it can punch again. The game never mentions how the X-26's winch is powered.
After it has attacked a number of times, the X-26 will break down and must be repaired again. Each subsequent repair has a cost identical to that of the initial repair. It cannot be repaired until it has fully broken down. Accordingly, relying upon the X-26 to protect you against a zombie attack while you are in camp is not recommended.