As part of our Mechanics theme this month, we’re giving away three signed copies of Dustyn Roberts’ awesome Making Things Move. This book is the perfect introduction to understanding basic machines and mechanisms and how to more intelligently incorporate them into your projects.

We’ve been having such a great response to using these giveaways as a way of building a crowdsourced Q&A on a given theme. So, to be eligible for the book drawing, tell us what some of your most pressing mechanics questions. Have trouble figuring out gear ratios? Need to know when to screw it and when to glue it? Need to understand the relationship between force and torque? Whatever your question, ask below. And, as always, if you answer questions from your fellow makers, you will also be eligible for the drawing. Deadline for the drawing is next Tuesday (3/15), 11:59pm PST. Winners will be announced on Wednesday.

Skill Set: Intro to Machines and Mechanisms (with an excerpt from Dustyn’s book)

Gareth Branwyn

Gareth Branwyn

Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. And he has a new best-of writing collection and “lazy person’s memoir,” called Borg Like Me.

  • Richard

    I constructing a fischertechnik 3D printer. What is the best way to prevent backlash for precise movement? Thanks!

  • Laura Baran

    What is the best material for a belt to prevent slippage when using a standard metal pulley?

    • Anonymous

      It depend on the torque. If the torque is low almost anything will work. As torque increases you have to think in terms of increasing the friction between belt and pulley so that the belt doesn’t slip. The two factors there are belt tension and belt “stickiness.” The tighter the belt the more friction but also the stronger the belt itself has to be. Automotive type belts are ideal as they are synthetic rubber, which is fairly sticky, and reinforced with fibers running long ways which increase the strength of the belt to prevent stretching.

    • Drew

      Without more details on size and power, it’s difficult to say. But realistically for prototyping, I would suggest seeing if you can get an O-ring that is the correct size. I’ve seen lots of students try to use rubber bands, Rubber bands usually don’t work very well, because they are too stretchy. For doner parts,you might be able to raid old audio cassette players and record players. For preventing slippage, you will usually need some way to adjust the tension in the belt, one easy way is used on makerbot, mount the idler pulley in a slot, so you can pull it back:

  • Katmando

    Yes, What gears to use and what ratio.

  • Anonymous

    How do you eliminate gear backlash under a given load? When do you use scissor gears, when do you use optical encoders, and when do you turn to more involved solutions like herringbone gears, ball screws, and pre-loaded gearing?

    • Honus

      An optical encoder wouldn’t really control gear backlash- it’s primarily used for determining accurate positioning by referencing motor rotation. For light loads (like a small home desktop CNC for milling wood and plastics) pre loaded ACME screws using Delrin nuts works well. For larger loads (milling metals) ball screws are preferred as they can sustain higher loads with minimal friction. Controlling backlash is usually a case of cost vs. packaging vs. friction vs. load requirements.

    • clide

      By using optical encoders directly on the shaft or linear position that you want to reference you can make it so that the position (as the computer knows it) is not affected by the backlash in the system. This is how they are used in printers, which allows them to do very accurate positioning with cheap motors and gears. It can also be used in systems like laser cutters and drag knife cutters.

      However on something like a milling machine where backlash can be a problem beyond knowing the absolute position of the components then you want to deal with backlash in other ways like Honus mentioned.

  • Raven Varela

    Exactly how does an internal combustion engine work?

    • Anonymous

      To answer at the simplest level it converts the chemical energy in the fuel into mechanical energy.

      Such an engine is a complex assembly of interconnected parts that is difficult to describe. The task is complicated by the fact that not all engines operate exactly the same way but I will try to give you the general idea.

      Gasoline is sprayed as a mist by the carburetor in to a stream of air being drawn into a hollow cylinder by the movement of a fairly tight fitting piston. A valve then closes trapping the fuel air mixture in the cylinder. As the piston continues in its up and down movement within the cylinder it compresses the fuel mixture. At just the right moment a spark plug strikes an electric arc within the cylinder igniting the compressed fuel. As the fuel burns it produces heat and gas. The expansion of the gas drives the piston back down. As the piston rises again a valve opens and the spent gases, exhaust, are pushed out of the cylinder so that the cycle can repeat.

      The piston, or pistons, are attached to what is called a crank shaft. As the piston rises and falls it turns the shaft much like your feet rising and then pushing on peddles turn the front sprocket on a bicycle. The burning fuel drives the piston down, turning the crankshaft and that momentum then caries the piston back up.

      The crank shaft also either directly or indirectly drives all of the other processes that keep the thing going. These processes vary from one engine to the next but may include running a fuel pump to feed fuel to the carburetor, electrical switching that controls the timing of the voltage to the spark plug and some mechanism to open and close the valves at the appropriate time and of course whatever the engine is powering.

