was whether or not they were easily
modified to be suitable as a robot
drive train. To answer this, I bought
one and stripped it down.
The drill used in this article is the
Power Craft Pro CDD24 (Figure 1)
which comes with a 24V battery, a
charger, plus some assorted drill and
screwdriver bits. A search online
revealed that the same drill is
offered by several different companies under different model numbers.
The first thing to do is to put
the battery on to charge as per the
manufacturer’s instructions.
We’ll need to remove the chuck
(Figure 2) before disassembling the
rest of the drill. The chuck is locked
in place by a small, left-hand thread
screw inside the chuck itself (see
Figure 3). If you’re lucky, you can
remove this just using a screwdriver
(remember to turn clockwise to
loosen a left-hand thread), but they
are usually too tight.
There are two methods which
will work. The first is to use another
drill to start drilling out the screw.
The heat and torque applied by the
drill bit will loosen the screw and it
will come out rather than be bored
out by the drill. The downside of
this approach is that you need a
second drill and that the screw
itself will be damaged. The second
method — and the one that I use —
is to get an “impact driver.” The
driver must be able to loosen or
tighten screws (many of the cheaper
ones only loosen right-hand threaded screws and will only make the
left-hand threaded screw tighter). A
McMaster Carr part 5610A2 (www.
mc master.com) will do the job.
I needed to use a 1/4” socket
and an extension piece to get it to
be able to reach the screw (Figure
4). Set the driver to turn clockwise
and with the chuck held securely in
a vice, give the back of the driver a
sharp tap (or two) with a hammer
and the screw will be loose enough
to easily remove. Keep the screw
for later use.
I would advise the use of
safety glasses and an absence
of spectators for the next step.
The chuck is threaded onto the
gearbox using a conventional right-hand thread. This will usually be too
tight to remove by hand but there is
an easy way to remove it. Fit the
newly charged battery to the drill
and place a large hex key or similar
(Figure 5) in the chuck. Set the drill
in reverse, spin it up, and then allow
the end of the hex key to strike a
solid object (like a vice or workbench). The shock will loosen the
chuck and it will come off easily.
There are two screws on the
front face of the drill under which
the chuck is attached (Figure 6).
Take out these screws and the
adjustable torque mechanism can
be removed. Next, remove the
screws that hold the two halves of
the drill case together and lift off
the top half. The motor and
gearbox (Figure 7) can then be
lifted out of the other half of the
case. Keep the two halves of
the case as we will use them later.
The gearbox has a lever
mechanism on the exterior that is
used to change the speeds. This is
shown in the high speed position
in Figure 7. The gear ratio was
established by marking one blade
of the fan on the motor and also
marking the out-put shaft. By
counting how many turns of the
motor is equal to one turn of the
output shaft, I found the fast speed
ratio is 15:1 and the slow speed is
45:1. The motor is attached to the
gearbox using a “bayonet” type
catch and can be easily removed.
The gearbox has all metal teeth
and the output shaft is essentially
the same as the one on the smaller
drills, so will match the existing
chassis on the robot and the hubs
on the wheels. The motor has a
standard 5 mm shaft and a large
internal fan that should help keep it
cool. Motor timing appears to be
neutrally timed so that it goes the
same speed in either direction. This
is important as in most applications
the motors will be turning in opposite directions on each side of the
FIGURE 2
FIGURE 3
FIGURE 4
FIGURE 5
FIGURE 6
SERVO 11.2009 27
