The original 8868 Air Claw Rig is a great model, packed full of amazing pneumatics but:-
a) The motor & pump should be in the crane body to avoid so many pneumatic tubes going through turntable.
b) The heaviest item (the battery box) should be used as a crane counter weight.
c) Improve the chassis to match the complexity of the rest of the model.
So the task for this design was to:
1. Mount the pneumatic pump & battery box in the crane body.
2. Use double rear tyres.
3. Add working suspension to the axles.
4. Add pneumatic stabilisers, essential with a working suspension.
5. Add air tanks to the pneumatics.
6. Make the pneumatic arm “fold up” to stow away neatly.
It quickly became obvious that to incorporate all these features my version of the Air Claw Rig was going to be somewhat bigger. Rather than just make it longer I decided to maintain something like the original proportions by using the bigger 24x43 wheels rather than the 20x30 of the original. This view shows how complex the chassis has become!
The first element was the double tire rear axle as this set the overall width (22 studs). Then came the suspension. Trucks do not use independent suspension (as on all the big Lego cars) but rigid axles sprung from the chassis. The photo shows one of the rear axles with its 4 spring units. Note the first stage gearing within the axle to relieve the torque on the universal joints.
This picture shows how the axle slides up & down within the chassis. There are 10 spring units in total, 4 on each rear axle and 2 on the front or in other words there is one spring unit per tire. I now had the general layout of the vehicle so next came the crane assembly.
To make the arm fold up neatly I adopted a 3-section layout. The increased arm size also suggested that twin cylinders would be required for the first section and this in turn meant a twin cylinder electric pump. After much experimenting I had an arm that folded neatly together with a reasonably compact crane body housing the pump, battery pack and the control valves, but the amount of pneumatic tubing was beginning to look daunting.
Next came the stabilizers. Those on the 8455 Back Hoe looked the part; they fold up nicely and with a slight modification can include a hinged pad.
The original 8868 had two built up fuel tanks. I used the same design but actually sealed and super glued the components together to make a working air tank. I not sure Lego would recommend this but it works fine.
The fact that I now had pneumatics on the chassis meant either an additional pump and battery box or a pneumatic line from the crane pumps through the turntable. As I wanted to retain continuous rotation of the crane a non-Lego part was required – a pneumatic swivel. This also allows the air tanks on the chassis to be connected to the crane pneumatics.
The opening hood/bonnet is particularly neat. The normal way of mounting the Lego engine cylinders makes a 90 degree V. This is wrong for a V6 but right for a V8, so that what it got. A nice feature is that the engine is mounted in such a way that it can be lifted out complete by the crane arm. You can’t do that with the original 8868!
The final body elements are really cosmetic but make it look the part although I think it would look better with more yellow bits.
This big heavy model is still not quite complete as powered crane slewing (Technic micro motor?) is still to be added. Note that even though when fully extended its arm is nearly twice as long as the Standard Air Claw Rig overall the vehicle is no longer or taller.