21st Century 1/6 scale M5 Stuart tank with Airsoft mod

I was originally going to make this a paint ball tank but I had trouble locating a paint ball gun that would fit. I’ve reviewed other sites that have done the conversion and I decided to go airsoft so I wouldn’t need to deal with the CO2 or other gas systems for power.

First I replaced the stock electronics with an ESC for track control, servo “guts” for turret rotation and a servo for gun elevation. I used a six channel 75Mhz ground radio with an eight channel receiver. One gimbal controls forward, reverse, left and right. The other gimbal controls the turret and cannon. Channel 5 on the radio will control the airsoft gun and channel six will move a wireless camera mounted on the turret for airsoft sighting.

My first attempt at installing an airsoft gun was with a spring pistol. I felt the pistol was small enough to easily fit in the turret, the only tough part was designing a cocking mechanism to load the gun. I mounted the gun on an aluminum bracket and decided to use a large servo with enough power to pull the slide back. I controlled the servo with my recoil board, this would cycle the servo to pull the slide back. The servo arm is connected to the slide by a strong spring so there’s a little bit of play is the system. It worked the first few times then the gears in the servo stripped, so I didn’t spec in a strong enough servo and it was a 1/4 scale HS-805 with metal gears. So I needed an alternate setup.

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My second attempt was a lot more successful and I was happy with it until the BB wouldn’t go through a paper target just a few feet away. I took a Well fully automatic Uzi and cut it down until all I had was the gearbox and barrel with a small portion of the plastic body to hold the two together. This gun was a gravity feed and since I had to mount the gun sideways I had to make a modification. A spring magazine (3) from a bolt action rifle fit the bill and I mounted it to the gun using an aluminum bracket that it attached to. A servo arm connected to a brass “U” channel rod controls the elevation (1).

I used my trigger circuit and a few 555 timers to control the firing of the gun (2). The trigger circuit set a one shot that triggered another one shot that in turn powered the airsoft gearbox. The first one shot controlled the firing rate, the second one was adjusted so the fully automatic gun would only fire one round when triggered instead of a burst. This setup was fine except for the weak airsoft, I really wanted something with more power. So I lived with this setup for a while then I started on the third configuration...

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Airsoft gun used

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Cut down to size

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Brass U channel for elevation

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The spring magazine was a bit too long so it sticks out the rear of the turret. I didn’t want to mess around with trimming it in fear of ruining it. The red pushbutton is an override to fire the gun without powering up the tank. The airsoft gun runs on it’s own battery. I did this to avoid the necessity of regulating the 12 volt battery to the airsoft voltage, it would have required a high current regulator/circuit so a separate battery was a better solution.

Third configuration with more Airsoft power

I used the gearbox and barrel from a JG P90 bullpup with the long barrel. I had to make an assembly to hold the gearbox to the barrel (and hopup unit) as the plastic body of the gun held them together but it wouldn’t fit so the body needed to be replaced. Many pieces of aluminum bar and angle with drilling and tapping and I came up with the assembly shown.

I was going to replace the mechanical trigger mechanism with electronics but testing revealed there’s a high current to power the motor (trigger is just a switch for the motor). I estimated about 20 amps and that required some high current devices with heat sinks so for now I just rigged up a servo to push the trigger mechanism. This is a similar setup using the trigger circuit and two timers plus I added a recoil board that controls the servo that pushes the trigger mechanism.

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P90 gearbox, barrel & hopup unit

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More to come . . .

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The barrel & hopup unit are press fit to the gearbox so I used aluminum bar and angle stock, the trigger servo and elevation bar are also shown. All the aluminum is painted red to easily distinguish it from the airsoft components.

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