Fundamentals of Mechanical Design

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Here is Gui's giant list of sources for purchasing components (at both a hobby level and real level) and learning about new mechanical design topics.

This is my working list of all of the sources of information and parts that I use on a regular basis as a mechanical engineer and designer, in addition to being a robot hobbyist.



Real Mechanical Parts

  • McMaster-Carr ( You can buy just about every mechanical part you could hope to use on McMaster-Carr, including materials of all shapes and sizes, power transmission parts, machining bits and pieces, and more. If it's involved in the operation of factory automation in any way, or the construction of factory automation, McMaster sells it. You will get it within 2-3 days no matter which shipping option you choose (I've packages arrive at work the day after I click "order" even when shipped ground)
  • Stock Drive Products/Sterling Instruments ( This is like McMaster-Carr except more focused on power transmission components. Gears, pulleys, belts, shafts, bearings, etc. - all well-cataloged and relatively cheap. Note that they have a "Metric" catalog and an "English" catalog, and the components are different.
  • W.M. Berg ( An alternate to Stock Drive Products, if they're out of stock or don't have the one type of component you're looking for. They tend to be a little more expensive and a little harder to navigate.
  • Motion Industries ( With warehouses all over (one of which is less than a 2 minute drive from Joy Street), these guys are a McMaster-Carr equivalent and can supply the same kinds of parts and raw materials - except they also have a storefront.

Hobby Mechanical Parts

  • Tower Hobbies ( All the hardware you could possibly want for remote-control model-sized hobby projects. Tiny spherical bearings, carbon fiber rod, random bits of fabric that are hard to find, propellers, you name it. Anything you need to build something the size and weight of a high powered remote control car. (Also a good source for hobby RC servomotors, for the record)
  • Hobby Lobby ( Like Tower Hobbies, but poorer documentation. Hobby Lobby tends to have cool assemblies (like propeller assemblies mated to motors) that Tower Hobbies doesn't - Tower Hobbies usually has parts that you can click together to make stuff, but they don't sell you finished assemblies.
  • Small Parts ( These guys straddle the line between hobbyist and real parts, but I put them on the hobbyist side because of their selection. Their name is their specialty: small parts you can't find anywhere else. I haven't found another source for surgical-needle size hollow tubes, for instance.

Real Motors/Controllers/Robotics

  • Maxon Motor ( If you want the highest performance motors and gearboxes, the buck stops here. Don't look any further. Prepare yourself to look through endless catalogs and configurations, and expect to pay at least $200 per gearmotor.
  • MicroMo/Faulhaber ( The runner-up to Maxon, these guys tend to have slightly less expensive, slightly less capable motors. They also tend to have sizes that Maxon doesn't have. Quotes required.
  • Elmo Motor Controllers ( The best electric motor controllers in the business. You can opt for cool options like shock-hardened, dustproof casings... but expect to pay for it. Quotes required.
  • Galil Motor Control ( For all your ethernet-enabled robots and mechatronic needs. These guys offer fairly low-current motor controllers, but the benefit is that their systems are rock solid and control huge numbers of motors at once.

Hobby Motors/Controllers/Robotics

  • Robot Marketplace ( If you're looking to build anything like a Battlebot (drives around on four wheels, weighs between 5 and 600 pounds, needs high-powered electric motors and remote control equipment), this is the place to check. All of the components are new, well-documented, and well-supported if you call them
  • Trossen Robotics ( If you're looking to build something more intricate and animatronic, Trossen Robotics is the place to go. It has all sorts of high-accuracy components like servomotors, and all sorts of sensors and robot controllers. If you want to learn from robot kits, buy from here. If you're looking for the highest quality servomotors and kits and have lots of extra money kicking around, check out their Bioloid kits.
  • All Electronics (, specifically You will not find a better source for inexpensive bargain motors. They're all overstocked, they have completely random mechanical specifications, but they all work. If you see anything from Maxon or Faulhaber, buy it immediately - these are precision-grade motors that just happened to be overstocked.
  • Lynxmotion ( For all your legged robot kit desires. These kits are cheaper than the Trossen Robotics kits (though, buyer beware, that means they're less capable), and some can be pretty cool looking. I highly recommend the SSC-32 servomotor controller - it's one of the easiest ways I've found to interface with huge numbers of hobby servos.
  • Robot Store ( If you need lots of sensors, or small/hard to find mechanical bits, you could check here. I don't use them as a primary source of hardware, but I check them from time to time and they occasionally surprise me.

Local Raw Materials Suppliers

  • Admiral Metals ( Tons of different kinds of metals available in all kinds of sizes, with a "storefront" to boot. All the way out in Woburn, but their selection is worth it.
  • Turner Steel ( A local supplier of really, really cheap steel and a couple of other metals. They tend to want to deliver in 21 foot lengths, so be careful when you order to designate what sizes you want the stock in....
  • Boulter Plywood ( Super close to Joy Street, these guys stock all sorts of hardwoods and softwoods. They also stock oversize sheets (5x10) if you need them.

Online Raw Materials Suppliers

  • Online Metals ( The best place I've found to go for arbitrary length raw materials of arbitrary types of raw materials, second only to McMaster-Carr (but way less expensive).
  • Aircraft Spruce ( For all your performance-grade materials delivered cheap, check out Aircraft Spruce. Their primary market is people making hobby aircraft, and their selection shows.
  • Exotic Wood ( All kinds of hardwoods available online. I've never ordered from these guys, I just know they exist.

