what is the best radius for a fillet in objects

According to wiki, the applications of fillets are:

1. to eliminate the stress concentration
2. to reduce aerodynamic drag
3. for manufacturing cost reduction(in milling)
4. it prevents the edges from damages
5. to eliminate the injuries from sharp edges
6. also it is given as an aesthetic feature

now, what is the best radius for a fillet in objects to eliminate the injuries from a sharp edge?
but before that another question should answer.

does a sharp edge really cause injuries?

A sharp edged object cannot make an injury as a knife does. because the included angle in the knife is really small to make the serious cut.

consider the sharp edge on a rectangular block.the included angle is 90 degrees. does it can make a cut on your body. if "burrs" are present on the surface obviously it will cause injuries. otherwise if the sharp edged block is having a surface finish like "i phone" it is difficult to make a cut.

is the electric car really green?

This is "Love Bird". India's First electric car made by Eddy current controls Ltd, Kerala. they manufactured this car long back in 1993.

"Lovebird" is a cute two-seater Electric Car of Eddy Electric series. Unlike the conventional cars that use petroleum fuels to power internal combustion engines, the electric car is run by a direct current electric motor powered by a rechargable lead acid battery pack. The electronic chopper controller gives smooth speed control. Four-speed with reverse gearbox will make your ride comfortable on all road conditions.

With the range of 60 Km per charge, lovebird suits most of your daily city drives which are normally within this range. After the day's trip it can be fully charged in about 6 to 8 hours and be ready for drive the next morning. The gradeability limit of 15 degrees can negotiate any gradient. Lovebird is built on a light weight high tensile steel chassis and fibre glass reinforced polyster body. The ride is noiseless and pollution free.
courtesy:Eddy current controls Ltd, Kerala

now many companies are making electric vehicles which are really powerful.

but is it really a greener vehicle?????

of course, it is not producing any direct emission. batteries are recharged with electricity.
but this electricity is produced in a power plant  which is emitting carbon dioxide.

now what is happening?

all gas cars are polluting atmosphere wherever they go.
all electric cars are not polluting wherever they go but more pollution near the electric power plants.

is it true?

material selection

A grocery shop owner approached you and asked to design a carry bag .
which material, you will suggest for carry bag? and why?

• polyethylene
• non woven fabric
• paper
• textile
• jute

Science behind a product

There will be one scientific principle behind the working of every product. Analysing a product is a great way of learning.

When the scrap paper vendor who collected old news papers from my house, he used his hand to measure the weight of the paper. But i told, we have an instrument to measure the weight and i showed him this instrument.

And it showed 3 Kg more than what he told. He was resistive to that but finally he settled 2 kg more. We also didn’t bargain much.

Now how it is working and can we trust this instrument?

This instrument is designed and made with a rod of varying diameter. A piece of rope tied around the rod, is used to balance the rod. When the rope is at the centre of mass, the mass of the rod on both side of the rope will balance each other and become horizontal. This point will be marked as reference or zero weight. The rope should move towards the hook side and balance horizontally in order to weigh the objects.

When we add a weight centre of mass will change. Then if the rope is in the new centre of mass again rod will be balanced horizontally. The rod should be pre calibrated for getting the actual measurement.

This is clever and simple instrument for measuring the weight.

The main disadvantage of this instrument is we cannot add more weight as it will become too heavy to lift and balance.

waste bin

 


this a waste basket with a lid. The lid can be opened by pressing on the lid. is it a good design?
Identify the problems of this waste basket.

Actually it seems to be a good design. because the lid can be open and close without touching on it. but it fails when form starts to follow the function.
here when we press on the pedal, the lid supposed to be open 90 degree to horizontal. but because of this poor design, pedal will touch on the ground so lid will not open completely(approx. 45 degrees).

so, while standing it will be difficult to put the waste into bin. another problem of this waste bin is, the inner volume of bin is actually less. since the pedal mechanism is consuming lot of space at the bottom of the waste basket.

problem with motion conversion

In order to design a machinery a mechanism is required to convert rotation to linear motion.
how many solutions?

some solutions are given here.. find out more.

