In this project I made a 3D-printed Differential. Designing this really was a good practice for my designing skills. I never really worked with gears in my designs before. Also, this differential was a very interesting subject. Every car has one, so we depend on it quite often.
Besides all of that, I learned something about gears and gear modules. All and all very useful. Hope you learn something too.
What is a differential?
The word ‘Differential’ has multiple meanings and use cases. In mathematics it refers to infinitesimal differences. Also known as, the derivatives of functions. But what we are looking at is the mechanical differential. “This is a gear train with three shafts that has the property that the rotational speed of one shaft is the average of the speeds of the others, or a fixed multiple of that average.” (Wikipedia,https://bit.ly/2zO6T0m) So, what does that mean? To clarify, we need some pictures.
First let’s have a look at what we see on this picture.
- Ring gear (Purple)
- Planetary gear (Green)
- Sun gears (Red and Yellow)
This picture gives an example for a differential with two equal forces on the sun gears. This means the torque from the ring gear is equally divided over the sun gears by the planetary gear. Resulting in the sun gears spinning the same rate.
When a force is applied to one of the sun gears, in this instance the red one, it creates a force allowing for the planetary gear to spin. When it spins it transfers this loss of speed to the other sun gear, thus the yellow sun gear will spin faster. By using this system, the force on both sun gear’s remains the same by allowing them to spin at different speeds.
Why would we need this?
The best example why one would need a differential is the automobile. The differential is utilized between the two driven wheels of a car. When a car takes a turn, the inner wheels travel a shorter circle than the outer wheels. The wheels reach the end of the circle at the same time though. This means the outer wheels must spin faster. To make this happen we need the differential. What’s more, the differential keeps the forces on both driven wheels the same. Resulting in more traction on the road. (picture of tire tracks)
This object was designed using Autodesk Inventor. This is a software package from the Autodesk company. Using this software, I made use of the gear design accelerator. This made it easy to generate the gearwheels needed for my design. After modifying the gears, I spaced them in a way it all fits.
For this model I used regular PLA for all the 3D-printed parts. Al parts where printed with a 0.15mm layer height. Except for the sun gears and the planet gears. Those were printed with a 0.10mm layer height.
- 11 3D-printed parts https://www.myminifactory.com/object/3d-print-91511
- 1 35mm motor with 2mm shaft
- 5 M3 bolts 25mm
- 6 M3 bolts 10mm
- 2 M3 bolts 45mm
- 13 M3 nuts
- 4 short woodscrews
- 1 piece of wood
- 2 15x30x10 mm bearings