Converting rotary to linear motions and Beard trimmer
Hey friends, Happy Wednesday!
Answering the question I posed last week
How does the auto-rotate function work on your phone? At different orientations of the phone, the mass in the corresponding axis of the MEMS accelerometer slides accordingly due to gravity (discussed in last week's issue). This data is coupled with magnetometer (measures the magnetic field nearby to find the orientation of the phone with respect to magnetic north/south) and gyroscope (senses the rotation of the phone) to decide and rotate the display screen likewise. This deserves a separate blog post! :)
I aim to write my newsletter issues in a way one can follow them while traveling on a bus, having a coffee, waiting for your food, etc. Let’s jump in!
Rotary to Linear Motion mechanisms
An object is in linear motion when it moves along a fixed line, and in rotational motion when it rotates around a fixed point. On many occasions, the technical problems to be solved require us to design and produce a linear motion of some form (Example - The pistons in an engine).
We have traditional electric motors widely available which convert electrical energy into rotational energy, thereby producing power that can be used for different types of motion. But the challenge we face is that we first need to convert the rotary into linear motion. There are countless mechanisms invented to achieve the same, and they can be seen everywhere once you start noticing.
The popular slider-crank mechanism is used in car engines. This was invented in 1206 by Ismail al-Jazari (He has key contributions to robotics and is believed to have inspired Leonardo da Vinci. He has built a robot band, an automated drink serving waitress, the flush mechanism used in toilets, water clocks, and a lot more.) Read his Wiki if you're interested, he is someone who also excelled at art.
Scotch Yoke mechanism is predominantly used in actuators in high-pressure gas and oil pipeline. Beard trimmer uses the same. Watch this 1 minute YouTube animation to understand their design HERE
Other examples of rotary to linear motion are rack and pinion (used in orienting the wheels of your car when you rotate the steering wheel), scissor jack mechanism (used to raise your car), and Screw and nut (closing your bottle with a bottle cap).
While I’m writing this, I have this random thought (You can skip this and move to the next section and you probably won’t miss a thing!!) – A table fan has blades that rotate. And the output is that we get air directed towards us linearly. If we inspect at a molecular level, the air has random motion and is not constrained to move linearly (they are simply pushed in one direction and they can drift away). But if we consider it as a whole, can I argue that this is a rotary to linear motion?
Blog post
My blog post S1E2 on beard trimmer is out! Read it HERE, happy learning!
Beard Trimmer Math
Just thought I’ll include a math section to paint a picture. The motor used in a beard trimmer is generally an 8,000 RPM one. As it’s using a scotch yoke mechanism - for every rotation of the motor, the blade oscillates back and forth once. Conservatively choosing the travel length of blades as 1 cm from end to end, the speed of the blade comes out to be 2.7 meters per second.
Question of the week
After reading the blog post, what other alternatives do you think can be used for the Scotch Yoke Mechanism? There are other options like slider crank mechanisms too. Why do you think they weren’t chosen? Share your thoughts by replying to this email, and we can have a discussion. I’ll answer this in next week’s issue.
I’m thinking of writing about bladeless fan or the pulse rate monitoring algorithm in a fitness watch for the next episode S1E3. Also, let me know if you’d like to read about a specific gadget/device.
Have a nice rest of the week, and take care!
Until next Wednesday,
Chendur
