Build Ergonomics

Intro

Build ergonomics - the level of effort for a build, can be evaluated meticulously. We need to define:

1. Number of steps
2. Time involved
3. Difficulty

Number of Steps

Any single step can be defined as one operation with 2 hands. For example, take a nut and insert it into another 3D printed piece. That is One Step. Or, take a nut and put it on a bolt. That is one step. Done manually - that is a minute - done with an impact wrench - it's seconds.

Time of Build

Counting the number of steps as such gives an idea of build complexity. A build with 3525 steps - with a minute per step, would take 60 hours to complete. That is a realistic estimate of, say, a tractor build.

About one minute per step is a reasonable, rough estimate for many actions. This principle is an effective way to assess overall build time: simply take the number of steps: say 254 - and guess that it it took ~4 hours to do a build.

To reduce build time - we can assess each step - and see what optimization can be made: such as using power tools, CNC tools, or redesigning for simplicity. The last point has the most impact on build time: it separates good design from bad design.

Difficulty of Build

In terms of human stamina - the most important determinant is weight of the build. Lifting 1 kg 1000 times is much easier than lifting a ton one time. Heavy objects fatigue a builder - such as when building a house or a tractor.

Jigs and hoists can provide mechanical advantage to make the work easy. Self-supporting design can make it easy: when you don't need to continue lifting/holding something to perform an operation, but instead do it on the floor, or on a support so that the only difficulty is moving the item into place.

Difficulty can be quantified, simply by totaling the pound weight of all the materials - every time they are handled or moved. For example, for a 3D printer, which ways 25 kg - the total weight lifted may be 250 kg - if you consider moving a certain part through multiple steps. For example, 1 kg of the frame may be moved 10 times, adding 10 kg to the weight. The ultimate limit of this example is 25 kg - where each part is moved only once.

The difficulty can be further clarified by multiplier for holding/moving things. For example - just lifting the object, which takes on the order of 1 second - is different than lifting and holding that object for 1 minute. Holding that object is then roughly 60x harder - as each second of holding is roughly comparable to one second of lifting.

Multiplying weight by time results in weight-seconds - a useful ergonomics measure. Thus, an useful measure would be weight-seconds. If a person is using a forklift to lift an object, the effort there is only the force equivalent of pushing a hydraulic control lever for the forklift, etc.

For example, lifting 1 kg has a kg-s effort, while holding it for 60 seconds has a 60 kg-s effort.

Complexity

Design determines complexity of build. Complexity can refer to the number of build steps required to build in a certain function. If a designer pays extreme attention to build complexity, then they will design something for easy manual assembly. Besides design - complexity can refer to tooling. Are simple, accessible tools being used? And most importantly - is it a simple design? That means: the simplest way to accomplish a function - in terms of materials, geometry, or principle of operation.

Part of complexity - is access to documentation that reduces complexity. For example, having easy-to-access tools and instructions for deconstruction.

In today's world - sleek-looking black boxes dominate the product landscape. What about designs that are designed for easy repair? The sleek-looking black box is good design - if it can be repaired/reused. For example, it appears that Tesla cars are not good in this regard - see Tesla Repair.

Links

• OSE Instructional Guidelines