Mission Possible C

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Description and Scoring

Students will construct a Rube Goldberg -like device which incorporates many Energy Transfers and Bonuses to accomplish a given task. Specific rules have varied widely over the years, so this wiki attempts to address the more recent iterations.

  • A Target Time is given with optimum points being awarded when the devices meets the Target exactly.
  • A limited number of Energy Transfer points will be awarded based on the use of the 5 Energy Forms
    • Electrical
    • Mechanical
    • Heat
    • Chemical
    • Electromagnetic Spectrum
  • The machine must start and end with a specific transfer, this being the given task, which is heavily weighted for scoring
  • Limits are placed on maximum device dimensions, battery voltage, run time, and danger level of components.
  • Penalties are assessed for violating construction rules and for touching the device during operation.
  • Bonuses of varying points are awarded for completing specific sub-tasks within the device. This article focuses primarily on satisfying such bonuses.
  • Additional bonuses are available only at the State and National levels of competition.
  • An Energy Transfer List (ETL) is required to list the steps that the device performs and the energy forms involved.
  • The BEST machine will satisfy all construction requirements, have working transfers for the requisite number of energy forms and for all the bonuses, complete the main task, and do all of the above in exactly the Target Time.

Theory of Construction

As with any building event, your actual approach depends largely on your resources, time, and expectation for success as a team. Regardless of those, however, Mission focuses tremendously upon reliability. A device may have all of the possible transfers, but if they fail to function properly, the participant will end up having to touch the device and will lose more points than the transfers were worth in the first place. This means that every part of your device must be designed to work repeatably and reliably, or it is not worth having it in the machine.

Solid construction is one way to improve reliability. Machines made carelessly of Legos, K-nex, or other toys have a tendency to fall apart during transport to competitions. Hot glue, while very convenient for testing your device, should always be reinforced or replaced with screws where possible.

For more complex machines that attempt to satisfy many of the bonuses, surface area within the device on which to mount transfers is often at a premium. Builders should consider using at least two side walls, which dramatically increases available surfaces without sacrificing accessibility. Three walled devices and multi-decker devices are common at national competitions, but make it a lot harder to access your device for setup and troubleshooting.

Tasks and Bonuses of the Past:

Magnet Start

Method A: Use a circuit that is sensitive to magnets.

  • Homemade solution: Have a circuit with a gap in it that is completed when a piece of magnetic metal on a pivot touches both ends. When the magnet is applied the metal bridge raises and the circuit is broken.
  • Boxed solution: Grab a magnetic window switch from a security system (<

Method B: Use the magnet to move something

  • Homemade solution: With Legos, for example: Attach a small magnet (preferably neodymium) to a short axle. Pass the axle through a block with a hole in it and have the very tip of the axle supporting a weighted pivot arm with a Snap-action switch underneath. When the main magnet moves in it attracts the small ones on the axle and releases the drop arm, completing/breaking the circuit.


Mechanical pneumatics

Method A: Use a piston to press a switch or push something (ball, test-tube on a pivot, etc)

  • Homemade solution: Hook two syringes together with aquarium tubing such that when one is pressed the other extends. Drop a weight on or otherwise depress one syringe so that the opposite one expands and performs the action. Experiment with different syringe sizes on each end if you need more speed/force.
  • Homemade solution: Anyone who has played with baking soda and vinegar knows that the combination of the two elements creates carbon dioxide. Combine the two in a closed-system balloon and you have both a chemical reaction and a setup for pneumatics. Try putting one component in the limp balloon and the other in a jar with a small neck to accommodate the balloon. Have the machine lift the limp balloon a little, spilling the component in the balloon into the jar below. Carbon dioxide builds up, inflates the balloon, and provides a mechanical push powered by air.
  • Boxed solution: Lego pneumatics can be used here do perform any number of tasks. The system has tubing, large two-way pistons, small two-way pistons, small one-way pistons, large pressurizing pistons, air tanks, and switches. That is all you need to do a great many things.
  • Boxed solution: Canned air comes in several forms, perhaps the most convenient of which is the kind used to clean PC keyboards. Make sure that you read the packaging on the cans when you buy them. Some will be flammable and thus illegal, others will not be illegal. Endust used to be flammable and may still be. Belkin was not. Perform your own, very careful tests if need be. Triggering the canned air is probably the most difficult part of the bonus, unless you use an elaborate CO2? system with purchased valves. A strong motor should suffice in any case. Depending on the amount of pressure available, you should be able to blow over levers or push small objects to trigger the next action. It is unwise to use high PSIs? as they may be regarded as unsafe by your supervisor for good reason. Stick to air cans for PC cleaning and the like if at all possible.

