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18 SERVO 01.2013
variations (Figure 3). The motors are strong — if a bit
noisy — and drive the robot at a good indoor clip.
The tail wheel turns well and doesn’t mess up the
robot when backing up — which is another great
engineering feat! The tail wheel on my red Roomba is
different than on my blue one, but both work well. One of
the first things I noticed when I hacked off all of the
vacuum cleaner bits and trimmed my Roomba down to its
bare bones is that when it slows down, the body lurches
up and both drive wheels “drop.” This causes the robot to
stop and lurch around.
One way to fix this would be to weaken the springs
on the wheel supports (Figure 4). I tried this, but was
unwilling to allow too much slop. If you look closely at
Figure 5, you’ll see two old six-cell RC car batteries stuck
to either side of the “cargo bay.” These add about a
pound of weight and (with a small stretch of the springs)
allow my robot to keep its “feet” on the ground when
Because I wanted to keep the auto pilot modes
available to me, I hacked the buttons out of the top plate
when I eliminated the unneeded bits (refer again to
Figure 5). I plan on doing something more elegant when
the final project is completed, but this keeps me going on
Now that we have described the physical aspects of
the Roomba, it is time to learn how to control it.
Fortunately for us, iRobot had hackers in mind when they
made the Roomba.
There is a serial port — typically just over the power
plug for the charger — which has a female mini DIN
connector; see Figure 6. I’m not sure where to find the
mini DIN connector used on the Roomba, but I know
where to get something that is close.
I have a collection of old mice and miscellaneous
cables, including PS2 mice and ancient Macintosh printer
cables. There is a little plastic registration stud in the
middle of these six mini DIN male cables that prevents
them from working in the Roomba connector. No