Ask any engineer how to flatten a tension curve, which is what EverTune does, and 9 out of 10 of them will say you should use a spring-and-lever system like the one I designed.
I watched "Moon" on video the other day, and suttonhoo asked my technical opinion of the Helium 3 harvesting machine in the movie.
Roughly I would say the size of the machine was 25 feet wide, 40 feet long, and 25 feet high. The harvester had wide spindly arms extending off each side that were upsetting the surface of the moon. The exact details of that might have been clearer on the big screen, on the small screen it looked like either some form of high pressure jet or laser. The machine ran autonomously on a huge pair of tracks.
The track drive is where the problems start with this machine. Track drives have three defining traits: they are high maintenance, they are heavy, and they give great flotation in soft conditions. The first two negatives generally outway the last positive trait. That's why your Honda has wheels instead of a pair of tracks.
In the context of the moon, high maintenance is a gigantic liability since there's only a single maintenance guy for a fleet of four harvesters. And maintenance is difficult in a vacuum, dangerous work for a single maintenance man. Helium 3 is going to be a very expensive product, and downtime in your operation will be lost millions. Compared to a wheel drive, track drives are in my experience roughly 5 times more maintenance intensive than wheel drives.
The huge weight of a track drive in and of itself is not much of a liability on the moon, except that those tracks have to be fabricated somewhere. If they are fabricated on earth, the cost of hoisting them into space would be probably prohibitive. So we'd have to assume that they'd be fabricated on the moon. But everything you do on the moon is expensive and time consuming. Tracks are a costly design proposition in both the earthly and lunar context.
This leaves us with the one compelling advantage of track drive: flotation. When NASA first landed on the moon they were afraid that there may be many feet of unpacked dust on the moon's surface, enough to swallow the entire lunar lander. In practice, however, the surface of the moon did not threaten to swallow any of the landers or men that landed there. Undoubtedly this was in part due to the moon's low gravity, about 1/6th of earth's. A typical car tire puts about 35-50 psi pressure on the ground.
A typical track drive applies 5-10 psi of ground pressure on earth. But a car tire on the moon, would only apply 6-8 psi of pressure to the moon's surface (with the same amount of tire squash). Effectively a wheeled vehicle on the moon would achieve flotation comparable to a track drive on earth. A track drive would be an expensive and unreliable overkill. If there were flotation concerns, a six wheel drive would be much more compelling. Six wheel drive would be lower maintenance, and allow for lifting a damaged wheel or suspension without stopping. Harvesting could continue until repairs could be scheduled or parts were available, allowing for minimal downtime.
The second problem with the Helium 3 harvester involves the scarcity of Helium 3. In spite of what the taikonauts may want you to believe, it takes a huge amount of lunar material to produce a pound of He3. The concentration of He3 on the moon is roughly .01 parts per million. Any harvester would have to process enormous quantities of lunar material in order to produce a trickle of He3.
I'd expect a harvester to have a huge scraper on front delivering surface material into the machine, and for it to eject over 99.99999% of the material as probably an extremely fine powder. It just didn't appear that nearly enough material was being handled to produce an economically attractive quatity of He3. I will acknowledge, however, the possibly that the lasers/high pressure jet device on the fronts of the machine were extracting the He3 using some futuristic technology. But if so, why were there rocks flying all over the place?
On a more political note, the lunar corp astronauts and employees probably should have been Chinese. Nasa was supposedly returning to the moon in this decade, but it appears that funding for that program will not exist. In fact the U.S. will soon lack any kind of lifter for astronauts, and we'll actually be buying astronauts tickets on Russian rockets. Not that I mean to disparage the Russian space program, they build the most reliable rockets in the world. It just seems a shame that with both the U.S. and Russia's venerable space programs, the real Lunar Corp logo may very well be in Chinese.
Joe-Henry,
The last unanswered question you asked was:
Q. What's the best thing about being a mechanical engineer?
A. We'll jump straight to the experiment on this one. You will be an aerospace engineer for a day. I will be a marketing guy for a day (ick).
