Free Body Diagram (Assembly Kit)

Motivation

As a Mechanical Engineer I have spent multiple hours drawing free body diagrams and calculating forces, moments, stresses, deformations and so on. But, although I was using my white board quite often for that sake, I came up with the idea of magnets in the shape of free body diagram objects long time after.  I assumed that it would be quite helpful to get a sense of how mechanisms move or how bodies deform. Hence, making this kit of free body diagram components which can be easily moved on the black board.

Usage

Assembling a free body diagram works in the same manner as you would draw it by hand:

1. Placing the supports
2. Stacking rods or beams on top
3. Adding force elements such as springs and dampers

However, using the assembly kit involves the additional steps of adding placeholder joints and cap joints.

A huge benefit compared to traditional sketches is that you can easily move all parts to the right positions.

Included parts …so far

Currently, there are four object types you can print. However, some object types subdivide even further:

• supports - either fixed or loose
• joints (standalone) - either as type cap or space
• springs - either of type torsion or tensile
• beams - represented as a polyline
• slider - sits directly on a specific rod (This will be added on GitHub in the future. For now, there is only a small collection on here)

• rods - represented as a polyline where each node is actually a joint. Furthermore, intermediate joints are equipped with an automatically generated stiffening. In addition to this there are engravings in the middle of each segment showing the distance between the adjacent joints.

In the future, objects such as beams, arbitrary polygons and further joint types are added.

The models provided here are only a minor collection of what is possible. If you want to configure parts on your own, I recommend checking out the generator on GitHub which you can access here. The Generator is written in Python and I tried to make the use of it as simple as possible without providing an extra UI. For the initial setup you just need to follow the steps in the README file.

Printing advice

General

I printed the models on a Creality Ender S1 Pro using black and white PolyTerra PLA-filament. The slicer settings in the Cura Slicer were:

• Temperature: 210 °C (Nozzle), 60 °C (Printing Bed)
• Printing Speed: 50 - 80 mm/s, except for the first layer (15 - 20 mm/s)
• Layer height: 0.2 mm
• Number of top and bottom layers: 3
• Number of contours: 3
• Infill: Lines, 20 %
• Supports: None
• Pause: at height = 3.6 mm (for inserting the magnet) and at height = 4.4 mm (for changing the filament)
• Ironing enabled

Please drop a comment on what worked best for you. Happy Printing!

Printing the Slider

Producing a rod with a slider requires slightly more effort:

1. Printing a rod which is meant to carry a slider using the advice given in the paragraph above. The corresponding STL-files contain “slider” in their names and can be found in the “rods” folder.
2. Printing the actual slider using three pause commands:
   • z = 4.2 mm for inserting the rod
   • z = 5 mm for changing the filament
   • z = 9.2 mm for inserting the magnet

Further remarks

• I set the tolerance of the chamber diameter for the magnet to 0.16 mm in the CAD-model. A little force is required to insert the magnets . If the tolerances are too tight for your case, you can change the diameter in the CAD-file yourself or adjust the diameter by scaling the model in the slicing software. I had to use a tight fit, because the magnets tend to get stuck on the magnetic fan cover of my printer - Yikes! 
• You might have to check if pausing the printing process can be handled by your printer. It mainly depends on the command the slicer is adding to the .gcode-file and if your printer can understand it. For most printers this should not be an issue, but for the Ender S1 Pro it get's weird. See the appendix for more information on that.

Changelog

[10/06/2024] - larger width of rods for clearer print of text

[10/11/2024] - added beam object to the collection

[10/18/2024] - added slider and slider specific rods to the collection

Appendix: Pausing and resuming printing of Ender S1 Pro

For adding the command to pause the print, I used the Cura Slicer. There, you have to navigate to

Extensions>Post Processing>Modify G-Code

Then, a new window with the title “Post Processing Plugin” should open. There you can decide where to stop and at which location the printer should park. You might want to set the Standby Temperature to your printing temperature so your printer is up and ready to continue. For Ender S1 Pro, you can use the Method “BQ (M25)”.

If you are done configuring the pause command, you can slice the model and start the printing procedure. If the printer has paused and you have performed the intermediate steps (inserting the magnet/ changing filament), I assume  you want to resume the printing process - here comes the weird part. The UI of the printer will only show the pause and stop button. Don't press the pause button! Instead, tap the menu at the top where you would usually change the printing temperature. Then, head back to the progress site. Et voila, the resume button should be visible. You can press it to continue printing. For a more visual explanation, you can refer to this video here (not mine).