Mechanical hydraulics

Method A: Use a piston to press a switch or push something (ball, test-tube on a pivot, etc)

  • Homemade solution: Hook two syringes together with aquarium tubing such that when one is pressed the other extends. Drop a weight on or otherwise depress one syringe so that the opposite one expands and performs the action. Experiment with different syringe sizes on each end if you need more speed/force.

-action switch such that the next action is triggered by the completion of the circuit and the pump is turned off simultaneously. This should be easy to wire if you give it a seconds thought and is extremely necessary, lest you burn out the pump or pop a tube off. It is also a very handy addition if you add a 6 contact, two/three position switch and wire it so that one setting has the pump going forward, the middle is off, and the other way has the pump going in reverse. This way, with a little care, the syringe can be retracted without disconnection any tubes or forcing the pump.

Home-made electromagnet

Method A: Engage/disengage the electromagnet to cause a circuit to be completed/broken

  • Homemade solution: Make your electromagnet out of telephone wiring, which is insulated and fairly small. Make very consistant, even wrappings until you have an electromagnet of the size you want. Try it on small voltages first and then go up. If you go too high then the electromagnet may be destroyed (the insulation on the wires can melt, not to mention making the whole thing a fire hazard). Use the electromagnet to pick up or drop a ball that rests on a lever arm. When the ball moves, the lever arm either engages or disengages a touch-sensitive switch (Snap-action). Use a switch that will allow you to both trigger the next action and turn off the electromagnet so that your battery is not drained.
  • General note: You can place the core of your electromagnet in a drill and have a friend with a steady hand pull the trigger. Many drills have a speed adjustment dial that, if you dial it to an appropriate point, will allow your friend to hold the trigger down completely for a constant, appropriate speed. The person with the wire should wear leather gloves...especially if their friend likes playing tricks on them.

Home-made battery

Method A: Use a chemical battery to power a motor, LED, relay, or other minimal-draw device.

  • Homemade solution: Grab an ice cube tray, hot glue, copper sheeting, tin sheets, wires, and vinegar. Copper tubing and zink galvanized nails from the hadrware store also work well. The squares or metal should be cut and sized so that two (one of each kind) fit completely in an ice cube spot with one opposite to the other. Solder a wire onto each square of metal and hot glue two into each cube of the tray that you want to use. You can wire cells together to increase either voltage or current, just as in batteries. So wire in either series or parallel or both to achieve the voltage and current you need. To use the chemical battery in your machine you can either have the battery completed, but the circuit it powers open or have the circuit closed but the battery not yet completed. If you chose the latter then you should probably make an extra battery cell with a glass jar large enough that you can manipulate the metal plates or vinegar without risk of spilling or the metal plates touching. Vinegar is probably the easiest and cheapest way to power your chemical battery. It is cheaper than lemon juice (or at least is where I shop) and can easily be bought en mass (comes in gallon jugs ? ). Make sure to use fresh vinegar before competition as ots effectiveness will decrease with use. It may be necessary to clean the metal plates with steel wool or stronger acid to remove corrosion. To help prevent corrosion, always empty and dry the tray when finished. As far as what the chemical battery can trigger, latching relays are probably the most reliable solution. However, LEDs? can be used and can gain you EMS transfer points at the same time. Motors are moderately less desirable than relays, but may be better than LEDs?, depending on what you are working with. Never put your chemical battery in the same circuit as a real battery so that there is no question as to the fact that the chemical battery is actually triggering the next action.

Chemical precipitation

Method A: Use the combination of two chemicals to produce a precipitate that distinctively changes the opacity of a solution. Use a light sensitive sensor to detect this change.