Reading Material


  • IEEE Automatons ( A robotics blog with ties to the defense, commercial, and recreational industry. These guys tend to report on all kinds of mechatronic developments.
  • Machine Design ( A free trade magazine that offers monthly tips on design practices, spotlights on new mechanical designs, etc. etc. To be honest, I got it for the advertisements - this is the primary venue for new mechanical engineering products to be advertised, so if you ever wanted to know what's the newest development in real mechanical design, you get this magazine. That being said... I've been trying to stop receiving magazines for the past two years, and I haven't gotten them to cease and desist yet. So decide now if you want to receive a mechanical design magazine FOR THE REST OF YOUR NATURAL LIFE.
  • Make Magazine ( Do it yourself TO THE EXTREME. These guys are the forerunners of the new national do-it-yourself movement, and strong proponents of hackerspaces and makerspaces nationwide.
  • ( A blog dedicated to robots and cool inventions. They have tons of fun stuff all the time, and are worth a check every month or so.

Online Education

  • How Stuff Works ( As corny as it is, I learned most of my initial foundation of mechanical engineering knowledge by reading How Stuff Works. They tend to have really well-thought out articles that, while not necessarily deep, are certainly good broad overviews.
  • Instructables ( A great place to go for DIY projects with really good explanations.
  • Let's Make Robots ( A fun, interactive community of people who post their hobby robots and how they made them. This project was started by the guy who made the Little Yellow Drum Machine, one of my favorite hobby robots ever (
  • This Old House ( I would be completely remiss if I didn't mention This Old House. Go get your home improvement on something fierce.
  • Open Courseware ( MIT is on a mission to publish as many of its courses as possible, and the result is Open Courseware. If you ever wanted to learn basic physics (or quantum physics, for that matter), check out their online syllabi and projects. I suggest attempting this with a friend, however, as it's super easy to just drop online courses like this without continuing motivation.
  • KMODDL ( The Kinematic Models for Design Digital Library, hosted by Cornell. These are basically the coolest kinematic models you'll ever seen, most of which were built between 1850 and 1925 (when mechanical engieners and machinists were Badass Heroes You Don't Fuck With). Any motion you could possibly want to make can be derived from the mechanisms buried here.
  • Technology Student ( You have to forgive the website, but this site contains everything you could possibly need to know to restore mechanical engineering and design as a profession if the apocalypse hit. Come, be prepared to withstand harsh graphics, and learn tons of stuff.


Homework Assignments

Homework 1

Sent out before the first class:

  • Go to and search for "Wood Screws". Select the "Wood Screws, Carriage Screws and Lag Screws" link. Note the little line underneath the title that says something like "1,444 products match your selections" - you're looking at a huge cross-referenced database of almost every type of wood screw known to man. Your challenge is as follows: I want to join a pair of 2x4s in a T shape that's meant to survive outdoors in all weather conditions. I want to drive two screws through the top horizontal plank and into the vertical plank's end grain. Sift through the 1,444 wood screws available from McMaster-Carr and select the one part number that you think would be ideal for this application. Write a brief paragraph about your reasoning.
  • Without looking anything up, estimate how much your car weighs. I want both an overall weight and a weight breakdown by subsystem - give me weights for the frame and body paneling, engine, powertrain (power transmission components like the transmission, shafts, etc.), interior, and gas tank. Give me a knee jerk reaction to the overall weight (spend no more than 1 or 2 minutes thinking about it, then write down a number) and then give me a breakdown that you've spent no more than 5 minutes thinking about. Write a paragraph about your reasoning for both sets of numbers
  • Without looking anything up, estimate how much force you think it would take to pull a 1/4" bolt in half by pulling on either end of it. Now imagine that you've threaded it into a thick wall. Estimate how much force you think it would take shear the bolt off at its base. No paragraph necessary, just numbers.
  • Why do you want to take this class? What's your motive to sign up for this here and now? What factors got you to press the Buy Now button?
  • What are you hoping to get out of this class? What would you like to walk away with?
  • What has been your most significant design failure (topic left intentionally vague, and no I will not clarify further)? What lessons did you learn from that failure?

Homework 2

Read up on these things:

Free Body Diagrams:

Screws and Bolts:

Ball Bearings:

  • This is a pretty good (if slightly hokey) intro to why we use ball bearings, and how they work:
  • Once again, head on over to . Search for "ball bearings". I want you to spend at least 10-15 minutes browsing through all of the categories of bearings they offer - start in the "Ball and Roller Bearings" section and explore that most thoroughly (being sure to check out all of the different ball bearing types for sale), then look through the other types of bearing (linear, mounted, thrust, etc.) as your interest carries you.

Wooden Joints and Construction:

  • Go here and read everything under the "Joints" heading: . This is a great set of examples of many of the different kinds of designs that can be used in wood to create structural joints. We'll go over their relative strengths and weaknesses in class.
  • Learn about the main categories and types of wood you'll be dealing with in your future projects here:
  • Check out the dimensional tables for lumber in this Wikipedia entry: . Note that the word 2x4 DOES NOT MEAN you get a 2" by 4" cross section. Only read the article if you really care, I'm mostly just interested in the tables.

Metals and Plastics:

Homework 3

Read up on the following:

Motors and Actuation:

Power Transmission:

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