Introduction: Retrograde-A K'nex Ball Machine

Picture of Retrograde-A K'nex Ball Machine

     Ladies and gentlemen (and the Instructables robot as well), I am proud to present my fourth ball machine on this site. Retrograde incorporates all the skills and inspirations I have acquired so far. In addition, Retrograde includes some brand new elements! 
     The ball machine is 3'5" (104cm) tall and 2'9" (84cm) wide. It has about 3,700 pieces, and would have had more aside from the fact that I almost ran out at the end. The machine has seven paths, which will (according to my custom) be dealt with in separate steps. I also used the Stepper Lift, and will be making instructions once I take the machine down, since there are none on Instructables already.
     So sit back, relax, and enjoy watching...Retrograde!

Note: Retrograde refers to the term retrograde motion, which is the process that make the planets appear to circle back on their orbits through the sky. I thought the name appropriate, because a lot of the ball machine's elements use circular motion.
The music in the video is Chopin’s Fantasy-Impromptu for piano in C sharp minor, Op. 66, CT. 46 and Mazurka for piano No. 23 in D major, Op. 33-2, CT. 73.

Step 1: The Stepper Lift

Picture of The Stepper Lift

     For Retrograde I tried several lifts, and finally settled upon the Stepper Lift. Through some careful analysis of I_am_Canadian's Twister pictures, I was able to reconstruct a fairly accurate rebuild. I built it four grey rods high (which is seven lifter mechanisms).
     Since I always build on a red rod support structure, this lift posed several design challenges. I had to get the lift to connect to the rest of the machine! I settled on the 4 grey rod height because 5 red rods is roughly the same as 3 1/2 grey rods...which was the height of one side of the lift. I simply put connecting rods across the gap.
     The other problem was the width - the yellow rod lift would not match my red rod structure, either. I solved this dilemma by placing the lift at a 45o angle to the rest of the machine. In this position, it fit perfectly. I curved the entrance and exit paths and voila! I could defy gravity!

Note: My gate mechanism may be a little different from I_am_Canadian's...that was out of necessity. There weren't any really good pictures of it, so I improvised... :-D

knexpert#10829476 created a motor housing and posted a picture in the comments thread.

Step 2: The Path Separators

Picture of The Path Separators

     While these are often not covered, they are a vital part of the machine! One special reason I want to cover Retrograde's path separators is because I invented one of them! I saw Sathothy's "ball lowerer" in his guide to ball machine elements. I liked it, and built it to use as an element. As I progressed, however, I realized it would be too tall to fit well as an element. Then I thought, if it goes at the top as a path separator, it would still fit well. So I modified it into a path separator!
     It takes two balls to work. One ball rolls across the "trapdoor" floor, and is stopped by the rod just on the other side of the hanging floor. When the second ball rolls across the floor, it is stopped by the other ball. Its weight then drops the floor and the rod holding the other ball, allowing the first to continue along in one direction while the other is tipped in the other direction by a bracket placed below the separator. It took some time to get the thing to work perfectly, but once I succeeded it looked great! I call it the "Dropper Path Separator".

Step 3: Now to the Paths! - Path 1

Picture of Now to the Paths! - Path 1

     Path 1 was actually built in combination with Path 2. Path 2's main element is integrally connected with the main element of Path 1...Kariah's Zig-Zag! As seen in the video, the Zig-Zag delivers enough downward thrust to punch the reset lever for the (in my opinion) epic iris diaphragm of Path 2. The ball then rolls off the Zig-Zag onto the ball return, which I've also included in this step. (I did add a few modifications to the Zig-Zag, including an entirely new counterweight material...a golf ball!)

Step 4: Path 2-The Wormhole

Picture of Path 2-The Wormhole

     Path 2 has my favorite element - my newly invented "Wormhole" element! I give credit for the basic design to GeekBeam ( When I saw it, I immediately thought "ball machine element!"
     Orignally, I conceived it as lying flat, but decided the reset would be much easier if on its side, as it is in Retrograde. I modified it quite a bit from GeekBeam's design: I made the blades more solid, and made the frame opening more circular. I then mounted the modified diaphragm on a larger frame to match my red-rod tower structure. I then attached two levers, one on either side, to control the opening/closing. One worked fine with a golf ball dropped on it, but the other needed more weight. I then thought of the Zig-Zag, built one, and attached the two as one unit. The mechanism worked (for those who use lighter Knex balls, a ball arm may be necessary on both sides). I then moved the frame about until I got the current configuration, and built everything else from there.
     Path 2 also sports a Classic Spiral using white snowflakes instead of yellow connectors (which I think looks even better than the original). The classic spiral leads to a "tire hole", which snakes down to the holding track of the iris (the iris was the first thing built, but the rest was the last path built, and I ran out of room...). The iris opens on a yellow connector path, which curves gracefully back to the ball return.