  • Homemade solution: I can speak to the effectiveness of the precipitate produced by the combination of common washing soda (Na2CO3?) and ferric chloride. The latter you will have to obtain either from your friendly chemistry teacher or a magazine. There are hundreds of chemicals you can use, but I am familiar with these two. Washing soda starts out as a white powder but, when dissolved in reasonable proportions with water, forms a clear aqueous solution. Ferric chloride starts out as nasty brown colored blocks (it may actually be powder normally, but mine was in blocks, perhaps due to moisture) and can be dissolved into a relatively clear brown tinted solution. If you have a colored component and a clear component, make sure that the light sensor is initially reading the colored component. This is so that you can easily argue that the clear solution itself did not measurably change the opacity of the solution and thus it must be the precipitate that actually triggered the light sensor. If you use the chemicals in the reverse order than it could be said that the colored nature of the chemical triggered the next action, rather than the presence of a precipitate. When you set up this bonus, it would probably be best to have the light sensor on one side of a test tube and place a light source on the opposite side. A small light source is all that should be necessary, but you can experiment to find out what your sensor requires. To conserve space, you may wish to use a standard size test tube but use glass cutting equipment to cut off the majority of the tube. If you do this, make sure to polish the cut edges with a Bunsen burner, propane torch, or other heat source. A funnel and a motor with a small container attached is all you should need to combine the elements in the test tube. As your chemicals may leave a residue on the test tube, always wash and scrub it out along with the funnel to prevent the reaction from occurring while you are setting up. Try to use small quantities of the chemicals and avoid cross contamination. Once you find a concentration of each chemical that resulted in a good solution, make large batches of each and drew on them for the entire season. This ensures that the light sensor would not have to be calibrated for a different opacity.

Increased Heat

Method A: Use the increasing heat to mechanically affect the next action

  • Homemade solution: Bimetallic strips are two sheets of metal of different kinds joined back to back. When heat/cold is applied, the two different metals expand/contract at different rates. Thus, whenever the temperature changes, the strip curls or uncurls. You can find bimetallic strips on the back of any cheap outdoor thermometer with an arm that rotates to point to the temperature. Clamp one end of the bimetallic strip down, place the heat source in the middle, and have the other end touch a switch when it uncurls. If your heat source is nichrome wire, design the circuit such that the nichrome is turned off as the next action begins. This can be combines with the Decreasing Heat bonus with a little thought to make a double bonus that requires no reseting.
  • Homemade solution: Moving a candle under a fishing line or otherwise melting through said plastic is an extremely easy way to demonstrate an increase in heat. With an anchor on one end of the line and a suspended weight on the other, you can easily depress a switch or move an object. Only downside is that this must be reset every time since you mutilate the fishing line. Note: you must melt the string to get credit, so don't use cotton or cloth strings. Melting is increasing heat, burning is chemical oxidation.

Method B: Use the heat to stimulate a sensor

  • Homemade solution: Light a match, move a candle, or otherwise heat a thermal sensor.
  • Homemade solution: Find some chemicals to create an exothermic reaction. You may have to create a stirring apparatus to achieve rapid temperature change.

Decreased heat

Method A: Use the decreasing heat to mechanically affect the next action

  • Homemade solution: This again uses bimetallic strips. The setup is the reverse of the one for increasing heat. The strip begins heated and when the heat source is removed/turned off the strip curls back up and presses or releases a switch. With the right setup, this can be combined with the increasing heat bonus so that your machine has a single bimetallic strip that does both bonuses. If you want to use a single strip, be sure to clearly document the flow of your machine and verify that it does not violate any looping path rules.

Method B: Use the decreasing heat to stimulate a sensor:

  • Homemade solution: Remove or turn off a heat source that was heating a thermal sensor.
  • Boxed solution: Go buy a first aid cooling pack. The cooling pack has a small bag of liquid in it, surrounded by many white balls of chemical. When you twist the pack, the bag bursts and the reaction. Adapt this for MPC by carefully opening the plastic packaging and removing the bag of liquid and the balls of chemical. You may wish to crush the balls, dissolve them, or otherwise speed up the rate of the reaction. The temperature change should be significant enough to trigger most any sensor. It may be difficult to get this step to function in a reliable time period.

Released spring energy, other than mousetrap

Method A: Use a precompressed spring to activate a switch

  • Homemade solution: Lego suspension springs are particularly easy to use for this bonus. The idea is that you place a rod in front of the compressed spring or otherwise prevent its extension, have a switch that is seperated from the spring only by said blocking device, and then remove the blocker so that the spring flips/depresses the switch. Lego suspension springs have holes on both ends, making them particularly easy to mount.