As your marketing director, I tell you that I want you to design a balsa wood airplane with a 12 inch wingspan. This is just how it works in real life except the marketing director will say something vague and nebulous like, "I want an airplane just like the Competition's -- only better". It's a good thing I'm your marketing guy.
You don't have to build an airplane if you don't want too. You can build something else instead, like a boat. But my experience is that if the marketing guy asks you to build an airplane and you build a boat instead, they get very upset, even if it IS a great boat. You'd be surprised how often this happens.
So hop in the Galaxy and go to the hobby shop with your Mom.
- You'll need a sheet of 1/8" thick balsa wood (usually 4" wide by 36" or 3" wide by 36").
- Also buy a stick of balsa 1/4" x 1/2" or 1/4"x1/4". They'll probably be 36" long also.
- Get some Elmer’s glue and some modeling clay.
- You'll need a little bit of sandpaper, but your Mom's nail file will also work if you use it when she's not looking.
- Also have your Mom buy a small x-acto knife if she doesn't have one already.
- Also buy 3 Mountain Dews (4 if your Mom wants one).
You should have enough materials to build two planes. Your Mom may complain that this is like $15 worth of stuff to build a balsa wood airplane. Assure her that prototypes are always expensive -- the production model will be much cheaper (she doesn't know this, she's not an engineer).
When you get home, measure out a 6" length of the 1/8" balsa wood. With a magic marker, lightly draw the shape you want your left wing to be on the balsa wood. YOU get to decide the wing shape because YOU are the aerospace engineer. Don't get too wild with the first design, save the more advanced designs for the second airplane. Have your Mom cut out the wing with the Exact-o knife. Lay it on top of the balsa wood sheet and trace it with a magic marker. Have your Mom cut it out, this will be your right wing.
Use the sandpaper to round the front edges of the wings off. Then use the sandpaper to sand the rear edge of the wing to a point (sand off the top rear corner of the wing). You are trying to give the wing a little bit of an airfoil shape. See the picture of the rounded front wing edge and the tapered rear wing edge.
This is the point where most science teachers would talk about the Bernoulli Principle being the explanation for why airplane wings lift the plane. But it turns out that's not really the main reason. It's just that Bernoulli's public relations department did a really good job convincing people that this was the main reason. In reality when flying the wing is tilted just a little bit back. The force of the air hitting the bottom of the wing pushes up on the wing.
The tail will be one piece. Make it about 1/3 the length of the wingspan (12"/3= 4"). Again: You get to decide the shape. Now make the rudder 2" long. The wood grain on the rudder should run vertically so it will be strong. As always, You get to decide the shape.
Now you will glue the wings together. You made a separate left and right so that you could put the wings at an angle compared to each other. This is called a dihedral angle, and it makes the airplane much more stable. Hit your Mom up for a stack of coins. Lay one wing on a sheet of paper. Put some Elmer's glue on the mating surface of the other wing, then use the stack of coins to prop the wing tip up off of the surface of the table about 2.5".
On another sheet of paper, glue your rudder to the top of your tail. Use the unopened Mountain Dew cans to hold the rudder in a vertical position. (See pic).
Pop open the other two Mountain Dews and take a break while the glue dries.
Cut a 12" long piece of the 1/4" thick balsa stick to be the fuselage of the airplane. Glue the entire tail assembly to the rear of the fuselage. Use coins to make the tail level.
After the tail has dried, glue the wings to the fuselage a couple of inches behind the tip of the plane. (See picture). Hit your mom up for a fistful of coins to use to hold the wings and tail even while the glue is drying. R&D costs money.
The last step is to balance your plane using modeling clay. The plane should balance on a pencil placed under the middle of the airplane wing. Add modeling clay to the nose or tail of the plane to make it balance under the center of the wing (see picture). You'll probably have to add weight to the nose.
Now take your plane outside and gently throw it against the wind.
STOP! The anticipation the second before the plane leaves your fingertips, and the satisfaction when it flies.... those feelings are the best things about being a mechanical engineer.
