Thursday, April 30, 2009

Work Completed
made drawings of parts
price quote on monday
decided _not_ to upgrade power supply
found new use for oscilloscope - in monitoring power supply.
you can plug your oscilloscope to the + and - of your power supply.
that way, when you run your experiments, if there is a surge in voltage or what have you, you will see it on the scope. of course for a dc power supply, the oscilloscope has a boring flat line for most of the time, but its purpose is really just for those moments when the machine might pull more juice or less and this is a great visual way to monitor and detect that that has happened.

Tuesday, April 28, 2009

Machine Design

The design of machines and machine components is a somewhat esoteric field that only a few poeple, like the hands-on engineering types can really handle with expertise.

By now we know a lot of different kinds of machines/devices that are in the market - all things mechanical, eletrical or electronic or some combination there of.

If we examined these products in the market and looked at the evolution of the product from someone or some team's creative design into its modern design form, we would probably find that when the initial design cycles identify the optimal template to adopt, the subsequent cycles are more focussed on finetuning the design and adding additional features.

In cases where the sub-optimal designs were chosen we will probably find that either they were disastrous to the company involved or that they had to make a major design change at some point or that some other company came up with a better design.

The interesting thing about designing a machine or a sub-assembly of a machine part is that there are two opposing interests that need to be balanced - suitability to the application we are creating and simplicity of machining, assembling and maintaining.

How opposing these two aspects of someone's machine is, determines how realistic it will be to expect that such a design will go on and become the defactor design of that machine, in the future as well.

A good design must reconcile the two and do it while taking advantage of the latest breakthroughs in any field involved.

Another tough problem is to then sublimate the design by incorporating as many off-the-shelf parts as possible.

This is where machine design becomes art - because sometimes a survey of available off-the-shelf parts (suited best for whatever other purpose it was made for) can upend the machine design cycle - this can happen because of either the lack of suitable parts or if you're lucky, by a surfeit of them that might allow you to simplify your design, but in so many ways, that you now have to choose from a confusing array of suspects.

I have found that it is possible to use everyday parts in new ways. Creative work like that can save a lot of money (and frustruation) in finding an executable design within your budget. A good hardware store is a lucky treasure to find as it allows for serendipity.
But ultimately, pencil has to meet paper - many parts have to be custom designed or atleast customized in someway, if only to fasten then in the properway to the overal assembly. Patience is perhaps the only prerequisite once you start putting a design on paper. Start with an isometric drawing of the assembly and work your way down to detailed Front-Top-Side views of individual parts. Make sure to note measurement units used and all relevant dimensions.

Tuesday, April 14, 2009

Mechanical And Electrical Filters

At the turn of the 20th century, it was proven that the propagation of electric waves along electric lines was analogous to the propagation of elastic waves along mechanical lattices. Vincent’s model of a mechanical filter and Campbell’s equivalent electrical circuit are shown above. A mechanical and its equivalent electrical low-pass filter are shown below

Low Pass Mechanical System and Electrical Circuit

Text excerpt from L. Brillouin, Wave Propagation in Periodic Structures, 1946, pg 42 The mechanical low-pass filter consists of point masses joined by elastic elements that we might visualize as springs. The elastic elements each have two ends, one connected to one mass and one to another mass, while the masses are represented by single points. An electric line having all its condensers shunting the high frequencies may be regarded as a single line with the condensers connected between the line and ground at regular intervals. Then the inductances appear as having two ends connected to different condensers and the condensers are essentially points in the structure. Another way of looking at the problem is to regard the elastic forces as coupling forces in the electric line, while the masses and condensers are thought of as supplying inertial forces to their respective systems. End Excerpt

Mathematically too, the equations for the propagation of electric waves along low-pass, high-pass and band-pass electric filters are identical to the equations for the propagation of elastic waves along similarly constructed mechanical lattices.
The question can thus be asked: Are the mechanical and electrical sciences then analogous to each other and formulating the same principles with two different sets of laws and equations when in fact one set of laws is sufficient to express all that there is to be expressed.