Current through a transformer

Method A: Use a 1:1 transformer hooked up to an audio jack to power an LED or activate a relay

  • Homemade solution: RadioShack? sells these tiny little green-wrapped 1:1 transformers. Aside from one of those, all you need is a battery-powered audio device (mp3/radio/CD/tape) with an audio port for headphones, an LED, and a pair of headphones to sacrifice to the heathen gods. Use wire cutters to clip the audio plug and a few inches of wire off of the headphones (you can make the headphones whole again post-MP if you really want to). Connect those two leads to the input for the 1:1 transformer (either look at the wiring diagram on the back of the box or take a close look at the transformer to know which wires you should be using). Finally, hook the LED or relay up to the other pair of wires coming off of the transformer. Now just set up the circuit so that the Input to the transformer from the audio is Normally Open and is closed by the previous transfer. The audio signal, which can be thought of as an AC input in this case, will be converted to DC by the transformer and will power the LED or activate the relay.

Stored spring energy (Not spring that released energy)

Method A: [Dead-end transfer]

  • Obvious Homemade solution: Drop a weight on a squishy spring and leave it there. This can be done as a side effect of something else in your machine falling. Just be sure that the weight does not fall off the spring, otherwise the energy gets released and the bonus does not count.

10 second baby rattle

Method A: Use a motor to spin the rattle

  • Homemade solution: Hot glue + motor + baby rattle.


Piezoelectric Effect

Method A: Use the sound from a piezo buzzer to activate a microphone circuit

  • Homemade solution: Grab a peizo buzzer from RadioShack?, certain music playing dolls/toys (should sound tinny), or some speakers. Get a cheap computer lapel microphone and hook it up to a circuit. Presence of the high pitch sound triggers the circuit.

Method B: Apply mechanical force to a piezo crystal to generate electricity

  • Homemade solution: Piezo buzzers work by converting electricity to mechanical vibrations. This conversion can be reversed. Gas grill lighters work on this principle. When you push the button it makes a clicking noise and then generates a spark. The clicking noise is from a spring being engaged and release with a metal tip on the end that strikes a piezo crystal. The force of the impact is converted into the spark that ignites the grill. Same with most butane lighters that have a long handle and a long barrel (not the flint/spark cigarette lighters). This bonus will require a you build a circuit or otherwise detect the generation of electricity. You cannot simply have the machine push the button on a gas grill lighter because that would be a black box. As far as the machine is concerned it is mechanical energy going in and electrical energy going out. You would not be able to claim points for the internal workings of the gas grill lighter.

Method C: Use the mechanical vibrations of a piezo buzzer to affect the next transfer

  • Homemade solution: Instead of relying on the sound produced by the buzzer, this bonus uses the mechanical vibrations produced to do something. You can do a number of things with this setup. If you put the buzzer on a piece of paper with paperclips resting on it then when the buzzer engaged the paperclips would slide down the paper. The weight of the paperclips could cause the next action. You could also attach something directly to the piezo buzzer. A vibrating blade would have to be shielded, but would be effective in cutting certain strings/lines.

Bernoulli Principle

Method A: Levitate a ball using a fan and detect its presence by having it block a light source

  • Homemade solution: The idea behind this Method is that, if you place a fan under a pingpong ball, you can levitate it. This works because of the pressure difference created by the stream of air that the ball is floating on as compared to the non-moving air just outside of the stream. The only trick to this transfer is finding a fan that will do it consistantly. I tried six different fans and of those six, only one did the trick. The fan I ended up using was from a Coleman inflatable matress. Fans that did not work failed either because they could not produce a sufficient air-flow (this was true of the muffin fans I tried) or created a swirling effect and threw the ball out of the stream before it could stabilize (this was true of fans with slanted air guides or excessively curved blades. Said fans were also from hair driers). If you can get a fan that works, the rest is really fairly easy. You just place a light source on one side of the place where the pingpong ball hovers and a detector on the other side. When the fan activates, the ball will hover and trip the detector. If you happen to be using a programmable system like the Lego Mindstorms or NXT, I would recommend that you code the transfer such that the ball must remain in that position for a second or two. This will both cut down on false-alarms and will give you a great arguing position for the fact that the transfer would not run to completion unless the ball was help in place, which is the Bernoulli Principle.

