The Construx Elevator


I have used the old Fisher Price Construx since I can remember, always kept it in good shape but with age the plastic has become a litle brittle and needs greater care then as a kid. I was trying to come up with something simple to try to build and control with the Omron PLC-PC, and after a few different designs ended up with an elevator.

The PLC PCSo to keep things nice and simple I decided I would do a detailed CAD design and show all the interconnections to make it all that much easier to build and wire. All the Construx pieces are the same size, how hard can it be? Well from there comes the great idea that not only is CAD required but a 3D model complete with rendered textures is a given. At this point I should explain that for me the design and building is all the fun and I have no plans whatsoever to actually find a use for this.


As with any child-like Construx project, I ended up having to strip down the bottom to get it built up on the the top - running out of pretty much every part along the way that I needed. The different levels at one point had actual floors, but they were salvaged to keep building up...

For the limit switches, a hot wire was located directly on the elevator and went up and down with the elevator cable (string) . Each floor had a wire fed too it, with the end stripped back a few inches. The middle of this stripped end was coiled to form the switch, with the rest of the bare end taped up.

Building limit switches with strips of bare wire wasn't overly successful, they constantly bent out of position and often didn't make contact long enough for the PLC to read them. From the photographs you can see large gobs of green electrical tape, used to protect the end of the wire which was looped around to make the "switch" .


The project eventually progressed into dismanteling old VCRs and CD-ROMs for motors that I could use to run the elevator, but not having any plan as to speed or torque it ended up being whatever motor would mount to the Construx and have enough power to lift the elevator up. In the end it is a VCR motor that was way too fast.


So with the limit switches bending, the motor way to fast and the counter weight constantly falling off it had its share of problems, but with some rubber-band combinations on the pulleys it would go from floor to floor for a while before it got twisted out of proportion.