Here are some cranes, bridges, a kinetic sculpture and a binary multiplier, I have built out of K'nex. I have always loved construction toys, and K'nex is one of the best. Two of my robots ERC and Speedy were also built from K'nex.

A Bridge to Nowhere

K'nex Arch Bridge, over 14 feet long, on a foggy day

This tied arch bridge at 14 feet 7 inches is the longest free span I have built so far. To build anything longer I will have to buy more K'nex.

K'nex Arch Bridge, over 14 feet long

When supported by its end points this bridge was very sturdy. When supported anywhere else the arch didn't function, and it was limp and fragile.

Arch Bridge at Sunset

K'nex Arch Bridge, about 10 feet long, at sunset, with Whidbey Island in the background

Single arch, supported deck bridge. This one had about a 10 foot span.

K'nex Arch Bridge

K'nex Arch Bridge

The deck structure provides some local stiffness helping the arch hold its shape, but the arch itself supports the weight.

K'nex Arch Bridge

Yet Another Arch Bridge

K'nex Arch Bridge, about 7 1/2 feet long

This one had a span of about 7 1/2 feet

K'nex Arch Bridge

Suspension Bridge

K'nex Suspension Bridge, over 11 feet long, with Whidbey Island in the background

At over 11 feet of free span, this is my longest suspension bridge so far.

K'nex Suspension Bridge

It's possible to build a suspension bridge longer than other types. However the towers and the support structure on each end use up a lot of K'nex, limiting the length that I can build. Also the road deck is in compression and can't be made much longer without trussing it to make it stiffer, and using up even more K'nex.

K'nex Suspension Bridge

Binary Multiplier

K'nex Binary Multiplier K'nex Binary Multiplier K'nex Binary Multiplier

This binary multiplier takes two, two bit numbers for its input, and outputs the four bit product. There are four input levers at the bottom (two for each input number), and about halfway up there are four levers that show the result. A lever in the up position indicates a one or true state, A lever in the down position indicates a zero or false state.

K'nex Binary Multiplier K'nex Binary Multiplier

The moving parts at the top are logic AND gates, the moving parts at the bottom are logic OR gates, the pulleys about a third of the way up are inverters (NOT gates). The pink strings transmit information up from the bottom to the top. The green strings transmit information down from the top to the bottom.

Kinetic Contraption

K'nex Kinetic Sculpture

This kinetic sculpture includes five gizmos and about two dozen deelybobs. When the rubber ball is placed at the top, it rolls down and energizes each gizmo one at a time.

Watch the video
Back side showing the ball tipping gizmos

Tower Crane

K'nex Tower Crane

With three hand cranks in the base, this construction tower crane actually worked. Using one crank the load could be hoisted up or down. Another crank moved the trolley in and out along the jib, and moved the counterweight half as far on the other end of the jib. A third crank would slew the jib.

Mobile Crane

K'nex Mobile Jib Crane

This mobile jib crane also had three hand cranks for three degrees of movement. I don't recall how tall it was but I am over six foot and it was much taller than me.

K'nex Mobile Jib Crane

Close up showing the hand cranks, counterweight, and slewing mechanism. Alas the tracks are just for show so it's not really mobile.

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Gary Teachout