Lessons Menu:

• Lesson 1 – Getting Started
• Lesson 2 - Choosing a Robotic Platform
• Lesson 3 - Making Sense of Actuators
• Lesson 4 - Understanding Microcontrollers
• Lesson 5 - Choosing a Motor Controller
• Lesson 6 - Understanding Communication Methods
• Lesson 7 - Using Sensors
• Lesson 8 - Getting the Right Tools
• Lesson 9 - Assembling a Robot
• Lesson 10 - Programming a Robot

Making Sense of Actuators

Now that we learned about robotics in general in Lesson 1 and that the type of robots to be made has been decided in Lesson 2, we will choose the actuators that will make the robot move.

An “actuator” can be defined as a device that converts energy (in robotics, that energy tends to be electrical) into physical motion. The vast majority of actuators produce either rotational or linear motion. For instance, a “DC motor” is therefore a type of actuator. Choosing the right actuators for your robot requires imagination, and a bit of math and physics.

Rotational Actuators

As the name indicates, this type of actuators transform electrical energy into a rotating motion. There are two main parameters governing them: (1) torque, the force they can produce at a given distance (usually expressed in N•m or Oz•in), and (2) the rotational speed (usually measured in revolutions per minutes, or rpm).

AC Motor

AC (alternating current) is rarely used in mobile robots since most of them are powered with direct current (DC) coming from batteries. Also, since electronic components use DC, it is more convenient to have the same type of power supply for the actuators as well. AC motors are mainly used in industrial environments where very high torque is required, and where the motors are connected to the mains / wall outlet.

DC Motors

DC motors come in a variety of shapes and sized although most are cylindrical. They feature an output shaft which rotates at high speeds usually in the 5 000 to 10 000 rpm range. Most DDC motors rotate very quickly, but are not strong (low torque).

To incorporate a motor into a robot, you need to fix the body to the frame. For this reason motors  often feature mounting holes which are generally located  on the face of the motor so they can be mounted perpendicularly to a surface. DC motors can operate in clockwise (CW) and counter clockwise (CCW) rotation. The angular motion of the turning shaft can be measured using encoders or potentiometers.

Geared DC Motors

A DC gear motor is a DC motor combined with a gearbox that gears it down.  This means that the motor’s speed is reduced which, in turn, increase the torque. For example, if a DC motor rotates at 10 000 rpm and produces 0.001 N•m of torque, adding a 256:1 (“two hundred and fifty six to one”) gear down would reduce the speed by a factor of 256 (resulting in 10 000rpm / 256 = 39 rpm), and increase the torque by a factor of 256 (0.001 x 256 = 0.256 N•m). The usual types of gearing are “spur” (the most common), “planetary” (more complex but allows for higher gear-downs in a more confined space, as well as higher efficiency) and “worm” (which allows for very high gear ratio with just a single stage, and also prevents the output shaft from moving if the motor s not powered). Just like a DC motor, a DC gear motor can also rotate CW and CCW.

R/C Servo Motors

Industrial Servo Motors

An industrial servo motor is controlled differently than a hobby servo motor and is more commonly found on very large machines. An industrial servo motor is usually made up of a large AC (sometimes three-phase) motor, a gear down and an encoder which provides feedback about angular position and speed. These motors are usually not used in mobile robots because of their weight, size, cost and complexity. You might find an industrial servo in a more powerful industrial robotic arm.

Stepper Motors

A stepper motor does exactly as its name implies; it rotates in specified “steps” (actually, specific degrees). The number of degrees the shaft rotates with each step (step size) varies based on several factors. Most stepper motors do not include gearing, so just like a DC motor, the torque is often low. Configured properly, a stepper can rotate CW and CCW and can be moved to a desired position. There are unipolar and bipolar stepper motor types. One notable downside to stepper motors is that if the motor is not powered, it’s difficult to be certain of the motor’s starting angle.

A geared stepper motor has the same effect as a DC gear motor; increasing the torque and decreasing the speed. Since the speed is reduced by the gear ratio, the step size is also reduced by that same factor. If the non geared down stepper motor had a step size of 1.2 degrees, and you add a gear down of 55:1, the new step size would be 1.2 / 55 = 0.0218 degrees.

Linear Actuators

A linear actuator produces linear motion (motion along one straight line) and can be described by three main distinguishing features: the amount of linear displacement they are able to produce or stroke (in m or inches),  their force (in Kg or lbs), and their speed (in m/s or inch/s).

