is a standard HS-322 or HS-325 servomotor.
Start construction by mounting the right and left drive servomotors to the
bottom rear of the chassis. Each servomotor is mounted using two 90 degree
servomotor brackets along with 6-32 machine screws, split lock washers, and
nuts. Next, mount the front caster style wheel (see Figure 4). The caster style
wheel uses a 1/4-20 screw through the chassis into a 1/4-20 coupler to which
the caster screws into from the other side of the coupler.
Mount the up and down servomotor to the top front of the chassis using
two 90 degree servomotor brackets, 6-32 machine screws, lock washers, and
nuts. A small 90 degree clip is mounted behind the servomotor using a 6-32
screw, washer, and nut (see Figure 5).
Get the top servomotor bracket and attach a round servomotor horn to it
using four #4 sheet metal screws (see Figure 6).
Place the plastic CMU camera bracket on the top servomotor bracket
and secure the bracket using two 6-32 machine screws and nuts. Then, attach
the CMU camera to the plastic bracket using two 4-40 screws and nuts (see
Rotate the top servomotor to its center position. Then, attach the CMU
camera assembly to the servomotor. The servomotor horn will fit into the shaft
of the servomotor. The back hole of the top servomotor bracket should line up
with the hole on the 90 degree clip (see Figure 8).
If you want to make your own servomotor wheels as shown in the
photographs, you can the follow the wheel construction details in the sidebar.
If you have suitable servomotor wheels approximately 2.0” in diameter, you
can use them.
FIGURE 4. Chassis with drive
servomotors and caster.
The schematic is shown in Figure 9. The circuit can be hardwired onto a
breadboard, or a printed circuit board (PCB) can be purchased from Images
Scientific. The LCD is a two line by 16 character display. You can use an LCD
module with a Hitachi 44780 controller or equivalent. These LCDs usually have
a 14 or 16 pin header.
We need to set one jumper on the camera and connect four wires from
our circuit to the CMU camera.
Look at Figure 10. Place a jumper on position 2. This sets the camera
baud rate to 38,400. The power is supplied to the two header positions
shown in Figure 11, as well as the header positions for the serial transmit and
For power, I used a six AA battery pack holder with rechargeable NiCd
batteries. The six batteries supply approximately 7.2 volts fully charged. The
CMU camera is powered directly from the unregulated voltage from this
The battery pack is secured to the undercarriage of the platform using a
molded piece of plastic as shown in Figure 11. The battery pack fits inside
the plastic and is secured to the platform using two 6-32 screws and nuts.
The entire circuit including the CMU camera has three power switches. I
would recommend placing the CMU camera power switch in the ON position
and using the main circuit board power switch to control power. The LCD also
has a power switch. The LCD display is used in the Test Mode and only in the
beginning of the Run mode. The power switch allows you to turn off the LCD
to conserve power.
Finishing the Assembly
With the battery pack attached to the body, all that remains is to secure
the PCB to the top of the robot’s body and we’re ready to go.
FIGURE 6. Top servo
bracket with round
FIGURE 7. CMU
to top bracket
FIGURE 8. CMU camera
bracket assembly attached
to up-down servomotor.