gear off the old motor and mount
it onto the replacement. The fit is
tight; avoid grabbing the teeth of
the gear with a tool to remove it.
Instead, place the jaws of a pair of
small needlenose pliers behind the
gear, and gently work the gear off.
Be careful that the gear doesn’t
come flying off the motor shaft or
you may never find it!
Solder 7” to 8” leads (use 18 to
20 AWG stranded wire) to the
motor for connecting it to the L298
module. Here’s a tip: It’s often a
good idea to add a small 0.1 µF
ceramic disc capacitor directly
between the terminals of the motor
along with the connecting wires.
The capacitor helps to reduce any
negative effects of electrical noise
induced by the motor. Be sure the
capacitor is rated at 25 volts or
higher.
FIGURE 6. Note the main points of interest on the Seeed Studio L298 board.
Check the datasheet for this product for a description of the jumpers.
For the Beginner Bot, leave everything factory set.
Connecting the
Motors to the L298 Board
Locate the two-terminal motor terminal blocks on either
side of the L298 board (see Figure 6 for the main points
on the Seeed Studio L298 module). On each block, the
terminals are labeled VCC and Gnd. Orient the robot so
that the heatsink on the L298 board faces away from you.
Then:
marked VMS. The black (–, negative) lead connects to the
power terminal marked Gnd.
Use a small flat-bladed screwdriver to tighten the
terminals so the wires remain snug.
Attach Battery Holder and
9V Battery Clip
The three-cell battery holder used in the Phase 1
Beginner Bot doesn’t provide enough voltage for operating
the L298 H-bridge. As a replacement, use a six-cell, double-sided (three cells per side) AAA or AA battery holder. Get
the kind with the two tabs for connecting with a polarized
nine volt battery clip.
Locate the three-terminal block at the bottom of the
L298 module. The strip has connections labeled VMS, Gnd
(for ground), and +5V. The +5V terminal provides five volts,
supported by the built-in five volt regulator on the bottom
of the L298 module.
Wire the nine volt battery clip to the L298 module. The
red (+, positive) lead connects to the power terminal
USING BATTERY CLIP
TERMINALS AS A SWITCH
FIGURE A.
Battery holders equipped with polarized terminals for
nine volt battery clips provide both an electrical connection
and a cheap form of switch. Here’s how: Snap on just one
terminal, and turn the clip so that there’s no contact to the
other terminal. This is the off position. To turn your robot on,
complete the battery connection by rotating the clip so the
other terminal touches its mate.
For this to work, the terminals must have a tight fit. If
there’s too much slop, carefully squeeze together the prongs
of the terminals to tighten things up. Don’t go overboard, or
you’ll bend the metal out of shape.
SERVO 09.2011 39