If the plane dives into the ground, move weight to the tail or remove weight from the nose. If the plane stalls (climbs quickly, almost stops in the air, then dives towards the ground), add weight to the nose. If it banks to the right, add clay to the left wingtip. If it banks to the left, add clay to the right wingtip.
A college professor once told me that design is an iterative process. Iterative means you do something more than once, and each time you do it you get closer to the right answer. Build another plane with the other half of your wood. Change all the things you didn't like about the first design. Experiment with your wing design. Put Jefferson Airplane's White Rabbit on the stereo. Dig being an engineer.
Your pal,
B1-67er
Ed.: aka The World’s Best Mechanical Engineer
Joe-Henry,
I'm postponing the answer to number 7 because it's going to take a little preparation to answer it correctly.
Q: What is the favorite thing you've designed?
A: That's like asking what's my favorite work of art in the Louvre (the Louvre is a big museum that the French think is the best). [Ed. I think J-H has put in some time there: we’ll wait for him to comment.]
Here's a few of my fav's:
- A cargo loader that you drive up to the airplane and unload big 15000 pound cargo containers (think of putting all the kids in your class AND the school bus in a big box). I liked this project because we worked on it for a long time and really perfected a lot of the machine. It would even tell you when there was something wrong with the electrical system, and what was wrong.
- A machine that generated electricity when you drove over it in a car. I liked this project because it was the most original idea that I have ever worked on. It was also a project that at first I thought was a bad idea, but as I did the math and figured out what was possible, I eventually decided it was a good idea after all.
- A machine for harvesting Spinach. I liked this project because it was quick and the design ended up being elegant. Elegant means both simple and beautiful at the same time. Tell your Mom she's elegant when she's dressed up. She might buy you a Mountain Dew. The machine has a saw, blowers, shakers, conveyors, and drives like a tank. But it has no electrical complexity at all, no computers or controllers. Most mechanics can fix it even if they've never seen one before. If they can't fix it they shouldn't be mechanics. They should be politicians.
- I also did some consulting for a motorcycle company helping them improve the reliability of their motorcycles. It was interesting because I learned a lot about instrumentation. Instrumentation is when you put special sensors on a machine that tell you things like how fast they are vibrating, how much they are stressed, or how hot they are getting. This is super useful if a part is failing and you can't figure out why. This job was also cool because it makes people say things like, "OOOH MOTORCYLCLES!". Their eyes light up. Sometimes the women swoon.
Pop open a Mountain Dew (your Mom should be stocking it by now) and check out pictures of some of the machines I've designed at www.scottharlanpe.com.
Your Pal,
B1-67er
Ed.: aka The World’s Best Mechanical Engineer
Joe-Henry,
Q. How do gears work?
A. Gears are an entire science of their own. They have to be designed and manufactured very precisely in order to function properly. The little bumps on gears that push on each other are called teeth.
Gears are used to speed things up, slow them down, make them more powerful, less powerful or to change the direction of rotation. But the thing to remember about gears is that there are no free rides. If you use a big gear to drive a little gear, the little gear will spin faster than the big one. But it will have less torque. Torque is a way to measure how hard it would be to stop something from spinning, like if you squeezed the shaft between your fingers.
If you use a little gear to drive a big gear, the big gear would spin slower than the big gear, but the big gear would have more torque. So more speed equals less torque, and less speed equals more torque. There is always a trade. Welcome to the first law of thermodynamics.
Gears are also used to change the direction of your rotating power. Older rear wheel drive cars had the engine in front, a drive shaft running down the middle underneath the car, and a gearbox attached to the axle. That gearbox is called a differential.
This brings me to the experiment. Normally I wouldn't suggest an experiment of this magnitude, but in our current situation I don't think it will happen any slower than the other experiments.
Look on E-bay and find yourself a 1966 Ford Galaxy 500 convertible. Have your Mom buy it. She may balk a little. Here are your sales points:• It won't go down in value, it's collectible.
• She'll look great with her hair flowing out behind her and the top down.
• It's so mechanically simple, you can fix it for her.
• By the time you're 16, gas will be so expensive you'll only be able to drive around the block once a week. That will help keep you out of trouble.