Step 5: Path 3

Picture of Path 3

     Path 3 includes the other reset for the Wormhole. It starts with a length of my Green Flex Path, drops onto Sandroknexmaster's Inverted Ball Dropper (whose length I modified to get slightly shorter), and then propels the ball onto the reset claw of the Wormhole. The ball then falls off onto a path which leads back to the lift.

Step 6: Path 4

Picture of Path 4

     Path 4 starts with the first ball in the Dropper Path Separator. The ball rolls onto a slightly modified Knextreme Ferris wheel, then to some pathing which leads to a tiny ball arm, and then drops onto the ball return.

Step 7: Path 5

Picture of Path 5

     Path 5 has another of my new elements...a pathing spiral similar to the Inverted Spiral Lift, in element form. But lacking tubing, I tried a peculiar alternative: glow-sticks. They fit perfectly in the connector holes! This element is like the lift, in that it is built in a yellow rod structure at a 45o angle to the rest of the machine.
     The path originates from the lower path of the Dropper Separator, rolls to the spiral, through a "Tire Hole" at the bottom, and onto a return path. Even though the glow-sticks don't light up anymore, it still works for my purposes.

Step 8: Path 6

Picture of Path 6

     Path 6 and 7 share Kariah's Spinning Basket from Metropolis...because I found out totally by accident that it can be a form of path separator!
     As I tested the machine, I used golf balls. At one point, I plopped a Knex ball on the thing...and it went a totally different direction! It has to do with the ball weights. I modified Kariah's element by taking off the blue rod which normally tips the basket inward, and instead placed two Y-clips on the red rod it would swing past. The basket bumps the Y-clips and tips outward. Golf balls are so heavy that they immediately fall straight down, onto Path 6. But K'nex balls are lighter, and the gentle bump simply knocks them over the top of the red rod, onto Path 7. It was a welcome discovery, for I was running out of room for my elements, and this added much potential.
     Path 6 goes through the Spinning Basket, and golf balls fall onto a length of my Green Flex Path back to the ball return.

Step 9: Path 7

Picture of Path 7

     Retrograde gets much of its iconic look from Path 7. After popping off the Spinning Basket (see Path 6), the K'nex balls are tipped onto a graceful yellow pathing curve, which I "dressed up" with arches and pendulums. The curve ends on another tiny ball arm, which deposits the ball onto a return track. If the Wormhole is my favorite element, this would be my favorite Path.

Step 10: Additions by Request...

Picture of Additions by Request...

     Some of you on Instructables have been very helpful in pointing out areas where a few more pictures are needed (notably the top of the ball return and parts of Path 2). I have taken some more pictures of these areas and uploaded them for the convenience of anyone desirous of building Retrograde. Explanatory notes are included on the pictures.
     Many thanks for helping me improve this Instructable! :-D

Step 11: Conclusion

Picture of Conclusion

     So there you have it. 3 brand new elements, 7 paths, and more K'nex ball machine fun...Retrograde! Thanks for viewing!


FanPlastic (author)2016-01-07

are golf balls about the same size as knex balls?

Roughly speaking. Golf balls are slightly smaller (and a whole lot heavier) than standard K'nex balls. I would not personally recommend using them all the time, but I must admit they made great stand-ins until I got more actual K'nex balls to work with. Hope this helps!

Yeah ive seen people use tennis balls ping pong balls and even raquetballs, but golf balls seem the best.

Roughly speaking. Golf balls are slightly smaller (and a whole lot heavier) than standard K'nex balls. I would not personally recommend using them all the time, but I must admit they made great stand-ins until I got more actual K'nex balls to work with. Hope this helps!

knexfun101 (author)2015-02-06

Can I use regular k'nex balls?

www139 (author)2014-07-13

How did you get it to sort out golf and knex balls on path 7??!!! I think that adds a whole new dimension to that element. Nice job!

Thanks! It has to do with the different weights of the balls.

How did you think of it?? Ingenious


Sorunome (author)2013-06-27

This vid is blocked too D:

hunter999 (author)2013-06-20

Nice, soooo great, I like it

:-) Glad you think so!

lopertt (author)2013-04-13

Movie maker isn't really good for high resolution video... haha. Use a program like Adobe Premere CS6 if you want to export in full HD. It also comes with a few more professional looking titles.
Get it for free at the above youtube video. :D

tedbear2 (author)2013-03-29

the 'portal' door is my favourite part of this.

I_am_Canadian (author)2013-03-24

This think is really, really good. Fine job good sir!! Thanks for the inspiration.

