# What is this area of study called?

Goldenwheatfiel
Hello all, I am a freshman enrolled in Mechanical engineering.
Growing up, I have always been fascinated by the LEGO technic toys and the real-life machines and wondered how do engineers design these machines and mechanisms.

When someone design a complex machine or a mechanism, how do they figure out the size of each components(gears, axle, pulleyes...etc) inside the machine? And how do they decide on what machine elements they are going to use and place them in which places inside the machine..etc ? Decisions on shape of each elements..etc
They must have the ability to see the big picture in the back of their mind and visualize the the whole mechanism working to achieve the desired functions.

As above, I want to know more on this area. But I do not know where to look for.
I asked a professor and he told me to look into synthesis or machinery.

Help would be greatly appreciated!

Sincerely,

Mentor
I found this pdf on functional synthesis where it goes into teaching computers how to be architects. I imagine a similar idea is used when designing machinery.

http://catdir.loc.gov/catdir/samples/cam033/2001025164.pdf

As an example, you are presented with a problem that requires some mechanical solution so you synthesis some idea. You test it and discover some weakness like the gearing takes too much strength to move so you adjust the design adding more gearing and now you find you must turn the primary gear too many times and so you continue to work it to minimize the strength and the number of gears... To get the final product.

I assisted a machinist one time to repair a tower clock where a gear had sheared and I asked him why that happened. It was part of his solution as he purposely used a softer metal for that gear realizing that in winter the mechanism would freeze up and rather than replace the whole gearing he designed in a simple fail point that meant fixing one gear instead of the whole mechanism.

Anyway, there are a lot of factors that drive a design that come into play and the experienced engineer has recipes for each problem.

Mentor
On a related note, I like to play with Knex building sets and I noticed the struts had a curious ratio.

Each strut was bigger by a factor of sqrt of 2 which made sense since you could easily construct 45 degree right triangles with it that were of various sizes. the toy designers must have started out with that premise and the rest of it came together.

In the case of LEGO, the original sets were the basic building blocks and as they evolved they kept the original design and added more components that fit in. Now LEGO has a gazillion parts that all Interoperates to varying degrees to build pretty much anything. Note though that when you try to build something new it's sometimes hard to get the design right because the parts impose certain limitations that you must either compromise on or work around.

timthereaper
In mechanical engineering, the closest study areas to that kind of product are kinematics and machine design. Kinematic analysis teaches about the basic concepts of position/velocity/acceleration/force analysis with emphasis on mechanics of kinematic systems (like 4-bar linkages, gear systems, cams, etc). Machine design covers mechanics of materials but with emphasis on application for machinery along with things like bolted joints, fatigue life, etc.

However, I would think a lot of that is just good product design. Toy designs can be complex, but most of the time you don't have to worry about things like fatigue in the parts or calculating stresses the material.

Goldenwheatfiel
Thank you jedishrfu and timthereaper ! You helped me a lot!