Project Accuracy-A K'nex Experiment

About: I love building. A mechanical engineering student, most of my instructables involve modeling projects, K'nex ball machines, and Lego creations. I am also a model railroader, and I enjoy science (astronomy is...

     This project is a little different from your average ball machine. Oddly enough, I designed it with the K'nex gun-builders crowd in mind. Project Accuracy is a "ball-machine gun target". In essence, it provides a challenging new way to hone your aim. And the coolest thing is, it even keeps score for you so you can determine your overall average!
     Since Project Accuracy works like a ball machine, there is a continual reload of the targets, so no manual reset is required. Turn on the motors, and the balls will be hoisted to the top. They will roll across a flat area with two exits: if you hit the ball as it passes, the ball will be thrust to the side, and take the back path (if the moving target is too difficult, there is an option for making the balls stationary for aiming and firing). If you miss, the ball will roll in a straight line and fall down the front path back to the lift.
     The balls that are hit drop down the back path, activating the scoring mechanism (a 360o ball arm with a peg to turn score counter one space). To get a tens place as well, getting the range of the scorer to 99, the balls are lifted up a second lift and run through an infinity switch, which only drops every tenth ball onto the second scoring counter, which is a mirror image of the first. At this point, all balls cycle back to the primary lift. (See pictures if this description is not clear enough.) By repeating this process, you can effectively count how many bullets you use (or how many in each mag, etc.) and compare that to the number of "hits" displayed on the scoreboard.
     While this machine isn't flawless (thus the word "experiment" in the title), it is a neat project I thought others might find useful. Also, I did use a few parts in my machine that were originally designed by other Instructables members. I will note these contributions when I get to them in the descriptions below, and sincerely thank them for their work.
     Hopefully you will find your targeting accuracy is better than mine! :-) Enjoy...
     A word of caution: These are not full instructions!

Step 1: Ready, Aim, Fire!

     The primary portion of Project Accuracy is the main lift, targeting area, and ball return for missed shots. The balls start by waiting at the bottom of the main chain lift to be hoisted up at regular intervals. Once they reach the top, they roll around a curve and onto the "gun range". This is where the machine becomes interactive. Once you see the ball coming, aim. When you are ready, shoot your favorite K'nex gun and (hopefully) the ball will spin backwards from a direct hit!
     However, none of us are perfect, so if you miss the ball will roll straight across into the nearer hole, dropping down a chute to the ball return. That way the balls will keep on coming!
     In easy mode, this ball return is bypassed, and of course any hit in either mode will send the ball to the back hole. While you congratulate yourself on your steady hand, it's time to see how this contraption keeps track of your hits!

Step 2: The Scoring Counters

     This is the part of Project Accuracy which makes it so unique. The scoring counters help you keep track of how many hits you have made, and when compared to the number of shots fired gives you your accuracy average. The counters are mirror images of each other in order to fit, so keep that in mind if you build. Also, they are really a modified combination of Shadowman39's Skeeball Machine Counters and sandroknexmaster's 360o Ball Arm. Many thanks to their inspiration and aid on this part of the machine! :-)
     Here's how it works:
     The ball falls through the hole in the floor (or pathing) directly above a 3600 ball arm. This ball arm is connected to a peg-like projection farther along the rod. When the ball falls onto the arm, it flips. The ball drops out underneath, the peg pushes a projection on the modified Skeeball counter, and momentum resets the arm. As always, if you don't understand the concept, make sure you read all the image notes, and see the pictures and/or the video in the introduction.

Step 3: Secondary Lift and "Every Tenth Ball" Control

     After leaving the first ball counter, I could have sent the balls right back to the primary lift (in fact, it would have been a lot easier). But that would mean only nine shots before the counter reset back to zero, a rather poor range. So instead of ending right there, I added a second score counter to register every tenth ball. That way, the machine would register up to 99 hits, a much better range of numbers.
    In order to work, the balls had to be hoisted back to the top via a second chain lift. At the top, a typical rocker path separator flips alternates balls between a path to the Infinity Switch (created by Sorunome) and a drop to the ball return. Because of this rocker switch, I was able to reduce the machine's length by half since the Infinity Switch needed to be only half as long (because now five balls bypassed it entirely, so only five slots would get me to ten).
     When the first four Infinity Switch balls enter the switch, they simply drop down onto short paths leading to the ball return track. But the fifth ball (really the tenth ball due to the above) drops through a tire hole onto the second score counter, thus counting out every tenth hit by counting each ball that cycles through!
     All the balls end up back at the primary lift at the end of their runs.

Step 4: No Finer (K'nex) Marksman's Tool...

     And there you have it! Project Accuracy is like no other K'nex device currently built.1 If it were to work without any problems whatsoever, the machine could stay continuously supplied by just a few balls, since they all cycle through just like in a ball machine. Even though the balls proved a little smaller and faster than I had expected, this difficulty can be remedied by adjusting the tilt of the target area floor or by setting in "easy mode" (see Introduction). I hope you enjoy honing your accuracy skills as much as I enjoyed honing my building skills!
    Until next time...

1I could not find any, at least.