..Check your inbox :-)

Thanks! :-D

knexpert#10829476 (author)2013-03-21

Also for future instructables, try to use zoom on your camera rather than just being close to the part because being close to the part won't constitute a clear picture. It's just like when you look at something really close it will be blurry. Just a friendly tip:-)

I did for the additions, sometimes the lighting and positioning are just problematic... :-}

Thanks for the advice, did help on some shots.

dannypalmer2001 (author)2013-03-19

can i have instructions

If it is alright with MarsCrystalMan for instructions then yes, I will make some since I copied it with some mods.


can you make it an instuctable

This is as close as you'll get to step-by-step instructions, although in a month or two I will post the instructions for the Wormhole and the Stepper Lift, and maybe the Dropper Path Separator.
See knexpert#10829476's pictures below...He built the whole machine from the pictures in the instructable! ;)

Don't you worry about that, I will take care of it for you:)

Thanks...I just don't have time to go back and make a true step-by-step how to build it of this machine. Also, I just added some more pictures like you asked for...a little late, but if you still need them. ;-)

knexpert#10829476 (author)2013-03-19

Thanks for posting these! They really helped! I never knew that the holding path had the orange connectors on it, maybe it will work this time:)

Glad they helped! :-)

I'm glad your aim in knex isn't all guns. Don't we have enough guns people?

Agreed...the guns are cool, but it is easier to be a pioneer in an area of K'nex with less volume of work already done. :-D Besides, while K'nex guns are often amazing, ball machines defeat them almost hands-down for "wow" factor (in my opinion, anyway)!

knexpert#10829476 (author)2013-03-18

Here is a working configuration of motor attachment since the little yellow gears strained it.

Perfect! Thanks for showing your motor housing! ;-)

knexpert#10829476 (author)2013-03-17

You sucked up all of my green connectorsXD. That has never happened to me before! Anyway, I enjoyed copying this. It's not exact because of some blurry pictures but it's 98% correct.

knexpert#10829476 (author)2013-03-14

One last thing, can you post a couple more pictures that are a little clearer than the very blurry ones, like use the zoom on the camera rather than just being close to the part? I want to try to copy this awesome machine.

I certainly can - just tell me which pictures you think need replacement (or at least the worst steps), and I will be happy to improve the instructable for you! :-) Also, I can take entirely different can just be a kinda broad task, so it would be nice to have some more specifics.
Also, thanks for wanting to build it...You've probably set a record for number of reconstructed MCM ball machines! ;-D

More pictures of the back with the track behind the wormhole, the track leading to that and the green path near the bottom how it connects to the yellow connector path. I also copied it with a couple mods to make it lean towards knex balls. I will post a picture of it in about 20 minutes. Thanks for posting!

knexpert#10829476 (author)2013-03-13

Can you please make an insttructable on just the wormhole element? I am very curious. Also, your best ball machine to date:D

Sure I can! It may be a while though...for the moment I can't bear the thought of dismantling the machine. :-( But maybe I can deconstruct and rebuild just that portion. Perhaps I even have enough elements now to start my own guide! :-D
Thanks for the compliments as well!

Yeah, I would probably shed tears if I took it down too early to. Thanks!

KneXtreme (author)2013-03-14

Awesome ball machine! The wormhole is one of the coolest elements I've seen in a long time. Keep up the good work :)

Thanks! :-D Glad you like it!

Shadowman39 (author)2013-03-13

Well done! Lots of interesting things in there. My favorite is the dropping ball collector. It's cool when mistakes lead to new elements. :-)

Definitely! ;-)

sandroknexmaster (author)2013-03-13

The wormhole is awesome, as well as the dropper path seperator.
I like the spiral element, can I try to build one for normal knex balls?
Thanks for the building (a modified version of) the inverted ball dropper! :p

And you can most certainly build a "glowstick spiral" for K'nex balls! It should only require a slightly wider gap between each loop of the spiral.

Yeah I was wondering if knex balls have a different diameter then these golfballs, but I don't think there's much difference.

Well, golf balls are about an eighth an inch smaller than original knex balls, and a little more than twice as heavy. Small differences in size and weight can make a difference though. For instance, Mr. Muggle's "Uh" element (the one on which the ball rolls back and forth falling through) won't work with golf balls because of the smaller diameter; they fall right through the center!

And like the spinning basket, there you can see the difference in weight.
BTW this deserves a feature :D

Yep, the spinning basket really does highlight the difference - it turned out so nicely, though. ;-) And thanks for recommending for a feature! :-D I really tried to upgrade the video quality in addition to the ball machine quality for Retrograde. Glad you like it!

Yay it's featured!!!

About This Instructable




Bio: I love building. I specialize in K'nex ball machines and Lego creations. I am also a model railroader, and I enjoy science (astronomy is ... More »
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