Method B: Something about a strip of paper in front of a fan...

  • Homemade solution: Blow a fan over one side of a strip of paper. The lower preassure caused by the moving stream of air will pull the paper into the stream. Detect the moving paper to score this bonus.

Single electrical source

Method A: Use a single, large battery to power the machine

  • Boxed solution: Buy a large battery and use it. Avoid automotive type batteries as they can produce hazardous currents and are not worth the safety risks. 12v alarm system batteries are a good bet.

Method B: Use more than one battery, wired together, to power the machine

  • Homemade solution: Note that the bonus is not for a single battery, it is for a single source. Thus you can have 2 or more batteries wired together in series and/or parallel to provide the voltage/current you desire. However, there should only be two leads from the batteries to the machine itself (and thus only one voltage). The machine can modify that voltage, but if there are more than two leads then there is more than one source. Large 6 volt flashlight batteries work very well for this. Use them in series to get 12 volts. Use diodes or voltage regulators to modify the voltage from the source.

Single visible light source distributed through fiber optics

Method A: Use a large single light to illuminate at least three fiber optic cables for the EMS transfers

-source and so less light ends up on either side of the tube instead of shining through the solution.

  • Boxed solution: Lego makes some excellent, relatively large bore fiber optic cables. Unlike the cables in the vast majority of fiber optic playthings, which are less than 1mm, the Lego cables come in two sizes. One has a 1mm base strand with a larger bore tip. The other is about 3mm down its entire length. The former is cheaper, the latter is more expensive but is also longer and delivers more light. With the large bore cables you should not have to use a bundle of fibers and you can end up with more light to work with. Many science catalogues also sell interesting fiber optic cables.
  • Boxed solution: Nowhere in the does it say that you must use commercial fiber optic cables. Clear hot glue sticks work great as fiber optic cables and can cary the light of a very bright LED with little loss. They are also rigid and can be bent with a blow dryer or similar heat source.

(State and National) Announce school name

Method A: Use a piston or other direct mechanical pressure to press the play button on a tape player.

  • Homemade solution: Hack open a Sony Walkman, wire it into your machine, and make a rig to hold it. Use a piston or dropping weight to depress the play button. Be careful to arrange the piston/weight so that it cannot accidentally press any other button. Pressing play and ffwd with sufficient force will result in playback, but not very useful playback.

Method B: Complete the circuit to power a tape player with the play button already depressed

  • Homemade solution: Tape down, clamp, or otherwise depress the play button on the tape player. Hack open the battery compartment and wire it into a circuit with the previous action.

Method C: Use a premade circuit to store an electronic recording

  • Boxed solution: Find a greeting card or picture frame where you can record your own message. Simply open the card or stimulate the frame to play back the recording. At some points, RadioShack? has also sold the recording/playback circuit alone.

Note

  • Be sure that your school announcer is loud enough to be heard over the racket of your machine and a noisy room.

(National) Shoelace overhand knot

Eject Ping-Pong and catch

Method A: Mechanically launch the ball

  • Homemade solution: Springs, rubberbands, mousetraps, pistons, or whatever. Cover the landing pad in double sided tape to keep the ball from bouncing out.

Drop a Quarter

Method A: Mechanically detect the quarter

  • Homemade solution: Just use a simple lever with a switch on the end.

Method B: Electrically detect the quarter

  • Homemade solution: Make two contacts out of copper and place them very close together. Solder on wires and you are set to go.

Mech to EMS

Method A: Make sparks by friction

  • Homemade solution: Grab a piece of sand paper or one of the sanding dremel bits and affix it to a motor. Find a piece of flint (Wal-Mart sells a flint/magnesium combo in the camping section) and put it on a pivot so that it rests on the sand paper. When the motor engages, the sand paper hits the flint and the sparks will fly. Instead of putting the flint on a pivot you can also rubber band it down if your motor can handle the added stress. The sparks are detectable by a light sensor, but it may be hard. You might try lighting flash paper with the sparks instead.

Method B: Make sparks by Triboluminescence

  • Homemade solution: Buy some Wintergreen Lifesavers and start hitting them with things. They will make some very small sparks. If you are altogether too ambitious for your own good, you may be able to detect these sparks. Method A is far easier and more dependable although Method B has been done once at competition.