DC Linear Actuator

A DC linear actuator is often made up of a DC motor connected to a lead screw. As the motor turns, so does the lead screw. A traveller on the lead screw is forced either forwards of backwards, essentially converting the rotating motion to a linear motion. Some DC linear actuators incorporate a linear potentiometer which provides linear position feedback. In order to stop the actuator from destroying itself, many manufacturers include limit switches at either end which cuts power to the actuator when pressed.  DC linear actuators range tremendously in size, stroke and force.

Solenoids

Solenoids are composed of a coil wound around a mobile core. When the coil is energized, the core is pushed away from the magnetic field and produces a motion in a single direction. Multiple coils or some mechanical arrangements would be required in order to provide a motion in two directions. A solenoid’s stroke is usually very small but their speed is very fast. The strength depends mainly on the coil size and the current going trough it. This type of actuator is commonly used in valves or latching systems and there is usually no position feedback (it’s either fully retracted or fully extended).

Muscle wire

Muscle wire is a special type of wire that will contract when an electric current traverses it. Once the current is gone (and the wire cools down) it returns to its original length. This type of actuator is not very strong, fast or provides a long stroke. Nevertheless, it is very convenient when working with very small parts or in a very confined space.

Pneumatic and Hydraulic

Pneumatic and hydraulic actuators use air or a liquid (e.g. water or oil)  respectively in order to produce a linear motion. These types of actuators can have very long strokes, high force and high speed. In order to be operated they require the use of a fluid compressor which makes them more difficult to operate than regular electrical actuators. Because of they high force speed and generally large size, they are mainly used in industrial environments.

Choosing an Actuator

To help you with the selection of an actuator for a specific task, we have developed the following questions to guide you in the right direction.

It is important to note that there are always new and innovative technologies being brought to market and nothing is set in stone. Also note that an single actuator may perform very different task in different contexts. For instance, with additional mechanics, an actuator that produces linear motion may be used to rotate an object and vice versa (like on a car’s windshield wiper).

(1) Is the actuator being used to move a wheeled robot?

Drive motors must move the weight of the entire robot and will most likely require a gear down. Most robots use “skid steering” while cars or trucks tend to use rack-and-pinion steering. If you choose skid steering, DC gear motors are the ideal choice for robots with wheels or tracks as they provide continuous rotation, and can have optional position feedback using optical encoders and are very easy to program and use. If you want to use rack-and-pinion, you will need one drive motor (DC gear is also suggested) and one motor to steer the front wheels). For stirring, since the rotation required is restricted to a specific angle, an R/C servo would be the logical choice.

(2) Is the motor being used to lift or turn a heavy weight?

Lifting a weight requires significantly more power than moving a weight on a flat surface. Speed must be sacrificed in order to gain torque and it is best to use a gearbox with a high gear ratio and powerful DC motor or a DC linear actuator. Consider using system (either with worm gears, or clamps) that prevents the mass from falling in case of a power loss.

(3) Is the range of motion limited to 180 degrees?

If the range is limited to 180 degrees and the torque required is not significant, an R/C servo motor is ideal. Servo motors are offered in a variety of different torques and sizes and provide angular position feedback (most use a potentiometer, and some specialized ones use optical encoders). R/C servos are used more and more to create small walking robots.

(4) Does the angle need to be very precise?

Stepper motors and geared stepper motors (coupled with a stepper motor controller) can offer very precise angular motion. They are sometimes preferred to servo motors because they offer continuous rotation. However, some high-end digital servo motors use optical encoders and can offer very high precision.

(5) Is the motion in a straight line?

Linear actuators are best for moving objects and positioning them along a straight line. They come in a variety of sizes and configurations. Muscle wire should be considered only if your motion requires very little force. For very fast motion, consider pneumatics or solenoids, and for very high forces, consider DC linear actuators (up to about 500 pounds) and then hydraulics.

Tools

In order to compute the strength (or torque), and speed required for your application, many (rather complex) computations are required involving the physics of the machine to be created. In order to simplify the design process, we have put together a few tools that can help you out.

