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Lego PC Bot Base
To get an idea of the construction let's have a look at the PC Bot without the laptop
or camera attached. Below you can see the scaffholding required in order to support
the laptop. Note that the laptop simply drops into the construction and is secure
enough for operation but will not be held in if the robot is tilted on its side or
carried in any other orientation but upright.
click on image for larger view
Laptop
The laptop fits snugly into this frame being supported by the web created above the
NXT. It is supported in the front with the small wall created between the camera
mount and the NXT based. You will also notice the asymetrical size holders (the
gray wall connected to the yellow pieces. The asymetry was due to a lack of
small straight pieces that were exhaused during the construction of this robot.
This was not problematic as the laptop's width is slightly smaller than the span between
these two side peices which allowed for one side to use a more curved lego piece. The
curved pieces excert more squeezing pressure and allow the laptop to better fit ontop
of the base.
Motors
We chose to position the motors in a vertical manner as apposed to angled as it made
the planning easier to work with. It also allowed the NXT brick to be mounted underneath
the laptop platform with enough ground clearance to avoid contact.
This orientation of the motors, while useful for this specific construction, do add
to the instability of the system. When the wheels begin turing
they cause the motors to experiance a twisting torque between the wheels and
the momentum of the laptop. Thus the robot has a tendency to "fall flat on its face"
if the wheels encounter too much resistance.
click on image for larger view
You can notice the excessive connections to the motor in the front view. Note also
the curved bar connection between the NXT and the front white span between the motors.
This addition helped tremendously to stabilize the robot and prevent the "face falling"
that would happen.
Camera
The logitech camera is built to connect to the top of a laptop. This might imply that
a straigh vertical attachment would be all that is necessary to clip the camera onto
the robot. However, we found that the better attachment as a small 90 angle which
would allow the camera to better clip onto the robot in such a way that it would not
move vertically during operation. Note that this required a tricky 90 degree connection
to connect a horizontal plan (the laptop base) with a vertically oriented piece.
Handles
Every robot needs to have a handle which can be used to quickly grab the robot as
it zips out of control towards the wall ... or worse off the tabletop! While
the we not able to create a design that could be used to carry the robot with one
hand we did settle on creating some grasp bars that do allow for easier pickup. You
can see these yellow pickup bars connected from the motor to the outmost left and right sides
of the laptop platform. These also created more stability in the system by connecting
the motor and laptop platform but also serve as grasp handles using two hands to
pickup the robot. Prior to these handles the robot would be grasped from the
underside using the NXT as a base. This had the unfortunate effect of accidentally
turing off or on the NXT base as the orange button on the NXT is slightly
raised with respect to the NXT base.
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