Introduction: 4 Bar Linkage
There are 4 configurations for this assembly, each of which will teach a different lesson to the user.
Kinematics Associated with this Device:
- Bar Linkages: In engineering there is a standard classification of four-bar linkages called the Grashof condition. A four-bar linkage satisfies the Grashof condition when Equation 4 is shown below;
s l < p q (4)
The different components of the device are provided in the BOM table displayed
Post Processing note: If you are printing with an FDM printer you should expect small ridges on parts where the extruder last touches the piece. Carefully inspect each piece after they are printed for these small imperfections as they will hinder the operation of your device.
 M. M. Wachowski, T. A. Walde, P. Balcarek, J. P. Schüttrumpf, S. Frosch, C. Stauffenberg, K.-H. Frosch, C. Fiedler, J. Fanghänel, D. Kubein-Meesenburg and H. Nägerl, "Total Knee Replacement with Naturl Rollback," Annals of Anatomy - Anatomischer Anzeiger, vol. 194, no. 2, pp. 195-199, 2012.
 M. Muller, "A Novel Classification of Planar Four-Bar Linkages and its Application to the Mechanical Analysis of Animal Systems," Philosophical Transactions: Biological Sciences, vol. 351, no. 1340, pp. 689-720, 1996.
 P. '. Hayes, S. Young and Doddy, "Buyer's Guide to Mountain Bike Suspension, Part 2," BikeRadar, 2010. [Online]. Available: http://www.bikeradar.com/gear/article/buyers-guid... [Accessed 2 October 2013].
 Wikipedia Contributors, "Four-bar Linkage," Wikipedia, The Free Encyclopedia, 5 September 2013. [Online]. Available: http://en.wikipedia.org/w/index.php?title=Four-ba... [Accessed 2 October 2013].
 E. Söylemez, Mechanisms, Ankara: METU Publication #64, 1999.
Step 1: Print 4 Bar Linkage Parts
Download the 13 .stl files and upload them to your 3D printer's system. The quality of each part will increase depending on the orientation of the part on the print tray. Print each respective part based on the orientations shown in the images provided.
Step 2: Post Process Individual Parts
Based on the brand and quality of your 3D printer, the tolerances of your parts will vary so your parts may not need any refinements, or they may need a lot. The steps we have provided are the techniques we found were useful for making the device run as smoothly as possible. The following tools were used to refine the parts; file (varying sizes), fine sandpaper, Dental picks.
For 4 Bar Linkage:
Ensure to bore/file out any thru holes so that the bars turn around the pivot axles with ease, but at the same time will allow the shape to remain in a polygon shape. Sand down the pivot axles as well.
Step 3: Assembling the Device
- Insert the Crank-Crank adapter into the base
- Insert 4 bar arrow pin into the Crank-Crank adapter
- Insert the 4" linkage over the Crank-Crank adapter
- Insert the 2" linkage over the Crank-Crank adapter
- Insert 4 bar Long arrow pin into 2" Linkage
- Insert the 4 bar pivot axle into the 2" linkage
- Insert the 6" linkage over the 4 bar pivot axle
- Insert the 4 bar short arrow pin into the 4 bar pivot axle
- Place the 7" linkage so that it fits concentrically with the 4" and 6" linkage bars
- Insert the 4 bar pivot axle into the thru holes of the 7" and 6" linkage bars
- Insert the 4 bar short arrow pin into the pivot axle
- Insert the 4 bar input handle into the 7" and 4" linkage bars
- Insert the 4 bar long arrow pin into 4" linkage bar and input handle square thru hole
Note that the base linkage for this configuration is the 6" linkage bar, the leftmost bar is the 2" linkage bar the rightmost is the 4" linkage bar.
Note that the base linkage for this configuration is the 6" linkage bar, the leftmost bar is the 4" linkage bar, the rightmost is the 2" linkage bar.
Note that the base linkage for this configuration is the 7" linkage bar, the leftmost bar is the 4" linkage bar, the rightmost is the 6" linkage bar.