An instructable for the K'NEX Mobile Crane Truck version 3 (https://www.instructables.com/id/KNEX-Mobile-Crane-Truck-versions-2-and-3/).
Instructions start on the next page and will be shown sequentially by the order of the pictures. I will warn you that the gears may slip and make a loud snapping noise and am therefore not responsible for any broken parts, human or plastic. :)
https://www.instructables.com/id/Knex-Supercar-Instructions/ --Imperar's Supercar. I have implemented the steering module as well as the wheel module from that car into my crane truck, so credit of that goes to Imperar.
http://www.jenniferclarkbass.com/lego/demag_crane.htm --the LEGO inspiration behind the K'NEX crane truck series.
Step 1: 1. Lower Middle Chassis
This is the lower middle section of the chassis.
(a) Connect each part together.
(b) The steering mechanism. Blue rod attached to orange connector attached to red rod through a yellow bevel gear attached to orange connector attached to blue rod. Pieces in between are for support, which will be shown in the next step.
(c) Step (a) and (b). White rods connect to blue and green connectors.
(d) Bottom part of the middle.
(e) Step (d) and (e). Be aware that the white rods go through the green connectors' holes. If you are unsure of what is going on with that, I recommend you look at the following link: https://www.instructables.com/id/S1MLHRGF4AQNWA1/
Step 2: 2. Steering Module and the Rest of the Lower Chassis
The steering modules:
(a) Built very similarly to the Imperar Supercar, a few of the pieces have been replaced by other pieces and others omitted. See that step for the original design: https://www.instructables.com/id/S1MLHRGF4AQNWA1/
(b) & (c) Another view of step (a)
(d) Rear steering module
(e) Rear steering module + middle chassis
(f) Front steering module + middle chassis
(g) Front + middle + rear. The six (6) blue rods protruding from the sides will become the axles.
(h) The completed bottom of the chassis.
Step 3: 3. Truck Structure: Rear
Now we will build the top part of the chassis. Note that any part of this is open to customisation (yes, including the lower chassis).
(a) The rear part. Build as shown.
(b) The top section of the rear part. Note the two white crossrods connecting to the yellow connectors, along with the white rod pointing downward. Other than that, a simple blue & yellow rod lattice.
(c) Bottom view of (b).
(d) Connection of top and bottom parts.
(e) , (f), (g) Different views of the rear part.
Step 4: 4. Truck Chassis: Crane Base
(a) The side rims of the base
(b) The base of the base. The bottom part of the blue connectors will connect to the white rods on the wheel modules
(c) The crane base.
(d) The bottom side of the crane base.
(e) Step (b) and (c). The crane base rests on top of the bottom base with no rod or connector connection.
(f) &(g) Add step (a).
(h) Connect the base to the rear
(i) Base connection to the rear
(j) Another view of (h)
(k) Base + rear complete
Step 5: 5. Truck Middle Top Chassis
(a) The two sides
(b) The top part
(c) Bottom view
(d) Left side, view from the rear
(e) Left side, view from top
(f) Right side, view from the rear
(g) Right side, view from top
(h) Steps (a) & (b)
(i) Crane base connection from previous step
(j) Close-up of the front part of the base connection
(k) Another view of (i)
(l) Rear + Crane base top connected to bottom
(m) Step (h) connected to the rest of the chassis
(n) Not quite connected from step (m)
(o) Close-up of steering module
(p) The model so far
(q) Another view
Step 6: 6. Driver's Cabin
This is where you can really go crazy with the design; here I have opted for a simple design. The pictures show the different views of the cabin, the connection between the cabin and the rest of the model, and the model completed up to this step.
Step 7: 7. the Crane Superstructure
I've also kept this step to open speculation; the pictures show a general idea of what it can look like.
From the motor to the crane boom, it has been geared down three times with small blue gears to large yellow gears. The "hydraulic" pump is no pump at all; it provides minimal support to the boom. The long grey rods may be used for the boom, although its black counterpart provides better stiffness.
Step 8: 8. Almost Done...
(a) Crane's wheel base on the truck.
(b) Another view of (a)
(c) Crane is now on the wheel base. Close-up of the green rod through the red connector of the wheel base.
(e) Outriggers. Make 4 pairs of these.
(f) Complete outriggers.