This article series will be discussing motorized (a.k.a., robotic) door control. Each part will discuss a specific motor type, as well as a specific limit switch type. In this article, I will focus on using servos for motion and optical limit switches. Part 2
will discuss DC motors using mechanical limit switches, and
the final Part 3 will discuss stepper motors using magnetic
switches and Hall-effect sensors. You can mix and match
motor types with limit switches as your project/application
Opening Doors with Servos
In the hobby world, moving linkages and small
assemblies can easily be done with standard hobby servos.
They’re used in many radio control planes, boats, and cars.
In fact, I have used hobby servos for many years in various
projects to move and control mechanical systems. I have
even used them to open and close small doors.
In Figure 1, you can see a project of mine called,
“Build a Better Mousetrap.” This project uses a standard
hobby servo to open and close a trap door allowing you to
capture a mouse without injuring it. A BASIC Stamp module
reads infrared sensors and controls the servo, which is a
standard hobby type. The thing about standard servos is
that you can control position based on the pulse value sent
to the servo. Standard servos have internal feedback and
know their position, but are limited to about 90-180
degrees of motion.
Standard servos can be used to control valves and large
mechanical switch assemblies. If you need to move
something with a servo that requires more range than a
standard one, then you might need to use a continuous
rotation servo. A continuous rotation servo is modified to
allow the servo to continuously spin, but at the cost of no
longer having positional feedback. Plus, it lacks the ability to
stop at a specific point. In a sense, they’re more similar to a
geared DC motor, except that they still require pulses to
Have you ever wanted
to build a project that
involved opening a
door or access panel
under motor power?
ways to accomplish
such a goal including
different types of
motors that can be
used, as well as
different types of limit
switches. I will also
discuss a few projects
in which these ideas
can be implemented.
By Chris Savage
42 SERVO 09.2016
Figure 1. Build a Better Mousetrap project.