FIGURE 2. Motor mount and battery detail.
After developing the platform up to Level 1, I saw it
would be easy to convert it between fully autonomous, fully
telerobotic, or somewhere in between. This platform can
accomplish much of what platforms like the Anybot or Texai
can at a fraction of their costs.
The original GoPHR platform was built in just a day. I
was going to use a plywood (excuse me, naturally derived
engineered layered composite) sheet, but I happened to
find an empty cable spool that was the perfect size. This
saved me from trying to find a band saw or using a hand
jigsaw to make the curved cuts. Since the initial design
worked so well, I acquired a second cable spool, and used
the plywood disks to add two more ‘decks’ to the robot. I
used steel electrical wire conduit to attach the decks
together. Figure 1 shows the entire GoPHR set up as a
Current attachments are a sweeper (“Shark”) and a
damp mop (Swiffer). A spatula/scooper will be added to a
deployable arm on the mid-deck in the near future.
FIGURE 4. Motor power and control.
FIGURE 3. Battery wiring.
The motors are two 12V Globe motors. These use
planetary gear reductions similar to what is used in cordless
drills. As a result, they are somewhat noisy. An alternative
would be to use a motor with a built-in worm gear
reduction. These are usually quieter, but may be harder to
mount. The motors were attached to the chassis by
constructing mounts from aluminum angle, scrap wood,
and plumber’s metal tape. These were attached to lawn
mower wheels using an aluminum axle and an axle bearing
block made out of plastic. (This was surplus cutting board
obtained at nominal cost from a plastics wholesaler.) The
most challenging machining issue was fashioning the shaft
couplers that join the motor to the wheel axle. This was
done on a metal cutting lathe using 3/4” aluminum rod,
and then drilling and tapping #10 machine screws to attach
the coupler. (See Figure 2.)
I used a 12 volt power system since automotive parts
are readily available, as are the sealed lead-acid batteries
used in UPS backups. It helps to use good connectors and
switches; be careful to tape all bare battery cables. I am
sorry to say I learned this lesson the hard way when the
chain holding the battery in place slipped and shorted
FIGURE 5. Ultrasonic range finder.
SERVO 11.2010 43