1. rack and pinion
2. CAM and follower
3. pulley ad rope
4. screw rod mechanism
5. slider crank mechanism
6. The Peaucellier–Lipkin linkage
7. 
   

suggest a meaterial

You are a designer, who working on a cooking pan design.
which material you will suggest for manufacturing from the options

• Stainless steel
• Aluminium
• ceramics
• China clay
• food grade plastic

Pressure cooker design

two designs of pressure cookers are shown.
in the first one, to close the pressure cooker, place the lid and  by turning the lid it will be closed.
in the second one, place the lid over the cooker body and then tilt and move the lid into the cooker body. then turn it to lock.
in the first design lid will be locked from outside and in the second design lid will be locked from inside the cooker body.

which design do you think that a better design?
what are the advantages and disadvantages of each design?

Why manholes are round

have ever asked this think why manholes and covers are designed in circular shape.There are multiple answers to this question.

you can read more about this: http://en.wikipedia.org/wiki/Manhole_cover

• A round manhole cover cannot fall through its circular opening, whereas a square manhole cover may fall in if it were inserted diagonally in the hole. 
• Round tubes are the strongest and most material-efficient shape 
• A round manhole cover has a smaller surface than a square one, thus less material is needed to cast the manhole cover, meaning lower cost.
• The bearing surfaces of manhole frames and covers are machined to assure flatness and prevent them from becoming dislodged by traffic. Round castings are much easier to machine using a lathe.
• Circular covers do not need to be rotated to align with the manhole.
• A round manhole cover can be more easily moved by being rolled.
• A round manhole cover can be easily locked in place with a quarter turn which makes them hard to open without a special tool. Lockable covers do not have to be made as heavy, because traffic passing over them cannot lift them up by suction.courtesy: 

Design of an Adhesive Hook

these types of Adhesive hooks are very popular. why the hook is at the bottom?

the hooks are designed in this way because it should withstand peeling stress. the adhesive is having a peeling strength. if the stress overcome this strength it will comes out from the wall. consider the side view of two hooks. the direction of force on the hook is shown.

in the second case its very easy to overcome the peeling strength because of the position of the hook at top. from the next figure it will be clear.

this is the reason to keep the hook at the bottom. here peeling stress will be more. if the hook is at bottom it will compress the adhesive layer and because of that peeling stress will be less. so it won't comes out from the wall very easily.

soap dispenser

 

two different soap dispensers are shown here.
can you identify some advantages and disadvantages of each soap dispenser?
which design is better?

How to harvest rain water?

                in the traditional way the rain water is harvested in a Ferro cement tank or plastic tanks. water collected from the rooftop is filtered and then stored in tank. This tank normally will be in the ground level or underground. water is pumped to the overhead tank using a pump when ever required. normally water collect during rainy season and stored for summer.




of course this is a good idea in rain water harvesting. but is there a better way to make it more efficient?

yes.. of course..

most of the houses are using overhead tank on the terrace or on the roof from which water is supplied through pipes. if we analyse the rain water harvesting cycle, first water from the roof flowing down to the tank through the filter unit. this is then pumped back to the overhead tank by a pump.

instead if the water from the rooftop collect first in the overhead tank after filtering.
then the overflowing water can be collected in the underground tank.
the advantage is during rainy season no energy is required for pumping water into the overhead tank.

Problem with Drinking water can Pump

this is a very popular "water can pump". this is very useful since the water can is very heavy to lift. 

but one of the main problem of this pump is when the water level decrease it fails to pump or too many presses are required to pump water.

One reason is, air is leaking through the tightening portion, which is loosened due to the repeated pressing action.

Suggest and Design a solution for the problem for this pump or design a new mechanism for pumping out the water from bottles

Clock Design

mechanical clocks are now antique pieces. compared to the modern digital watches it's interface is very simple. only numbers from 1 to 12 to show the time.

here in the picture you can see a mechanical alarm clock. in this, can you tell the significance of the some letters along with the numbers. 

is it indicating anything?

Actually these letters are "BANK OF COCHIN". 

Is it a good way of representing something? what do you think.