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 overhead.

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 (http://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 (http://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 http://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.

If all else fails, you can resort to deconstructing Wii remotes and other devices. However, it’s probably better to spend your time and efforts on the robotics, and let someone else engineer the controllers. That is, unless your focus is robotic control and communications. If this fits your profile, then you’ve probably been trying to figure out how to use one of those mind control interfaces such as the one sold with Mattel’s MindFlex Game (http://www.mindflexgames.com) to control your robot.

Mind control may be the ultimate robot controller, but we’re not there yet. So that means you’ve got an opportunity to make it happen ... what are you waiting for? SV

Posted by Michael Kaudze on 11/15 at 10:30 AM


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