Introduction: Knex Mobile Folding Crane

These are the instructions for building the Knex mobile folding crane as I have designed and built it (by trial and error).

It's pretty big and sometimes quite tricky to construct, but I'll try and guide you through it.

One thing though: she's not able to carry any weight and there are no wires, nor a pully or a hook. The complicated matter of getting wires to stay in the right place when folding the crane seemed too daunting a task. Apart from the fact that the boom trolley has to be taken out for folding...

I have not got a list of parts. She's too big too start counting. Sorry. Safe to say you need a lot. I completely ran out of white rods.

The biggest fun was in the design and building and with each step thinking: now how can I do that. It seems impossible in Knex. But in the end all has worked out, sometimes even better to my surprise.
And then the biggest fun is folding her down and building her up again, astonished at the small package, that actually drives and steers, which unfolds to quite an impressive crane.

Inspirations to this model:

Very nice mobile crane:
Very interesting Knex techniques:

and several projects I came across, none of which however provided me with the answers or solutions I was looking for.

Enjoy, built and/or be inspired!

(I am by the way impressed by the effort it takes creating this instructable. The crane build took longer, but boy, this took nearly 3 days. A challenge in itself!)

Step 1: Video 1: How to Set and Deploy the Crane

First have a look at this video showing how to built up or set up and fully deploy the crane.

Step 2: Video 2: Overview of Overall Construction

Then watch this video which gives an overview of the overall construction.

By pausing you may well find out most there is to know about how it is all put together, save for some parts that are too deep inside the chassis.

Of course this is not a detailed building instruction. This will come soon with detailed pictures!

Step 3: Make the Mast: First the Bottom Mast

You need to make these two masts, which are what I call a basic Knex box structures.

First make the bottom mast part. Just follow the images and you should be fine

I've laid out the pieces you need for this.

At the bottom fit the two double blue pieces.
Next, fit the red rod into these as shown: to this the long red hinge rods will be attached.
Next add the gray guides as shown.

Finally fit the two orange guides at the front as shown: these and the grey ones will hold the boom in place for transport.

Step 4: Make the Smaller Top Part of the Mast

Now make the smaller top part of the mast. This is a smaller variant of the basic Knex box construction.

To finish the bottom part, add two purple pieces to form a square bottom.

At the top finish with two double blue pieces: these will hold the hinge for the boom.

Now you have two mast parts which fit snugly into each other.
To keep the upper mast in place, fit in the yellow rod bracket. Not very esthetic, but basic functional.

You may find as you slide the smaller mast into the larger one that it gets stuck.
When I first constructed this crane it jammed when moving top or down. It's the purple pieces that are slightly sticking out. Oddly enough after a while the sliding was much smoother. Now rebuilding the mast for these images I find it jams as before. So apparently the pieces settle down or the tension subsides thereby making the purple pieces slightly smaller.
Anyway, don't say I didn't warn you.

Step 5: Make the Mast Bottom

The mast sits on the turning base.
In order to be able to disconnect the mast from this turning base, a special bottom is added as shown.

Then later on two yellow rods fit in to keep the part together and when removed the whole mast hinges down to rest on the counterweight.

To achieve this, build this and connect it to the bottom of the bottom part of the mast.

Step 6: Make the First Part of the Boom

This is what you need to make: the boom which folds in half and eventually the second parts folds next to the first for transport. But let's not get hasty.

Make the basic boom construction, consisting of two parallel strings of yellow and purples connected with whites.

For the boom end at the mast: two greens and two yellows to hold the hinge which will be attached to the boom.

The rails are made of a long row of orange pieces. These are hung onto the boom on green connectors.
To make sure the rails stay in place during handling and transport, make two brackets which slide down holding the rails in place.

That's the first part of the boom.

Step 7: Make the Second Part of the Boom

This part is almost identical to the first part, safe for the end. Look at the images and you'll see the difference.

Construct this part as you did the first part.

Then place the green parts and the end rod.

Make the two brackets/hinges as shown and place them on this part of the boom.

Make the other brackets/hinges and fit these to the first part of the boom.
These will connect the two boom parts when folded down for transport.

Step 8: Make the Boom Hinge

This a special bit which serves multiple purposes.

Firstly it makes the two boom parts fold in one on top of the other.

Secondly it holds the two boom parts firmly in place, because of the bushels on top which press against the yellow pieces.

Thirdly the middle of the rigging is attached to the first part of it.

Fourthly, when the boom is folded and you have secured the brackets/hinges, you can then remove the blue rod in the second part of the hinge and fold down the upper second part nestling it besides the first boom part. This makes for quite a compact package for transport.

