Contraption - Tips about Energy Conversions

by piscianemperor

Robotics is all fine and dandy..i mean you use micro-controllers and motors to do some amazing stuff . But somehow i have always felt that robotics competitions,especially those held in Pune or those that i have seen at various colleges,allow limited latitude for innovation. Suppose it is a race,for which there is a limit on weight and size of your bot. What more can you do,except fit faster,stronger motors (Johnson motors ?) and make your bot light ?

Now Contraption or Rube Goldberg Machine is a different ball game,undoubtedly a more fascinating one,and my First Love ! As you must be knowing,in a contraption,you have to complete a particular task using maximum possible energy conversions ,for example- Kinetic—>Potential, Wind—>Kinetic . This requires a level of perfection and innovation that really appeals to me. i have participated in many contraption competitions until now,and have won in many places too. Today we shall go over how to go about some tricky energy conversions and rake up crucial points.

Kinetic and potential energy conversions are easy enough to achieve-indeed,any form of energy can be broadly classified into either of these 2. eg: Chemical energy can be said to be Potential energy. But in case of contraption,all these are counted as separate.Yes…vibrational,chemical,sound,electric,wind,magnetic,light,rotational etc. are all distinct.

• Sound Energy—->Electric Energy :The easiest way of going about this is a Clap switch.  A clap switch has a Electret Microphone attached to it,from which the input is obtained. Whenever a loud enough sound a produced (a clap,a book falling) , the switch gets closed,and whatever is attached to the output turns on (like a bulb,a fan,a motor…i’m just giving you ideas). How to make a Clap Switch ? You can check that out here. i could have easily posted the circuit here,but i think due credit must be given to the original author. i have tried the upper circuit a year back,and it works. Here is the pic . Yes,that is cardboard on which i have made the ckt…you really don’t need PCB’s for everything ! If you have problems with the circuit,just get in touch.  Note: Clap switches are sensitive. Even the slightest noise(a foot tapping) may set them off. Always use Clap Switches at beginning of the contraption;later on you don’t care what it does.
• Wind Energy—->Kinetic Energy : You can use a computer fan (the one inside the CPU,over the processor to cool it) for this. You’ll get that for 1 $ or less. You may also use a plastic  lightweight fan,where in the blades are attached to a axle.A string is tied to the axle and wound round and round around it. A weight is attached to the other end of the string.Something sets off the weight and causes it to fall,which pulls the string and the fan rotates. Both of these can be used to push ping-pong balls(table tennis balls).

• Using Dominos : Well,i say dominos here to specify what i mean,but the ‘domino’ may just be anything…CD cases,books, casette cases,even light wooden blocks cut to size. You can use these innovatively.Simplest use may be just to push something at end of the stack ;but it may also be used to complete a circuit (attach a metal sheet to the last block..let it fall on 2 wires,completing the ckt). Hell,it may even be the weight attached to the Fan i was talking about in the above case !

• Light energy —-> Electric Energy : yep,you guessed right. Use LDR’s(light dependent resistors) for this.There are just two ways of constructing the voltage divider, with the LDR at the top, or with the LDR at the bottom:

Remember the formula for calculating V_out :

• Vibrational Energy—-> Kinetic energy : Easy,isn’t it? Just use a mobile phone kept on a slope. There’ll be  different ways of going about this. You may either use one phone to call the one on the slope. For that you’ll need a lever attached to a motor or something to push the ‘call’ button. You may also use timer alarm if your phone has the facility . Note : Only some phones have a vibrator strong enough to set it sliding.Also consider Network Congestion !
• Chemical Energy—-> Electric Energy : this one’s bit tricky. For starters,it raises unhappy memories of that chemistry exam you barely cleared,doesn’t it ? Secondly,electrochemical cells have a very low output voltage( < 1 V). So you’ll probably need a amplifier at the output.. i’ll just tell you about how to construct a electrochem cell, namely Copper-Zinc . Details of the reaction you can check here. A copper or zinc electrode will be a Cu or Zn plate,nothing less,nothing more. You’ll get it in some chemistry shop for around 2$ . For the salt bridge,use a blotting paper or paper napkin wound in a small roll. Either ends of the roll are dipped in the 2 solutions ( CuSO4 and ZnSO4). Dip the paper in salt solution (salt+water is a good conductor) before using as a salt bridge. You’ll have to think out of the box for this…all liquids conduct,don’t they ;-) ? What if the salt bridge is a wire,and the only work the solutions are doing is completing the ckt  ??? i know i’m wicked ..
• Chemical energy —-> Heat energy: this is my favourite. Use Glycerine (solution) and KMnO4 -potassium permanganate for the uninitiated (crystal powder). Glycerine+KMnO4—>Heat . Use it to burn some thread.Tip: The reaction is ordinarily a little slow.You don’t want your spectators to get bored waiting for the powder to catch fire,due you ? To quicken the pace,put a drop or 2 of water on the power. Also,use more powder and less Glycerine. CAUTION: the heat produced is intense,and the flame is white. But don’t worry,it is not explosive or anything.
• Electric energy—->Magnetic energy—->Kinetic Energy : Again a little tricky. You’ll need a electromagnet for this. The problem is,even for a attracting distance of just 1cm ,you’ll need around 2 Amps current. Moreover,you can’t just keep the electromagnet on …above 30secs,it’ll just over heat and the coils around it will melt up ! So you’ll need a mechanism for turning it on,making it do some work(like attracting a iron ball,which will stick to it) ,and turning it off again(it’ll make the iron ball fall). See,i’ve given you a clue for the next step.
• Electric—->Heat: Solder Irons anyone ?
• Using Reed Switch : Wikipedia does it the best !
• Using Bows, See-Saws,Candles…all these are really common,and there’s not much to explain. You’ll also find plenty of stuff on Youtube ( the Japanese or Chinese ta-da-pa-da-pa-di-pi videos will look nice,but won’t be particularly helpful)

Ok. These are videos of my own(there were 4 other friends with me..so lemme say…our own) contraptions. i’m afraid they aren’t particularly enlightening,because i haven’t shot them myself…was too busy ensuring that they work well.Also both have 2 different setups.But go through them if you want more ideas. One is of a stationary setup,the other of a working one.

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