When designing your project, it would benefit you in the design process to think about how you want the project to work, then to pick the appropriate parts which meet your needs.
The following are typical types of movement you might want to make with a motor:
This is a very common movement. Do you want a vehicle to move around a room? An airplane propeller to turn? Let's see how to do this.
It's best to look at how we make other things move and model after that. The most common methods (in order) are:
- Tracks (wheels with connected treads like a tank and Johnny 5 in Short Circuit)
- Friction (a crawling motion)
Most robots needing to roll use continuous DC motors for their speed at an affordable price. Continuous rotation servos can be used - we'll cover that after motors.
Go over the five points for continuous DC motors to decide what kind of motor you want to use.
For small rolling robots with wheels, spinning a platter, and other rotational movements that do not require high speed but do offer ease of use, Adafruit recommends gearbox TT motors. They are easy to mount with screws and brackets, they offer good speed & torque, you can connect a variety of wheels, and they are low cost. The following TT motors are available from Adafruit:
- Yellow TT Motor - 200 rotations per minute, 3 to 6 volt DC, plastic gears
- Blue Bi-metal Motor - 120 rpm (at 6v), 3 to 6 volts, tougher steel gears but more noisy
- Blue All-metal Motor - 120 RPM (at 6v), 3 to 6 volts, toughest gears (also loud)
You pick based on your speed needs and durability. If you are spinning something that will not have anything heavy on it, yellow is fine, but spinning something heavy might be better for the blue versions. Likewise, for a flat terrain, low cost robot, yellow is fine vs. an all terrain Mars rover would benefit from the tougher gear versions.
The nice thing is these motors are similar size - you can start with one and if you find you need something more or less beefy, the others should fit if the length isn't too tight.
Adafruit carries a selection of wheels for TT motors and other shaft connectors including an adapter for lego gears which is very convenient for many projects.
To the left you can see TT motors attached to one of the Adafruit robotics chassis as an example of mounting.
Two TT Motors (yellow) attached to wheels and a chassis. A controller, such as Crickit, can be mounted on the opposite side.
Physics, cranes and puzzle rooms offer us ideas for getting motion in many different angles. Something moves and pulls something up or slides something. Here are some pictures of this type of movement:
For this type of motion, you will want to consider a pulley. A pulley can be driven by a motor directly or have a belt or string drive the pulley from somewhere else. It translates a rotational motion to a pulling motion
Adafruit carries pulleys for:
- Continuous DC TT Motors: 36mm diameter
- Stepper Motors: Timing Pulleys for GT2 Belts
You can also find different sized pulleys and other similar materials on the Internet. You can use dowels (round rods from craft and wood stores) to make your own pulleys. The time tested favorite is an empty thread spool affixed with something like a nail or screw.
For belts, you can use precision belts for specialized applications. But the easiest items for simple projects are usually around the house or craft store. Using rubber bands or thread are the two favorites.
You want enough slack so things will not break during use but not so loose that the mechanism slips when turning.
This type of motion is where Servo motors shine. Servos can move to any angle you want within a 180 degree arc.
For an excellent example of how to use a servo to create motion, look over this guide on animatronic eyes. You can see how two servos provide motion in two different directions. Or look at the animation below:
You can use a servo where you might consider a motor or pulley but the motion is not very big. Reviewing the different horns that can be attached to servos might help you visualize how the servo motion might map into the motion needed on your project.
Take, for example, a locking mechanism. You might have a servo move something that unlocks from the inside.
Servos go back and forth but they rotate when they do that. If you absolutely need motion that goes back and forth but can move just a short distance (a few millimeters!) a solenoid can work.
A solenoid is an alternative to a servo for very short, straight motions. Solenoids use a coil of wire, similar to a motor but fixed, such that metal inside the coil will move in when energized.
Solenoids use a ton of power, are not very strong, and only move a few millimeters!
Adafruit sells several types of solenoids for such applications, but for use with Crickit, we only have a single solenoid that works at 5V. You can see in the animated GIF below, it doesn't move very far!
OK now're at the hard stuff. You want precision motion, like a drawing robot?
You really need to consider your project if you believe it needs a level of precision. You should ask:
- Will a servo be precise enough?
- Is a stepper motor the only way to accomplish this?
Stepper motors are generally a bit more expensive and controlling them takes different circuits than the other motors discussed. But they can travel a full 360 degrees like continuous motors and servos in very precise steps, both backward and forward.
If a stepper motor provides the motion you are looking for, you should decide how the connections will be made to the shaft. You can directly connect to the shaft, use a pulley system or use a toothed belt system.
For direct connections, you will want to use a piece known as a coupler. These are cylinders with a hole in the middle for the stepper shaft and the item you want to spin. There are tiny set screws on the side to hold things in place.
For belted connections, you will need to consider your use. Adafruit sells a nice selection of belts and pulleys adhering to the GT2 standard. GT2 has more rounded teeth and make for a very secure, reliable system.