Mike and Joe with Ramming Speed at BattleBots in May '01
Dewalt released a new version of it's cordless drill 18v motor
and gearbox in the spring of 2002. The following description is based on parts
ordered from a Dewalt DW988K-2 18v Hammerdrill. Their are other models that
appear to have the same combination of motor and gearbox.
The motor provides 450 in./lbs of torque at 18v. The gearbox offers three selectable
speeds, with the highest (called 'MAX 3rd Speed') being 38% faster than the previous model
at 2000rpm. The previous 18v combo was heralded for its ease of mounting, as the
gearbox actually attached to the motor with four screws. The new version offers
no such luxury. Their is NO physical connection between motor and gearbox,
requiring you to create a custom solution. The gearbox, having more
capabilities, is much more complex, but offers ALL METAL gears. The motor is
easier to disassemble than the previous model, and the magnets are easily
removed, so neutralizing the timing is fairly easy, and their is room inside for
capacitors.
The part numbers for this combo, available from a Black &
Decker service center, are:
Description
Part Number
Cost Each
Motor & Pinion
396505-03
$39.95
Transmission
397892-01
$37.95
Overall length is 5.375" from end of motor shaft to tip of end
plate holder. Diameter at widest point is 2.22". Total weight is 29.2oz.
The Motor
Weight: 15.7oz
Diameter: 1.85"
Overall Length: 3.5" (from both ends of shaft)
Length of case: 2.62" (from outside of both caps)
Click
images for
larger version
Here's the motor, straight out
of the box. Note the end cap with the brush holders is much different. The
end cap nearest the output gear is also different, not including the
mounting flanges of the older motor.
A better view of the end cap
near the brush holders.
A better view of the end cap
near the output gear. Note that their are three threaded holes in the end
cap, but they are not used in the drill application, as the gearbox butts up
against this end, and has no threaded connectors.
The end caps are held on threw a
few tabs that are 'crimped' into place. By gently hammering a small
screwdriver into the gap, the cap can be coaxed off. Once removed, the
inside of the cap clearly shows the brush holders/brushes.
Here is the motor without the
end cap.
Here I've started to pry the end
cap nearest the output gear. This is slightly more difficult, as their is a
plastic fan epoxied to the windings that catches on the magnets, preventing
removal. By gently prying around the cap, and listening to cracking epoxy,
the fan will come unattached, so the motor can be disassembled.
Here you can see the fan piece
removed.
Once the fan piece is removed,
the rest of the motor is easily removed from the case.
A view inside the case shows the
magnets are epoxied to a metal ring, that is inturn spot-welded to the outer
case. A keen eye will also notice that the magnets are mounted 15 degrees
off of the brushes.
Here's another view of the
magnets in the case. Note that this setup makes retiming the motors very
easy. Instead of having to alter the mounting of the brush holders, or end
cap, the magnets can be directly rotated inside the case.
To free the magnets, I cut a
wooden plug that fit over the magnets. One sharp blow with a hammer easily
breaks the spot welds so the magnets can be pushed out (still attached to
the metal ring).
To hold the ring and magnets
once reinstalled, I drilled and tapped a hole for a set screw. I put the
hole directly across from the seam in the case, which will end up aligning
with the gap between the magnets.
Here you can see the magnets
reinserted into the case. Note the alignment is now different, with the
middle of each magnet now aligned to the axis of the brushes. Notice the
dimple in the gap between the magnets which is from the set screw.
Here you can see the set screw
in the side of the case.
I used JB Weld to reattach the
fan to the windings. It is rated to 600 degrees, and is very strong.
Here the piece is in place.
Since the motor is completely
open, capacitors can be placed inside the motor to give better resistance to
noise. I soldered three .1uF ceramic capacitors inside each motor: one from
the positive terminal to the case, one from the negative terminal to the
case, and one between the two terminals.
The end cap can then be
reattached with a few gentle taps from a hammer.
The Gearbox
Weight: 13.5oz
Overall Diameter: 2.22" (at widest point)
Diameter: 1.85" (main case without shifting collar)
Overall Length: 2.55" (from base of case to tip of end
plate holder)
Click
images for
larger version
Here's the gearbox straight out
of the box, wrapped with two rubber bands to hold it all together. Their is
a plastic cover that goes over the new shifting ring.
A view from the end that
connects to the motor.
Here is the new shifting ring.
The gearbox allows three speeds, and does this by moving two metal gears
inside, instead of the one plastic gear that the old gearbox used. By
altering the positions of the two gears, three rpm selections are possible.
Here you can vaguely see the small metal pins connected to the gears,
sticking out in the two grooves.
Here the ring has been rotated
so the pins are in their 'middle' position. Note the top pin at the top of
the 'hump', while the lower pin is at the 'knee' of the slot.
The gearbox with the top plastic
retainer removed. The retainer is a plastic ring, with a piece of spring
steel that clips into it, and helps hold the gears in.
Here the top components are
removed. They include a ring that appears to hold the upper components in
place, and the piece that the spindle fits into. Notice the shape of the end
of the spindle has changed. Their are also small pieces of bearing like
shafts that fit loosely in between the ring and the spindle receiver.
Here's the spindle receiver from
the 'bottom'. Notice it includes metal fingers to lock into the gear set
below it. The black is rubber, apparently to cushion the piece, as this
gearbox is from a hammerdrill.
Here is the set of gears that
the spindle receiver interlocks with. They are shown upside down here, with
the 5 gears themselves receding into the gearbox.
Here is the upper shifting gear,
with the wire gear holder that fits into a groove in the gear, and
protruding out the side of the gearbox case.
The next set of gears. The
single gear in this combination fits into the void between the 5 gears it
the set pictured above.
To get at the rest, you have to
come from the bottom. Their is a spring steel cap that fits into the case
quite well, retaining the gears. Removed, it reveals a metal ring gear at
the base, with 4 gears on an assembly that ride inside.
The ring gear is removed, as
well as the lower gear assembly that rides within it. Notice the ring gear
has some humps on the upper/inner surface. This appears to be part of the
clutch mechanism.
The lower shifting gear removed.
Note the wire holder still in the case.
A spring mounted metal pin that
rides against the ring gear at the base as part of the clutch mechanism.
