Hi all, been a while since I joined, finally gotten a chance to start building something (after learning a lot from yours on this site! ). I am starting a 1:14 scale RC model of a Cat 340D excavator, based on this die-cast model that I found:
I took side/top/bottom/front photos, and traced them into a 3D design in Fusion 360 so I could scale it up and print out model-size patterns to build from. I would love to make it fully hydraulic, but thought I would give a lead-screw based electric version to see how it works out, mainly for cost reasons. After finding the leadscrews and gearmotors over on ServoCity's website, and doing some experimenting, I wound up with this design for the pseudo-hydraulic pistons:
The leadscrew is the pale blue down the center, the follower is the pink bit inside the orange tube. The piston tube and the cylinder were made from DOM steel tubing, which are a loose telecoping fit. At the back, the red part is a steel turning, riding in a set of ball bearings to take the forward/back thrust. The light green section fits around the bearings, and connects to the main cylinder tube. Here is what the finished parts look like:
And as assembled into the first full unit:
I put a u-joint on the drive rod on the end (the red part in the drawing above), so I can put a gearmotor down inside the boom. I'll put limit switches inside the boom on the pivots, to keep it from over-extending, and drive the piston with a ESC from the radio. As a test of the power it has, here is a short video showing the movement with it driven by a variable power supply set to 9 volts:
https://youtu.be/fryEKQaH3uY
It worked quite well, lots of force in both directions.
Now that I know it will work well, I'll make up the rest of the cylinders, and start in on the booms which will be framed in steel and clad in aluminum sheet. Progress on this will be a little spotty, since I am in the middle of a build of a 1/4 scale Stanley Steamer auto engine. If you are interested in that, am posting a build log over on the Model Engine Maker forum. There is also a build of a model of the Marion Model 91 steam shovel (not RC) that is near me in LeRoy NY, built at 1:16 scale.
Chris