• It's the engineers’ choice.
You'll also need a pair of jack stands, a jack and of course, a case of Mountain Dew in cans. Take a spin around town with the top down, and a Mountain Dew in hand. Your Mom will feel SO GOOD she'll realize she should have listened to all of B1-67er's engineering advice. Tune the radio to an oldies station, preferably something with some soul. If you hear any song by the band "WAR" (the World is a Ghetto, Low Rider, Summer, Me and Baby Brother, etc, etc) you will reach Engineering Nirvana. Ask your Mom to spin by Radio Shack for some of that motor wire.
When you get home, have your Dad or Mom help you put the rear end of the car up on the jack stands. Set the case of Mountain Dew under the car too for added safety and to get the Mountain Dew into some shade. With the emergency brake released, spin one of the rear wheels of the car. Surprisingly, the other rear wheel will turn the opposite direction. That's because the differential (the gearbox at the back of the car) is a very special gearbox that allows the two back wheels of your car to travel at different speeds. This makes a car drive smoothly around corners. If you think about it when you turn a tight corner in your car, the two wheels on the inside of the corner don't travel very far, but the two on the outside of the corner travel a long ways. If it wasn't for the differential, your car would kind of have to bounce and skip around corners.
Pop open a few Mountain Dews and admire your Galaxy glimmering in the sun. And here's a little tip for when you're 16. If reverse isn't working too good in the galaxy, don't park with your girlfriend with the front wheels pointed downhill against a parking block. If you don't believe me, ask B1-66er: he tried it.
There is an alternative to the admittedly costly but rewarding Galaxy experiment. You can stop by Midas and ask them if they have any rear wheel drive cars up on their lifts. If so, ask them to spin a back wheel for you.
— The World's Best Mechanical Engineer
Joe-Henry,
Tell your Mom that your young mind is still very pliable. Tell her that if you don't get some science stimulation soon in the way of experimentation, you may reallocate that part of your brain to Gangsta Rap.
Now on to Airplane doors.
Q. How do airplane doors work?
A. There is no easy answer here because there are many different door designs. I'm actually somewhat familiar with them because I used to design machines that loaded cargo into aircraft.
Now since you are becoming a prodigy in Mechanical Engineering, I can run through this pretty fast. Some of the doors are moved with hydraulic cylinders, some are moved with pneumatic cylinders. For the most part latches on aircraft doors (the part that keeps it closed) are purely mechanical (no electric, pneumatic, or hydraulic latch). This way a loss of pneumatic pressure or hydraulic pressure won't cause the door to come open. Doors coming open on airplanes flying 500 miles per hour would be a BAD thing.
The pilot has indicator lights so he can tell if the door is open before he takes off. I don't know this for sure but there are also probably safety interlocks on the doors. Interlocks are cool and sometimes ingenious features that engineers add to complicated machines to help prevent people from being boneheads. They probably have the doors interlocked with the gages in the cockpit so that it does not allow you to open the plane door when you are high in the air or traveling at 500 mph.
Unfortunately you can't build an airplane door in your back yard. You can however, see the inner workings of a similar door. Hop in the car with your Mom and go to 7-11. Let your Mom drive. Buy three Mountain Dews. Now drive to a bank. Your Mom may already know of one that has a vault with glass on the inside of the door. Offer the bank manager one of the three mountain dews if he'll let you look at the back of the door up close.
If he says no, tell him a mechanical engineer told you it was imperative for your brain development.
When you're done looking at the door, bust out the other two Mountain Dews on the way home.
Then carefully drop the hint: we COULD stop by Radio Shack......
— The World’s Best Mechanical Engineer
Joe-Henry,
Q. How do you move the wings on the end of an airplane up and down?
A. I think you're talking about the ailerons. They are used to control the banking (or leaning) of the aircraft.
Almost all of the moving devices on an airplane are controlled by hydraulic cylinders. Hydraulics is one of my specialties, as much as I have a specialty. A hydraulic cylinder works just like a pneumatic cylinder, except it uses oil instead of air to move the cylinder.
