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A simple reverted gear train consists of two shafts each of which carry multiple compound spur gears. A compound gear consists of two gears of different pitch diameters attached to one another. This reverted gear train consists of 4 double spur gears each with a gear ratio of 3:1. This assembly has two configurations. The 1st configuration allows the user to convert a a slow shaft input speed to a fast output speed. The 2nd configuration allows the user to convert a fast shaft input speed to a slow output speed. The user can change from config. 1 to config. 2 simply by dis-engaging the crank component from one shaft and re-engaging it to the opposite shaft. This device teachers the user the fundamental engineering principles of shaft speed ratios, gear ratios, and torque.

The different components of the device are shown in the BOM table.

The Lesson Plan for the Geneva Mechanism is attached to this page for the Instructors who wish to teach students about this device.

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.

Step 1: Print Reverted Gear Train

Download the 5 .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 in the following orientations;


1. Compound Spur Gear: Horizontal (Face down)
2. Arrow pin: Horizontal
3. Crankshaft: Horizontal
4. Base: Vertical (Bottom down)
5. Shaft: Horizontal (Ensure the key is facing 12 O'clock)

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 Reverted Gear Train:
Ensure to sand both shafts to get rid of ridges and sharp points. Ensure to file/bore out any thru holes on the assembly.

Step 3: Assembling the Device

Now that all the parts are refined they are ready to be assembled to create the Reverted Gear Train.
Configuration 1 (fast to slow)
  1. Insert the Short shaft into the base (ensure the key on the shaft slides through the keyway cutout on the base)
  2. Insert the Short shaft through the Double spur gear (small gear facing away from insertion point)
  3. Insert the Short shaft through the second Double spur gear and finally through the second base column
  4. Insert the Arrow pin into the short shaft
  5. Insert the Crank over the Short shaft until you feel it click into place
  6. Insert the Long shaft into the base (again ensure the key on the shaft slides through the keyway cutout on the base)
  7. Lock the Double spur gear into place with the respective gear on the short shaft. Then insert the Long shaft through the Double spur gear
  8. Insert the Long shaft through the second Double spur gear and finally through the base column
  9. Insert the Arrow Pin into the Long shaft to retain it
  10. Insert the Arrow Pin into the Long shaft to retain it
  11. Insert the Crank over the Long shaft
Congratulations! You now have a fully functioning Reverted Gear Train!

Configuration 2 (slow to fast)
  1. Disengage the Arrow Pin from the Long shaft
  2. Push the Long shaft so that the key on the shaft becomes engaged with the second Double Spur gear

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