Sunday, July 15, 2012

Experimental PF Tank (Very Old)

Focus of project: Mere functionality

After digging through some ancient computer files I came across a few pictures of my first PF tank. It wasn't very impressive in relation to what Lego builders make nowadays but it was one of the funnest things in the world to operate. It's structure was pretty primitive but I do remember the first prototype breaking down altogether. This was way back when I only had about 10 gears in my inventory, another reason why this build wasn't so developed.

As you can see, there are two guns attached to the turret. This "gun permutation" was one of three, and two permutations had a sidearm as we see here. The main gun is the one with the ugly black magazine that protrudes straight up. It was, technically, "fully automatic", but its rate of fire was about 1 round every 2 seconds. Pictures of its mechanism can be seen below:

The line of gears is powered by nothing more than an M Motor. The reduction is so heavy that the "bar" (so I call it) has the strength to pull back a couple rubber bands (can't be seen here) and when the bar rotates 180 degrees the rubber bands release, firing the shot. The gravity-fed clip moves down once the firing pin is pulled back again, and the next rotation of 180 degrees fires the next shot. This mechanism is very primitive but it was technically my first automatic Lego gun.

You can see the bar much more clearly here. It's the black diagonal piece. Its pivot point is in its central pinhole (hence the 180 rotation every shot).

In all the pictures seen thus far, you may notice the turret movement mechanisms. The turning mechanism used an XL Motor with a heavily reduced gear ratio. It worked well but looking back I'd say a worm gear would've worked better. The vertical aiming was driven by a single linear actuator, since I only had one of them when I made this. It did the job, but the junction between both cylinders always bent when a heavy gun was mounted to the turret.

Here the 15 round magazine for the bar gun is opened at the top to reveal the ammo, which are 1-stud Technic bushings. Also, to the right of the picture, you'll see the sidearm of this gun permutation, which I basically took from YouTube username erahaar. Unfortunately, the video was taken down, possibly due to copyright issues with the background music. The gun basically was a really short piston that punched out the pins that are loaded on that protruding yellow clip. Its rate of fire was very high, but the range was very, very short. I considered it to be more of an automatic "flare" or "mortar" launcher.

Unfortunately, I wasn't considerate enough to take more pictures back then. However I do remember exactly what the other gun permutations were. For the first one I made, the main gun was a Bionicle sphere launcher (shown right) with an automatic mechanism. An XL Motor powered a piston that would blast the ball out of the grips in the cup, and a clip on top of it would feed the next ball in. The balls were pushed down by a rectangular piece loaded by a rubber band. The sidearm was a spring loaded missile (shown left) dubbed "Technic Competition Cannon". A motor pulled the lever on top and a compressed spring would launch the missile straight out. As you might imagine, such sidearm only had one shot. The second permutation was the one documented above. The third one was a revamped version of the bar gun. It was powered directly by an XL Motor (no gears) and the clip was not gravity fed. Also, the bullets actually looked like bullets. If I remember correctly, the magazines (there were 3, easily re-loadable by hand) each held 9 rounds. Like the sphere launcher weapon, the bullets were fed by a rectangular piece loaded by a rubber band. The rate of fire and range for the last permutation surpassed the other two, but there was no sidearm. Again, I apologize for not having any pictures of the other two weapons, but the most complex one was the one posted above.

On a side note, each receiver was marked with the corresponding amount of clear-orange studs to easily tell which channel it was on. There was also a set of LEDs on one side of the tank for nighttime scouting.

Thanks to YouTube username markdykstra36 for reminding me about this project (as I'm sure I wouldn't have posted it for a while) and for sharing his lego tank with me. His gun works much better than all the ones described above. Check his blog at

Experimental PF Tank
PF Contents (including the motors required for all gun permutations to function):

2 Battery Boxes
2 XL Motors (1 for the chassis)
7 M Motors (5 for the chassis)
4 Receivers
2 Remotes
1 Speed Control Remote
1 Pair of LEDs
1 Linear Actuator


  1. Cool! Even then you had more PF stuff than I do. That beam cannon looks similar to my original lightning launcher in mechanism. From the description, the Zamor launcher was actually your first full-auto gun (I dabbled extensively in Zamor machine guns, making the fastest ones in the world, the Hurricane launchers). All of the guns described except of course the missile are full-auto, that's really the only way to go with motorized Lego guns.

    By the way, why did the drivetrain need 5 M motors?

    1. Never mind about the fifth motor, I realized that you consider the gun tilting motor to be part of the chassis, though I would have considered everything above the turntable part of the turret.

    2. Yeah the turret never had to be dismounted to change guns, only the guns themselves. Listen, you seem like you'd make much more if you had more PF parts. Are you aware that they're sold individually? On another note, your tank is looking real good. You're inspiring me to start working on a new one of my own. In fact I'll mention your YouTube username in this very blog right now. The thing is though I'm planning to order parts for a 4x4. A friend of mine and I agreed that each of us would make one and race them at school when school starts (I'm going into my senior year of high school btw). The project focus will be good suspension, 4 wheel drive, and speed (with God's help I'll pull that off). Then I had plans for making a walking biped...but I first have to finish my gun! (which has been lying dormant since I got so much other work on my hands). Thanks for checking out my blog.

  2. Yes, I know PF parts are sold individually, that's where I got the ones I have now. I think I might order some more really soon, with my summer job this year I have plenty of money to spend. That 4x4 sounds pretty awesome, though if I were in your situation I'd have set up the game to allow tanks and built some sort of a cross between Cheetank and Storm Surge. =) I'd recommend that you not include differentials to improve off-roading, but you probably already know that from searme's vids (I noticed that you watch them too).

    1. Whoops forgot to say; my friend and I aren't planning to race on dirt; just in school...with some artificial "terrain". We hope to cause a huge distraction in the minds of the students around us lol.

  3. Yeah differentials can be evil. I only have a single one so I need some more. There is a way to make differentials work in all situations; check out (maybe you've already visited that website) to see searme's differential lock idea. On the other note, I checked out Cheetank and Storm Surge. I liked Storm Surge much more except for the manually operated gun (but I know you didn't have all the parts you needed). Racing tanks sounds like fun but my friend and I are focusing on speed by tire. Also, he doesn't have the track link parts. Btw, actually taking a lego vehicle on dirt can be very bad for lego parts, unless the dirt is somewhat wet. I had a really bad experience with my Arm Rover when I filmed with it in a desert area (the film totally sucks; it was for my school film fest. Look up Title Classified on YouTube, first link. I'm redoing the whole thing as a sequel right now. Special thanks to YT usernames freddiew and corridordigital for inspiration. If I were the one who did the effects in Title Classified the film might have been decent). Anyway, I also have a summer job, and I'll hopefully order my parts soon without any parental stress. They think I have too many parts (cuz my little bro has a lot of his own; we just share them) but they're beginning to understand that as many parts as I have, I don't have the right ones for a 4x4, which I simply must make. And yeah, get yourself some PF parts that you're sure you'll use. Who knows, you might make a tank better than the one YT username gyuta97 made (called Autoload LEGO RC Tank).