Hydraulics are way more powerful than pneumatics. All the big machinery that you see is hydraulically powered, things like cranes, forklifts, and bulldozers.
Pneumatics operate at around 100 pounds per square inch (about the same as your Mom accidentally stepping on your toe). Hydraulics usually run at around 3000 psi (about the same as a Tyranosaurus Rex stepping on your toe). Because hydraulics are so powerful, you can put a very mighty device in a very small space. That's why they use them on airplane ailerons.
Armed with the power of hydraulics you will now amaze the world by lifting your Mom. Here's how:
Go to the grocery store and buy three things: a roll of duct tape (the good stuff, not some crummy no name brand), a pair of rubber gloves, and that's right... you guessed it.... a two liter bottle of Mountain Dew. But this time the science isn't just an elaborate ploy to get great soda. You actually NEED the Mountain Dew ......bottle. You'll also need a board, like a piece of plywood, big enough to set a chair on.
Then go to a good record store and buy Thomas Dolby's "The Golden Age of the Wireless" CD.
Go home and chug that bottle of Mountain Dew with your Mom. Now squash the two liter bottle flat (but don't put any holes in it). Take the bottle, rubber gloves, a chair, and duct tape out to the garden hose. Dry off the end of the hose, and the top of the bottle.
Put the end of the hose against the end of the bottle.
Now wrap the rubber glove tightly around the connection between the bottle and the hose.
Secure the glove with duct tape. Now wrap the entire joint thoroughly with the duct tape. Overlap a lot of the bottle, and a lot of the hose.
When you think you have enough, put some more on, you'll probably just get one shot at this. Now set the bottle on the ground flat. Set the board on top of it with the hose and bottle neck sticking out, and the chair on top of the board in arms reach of the water spigot.
Put the Thomas Dolby in the CD player and put on "She Blinded Me With Science". Have your mom sit in the chair. Yell, "SCIENCE!" with Thomas Dolby, and turn on the hose just a LITTLE. Hop on your mom's lap, she'll cushion your fall if something goes wrong. The water will lift you and your mom up until the bottle is full or nearly full. If your connection between the hose and bottle leaks, turn up the flow. When the pressure becomes too great, your duct tape will come loose, and the board, chair, Mom and scientist will all drop back to the ground, so keep the fingers and toes out from under that board.
You just lifted your Mom with a few psi[1] of water pressure. Just imagine what you could do with thousands of psi! A cylinder the diameter of a golf ball can lift your Mom's entire car. A few small cylinders could lift your house!
— The World’s Best Mechanical Engineer
Joe-Henry,
Q: How does the driver of the max train control the doors?
A. This is probably the most complicated question you asked, so tell your Mom to get the car keys.
The pneumatic cylinder in the door is controlled by a solenoid valve. A solenoid is a magnet that you can turn on and off using electricity. This magnet moves a valve that allows air to flow to the pneumatic cylinder. A valve is something that turns flow on and off, or redirects it. When you turn on the water in the kitchen sink, you are turning on a valve.
Why don't they just put a bunch of valves like your kitchen sink in the driver’s compartment you ask? Because there are so many things for the driver control. Every car in the train has lights, brakes, doors (probably on both sides) and maybe a bunch of stuff we don't even know about. The driver would need a huge room of controls and there would be hundreds of air hoses between the cars of the train. If you look between the cars, there is probably one or two electrical cables connecting them.
Now it is time for you to make a solenoid. Go to the Radio Shack and get a spool of wire. Preferably "Motor Wire"- thin wire with thin clear insulation. If you can't get motor wire, get the smallest diameter regular wire that you can find. Sometimes radio shack has magnets. If they have any magnets shaped like small rods, buy at least one. Buy a D size battery too.
Now go to a good hobby shop. You need to get a piece of tubing that is just a little bigger around than your rod shaped magnet. Brass is ok, aluminum is ok, plastic is ok, even cardboard is ok. Don't buy a steel tube. If you couldn't get a rod shaped magnet at Radio Shack, the hobby shop should have something. The rod shaped magnet should slide easily in the tube. If all else fails you can make a tube by curling up a piece of cardboard, but it will be kind of hard to work with.
