Continuous DC Motors in Detail!
This is the type of motor most people are familiar with in battery-powered toys. A motor body, usually round, drives a mechanical shaft at a certain rate of speed. If you connect something like a wheel or pulley to the motor shaft, the wheel or pulley turns.
Continuous DC motors turn when the electricity in coils makes a magnetic field which is opposed by permanent magnets in inside the case. Contacts (between the yellow and green wires in the diagram below) change the direction of the current every half cycle, ensuring the coils continue to oppose the magnets and maintains motion.
Continuous DC motors are cheap and plentiful - they're available in nearly any size and speed. Often they are customized to the exact needs of a product!
Motors have a body (the main bulk of the motor) and a shaft (the part in the center that turns). Some motors have a gear attached to power something.
The motors above most likely need a motor mount - a bracket of some sort to hold it in place. Common mounts are aluminum or plastic (3-D printing is good for mounts).
Geared Motors
Continuous motors are very fast - rotating at thousands of RPM. This is often too fast for a project, so to slow it down we use gears. The gears slow down the motor and at the same time increase its strength ("torque")
When the motor comes with several gears as a package, like the one below, it is called a Gearbox DC Motor.
Geared motors likely turn slower than the actual motor shaft. But due to the gearing action, the motor is able to provide more torque - a stronger turning force - which is great in effectively moving a load.
The yellow motor above, called a TT Motor, is a common size for hobby projects as it is powerful and affordable. TT Motors also are easy to mount due to the body shape and provided mounting holes.
As you can see on the right it uses a fully plastic gearbox. This makes it inexpensive and light.
You can also get TT motors with metal gearboxes. They look a lot like our yellow all-plastic-gearbox motors but these have all of the motor gears machined from steel, so they won't strip as easily, and they're twice as slow (and twice as powerful) given their lower gearbox ratio. The metal gears also mean they're louder when running.
Picking a Continuous DC Motor
When looking at continuous DC motors (geared and ungeared), you will want to look at the following characteristics:
- The body size, shape, and weight. What type of mounting points (screw holes, brackets) does it have?
- What type of connection is on the shaft to help connect a wheel, pulley, etc. to the motor?
- How fast does the motor shaft spin at full speed? How much torque (rotational force) does the motor have?
- Does my application need the speed & torque that a geared DC motor provides?
- What voltage does the motor run on and what electrical current does the motor draw when
- starting up
- running full speed
- stalled (if the shaft is grabbed so it cannot rotate)
Buying Guide
Here are some motors in the Adafruit Shop which have been hand-picked for various applications you may be looking for:
Gearbox DC Motors
Accessories
The main accessory you should consider is how to hook the part of your project that needs to spin to the shaft of the motor.
For larger shafts (5 mm to 10 mm), Adafruit sells shaft couplers that fasten using set screws.
TT Motors have a specific shape to their shaft, making it easier to press fit various parts made specifically for a TT motor shaft. Parts including various types of wheels, pulleys, and shaft adapters make for flexible connections.
TT motors also easily support attachment of special disks that, when used with a sensor, can help encode the position of the shaft.
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