Step 9: Make the Boom Rigging

The whole rigging consists of either folding rods and/or sliding in/out rods.

The single grey holds the long grey rod nicely in place.
But when too much force is out on the boom, these bits sometimes snap off. So be warned.

Step 10: Make the Trolley

This piece is just a fantasy as the crane cannot carry any weight. Sorry to disappoint you at this stage, but Knex is simply not strong enough to withstand very large forces.

This trolley slides along the rails beautifully and at the same time holds the rails nicely together.

Just follow the images and you should work it out fine.

Step 11: Make the Mast Rigging

On top of the mast is a series of rods transferring the pulling force from the boom over the top of the mast down to the turning base of the crane.

The whole rigging consists of folding in rods and hinges and rods sliding in and out.

Look carefully at the images and things should be clear.
Mind the two bushels which give the rigging its correct length.

Step 12: Make the Turning Base: Crane Support

The turning base is thé base of the crane. It makes it able to turn, the counterweight is attached to it, the rods are attached which make it able to fold down.

First make the basic construction.

Then put together the white which will hold the turning axle.
To prevent the turning axle holder from unsnapping, snap 4 whites in and snap 4 greys on them. These cover the main grays connection, thus preventing unsnapping.

Mind how the holder for the two blue rods for the folding down is positioned.

Next make the two pieces which support the mast when folded down. They prevent the mast from folding too far or tip down as you erect the mast.

Step 13: Make the Turning Base: Turn Support Part

This is like skirting which will run over the wheels in the chassis for the turning of the crane.

It'll hurt your fingers, but works quite well.
It's snapping a lot of yellows on 4 red rods and then make as many connections between these 4 rods and the crane base.

Step 14: Make the Counterweight Box

The counterweight is a simple box structure attached to the turning base. It takes all the weight and force of the boom.

Make the box structure.

Attach the single grey to which the rigging is connected and place the anti-snap pieces at the back.

Place the guides on top.

Make the filling in to cover most of the box.

Finally make the swiveling feet. Most of the weight of the crane when folded down for transport is at the back which makes these feet necessary unfortunately. They transfer the weight down to the chassis. It also stabilizes the whole for transport.

Step 15: Crane Assembly Part 1: Mast and Base

Now we can assemble the crane.

Firstly place the mast on on the turning base. Simply put the two yellow rods in and it's lock down.
Attach the toe blu and two red rods which will hinge the crane when folding down.

Next attach the counterweight box at the back.

Then attach the main rigging to the grey at the back and on top of the counterweight.

There she proudly stands on her own!

Step 16: Crane Assembly Part 2: Attach the Boom

Now to be able to attach the boom, we need to fold it in two as else it will drag on the floor. That's not a real issue, but I just like to do it the way as is done for real.

Fold down the brackets holding the rails in place.
Then carefully unsnap the green connectors in the middle of the rails right underneath the boom hinge.
Now fold the boom parts on top of each other.

Next, remove one rod of the boom hinge, swivel the top part down next to the other part and connect with the brackets/hinges.

Now carefully spread out the grays on the hinge axle and attach to the mast hinge holders.

Step 17: Crane Assembly Part 3: Rigging, Counterweights, Build Up

Attach the boom rigging to the top mast rigging.

Place the counterweights, actually anything you may have, but make sure it has some considerable weight.

Carefully lift the upper mast and lock it with the yellow rods.

Unfold the boom, place the trolley and enjoy the looks!

Step 18: Crane Assembly Part 4: Folding Down

For the folding down, take out the two yellow rods at the base, carefully fold the mast down into the guides.

Next, undo the boom rigging and attach the mast rigging to the top mast rigging.

Then undo the blue rod in the boom hinge swivel the top part down so it rests on the bracket/hinges next to the other part.

Ready for transport!

Step 19: Make the Chassis Part 1: Back End

The chassis is a very important part. It supports the whole of the crane on turning wheels, underneath the steering and wheels are fitted. The front has the cab and steering wheel and there various bits and pieces to finish the whole thing of.

To make it really strong, it is again the basic Knex box structure, same as the top mast, but now 4 next to each other, all connected by blue and white rods. They are both positioned in two directions so as to make the whole as stiff as possible.

I hope form the images you can work out how it is al put together.
Always keep the box structure in mind when building.
Mind where the different bits go, such as a blue/purple piece of a double blue one.

Step 20: Make the Chassis Part 2: Hinges (1)

The 4 hinges on the chassis are for the supporting legs. This is a crucial bit as these 4 carry the entire weight and Knex is not always that strong. So to make sure these hinges are strong they are supported by two blues and 3 yellows, all interconnected through the chassis and directly underneath with two red rods (the second one will be fitted later on).

