How do you select a motor?
The next few pages will help you with what various types of motors can do and you can match capabilities to your project needs.
We will cover all these motors in greater detail in each section, with tips, tricks & gotcha's
For now lets take a quick tour of the different types of motors you can use!
Motor Types
There are the four types of motors that Crickit can drive:
- Continuous DC Motor (ungeared or geared)
- Standard/Hobby Servo
- Continuous Rotation Servo
- Stepper Motor
Here are the two types of motors that Crickit cannot drive:
- AC Motors
- BLDC/Brush-less DC Motors
Crickit can control different motors. Which type of motor you choose depends on the type of application you have in mind. Here is the list of motor types and an idea for when a certain motor may be appropriate for a certain type of movement.
We'll go into these in more detail but here's a rough overview:
Continuous DC motors can turn all the way around like a wheel. You can get them un-geared where they turn at a stunning 2000 to 6000 times a minute (RPM) or geared where they turn at only about 250 RPM.
With Crickit you can control the direction the motor turns (clockwise or counter-clockwise) and the speed, from stopped to full speed.
All DC motors have two wires that are used to power and control them
Ungeared DC motors are good for fans and pinwheels and other light-weight spinning things, but they're too fast/weak for car wheels or moving something around.
Geared/Gearbox DC motors have a 'gear box' a collection of gears that slow down the motor but increase its strength at the same time. They are good for car wheels, zoetropes, cam followers, or other items where you need strength but not a lot of speed
Why Use Them?
- They're really inexpensive compared to servos
- They are both strong and easy to use
- Perfect when you want something to rotate!
"Hobby" Servos are also sometimes called "Standard" or "Micro" servos, are small boxy motors.
The size of the 'box' may vary but they always have three wires for power and control and the three wires are connected together into one 3-pin plug
Servos are a lot different than DC motors because while DC motors turn all the way around, standard servos only move back and forth about 180 degrees. (Note there are 'continuous servos' but we'll discuss these later.
With DC motors you can control speed & direction only! You can't make the DC motor move to a specific location or move just 15 degrees. It either spins or not
With hobby servos you can control angle/location only. Since the servo doesn't turn all the way around, you can be specific about where you want it to move. But they don't spin
Servos are great for small precision movements. For example here's two servos (one standard, one micro) that are used to control a robotic eyeball:
As you can see, you don't need the eyeball to rotate all the way around (that would be way too creepy). Instead, we can have it tilt up-down and left right by using the two servos. By attaching them together we get a full range of 'realistic' eye movements.
Servos also tend to come with horns - these are snap on parts with little teeth that come in different shapes and sizes but are often round, X cross or | linear shaped. You can change the horns by simply removing and replacing, but using a screw with make the connection stronger
Why use them?
- They're the best and only way to have precision motion
- Dozens of brands are available, with different prices, strengths, and some range of sizes
- Very easy to use - set the angle you like and you're done!
- Replaceable horns snap on and off
Continuous Rotation Servos
OK so you know how I just said that servos are good for precision back-and-forth motion only?
Well, I didn't tell you the whole story. There's also another kind of Servo called "Continuous Rotation" which does pretty much what you expect:
Instead of moving back-and-forth with precision motion they rotate all the way around like a DC motor
Now you might be wondering - why on earth are there two different kinds of servos?
Well, many many years ago, robotics started with just the 'standard' back and forth type. But then some makers realized that they rather liked the small square box of a servo and they modified it so it would rotate all the way around.
This makes it act a lot like a DC gearbox motor but continuous rotation servos are usually much smaller, and more expensive!
Why use them?
- They're smaller than DC gearbox motors, and lighter - for when DC gearbox motors won't fit or are too heavy
- For some small robot cars, they can act as wheel drives
- Some robotics boards don't have DC motor drivers because of the cost or complexity, they just have servo drivers.
- The enclosed box shape and horns may be easier for you to use than a DC motor!
Finally we come to stepper motors. Much like their name implies, they "step" along.
These come with four, five or six wires
Like DC motors, they rotate all the way around. But they do so very slowly, because of the little steps they have to take
Like Servos, they have precision motion. But not the way servos do, where you can set a specific angle. Instead you can rotate forward and back by little steps.
For example, here's an animation of a stepper with a flag on it. As you can see it rotates around at a slow but steady rate and can move forward or backward
What you can't see in the video is there's 200 "steps per rotation" and the flag is stepping along 200 times. From this distance it looks like a smooth rotation
You'll see steppers a lot in precision electronic devices like CD/DVD players, 3D printers, scanners and inkjet printers.
Often times the stepper is connected to a gear or pulley that will turn the rotation of the stepper into linear motion. That linear motion is very precise.
But that precision means they're slow to rotate. So even though you could put a wheel on a stepper motor, it would be a very very slow robot car. (That said, it would be a very precise moving car, which is sometimes used with drawing robots!)
There's one catch - you can only step forward and backwards. You cannot tell the stepper to move to a particular angle like a servo. So for example you can rotate a servo 15 degrees clockwise, but you don't know where the stepper is exactly, just that it turned. Sometimes people set up limit switches or sensors to help detect the location of a stepper for this very reason
For example, this 3D printed camera slider project uses a stepper motor
If you tried to connect a DC gearbox motor to the pulley it would whip back and forth and the speeds would be hard to control!
The stepper moves the phone along the railing in slow and deliberate steps.
Likewise the Axidraw use two steppers to make an X-Y moving draw-bot
The movement is very very precise. So much so it can draw intricate patterns with a pen. But it's slow, and complex drawings can take an hour or more!
Why use them?
- They're very precise. Many steppers have 200 or even 500 steps per rotation and you can move one step at a time
- They can 'hold' the current location like servos, but also rotate all the way around like DC motors.
What about AC and Brushless DC motors?
There's two kinds of motors we won't cover at all here, AC motors and Brush-less DC (BLDC) Motors
AC motors require power from the wall, they're used for big devices like floor-standing fans, sewing machines and washing machines. These motors are powerful and need that 120 or 220 Volts from an outlet. Because they are so powerful an high voltage, you cannot control them from a Crickit like you can DC motors. Instead, look at using a relay to switch the motor on or off.
We recommend a enclosed outlet power relay like this one:
Brush-less DC (BLDC) motors are often used in either high-power portable electronics like electric skateboards or drones. These motors require a more precise timing motor controller than we have on Crickit.
While there might be a future Crickit with BLDC drivers, there isn't one right now! To drive BLDC motors, check the place you purchased the motor and ask if they have a recommended driver.
Both types of motors (AC and BLDC) require a lot more care and effort to use so we recommend them for experts only!
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