In 1991, LEGO Technic introduced the Flex System . With two generations it was used in several Technic sets, between 1991 and 2003.
The Flex System was a brilliant LEGO Technic realization, based on real concepts, but which was rarely used to its fullest potential. It was only ever included in 17 LEGO Technic sets, probably due to the fragility of its cables if not handled with care.
Probably the most important sets using this system were the:
- 8856, Whirlwind Rescue which was on the sets introducing the Flex System in 1991.
- 8479, Barcode Multi-set from 1997 - IMHO the pinnacle of the LEGO Technic studded sets.
This system was used in a few main applications:
- A flexible push-pull cable system (Bowden cable) in a standard link configuration, to transmit force around curves, corners or even straight links.
One pair of these combined with some other specific parts, allowed to build a cyclic motion for the main rotor in the large helicopter (8856).
- A diagonal brace system for trusses and booms, like in 8074 and 8856.
The Flex System main components:
- The central cables - A flexible plastic cable with a small neck on either end used for clamping. The cable was produced in a variety of lengths over the years, from 4L all the way to 33L.
- The sleeves - A flexible and hollow cylindrical tube which is not brittle like the inner cable. It serves as a sheath for the cable, guiding it through the structure and preventing buckling under compression loading. The same type of tubbing became later also used as an extension and connector for pneumatic tubing.
- The connectors which were available in a few configurations and had one slot with a tab to grab the necked portion of the cable in each end. The cable snaps into place when inserted from the side.
The configurations available included a pin connection (part 2900) and one ball joint connection (part 2901). Both were later replaced with different versions which were easier to install and less prone to damage the cables (respectively parts 6643 and 6644).
The 2nd generation connectors included also a double-end with central pin connection (part 6642).
Below, two great examples on how the Flex System was used in the sets above mentioned and what it allowed to achieve, without complex and space consuming designs with shafts and gears.
On the left one illustration from 8479 building instructions, showing how the two Bowden cables control the front claw movement and another two Flex cables to enforce arm stiffness on each side.
The CAD representation on the right, shows the control of the Cyclic mechanism from a stick in front of the pilot's seat. There is one flex cable and sleeve for each axis. Fore and aft motion of the stick pushes and pulls the cable using a ball joint. The flex cable runs up to a link which lifts the swashplate using a suspension control arm. Lateral motion of the stick rotates an axle which runs aft. At the end of the axle is a ball joint which connects to another flex cable. This flex cable attaches to a ball joint on the side of the swashplate.
The cables are made of a different type of plastic than regular LEGO parts. While flexible up to a point, can easily end up with brittle fracture if bent too far. This is especially a problem when removing the ends. Later, different connectors were introduced which made it easier to attach and remove them.
Given a bit of an explanation about the old Flex System, let us ask your opinion.
Would you like to see the Flex System returning into future and even more realistic Technic sets?
Choose one option from the poll on the right colunm, running for the next two weeks.
If you have specific concerns regarding the Flex System parts fragility, you may express them leaving your comments to this post.