• DC Drive Motor Selector (useful for robots with wheels or tracks). Also consult the Drive Motor Sizing Tutorial for further details.
• Robot Leg Torque Tutorial
• Robot Arm Torque Calculator

Practical Example

In lesson 1 we determined the objective of our project would be to get a better understanding of mobile robots, while keeping the budget to about $200 to a maximum of $300. In lesson 2 we decided we wanted a small tank (on tracks) that could operate on top of a desk.

First, let us determine the type of actuators that would be required by answering the five  aforementioned questions:

1. Is the actuator being used to move a wheeled robot?
   Yes. A DC gear motor is the suggested type of actuator and skid steering is appropriate for a tank, which means that each track will need it;s own motor.
2. Is the motor being used to lift or turn a heavy weight?
   No, a desktop rover is not heavy.
3. Is the range of motion limited to 180 degrees?
   No, the wheels need to urn continuously.
4. Does the angle need to be precise?
   No, our robot does not require positional feedback.
5. Is the motion in a straight line?
   No, since we want the robot to turn and move in all directions.

Since rotating a wheel needs rotational motion, we could quickly eliminate all linear actuators and choose a DC gear motor. The next logical question was “which one?” A search online shows that there are not too many track systems intended for small robots, which in itself would restrict which motors we could consider.

The Currently Available Track Systems

At 2″ and 3″ wide, the Lynxmotion tracks are more intended for medium sized robots, so we’ll omit them. The price does fall within the budget though.

The Vex Tank Tread Kit is definitely a good option, but it would restrict us to one specific motor.

The Tamiya Track and Wheel Set is definitely a good option, and would limit our choices to Tamiya motors  and gearboxes. This would also be within the budget.

There are several Johnny Robot Track Kits, one for a Hitec continuous rotation servo (which is essentially a gear motor in a servo’s body) another for a Futaba continuous rotation servo, one for Tamiya motors and another for Pololu or Solarbotics motors. This is definitely a good option and also within our budget. Mainly because of aesthetic and motor compatibility reasons, we are going to stick with this choice.

There is always the option of hacking a toy such as an R/C tank and convert it into a robot.  This option would also give us compatible motors, however, the objective is to design our own robot and not hack another product.

Computing the motor requirements

The next step is to fill out the DC Drive Motor Selector Tool, using approximate values.

Data Details

• Total mass of robot: 200 g  encompass everything, including the motors and batteries.
• Number of drive motors: Two motors are required for skid steering.
• Radius of drive wheel: from 0.5” to about 1” should be an appropriate size for a desktop robot.
• Velocity of robot: 0.2 m/s would be nice for a desktop robot.
• Maximum incline: Climbing some books would be cool, let us choose 30 degrees.
• Supply Voltage: Uncertain at the moment, so we choose the default 12 V
• Desired Acceleration: Not sure, so choose default 0.2 m/s²
• Desired operating time: 30 minutes is reasonable.
• Total efficiency: Not sure, so we choose default 65%

Using 0.5 as the wheel radius we obtain 150 rpm @ 1.4 oz-in. When using 1”, the calculator provides 75rpm @  2.8 oz-in.

Selecting the Motor

Thus, the motor we are looking for must turn at approximately 75 to 150 rpm and provide 0.49 to 4.9oz-in of torque. We can use the DC motor Comparison Table in order to find the appropriate motor.

There are many motors available that fit the Johnny Robot Track Kit :

The Solarbotics GM8 and GM9 feature 70 rpm @ 43 oz-in and 66 rpm at 43 oz-in respectively. Both sell for $5.46 each.

All Tamiya gearbox ad motor combinations sell for approximately $11 and up and provide a wide range of torques and speeds.

Hitec continuous rotation servo and Futaba continuous rotation servos sell for  $17  and $14 respectively.

In the end, we opted for using a pair of Solarbotics GM9 in order to use skid-drive, mainly because of their low cost.

I get a lot of emails and comments posted from folks asking questions about robotics. Unfortunately, most of them are rather specific and I just don’t have the time to answer them all individually.

Thankfully, that’s where a few cool products, books, and websites come into play. Back when I first got started in robotics (back in 1998 or so), there were very few books on the subject and even fewer websites or nifty products.

But, times have changed folks! Robots are now almost as cool as iPods and Emo.

I’ve put together a small list of items that you can use to 1) start your journey into robotics and 2) enhance your knowledge. Feel free to leave comments on other useful items. This is meant to be a starting point. It’s also a good place to find good gift ideas … hint hint hint.

