Advertisement
The power configuration for this robot is slightly unusual.
10 miniature servos combined can draw more than 3amps when the robot is running around. This is far
more than the Magician's regulator can handle. The magician board does allow you to power up to 8
servos directly from the battery but the servos are rated at 6V and the battery is 7.2V!
To solve these problems, the pan and tilt servos which are not heavily loaded are run from analog pins
4 and 5. These pins have been converted to servo outputs in the software and have power supplied by
the 5V regulator (normally used for sensors). This leaves the 8 leg servos to be powered directly from
the battery.
What we do here is to use diodes to drop the voltage to a safe level. Most silicon diodes have a forward
voltage drop of about 0.6V regardless of the current. The Magician controller already has a 3A diode in
series with the battery to protect against accidently connecting the power around the wrong way.
This diode will drop the voltage by about 0.6V. By adding a second diode in place of the jumper that
selects the servo power we effectively have two 3A diodes in series with the battery that is reducing the
voltage to the servos by a total of 1.2V. Our leg servos are now getting the 6V they are rated for.
The leads on a 3A diode are slightly thicker that a male header pin. bend the leads close to the body of
the diode as shown and fit two small female to female jimper wires. they will be a tight fit but this is
good as it ensures a good electrical connection. Fit a red wire to the anode and a black wire to the
cathode.
Now remove the servo power selection jumper and fit the diode instead. Attach the red wire to VBAT
and the black wire to the center pin. The servos will now receive power through this diode. If you
accidentally connect the diode the wrong way around then the servos will not get power but no damage
will be done.
NOTE: If you want your robot to stand on it's hind legs with NiMh batteries then you may need to
leave the diode out and use the original jumper. This will give your servos 6.6V and more power. You
will increase your risk of damaging the servos slightly if you do this.
Step 20. Connect the leg servos
Advertisement