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    29 Discussions

    I'm almost done copying this awesome machine( with a few modifications). Is it alright by you if I make an instructable of it? Also, I love your newer ball machines! I haven't been active due to college but decided to go on and see how this contraption worked and I love the counter mechanism! I'm on the counter wheels now. After that the chains then I will be done! I might rig both chains with one motor. Again, if it is alright with you my friend to make a instructable just as long as I give you full credit then I will start it:D

    4 replies

    Also those wheels, what is keeping the so round, black hinge sockets? Also, how are the tension wheels connected at the bottom? This is all I have to do and I'm pretty much done.

    There is a white rod in the middle slot of each yellow connector on the counter wheels; the black hinge socket tips rest in one of the grooves on the rod sides, and when the wheel is finished keeps each side at an equal angle from the slight pressure thus applied. The tension wheels are only attached in one place, to a blue rod behind and under the counters. The front (wheel portion) is held up by the rubber band(s), which are looped around the rod that holds the wheel and then attached to another point above it on the machine (I used some orange connectors on the front). This allows the wheels to bob up and down as the counter turns without overly constricting the movement of the counter. Hope this helps!


    5 years ago on Introduction

    Well I watched the video and now I like this even more! Very awesome job!


    5 years ago

    Beautiful! I LOVE contraptions like these. I will deffinitly need to build this. My only complaint is why can't I watch the video if it's not from my country?


    5 years ago on Introduction

    This is a cool concept, I really like the use of balls as a gun target! And it's even better that there's an option for moving targets or stationary ones.

    About the counter though, people keep on complimenting it for it not using a motor, but it does use motors, the ones in the lifts. So it technically is not motorless. I'm also not sure why people are thinking it's such a huge achievement, since all you did was copy my wheels and Sandro's arm element and hooked them up, lol. It's strange that people are comparing the two versions and saying they're both just as good as the other, since there are so many differences and reasons why mine had to use one motor per wheel. I was actually going to design a counter like this one, that didn't use a motor per wheel, but that wasn't possible due to the balls having to activate the counter from underneath. This version is nice for this particular project though, and I like the way you made the tenths place move up.

    Sorry about the long comment and getting off topic by talking about my stuff (It sounds arrogant, but I'm not meaning it to be. I just wanted to explain why I said things). :-)

    11 replies

    Thanks for your comments! I must admit, I was just as surprised by the general response. Maybe it's because the application is new and different? :-)

    I see your point about the motors. My thought was that if it were included in a larger (ball) machine as an interactive element, the lifts would already be required. I suppose you could place the counters over top of each other to use one motor/lift for multiple wheels, but it wouldn't look as good. The point is that the motor is not a direct part of the mechanism. Also, about using your wheels and sandro's ball arm, I played around with a few other ideas as well, but both your mechanisms were hard to top. :-) Since I didn't have any good ideas on how to improve them, I did what most good ball machine builders do: make a few modifications (such as weighting or changing some pieces) and then make sure to give full credit. I hope this is alright, and am willing to add further references to your being the inventor if you think it necessary.

    Again, thank you for your comments: I enjoy a little constructive criticism to help me improve! ;-)

    P.S: When they say mine is as good as yours, they don't know what they're talking about. Yours is WAY better! :-D

    Ha, the application is new and different, I've ever seen something that uses balls as targets and counts them as well. And I agree that the motors would already be in the ball machine. One thing I just now noticed about my above comment was the sentence about copying the wheel/arm, and I forgot to add something to it, and it sounds rude without that addition. Sorry about that. :-S What I meant to say there is that even though you took other people's ideas, it's nice that you were able to combine them in a way that works well. And I don't think it's necessary to add any more credit, you've done a great job with that already (I've seen people that don't give credit at all :-P). I fail to see where any criticism is in my comment though, other than the rude parts. Again, sorry, it was not meant that way, I should have reviewed it more before posting.

    Thanks, and I perfectly understand! Besides, the key word is CONSTRUCTIVE criticism. You asked about my machine with some suggestions; I responded. That's how good collaboration works! (Indeed, I find "constructive criticism" a contradictory phrase, but then I didn't write the dictionary. ;-)

    Glad you like it, and I hope to see more of your spectacular K'nex creations in the near future...maybe?... :-D

    Haha, I believe in constructive criticism as well. And I wouldn't count on it with seeing me post something soon, I'm too slow of a builder and am not too interested in Knex anymore. Well, with ball machines anyway. If Citadel is ever finished I won't make a ball machine for a very long time. :-P


    Reply 5 years ago on Introduction

    "Not interested in K'nex" :-(.

    Please shadow, don't die out like the other old great builders - Hiyadudez, ~KGB~ etc.

    I guess that means we'll all just have to wait about 50-60 years until he retires from the workforce and has plenty of time again... :-}

    But seriously, thank you for your great achievements. So many people have learned from your work, myself included. My first ball machine (which I never posted on instructables) was inspired by Cataclysm, so I guess it's just sad to see that era coming to an end.


    Reply 5 years ago on Introduction

    Oh right.

    I must admit that your counter in your Skeeball machine was ingenious! One Q - How many motors did it use to run the counter mechanism?


    Reply 5 years ago on Introduction

    Ha, thanks, I never really liked that counter after I came up with an idea to make it use 1 motor, which is why I never planned on instructions for that one.


    5 years ago on Introduction

    Nice idea! This is just awesome, i like the counter, no motor! :)