Robot Builder’s Sourcebook

Linear motion is also used
in many forms of robotic
arms and grippers. For
instance, a roving wheeled
robot might be equipped
with a kind of forklift arm in
the front that can grab
objects. With a linear mechanism,
the forklift raises up
or down to carry objects
around the room.
Finally, certain advanced
legged robots use linear
Actuators-motion products 9
This Rokenbok radio-control
"robotic" toy is outfitted with a
linear motion forklift gripper.
motion mechanicals to replicate walking gaits. One motor swings the leg back and forth,
and another motor lifts the footpad of the leg. To walk forward, the leg is lifted up and
positioned forward. The leg is lowered, and then moved to the back. The process repeats
itself for each step of each leg.
Build Your Own Linear Translation Table—For
Under $20
Industrial linear translation tables cost big bucks because
they are engineered to provide high accuracy under fairly
heavy loads. But for many home-shop and amateur robotics
applications, supreme accuracy under heavy-duty use is
not critical. This makes it possible to build a workable linear
motion translation table for little spending money. Nearly all
of the materials are available at hardware stores. Here's
how:
A walking robot can use linear
motion to lift its legs for each step.
Photo Jim Frye, Lynxmotion, Inc.
A clamping-style coupler can
be used to connect the allthread
to a motor shaft.
Start with a length of 3/8-inch all-threaded rod. The rod is available in 1-, 2-, and 3-foot
lengths. Get the length you need for your application—if you're building a translation table
that requires an 18-inch travel, you'll need a 2-foot length. The threaded rod will act as the
leadscrew.
For the leadscrew nut purchase one 3/8-inch coupler. The coupler looks like a very long
hex nut, and in fact, that's exactly what it is. You will need to glue this nut to the moving
carriage of your translation table. Use a fast-setting epoxy. Don't use superglue or its ilk,
as it won't stand up to the mechanical stress.
You will need at least one guide shaft, and two is preferable. Look for a pair of 1/2- or
3/8-inch-diameter steel cold-rolled shafts at the same place in the hardware store as you
found the all-thread.
The carriage transport can be made out of a block of wood or plastic. Plastic is marginally
better as it doesn't swell with moisture or heat, but a good hardwood such as birch will also
work (don't use oak as it's too heavy, and don't use pine because it absorbs moisture like a
sponge). Drill three holes in a triangular configuration, with the center hole near the top. The
two holes for the shafts should be drilled carefully and should be only slightly larger than the
diameter of the shafts. Drill the larger center hole so that it accommodates the 3/8-inch
coupler. Measure the coupler at its widest point, and select a drill bit accordingly.
The front of the translation table requires careful drilling as well. Drill two holes for the
guide shafts just large enough so that you can firmly seat the shafts into the wood. You
can always apply epoxy if there's some play. You may wish to drill the holes for the car-