Chem to Mech

Method A: See Mechanical Pneumatics Method A 2nd solution Method B: Create a pressure jar

  • Homemade solution: Inside a sealed mason jar, combine two chemicals to create a gas - MnO2? and H2O2? work well. Vent the gas through a tube running through the lid and use it to triger the next action. This bonus can be combined with the mechanical pneumatics bonus for double points.

Chem to Heat

Method A: Melt wax

  • Homemade solution: Attach a string to the side of a beaker with a small dab of hot wax and suspend a weight. Inside the beaker, mix two chemicals that create an exothermic reaction. The heat from the reaction will cause the wax to lose its grip on the beaker, dropping the weight. Check with your chemistry teacher for safe and viable chemical reactions.

Chem to EMS

Method A: Use glowstick chemicals to produce light

  • Homemade solution: Go buy a couple glowsticks and very carefully cut the top off of one. Pour the liquid inside into an opaque container. Carefully extract the glass tube inside the plastic glowstick tube. Put the glass tube in another opaque bottle. If you break the glass inside the bottle then you can just use a syringe or pipet to extract the chemical. Combine the two chemicals in your machine (the Chemical Precipitation section talks some about making a rig) and use a light sensor to detect the output. Use opaque containers and do not open the glowstick packagins until you have to because some of the chemicals may photodegrade, rendering them weak or useless. Some of the chemicals also stain in interesting and permanent colors.

Chem to Elec

Method A: See Homemade Battery bonus

Therm to Elec

Method A: Complete/break a circuit using a thermal sensor

  • Boxed solution: Buy a thermal sensor from your favorite electronics supplies (American Science and Surplus [-off period, it is recommended that you have the sensor start and room temperature and be heated by the machine. If the transfer relies on the removal of heat source, it will be difficult to have the transfer occur in a predictable fashion for timing.

Method B: Break a circuit using a thermal cutoff switch

  • Boxed solution: Buy some thermal cutoff switches (SciPlus?.com sells a package of 4 for $3). They are not reusable, so you should be prepared to buy a large quantity and spend a fair bit of money, which is why either Method A or the homemade solution for this Method is recommended. In any case, simply place the switch, which looks like a resistor, in a circuit and, when you apply the heat to the switch, it will melt and break the circuit.
  • Homemade solution: All you need for this solution is a fairly thin conductor THAT MELTS and subsequent transfer that uses a low current motor/LED/relay. What you want to do is places the thin conductor in a closed circuit and rig the machine so that the heat source will melt that segment of the circuit. It is important that conductor is melted rather than burned. Solder is an example of a conductor that would fit the bill.

EMS to Therm

Method A: A very concentrated light source such as a flashlight with a good reflector can be used to heat a Temperature sensor if passed through a lens. === Method A: Transfer is a dead-

  • Homemade solution: Just grab a little fan from something and have fun.

Method B: Transfer is not a dead-

  • Homemade solution:

Method C: Transfer is not a dead-

  • Homemade solution:

(State and National) Have a lighter than air tethered device rise completely out of the device. More points for displaying a facsimile of the state flag

(National) Draw a 5-7cm diameter circle with pen/pencil on a piece of paper.

Ring a mechanical bell

Tasks and Bonuses of the Future:

Increasing/Decreasing sound level (sound level must always be a clearly nonzero value) Increasing/Decreasing air pressure (air pressure must always be a clearly nonzero value) Increasing/Decreasing friction (friction must always be a clearly nonzero value)) Increasing/Decreasing voltage (voltage must always be a clearly nonzero value) Increasing/Decreasing velocity (velocity must always be a clearly nonzero value) Increasing/Decreasing water pressure (water pressure must always be a clearly nonzero value) Thermal expansion of a solid

Capillary action (spur) Squeezing 1cm to 2cm of toothpaste from a commercially available tube of toothpaste onto a commercially available toothbrush. Homemade motor An operational amplifier A pendulum The gyroscopic effect Flip a quarter (rotate a coin at least 360 degrees along a radial axis) Move an unmodified Post-It note from one vertical surface to another

Battery Choices

Alkaline: Advantages: Low per unit cost. Highly available. Wide variety of useful voltages. Disadvantages: Non-rechargeable. Must be replaced periodically. Mediocre-low Amp Hours.

