Crank rocker example

thingiverse

# TL;DR This is an example of a crank rocker four bar linkage that I created as I've been reading on kinematic mechanism, linkages, and grashofs law. The print details and settings I used: - PLA - 10% infill density (though I'm sure you could get away with 5% or 0 with an extra wall perimeter) - Supports everywhere (to help with the overhang on the pegs) - 0.2 layer height - 0.4 mm nozzle And you'll need to print the following part quantities: - 1 base - 1 long peg - 3 peg wedges - 1 crank handle - 1 crank arm - 1 long bar - 1 rocker - 2 short pegs - 1 base foot The wedges fit pretty snug so be careful slotting them in. I haven't broken a peg, but I can see how you could. Also, some of the videos showing in the preview aren't mine, they're links to videos I found helpful when studying this topic. I guess thingiverse looks for video links in your summary and pulls them up. I can't remove them so just know some of the vids are references I found helpful and not my creation. # The detailed explanation My current project as of this thing creation is a treasure chest that will open and close, play sounds, and trigger LEDs within the box when you walk up to it. This will be the first project I've worked on where I'm trying to incorporate motion and a kinematic mechanism. I don't have any background in mechanical engineering outside of, you know, legos, so I've been doing a lot of article reading, video watching, and 3d modeling trial and error-ing to learn the what, why, and how on opening and closing the box. I've been doing most of the testing inside of Fusion 360 with joints to simulate the movements. My models either kept locking up when I hooked them into the model of the treasure chest or would move erratically when I spun them freely. After doing more searching and reading it turns out the joints were failing because they were not measured out and arranged according to [Grashof's Law](https://me-mechanicalengineering.com/grashofs-law/). After studying this concept a bit more I created a fresh proof of concept model for each of the mechanisms that are a result of applying Grashof's equation and the specific arranging the bars. I knew I wanted the crank rocker arrangement for the treasure chest project so I took a bit more time with it's example so that I could model out a 3D printable version and here it is :) I'm posting this thing after getting the first working version printed (I had to do some adjusting and scaling in Fusion 360), so there's still a bit of room for improvement. I'll update the parts as I go. # Resources that I found helpful while studying kinematic mechanisms: - [helpful article with fantastic interactive simulations](http://dynref.engr.illinois.edu/aml.html) - [helpful video with visuals of linkages working](https://www.youtube.com/watch?v=Vh8r_Cpfb8Q) - [a very clear explanation of grashof's law](https://me-mechanicalengineering.com/grashofs-law/) - [nice video on the crank rocker mechanism](https://www.youtube.com/watch?v=s6Y_L4rncN4) Here's more than this. I'll try to post more links later.