If all teapots had no date of manufacture stamped on their bases, we wouldn’t be able to differentiate a modern one from its historical predecessor ‘made’ about 50 years ago! Seems, evolution spared this utensil! The aim is to design a better teapot, better in the functional sense. One that pours evenly throughout is a good one.
All teapots sold in the world so far (right from its first one till the last one) pour very abruptly at the beginning when the pot is near-full. Mathematically a small angular movement of hand causes a large, uncontrolled amount of tea to flow out. Towards the end of pouring when pot is in a near-empty condition, reverse happens; a large angular displacement of hand is compellingly and perhaps uncomfortably required to bring out the last, remaining drops of tea.
The common factors amongst start and termination of tea-pouring are turbulence, discomfort to the user (usually the lady of the house) and frequent spillage. Minor irritants include difficulty in balancing with one hand and fear of hot lid falling over the tablecloth (staining it). The former irritant gets worsened if the other hand is used to touch the teapot to offer it stability – this other hand gets scalded with burns as it touches the hot surface of the pot. The second irritant too gets enhanced as the lid-free teapot permits escape of steam: steam burns are dreaded - courtesy, high latent heat of steam.
Middle period is seemingly then easiest, safest and hence requires least design attention; the flow is laminar and medium-paced herein. What can be done to make the pouring by a tea-pot a completely and uniformly likeable process? Thus, we need to redesign a teapot to add a new function. Design for function, as we may put it.
A conventional mechanism synthesizer would choose the following sequence of events : manually pouring the tea from the teapot against a two dimensional graph paper (grid), plotting multiple graphs of position-time, velocity-time, acceleration-time of critical points of the teapot (say the tip, the center of mass, the handle, etc.), superimposition of some of these to attain the time-independent trajectory, calibration and measurements, filming the motions using prescribed frames-per-second, importing these correlations into a sophisticated so-called design software sold in the market, composing possible mechanisms that could accomplish the given kinematic tasks, short listing the better ones, choosing the final one, checking the accuracy of the final one by superimposing the Cartesian plot of the mechanically generated curve over the experimental video data & in particular noting the number of intersections of the two curves, optimizing and iterating dimensionally to conclude the kinematic aspect of design. Further, to complete the dynamical aspect, masses and loadings need be accounted for. The teapot machine could end up being consisting of linkages, cams, train of gear wheels or a combination of these. Although solutions using this systematic approach could be over-abundant, most of them would lack elegance and efficiency.
One such good design-fit is obtained by snugly holding the teapot through an outer casing and making that casing a part of four-bar motorized linkage. It must be added that this procedure can be very time consuming and has the danger of engineer getting involved in trivialities rather than graduating to an inventor. One of the many intuitive ways to add this function without disturbing other existing functions* is to couple a gear-box between the hand and the handle. The gearing would retard the teapot’s rotation at the beginning and fasten it towards the end. It is like engaging first gear at start, 2nd in middle and 3rd at the end! There are no 4th or 5th gears here! Note that 'gearing' in this context ought to be taken in a broader, functional sense. It should be interpreted as a ‘velocity ratio’, which can be achieved by several feasible mechanisms: levers, cogs, conventional meshing toothed wheels, windlass, etc. ONLINE VIDEO : https://innovation.ed.gov/ideas/pitch/VGRjlcx/