Zinc Carbon (Heavy Duty/Common non-Alkaline): Advantages: Extremely low per unit cost. Highly available. Some variety of voltages. Disadvantages: Non-rechargeable. Must be replaced constantly. Low Amp Hours.

Lead-acid: Advantages: Rechargeable. Limited availability. Extremely low variety of voltages (Vast majority are 6/12V). High Amp Hours. Disadvantages: Relatively high cost. Larger than most rechargeable batteries. Buy one good 12V one (>10Ah) for around $30 Buy one good 6V one (>10Ah) for around $20

Lithium-ion: Advantages: Disadvantages:

Nickel Cadium: Advantages: Disadvantages:

Nickel Metal Hydride: Advantages: Disadvantages:

Interesting notes found in research: Energizer batteries of equal voltage should last longer, given their specifications (more Ah).


Type Alkaline Heavy Duty (Zinc Carbon) Nickel Metal Hydride Nickel Cadium
Large Lantern 6/52 6/10 - -
Small Lantern 6/26 - - -
9V 9/.625 9/.33 7.2/.15-.175 7.2/.12
D 1.5/20.5 1.5/5.9 1.2/2.5 1.2/1.8
C 1.5/8.35 1.5/3 1.2/2.5 1.2/1.8
AA 1.5/2.85 1.5/1.1 1.2/1.7-2.5 1.2/.65
AAA 1.5/1.25 - 1.2/.85-.9 1.2/.22

As you can see, Alkaline batteries have the most Ah of those 4 types. Alkaline batteries will cost twice as much as Zinc Carbons (the most common non-Alkaline battery), but they will deliver more than twice as many Amp hours. Thus it is always better to buy an Alkaline battery. They will last more than twice as long on the same equipment or will let you use higher draw equipment. Lantern batteries are wonderful for high-draw applications and should last quite some time. One of my teams used a pair of large lantern batteries in four machines over 6 years, the latter two years of which made significant use of nichrome wire.

If you or your school is looking for a cost-effective high power Mission, especially over multiple years, you should strongly consider a rechargeable lead-acid battery. A properly maintained lead-acid battery can last for years. It is a high initial cost, since you have to buy both a fairly expensive battery as well as a way to charge it, but you shouldn't have to buy another. I would highly recommend that you do some of your own research from manufacturer's websites on properly charging lead-acid batteries. If you do not charge your battery properly and in the right conditions, it can be both dangerous to you (nasty fumes) and can result in the loss of the battery.

A Note on Lego Mindstorms and NXT sets

The programming environment/language included in the Mindstorms set is horrible for MPC

  • I would strongly recommend that you use a third-party programming language to code your machine.
  • Look for a text-based language. All of them will be vastly more powerful than the visual language included.
  • NQC is an excellent programming language for Mindstorms. It will take a little while to learn, but the manual is good and the payoffs are enormous. A good programming environment can be found here while the actual NQC site can be found here. If you are using the NXT, substitue NBC or NXC for NQC, both of which can be found here
  • Look for a MPC guide to NQC/NBC/NXC guide to appear sometime.
  • You should always "SetSensorType(SENSOR_#, SENSOR_TYPE_NONE)" for touch and temperature sensors. It is also useful for light sensors if you need to disable the red LED, which can hinder readings for the presence or absence of light. If you are trying to determine the color of an object, leave the TYPE as LIGHT and if you are using a rotation sensor, leave the TYPE as ROTATION.
  • Regardless of the sensor type, use "SetSensorMode(SENSOR_#, SENSOR_MODE_RAW);". This will prevent the RCX from even thinking about using % for any of the readings, which lets you get more accurate results.

A Short Guide to MPC Programming

  • Always include a copy of your code whenever you are asked to submit your ETL.
  • At least one person present for the running of the machine should be able to fully explain the code.
  • Comment your code enough that a reader will at least get the general idea of what is going on.
  • Be especially clear in your comments whenever you use a timer or wait(variable) command. The last thing you want is for a judge to begin thinking that you are running a parallel timer to keep your MPC hitting the exact target time.
  • When you can, code the transfers so that they trigger at variables that are dependent on the current environment, rather than a static number. What I mean by this is that you should try to include sections of code that let your machine adapt to the current light/sound/temperature conditions. Take a sample of the conditions and then have the transfer trigger whenever the sensor reaches "conditions + 5" or whatever is appropriate.