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State of the art

Here I will put some research I’ve done on the subject as well as other project available online. While I was working on this project, the interest in 3D printed actuators raise and became a great challenge for every robotics enthoutiast. What a chance to work with the opensource community !


Strain wave gearing (Harmonic drive)

Strain wave gearing (Also known as harmonic gearing and harmonic drive) is a type of mechanical system that has no backlash, high compactness and lightweight. They also have other advantages such as :

  • High torque
  • Coaxial input and output shaft
  • Gest reduction/ volume ratio of known reducer

Strain gear offer ratio from 30:1 up to 320:1 in the same space in which planetary gears typically only produce a 10:1 ratio

The basic concept of strain wave gearing (SWG) was introduced by C.W. Musser in his 1957 patent.

Here is the main idea. I plan to use a Nema 17 stepper motor as my main actuator. Nema 17 are very common nowadays and cheap thanks to 3D printer manufacturer.

Harmonic gearing are composed of 3 parts :

  • The flex spline ( flexible gear )
  • The circular spline ( static gear)
  • A Wave generator ( eliptic bearing )

The reduction ration can be calculated this way :

Cycloidal gearing

I also want to explore an other kind of reducer named cycloidal gearing. This type of gearing seems easier to make but also weaker… The gearing ratio is lower since it has less teeth. Maybe the solution will be just between cycloidal gearing and harmonic drive.

Servo motor

Usually, kid learning robotics may use easy to use actuators. Modelism servomotor are now mainstream and cheap. There are also very simple to use. Want I like with servomotors is how simple it is to control them. You can basically tell them where to go (angular position) and they will to there best to reach the requested position.

The servomotor control il pretty much the same for all prototyping servos. They are using pulse width modulation to be controlled using only 1 command wire.

This may be a cool feature of my final project.

Other project

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Last update: June 28, 2022