EC750E Cylinder, linear actuators, pistons, etc...

The small cylinder problem. Lego linear actuators are 11 studs long, has an actuation length of 5 studs and a width of 2 studs. From the dimensions page for the EC750E the linear actuator (aka. cylinder) should be 19.5 studs long and 3 studs wide. This is clearly a grossly undersized cylinder. What if we could fuse two of them together. Would they still work? If connected plunger end to plunger end the new cylinder would be 22 studs long with a 10 stud actuation length. Unfortunately this does not work because the first cylinder can not spin around to activate the second cylinder. A simple solution to that is to let the driven end of the first cylinder to spin freely so that it can drive the second cylinder. This does work, but having the first cylinder not pull out from the driving axle becomes a problem if the cylinders are pulled out of instead of pushed into the axle. Another way to connect them is driven end to driven end. This leaves no shaft to drive, but this can be solved as whichever end will be driven simply has to be able to spin freely. There is another benefit to this arrangement, overall length is now 20 studs as one stud from each cylinder's driven end overlaps the other:

The overall extended length is 30 studs giving a better extended to retracted length ratio than the original cylinder.

Now the problem to solve is how to go about mounting this. The end that we choose to be the "plunger" end can be connected with a pin or axle as normal, but the "driven" end needs some way to be driven to spin around and handle both pull and push pressure just as the single cylinder's original mounting bracket. Thankfully Lego has a turntable that is just the right size for this.

The cylinder's driven end can be mounted to the geared portion of the turntable so as to be driven by gears or alternately the pictured grey axle connector with the 3L pin can be inserted so that it may be driven by an axle.

Lastly one could do both. That is have an axle and gear drive at the same time. For example one may need to drive a second cylinder from one axle source. Red axle powered by an XL motor drives a cylinder through an axle and the gear at the base of the cylinder drives the cylinder on the other side that lifts the boom.

This joint seems like it should work, but the small gears keep skipping because of the high stress of directly driving two cylinders under high load so this will have to be done in some other way.

Here is the overall view of how these double cylinders are used to mechanize the model's boom, arm, and bucket.