Mind / Iron
by Bryan Bergeron, Editor
Robot Control Options:
Don’t Forget Your Feet
When it comes to controlling a robot arm with six or
more degrees of freedom or directing a rover through a
complex maneuver, it can be challenging to direct
movement in real time. There’s only so much you can do
with two hands and a standard game controller, and a
cumbersome keyboard is often less than optimal.
There are a variety of commercial solutions, such as
3D joysticks. However, these tend to be expensive and
optimized for software control, and not for directing a
robot. Voice recognition is another option, if you use a
dedicated voice recognition chip with low computational
Another option is to look outside of the traditional
controller market, especially in the market that serves
electronic musicians. For example, take a look at the
range of music controllers available for piano, percussion,
guitar, and other musical instruments. My favorite
controllers in the music realm are the various foot pedals
that enable guitarists to change their tone or volume
without interrupting their guitar play. The simplest
volume control foot pedals have a potentiometer that’s
coupled to the pedal. Press your toes down and the
resistance goes up; press your heel down, and the
resistance goes down.
The problem with most guitar volume control pedals
is that they stay where you leave them. If you need a
spring return like a gas pedal, then you can use a high-hat controller. These pedals are designed to operate
virtual high-hat cymbals in an electronic drum set. You
can see a profile of my pedal in Figure 1. This pedal
happens to be made by Roland which is one of several
manufacturers in this space.
You can also use music control pedals for on-off or
single-shot applications. For example, take the piezo-based sensor that’s used in place of a base drum.
Figure 2 shows my drum kicker attached to one of these
piezo sensors. Stepping on the pedal causes the
hammer to hit the piezo sensor which generates an
impulse that can be sensed by a chip. Of course, you
don’t have to use a drum kicker to set off the sensor.
As with the first foot controller, this sensor is made by
Roland ( www.roland.com), but equivalent units are
available from Yamaha and others.
Other foot-operated sensors or switches include
on-off switches sold for dictation machines and line-operated hand tools. My favorite in the latter
category is the Proxxon FS foot controller
( www.proxxon.com). It’s good for about 5A at
120 VAC. For most robot control circuits, you’ll
want to use the switch to do something other than
switch the mains connection to a power supply.
You’ll get more immediate response by switching
the DC out of a supply because the filter capacitors
retain a charge after the AC is disconnected.
The point of this discussion is that there are
lots of off-the-shelf alternatives to game pads and
joysticks out there. You just need to know where
to look. I suggest that you use one of the music
supply websites – such as www.sweetwater.com
or www.musiansfriend.com – to learn the range
of control options available. Then go to eBay and
purchase what you need at a discount.
6 SERVO 12.2010