LEGOs are really great to build all kinds of robots. I'd like to introduce you the Egglift.
The Egglift is an appliance to cook boiled eggs made out of LEGO bricks, powered and controlled with LEGO Mindstorms.

Acknowledgment:

The original Egglift idea is from famous French inventor Roland Moreno.
The black-and-white wheel light sensor is an original idea from Benjamin Erwin in his excellent book Creative Projects with Lego Mindstorms
Thanks to [http://mailto:r.olivero_at_wanadoo.fr Richard ''Vauban''] for his help and advices.
LEGO is a trademark of The LEGO Group. This document is not endorsed, sponsored, or authorized by The LEGO Group in any way.

Step 1: Description:

The Egglift is mainly composed of four elements:

1. A metallic perforated non-LEGO basket where you lay the eggs. The basket, made of metallic wires, is fairly small and can contain 2 eggs maximum.

2. A winch that contain a motor to pull up or down the basket through a string and also a light sensor to detect the position of the basket. (in red)

3. A LEGO RCX to pilot the basket through the winch and a 180 seconds temporization (adjustable). (in yellow-grey)

4. Finally, a LEGO structure where the three above elements are graft. (in blue)

Step 2: Instructions of Operation:

Fill up a pan with water, and place over a cook top.
Place the Egglift (with its basket in up position) above the pan, in a way that when the basket is in down position, it fully goes in the pan.
Place one or two eggs into the basket.
Turn on the cook top.
Push the button Run of the RCX.

That's all for the human operations: the Egglift will automatically detect when the water reached its boiling point. The basket will then automatically drop down until it is fully submerged in the boiling water. After three minutes, the basket is automatically pulled up and an alarm rings, warning you the boiled eggs are ready. Just pick them up and enjoy !

Step 3: Detecting the Position of the Basket:

To obtain a reliable cooking system, it is relatively important the lower (and less importantly the upper) position of the basket remains constant and precise: the eggs have to be fully submerged in the boiling water for a safe cooking.

The choice of a temporization in the program (turn on the winch for 5 seconds before turning it off) would have not been well suited for this application.

Because of inaccuracies in the motor, in the gear train and the weight variation of the eggs, to basket would have not returned to the same place every time.

The position of the basket can be detected with a light sensor aimed at the black-and-white circle on the left stuck to a 40-tooth wheel.

This wheel has 24 divisions, alternatively black-and-white. When the motor that control the basket is on, the light sensor counts how many divisions had passed by, thus letting know the RCX a fairly accurate representation of the position of the basket.

This method is not too accurate, but it is accurate enough for this type of application.

Step 4: Detecting When the Water Reached Its Boiling Point:

A LEGO temperature sensor (ref# 9755) is connected to the RCX. The drawback of this sensor is its range: it only works at temperatures between -20 degrees C and 70 degrees C (-4 degrees F to 158 degrees F). That's a long way from the water boiling point 100 degrees C.

Thus, the LEGO temperature sensor had to be relocated to a spot where it reach its maximum range (approximately 70 degrees C) when at the same time, the water reach 100 degrees C.

Typically, it is approximately one Inch (35mm) above the water level.

The use of a DCP Microdevelopments ProTemp sensor (ref# D10047) dipped inside the pan would most likely get round this major drawback.

Step 5: Cooking Time Selection:

Even if Egglift's primary function is to cook boiled eggs, it can also cook softboiled and hard-boiled eggs !

Actually, a cooking time selection button is conveniently placed next to the RCX. Each press on the button selects cooking times.

Step 6: Estimated Cost & Advantage of the Egglift:

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Estimated cost:

If the Egglift had to be mass product (I'm still looking forward any potential investors who might be interested for a joint venture), its production costs would be roughly $190.00 USD. (This is only including raw materials and not including assembly costs).

This is very competitive compared to other Steam Egg Cooker on the market whish retail for around $25.00 USD.

The Egglift is more aimed at wealthy connoisseur customers who want to cook their boiled eggs a l'ancienne but with a touch of modernity.

Advantage of the Egglift:

The Egglift features countless advantages over other competitor steam egg cooker:

It is cheap.
It is compact.
It is convenient.
It can be conveniently stored.
It can cook eggs in large quantity (two at a time) for large family.
It is dishwasher safe (after removal of the RCX, the motor and the sensors).
It will not break up the look of most gourmet kitchen.

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Step 7: Make Your Own !

So if you too have some LEGO bricks laying around and a set of LEGO Mindstorms (or the new one LEGO NXT), you can actually redo this robot. It doesn't even have to be LEGO, use your imagination!

I have attached the NQCprogram I'm using for the Egllift. (egglift.nqc) NQC for Not Quite C is a simple language with a C-like syntax that can be used to program Lego's RCX programmable brick (from the Mindstorms set). You can get NQC for fee here.

Also attached is the CAD model of my Egglift if you want to build the exact same thing. (egglift.mpd) (but it's better to use you're imagination and re-engineer it so you can make some improvements) You have to open my CAD file (egglift.mpd) with the software MLCAD LDRAW available for free here.