Have your Mom stop at 7-11 and pick up a six pack of Mountain Dew on the way home. This is going to take a little while.
When you get home, wrap a piece of tape around and around and around the outside of the tube at the end. Do this until the tape is about 1/4" thick. Now do the same thing again about an inch down the tube.
You have made a spool to wrap your wire around. Now wrap your wire around the spool as tightly as possible. Leave about 6" of wire outside of the spool at the beginning. Start at one end of the spool, and wind to the other. When you get to the end, bring the wire back to the beginning of the spool and start winding again. The more layers you make, the more powerful your solenoid. So wrap until you're out of wire or until your Mom starts talking about bedtime. Leave about 6" of wire hanging off the end also. Wrap a little tape around the wire so it doesn't come unwound. Scrape the insulation off of both wire ends.When you get to the end of the spool, bring the wire back to the beginning and start winding again.
Pop open one of those Mountain Dews. Enjoy the anticipation of firing up your creation. Share one with your Mom.
You're ready. Put the magnet inside the tube. Touch one wire to one end of the battery, the other wire to the other end of the battery. One of two things will happen: either the magnet will get sucked into the tube, or the magnet will get shot out of the tube. Reverse the wires, and the opposite will happen.
This is how a valve gets shifted by a solenoid. Most pneumatic cylinders are controlled this way.
— The World’s Best Mechanical Engineer
Joe-Henry,
Q. Do the black strings stretch on Max Train?
A. Springs are made out of special steel that is very, very strong. Steel is mostly made of iron, but they add tiny amounts of other things to make it stronger or make it so it won't rust. Spring steel has more than the usual amount of carbon added to it, which makes it super hard to bend. Carbon is an element that many things contain, all plants and animals. Your pencil lead isn't really lead at all, it is carbon. Diamonds are crystals of carbon.
Carbon is common and not rare or expensive. The reason they don't add it to all steel is that it makes the steel very hard to work with. It's difficult to drill holes in, and you can't weld it (join it to another piece of steel by melting it). So mostly just springs are made of this material. The other thing they do to make springs very strong is heat treatment. If you heat and cool steel in the right ways, you can change it's properties, for example make it harder or stronger.
Ten
Originally uploaded by Big-E-Mr-G.
To see how this works, you can heat treat a coin. Have your Mom help you with this. Get a very shiny nickel, dime, and quarter. Set them on the oven burner on "high". When the burner turns red hot, you will see the coins gradually turn different colors. Probably browns and blues. Use tongs to take them off the burner when you like the color.
Drop them in a glass of ice water. You now have colored coins. Heat treatment works just like this but at higher temperatures. Tell your Mom you have to keep them as part of your scientific research.
So springs are made of very strong steel. If they are designed properly, they will not break, even over long periods of time. But they do tend to, "break down". This means if they are pushed on for many years over and over, they tend to get a little shorter over a long period of time. So now they aren't quite as springy as they used to be. Sometimes they have to be replaced because of this.
— The World’s Best Mechanical Engineer
Q. How do the doors on the Max train open?
A. I'm not familiar with this particular train, but I can probably answer this question right anyway. Almost all doors on trains that are automatic are pneumatic. This means that they are moved with air. Air is blown into a device called a pneumatic cylinder. It is basically a tube that is plugged at one end, and has a movable rod plugging the other end. When you blow air into the tube, the air pushes the rod out of the tube.
To see what I mean, go to Taco Bell. Order a large Mountain Dew. Make sure to get a straw that is covered that is covered with paper. Tear the paper off of one end of the straw, but leave the rest of the straw covered with paper. Blow hard into the open end of the straw. The paper cover will go flying off of the straw.
Congratulations, you've just made the world's cheapest pneumatic cylinder. Celebrate by drinking your large Mountain Dew.
The beauty of pneumatics is that they push hard, but not so hard that you'll squash someone like a bug. Pneumatics are lightweight and can be fit into pretty small spaces, like the train door.