Kits

1. LEGO Mindstorms

The venerable granddaddy of all easy-yet-powerful robotics kits, LEGO Mindstorms now comes in two flavors, the old version RIS 2.0 and the new version Mindstorms NXT. LEGO Mindstorms NXT sports an impressive array of new features, like ultrasonic range finders, powerful graphical programming environment based on LabView, and bluetooth, the old version Robotics Invention System 2.0 is still a good buy. You can pick up a set for under $200 off of eBay or perhaps find it on clearnace at your local toy store. Either way, LEGO makes outstanding building systems, and no roboticists shop is complete without it.

2. VEX Robotics Development System

I don’t personally own a VEX system, so I can’t say based on person experience, but I’ve heard lots of good things about them (if someone at Innovation First is reading this, hook me up). The kits are similar in design to an erector set of bygone years, and are very sturdy and well constructed. Vexlabs.com sells a wide array of add-ons and expansions that make the possibilities vast and varied.

3. Viper Robotics Development System

I recently did a complete review of the Viper robotics development system from Microbric. The kit is unique in that it has various modules that connect up to the central motherboard via little plastic connectors that also form the electrical connections. The kit is attractively priced and is well worth it, for the components you get.

The system is programmed in Visual Basic syntax and is based on the Atom processor from Basic Micro.

Books

Why learn the hard way, when you stand on the shoulders of others? These books will expand your knowledge and give you confidence about moving to the next level. Check your local bookstore, or use the links below to order off of Amazon (and help GoRobotics.net out!).

1. Robot Builder’s Bonanza, Third Edition (Robot Builder’s Bonanza)

An oldie-goldie. Gordon McComb does a bang-up job of introducing robotics to the real world. Check out our review of the 2nd Edition of Robot Builder’s Bonanza here.

2. Build Your Own Robot!

Karl Lunt wrote for Nuts and Volts (more on this later) for years. Afterwards, he assembled all his articles into this fabulous book, filled with nifty ideas on how to build a robot. This is great for your bookshelf. You can read our review of Build Your Own Robot! here.

3. Intermediate Robot Building

This is David Cook’s second book, in which he covers the topics of robotics in a bit more detail than his previous Robot Building for Beginners book.

Magazines

Books are great to have, but it’s always nice to have a steady stream of new information coming your way. This is a great motivator, and there’s no better way that by subscribing to some of these magazines.

1. Robot

ROBOT Magazine is a new magazine that focues on the educational and hobbiest market. The high-quality magazine always has interesting and informative articles for both the advanced user and beginners.  You can read our review of the first issue of ROBOT Magazine here.

2. Servo Magazine

Servo Magazine covers all things related to robotics. Not nearly as pretty or well layed out as ROBOT Magazine, but still informative. If anyone from SERVO is reading this, how about a little love and giving us a subscription!

3. Make: Technology on Your Time

This is one hefty magazine! Published quarterly, you can expect to find over 150 pages in this high quality “mook” (magazine + book). They cover all things related to hacking and making things, including robotics and electronics. Well worth the price.

4. Nuts and Volts

A great hobbiest magazine related to all things electronic.

5. Circuit Cellar

This is a bit above most beginners heads, but a great addition for the more advanced user.

Websites

Obviously, since you’re reading this, you’ve discovered the power of the web. Amplify that power by visiting these websites to learn about robotics.

1. GoRobotics.net

Of course we’d list ourselves first! Features robotics news, projects, and reviews.

2. The NXT Step

This a resource site for all things related to LEGO Mindstorms NXT (the first item on our list).

3. Robots Dreams

This site covers all the great robot news from Japan. Gives a fresh perspective on the other side of the world, and it’s in English!

4. Bot Junkie

More robot news to ease your cravings.

5. MAKE Magazine

Hackery and making from all around the internet. TONS of information.

6. Hack-A-Day

New hack every day. A must visit. Submit your hacks.

7. Engadget

All things gadgets. They also frequently link to us, so give them some love!

Toys

1. Pleo

Pleo is a life-like pet dinosaur. You can find out more about Pleo at PleoBot.com. Designed by the creater of the Furby, Pleo will learn and grow like a real animal. Pleo is a big favorite with adults and children alike.

2. Robosapien V2

WowWee toys makes a whole line of robots that are lots of fun and great for hacking. The RoboSapien is probably the most popular.