  • Léo Marius

    I’d like transform an vertical rotation from a motor in multiple horizontal translation (back and forth) all around the axis in an small space, what’s the best way to do ?
    For now I think I’ll use an decentered weel and put spring on the horizontal axis, I’ll use ABS (RepRap), did it’s durable ? Did I’ll need to put something on for solidify ?

  • Anonymous

    Gear ratios! I am still learning my circuitry too.

  • Anonymous

    Is there a formula for the size of gyroscope one would need in a project? I’d like to be able to use the smallest lightest possible and still have it work for stability.

  • B.r. Green

    Given requirements such as maximum acceleration, velocity, total weight; what is the most correct way to work backwards to gear ratios and engine requirements.

  • Daniel

    How do I make a gearbox?

  • Colleen Cole

    What would cause brakes to squeal more when it rains or during the winter?

  • Victor Hugo Elizondo

    Is it possible to make a perpetual motion machine?

    • Engineer Zero

      It depends on whether you mean by ‘perpetual motion machine’ what many people mean, which is a machine that produces more energy than it takes in. According to the known laws of physics, that’s impossible.

      If you mean a machine that is perpetually in motion — ie, moves forever — then the Voyager and Pioneer space probes are good approximations of that as they are machines and they’ve been in motion through space for decades and will likely continue to be in motion for thousands if not millions of years.

      On Earth, supercooled superconductors have been shown to retain electric current without significant loss for years.

      There is a magnetic top toy which ‘levitates’ when spun. If spun in a vacuum, and assuming that the base is properly secured to prevent loss of energy through vibration, then I suppose it could continue in motion for some time as well.

      If I understand Stephen Hawking as filtered through science journalists correctly, the laws of physics mathematically require the creation of the universe. So math is a heavy subject after all, but how you could harness this for practical use is beyond me. Apparently, you can create something out of nothing providing that there is nothing there to begin with, but once there is something, that’s all you’re going to get. Like I said, beyond me.

  • Jeff Proefrock

    What is the difference between a single and double acting steam piston/engine?

  • Rob Colby

    How can I make my own gears from wood and other such materials. Like how do I figure out tooth size and spacing as well as strength gained from said gears. Ultimately I want to learn to build a wooden clock, but I want to start with the basics. Maybe someone knows a good book?

  • Benjamin Daniel

    How is the tip of an scanning tunneling microscope get made? It can’t possibly be lathed out, since it’s only a couple atoms wide at the tip. Is it a chemical process (like growing crystals in a jar), a mechanical process (drawing the tip out with magnetism?), or some physics/quantum mechanics method?

  • Matt

    What is the technical difference between a motor and an engine?

    • Honus

      In simplistic terms, typically a motor is defined as a device that uses electrical energy and an engine is regarded a device that uses thermal energy. If you want to get really technical it’s more involved than that as a rocket motor is not electrical…

  • Breton Bienvenue

    What should I have as a basic toolkit for mechanics projects? How much overlaps with woodworking or electronics tools and how much is unique?

    • Anonymous

      Mostly they overlap. You would definitely need wrenches and a good socket set though.

    • Drew

      Here are some tools I find very useful with metal (and plastic) that I don’t use much with wood or electonics.
      Digital Micrometer, Metal files, Micro files, Metal scribe, centre punch, Hacksaw and junior hacksaw with fine toothed blades for metal, metal set square, 15cm and 30cm Metal rulers. Allen keys (buy good quality), socket set or spanner set (start with at least 1, you will eventually buy both), Hand cleaner (Swarfega or similar), and a good box to keep it all in.
      200-300 USD should sort you our with a good starting kit.
      Please google any that don’t make sense.

  • JAmes

    Why do boobies bounce?

    • Drew

      It’s part of the mating ritual:

      They don’t so much bounce as rock side to side ;)
      link is SFW, Drew

  • Anonymous

    Is it possible to use a worm gear to increase torque, then to use gear ratios to increase the speed of the output or will that just cancel out the torque increase of the worm gear?

    • Honus

      In regards to gearing, increasing the speed has the opposite effect of increasing torque. If you know the final speed an output shaft needs to turn you can find a motor that has a higher speed and then gear it down to increase the torque output or you can get a higher torque motor that is lower rpm and then gear it up to get your necessary final speed.

      Of course this doesn’t take into account things like motor efficiency or power draw.

  • Taylor

    I’d like to understand how to make gears efficient for different purposes

  •[email protected] D H

    What is backlash?