It takes a lot of fiddling and painful fingers to fit the two yellow rods in place. I broke one during disassembly....

Step 21: Make the Chassis: Turning Wheels

This is what you'll make: the middle part with the turning wheels. There are 8 wheels to support the turning base of the crane.

First build one side, then add 3 wheels.

Then build the next part and the middle part.

Then build the other side mirrored from the first build including the 3 wheels.

Then add the final 2 wheels at the back and front end with the orange supports.

Assemble and add diagonal whites inside, on the bottom and on top for strength.

Finally attach to the backend.

Step 22: Make the Chassis Part 4: Hinges (2)

These are exactly the same as the other two hinges.

Mind that both the back and forward supporting legs slide in in the same direction.

Step 23: Make the Chassis Part 5: the Front End

The front end is a larger part, but again the basic box structure. To this the cab will be attached.

Just mind where all the different bits go, like the blue/purple and double blue pieces.

Also watch where a couple of grey pieces go.

Finally you have the whole basic chassis.

Step 24: Make the Steering Mechanism Part 1

First two bits need to be added to the frame before we build and fit the steering mechanism.

This is what needs to be build. It's a series of 3 grey rods running the entire length of the chassis.

Lay out 3 long grey rods and gradually build the whole mechanism.

Step 25: Chassis Fittings

Now the steering axle is in place, we can add all kinds of bits to the chassis: supporting rods for the hinges to level out pulling and pushing forces, support for the fixed axle etc.

The axle for he turning base is a bit of a fiddle to put in. I delayed this so you can turn the chassis upside down.

Step 26: Make the Subframe

This what you have to make.

The subframe is there to strengthen and support parts of the axles and wheels, preventing them from spreading outwards, and also to secure several small parts underneath on the side of the chassis.

The images should be clear enough to know what to do.

Step 27: Fit the Wheels

The wheels and steering axles have 3 configurations.

First is the fixed axle which is easily put in place.

Secondly are the front and back axle.
These need 3 grey to make the orange steering axle low so the long arm off the steering mechanism will fit and these wheels make a small radius.

Thirdly the inner steering wheels need a high steering axle so the short arm off the steering mechanism fits and produces a larger radius.

The two back steering wheels have the steering axle at the back of the wheels, thus steering in the opposite direction from the front wheels which have the steering axle in front go the wheels, obviously.

And so the wheels steer not only opposite, but also at different radii.
I'd like to know if this has been used elsewhere. I couldn't not find out and came up with this myself.

Step 28: Make the Cab

The cab is not ideal, but I like it anyway.
It has a suggestion of an engine with the black pieces.
It has the steering wheel on the roof, opening doors, rear view mirrors, a bumper, some lights.

Step 29: Make the Steering Control

First make the reduction gear axle and place it inside the cab.

Next make the actual steering column ad fit it to the roof.

It's not the best cab, but the impression is just fine and I'm might please with the whole steering setup.

Step 30: Make the Back End

At the back just one length on standard box needs to be added, but not on the full height.

Place the bumper and 'lights'.

Step 31: Make the Wheel Covers

The whole side has covers, partly made up by the supporting legs, partly with specially fitted covers.

Some planning of the covers is fiddly, because of tight snapping. You can remove other parts to free up holes so the snapping in is easier.

Step 32: Make the Supporting Legs

These are very nice if even I say so. Not just the looks, but they actually are fully functional. They are able to share the full weight of the whole crane.

They are made of two rows of yellow pieces and white rods. Two greens asset to connect this leg to the chassis hinge.

The weakest point is not only the hinge, but also the 90 degree snapped in grey pieces. Still, with all the strengthening I was able to come top with they really hold up very well.

The pulling force of the bottom hinge of the leg is quite large and really needs to be controlled.
Most important: the 90 degrees snapped in grey is covered by another grey which is held firmly if even very firmly held in place by a tan piece. This is difficult to get on but it prevents the grey from spreading and thereby unsnapping.

The legs are attache via a yellow rod into an orange rod inside the chassis which gives nice resistance, so the leg stays in position when swayed out.

Step 33: Make the Material Rack

Thuis is a bit of nonsens, but every crane has a place to stack material.
This holds the four types under the feet, the trolley and the rods for the mast.

Step 34: Finally: the Crane Build Up!

Not that the designing and building the crane wasn't fun, but building her up and folding her down is the biggest fun of the whole project, next to of course searching for the right construction solutions.

I hope you enjoyed this, build her, be inspired by her and be Knex creative!