Hopefully, these links should get you started on your journey. If you have anything to add, please leave it in the comments below. Happy robot making!

This post is part of the ProBlogger group writing project!

Do not miss the new up-to-date and detailed How to Build a Robot – Grand Tutorial Series.

The following article will show you how to build a simple robot, called “The Beetle Robot”, created by Jerome Demers. It’s great for beginners and easy to do.

This is the Beetle Robot v. 3 you are going to build:

Before starting, I suggest you to read the complete tutorials. This will greatly lower the chances of you making a mistake.

Tools Needed:

• soldering iron  ( here’s a helpful tutorial on soldering )
• electronic solder
• diagonal cutter
• Mini glue gun

Components for the robot

• 2x – small 1.5 Volts motors
• 2x – small paperclips
• 2x – big paperclips
• 2x – batteries AAA or AA
• 1x – battery holder AAA or AA
• 1x – 2 cm of heat shrink
• 1x – wooden pearl  (for the caster)
• 1x – meter of electric wire
• 2x – Sub-mini lever SPDT switches
  

(more…)

Ok, so you know nothing about robotics huh? Well, you’ve come to the
right place. Unfortunately there are lots of people like you out there.
Robotics isn’t an easy hobby, and there really isn’t a whole lot of
information out there, especially compared to other hobbies. But, with
a little diligence and hard work, you’ll be up and running in no time.
Below are 10 hints and tips to getting started. Hopefully they’ll help
you avoid some common mistakes.
(more…)

This is a little how-to guide on crimping connectors for various electronics projects. The art of crimping is sometimes a difficult one, but necessary for 1) reliable and 2) decent looking connections. Breadboards are nice for quick wiring projects but in the long run they are unreliable and look pretty nasty.

To crimp you will need:

• Crimper (or needle nose pliers if you’re really good)
• Wire (24 -26 gague usually)
• Crimp pins
• Housings (possibly)

Good crimpers don’t come cheap. Expect to pay $30 – $60 dollars for a good one. If you shop around you can find ‘ok’ crimpers for less. Most crimp tools you find in a automotive section of a store aren’t suitable for small wired electrical projects. You need to find something that will fit 22 – 26 gague wires. This crimp tool from Jameco works well for connetors for D-sub serial cable pins (it can also work on female/male crimp pins).

Take the wire you want to crimp something to and strip off about 4 mm from the end. You basically want to strip off enough insulation so that the exposed wire rests in the wire channel (the smaller second one) and the insulation rests in the insulation channel (the larger first one).

The wire should fit into the channels like the illustration shows. Make sure you have stripped enough insulation, but not too much.

Next, grab your crimp tool. On many tools there will be two different "levels" on the tooth of the tool. This makes sure that the insulation channel has a big crimp than the wire channel, since the stripped wire has a smaller diameter than the insulation. For tools that don’t have two different sizes on the tooth, you will have to make two crimps one for the insulation and using a smaller size, crimp the wire.

You can see the two different groove sizes in the picture to the left.

The next two images show how the pin is placed into the crimp too. The larger side of the crimp ‘tooth’ should be where the insulation channel fits.

Sorry for the blurry picture, but you can make it out, the pin is sitting in the groove with the ‘tabs’ facing into the groove. It is placed so that when the crimp too is squeezed the tabs bend inwards and create a "heart" shape.

If you apply light pressure to the tool at this point the crimp pin will slide up into the groove and be held in place.

At this point you can put the stripped end of the wire through the hole that is made by the crimp too and the insulation channel, like pictured:

Do your best to make sure the insulation channel only covers the insulation and the wire channel covers only the wire.

Apply firm pressure to the tool and it should perfectly bend the crimp tabs inwards so that they "bite" into the wire and insulation and form a solid contact.

It should look a bit like this:

You can seein the picture how the wire channel tabs bend inwards and bite into the insulation.

The pins pictured above are pins that would fit into a D-sub serial connector housing with which you can make a serial cable.

To connect something up to a bread board you can crimp on male crimp pins, like the ones I used on a programming cable I made for a Basic Stamp + breadboard.

If you wish to have crimp connections that connect up to square male pin headers you can buy handy female crimp pins.

The final step to making good connections to buy buy some housings to put your crimpped pins into. The housings keep all the pins seperate and easily pluggable.

I hope this helps someone avoid nasty wiring messes in the future. Happy robot hacking!