    • Brian Givens

      When two gears mesh, ideally the teeth of one gear fits perfectly into the gap between the teeth in the other gear, so that there is good contact between the gears however they are rotated. This is never true in reality, so there is always a gap. When one gear is rotating and moving the other gear, then the direction is reversed, this gap will cause a delay in the driven gear starting to rotate, while the gap is being taken up. That is backlash. This matters when the gear train is used for positioning, such as the X-Y table on a milling machine. When you turn the handle to move the table +0.25 in X and then back -.125, you will ideally be +.125, but you will be a little more than that because the beginning of the – move was closing the gap between the teeth in the gear train, not moving the tale in the -X direction.

  • Priscilla Kinter

    I’m totally stumped by gear ratios. I get them in theory, but putting them into practice is another matter. This book looks like a cool introduction.

  • Gaspar Quelhas Lima Tameeris

    How does one power a three degree of freedom joint (sort of like a hip joint) in all three directions?

    • Anonymous

      With limited range of motion, you could have a peg through the back of the socket that was pulled in various directions by a type of cable, but that wouldn’t allow twist very well. Probably the way various muscles are attached in an actual leg is the best solution. Could your application use linear actuators attached like that?

  • Stephan Metelica

    Please teach me how a sprag clutch works in a helicopter?

  • Drew

    Can you suggest lots of easy ways of fixing a small electric motor to a gear or pulley? Methods are especially suitable for making with simple tools at home workshop, for 1 off prototypes.
    Thanks, Drew

    • Dustyn Roberts

      Hmm I cover this in a section in chapter 7, I’ll see if I can get you an excerpt! Basic run down: set screws, shaft collars and epoxy putty, dowel pins, mounting flange… it’s best to get a gear or pulley designed with a clamp hub or set screw hub already so it makes your life easy. Check out, they have lots of gears and pulleys designed to fit on the motors they sell.

  • Laura F. Walton

    What would be the best way to create three-jointed arm movement (shoulder, elbow, wrist) in a very large one-armed puppet? The arm will be around fifteen feet in length, but fairly light. Should I consider attaching motors and pulleys to the ceiling? Or servos in the joints themselves? Or…?

    • Dustyn Roberts

      I think your motors and pulleys attached to the ceiling idea sounds great! Then you can use some braided fishing line or something to move the parts. Anything 15 feet in length will be pretty heavy, and each motor you put on adds weight that the next motor down the line has to compensate for.

      • Laura F. Walton

        Thanks, Dustyn! I think you’re right; this method should also mean less unwanted freedom-of-movement. The puppet will be onstage during a concert– lots of unpredictable activity going on– and so the more robust and less complex, the better.

  • Steve in Bloomington

    Our hackerspace has taken it upon ourselves to build a Straandbeest for our town’s annual 4th of July parade.

    Needless to say, though we have some nice plans for building the legs, this introduces a host of mechanical problems to solve, so it’d be great to have a reference to consult. (For example, how best to mount the legs so as to ensure smooth operation).

    • Dustyn Roberts

      Madagascar Institute made a big metal version of these legs – try Googleing around for pictures or send them an email!

  • Christian Restifo

    Some hints on cheap, DIY dynamic braking would be helpful. I’ve got a couple ideas for projects where I want to accelerate something and then quickly slow it down without a hard stop. Sort of like the stop you make on the forward cast when fly fishing: a very quick stop but not a “snap.”

    • Dustyn Roberts

      If you can can reroute the motor leads to a resistor when you want to break, that will be faster than just turning off the power supply and letting it coast to a stop. You can also reverse the polarity of the power supply (called countercurrent braking) for a short amount of time to get it to stop really fast, but then flip it back before the motor starts to turn the other way -you can do this with an h-bridge.

  • Addidis

    One of my goals is to make a robot army and take over the world. Ive figured out how to make motors servos and steppers move at various speeds but now to continue this very important work I will need to be more familiar with gear ratios , transmissions , and virtually every other bit of knowledge I can get my hands on. :) But on a serious note if I see something and cant figure out how it works Im going to have to disassemble it . Having a book to learn as much as I can before I see something I dont understand would save me money :)

  • Anonymous

    I would like to learn more about gear drives as my Kinematics course did not cover this.

  • subreyes94

    I’m trying to make a lot of space-saving things that expand like a folding cane. How does a folding cane work?

  • Anonymous

    I’d like to learn to play with clockworks. I have some cool steampunk like art designs that I want to implement. Some advanced math processes I’d like to encode in gear trains… I made the mistake of picking up some of the more advanced engineering text books but I lack the fundamentals those books assume you have.

  • Anonymous

    I would like to hear ideas for a good beginner project to build with children ages 2-8.

  • starrett micrometers

    Aw, this was a really good post. Spending some time and actual effort to generate a top notch article… but what can I say… I procrastinate a lot and don’t manage to get anything done.