www.servomagazine.com/index.php?/magazine/article/november2010_Verhage
This shows the placement of parts for the
lift fan circuit. The arrangement of wires
in the circuit’s control cable is the same
as a servo, so I recommend using a
similar color scheme.
fan. This circuit gives the HoverBot the
ability to take off and land under
automatic control (pretty cool). It only
takes the HoverBot a second to fill its
skirt and lift off, or to dump its skirt and
land. To reduce the number of different
parts, the HoverBot uses the same relay
for both the lift fan and the drive fan
circuits. The fact that the HoverBot only needs a SPST relay
to control the lift fan means the circuit wastes half the
relay. While probably not necessary, a reverse-biased
1N4001 diode across the relay coil protects the robot
controller from the relay coil’s kickback.
The three holes at the bottom of the copper pattern
(available in the SERVO downloads) are strain relief for the
wires connecting the circuit to the robot controller. The four
larger pads in the corners of the PCB are its mounting
holes. Use small nylon spacers or a foam neoprene sheet
and 2-56 bolts to mount the lift fan circuit to the
HoverBot’s top deck. I strongly encourage the use of
nylocks because like an airplane, you don’t want FOD
(foreign object debris) getting into the HoverBot’s fans. The
operation of the fans will loosen up regular nuts over time.
The HoverBot relays are NEC DPDT relays; they are
available from Jameco as part number 2081650 and cost
$2.49 each. You’ll need to order five of them to build the
two circuit boards for the HoverBot. This is a list of the
remaining parts you’ll need to make both circuits for the
HoverBot.
backwards (no harm done, just switch it around).
You’ll find the length of the ducted fan wires will need
to be extended to reach the circuit boards. GWS does not
terminate the wires of the ducted fan, so you’ll need to
solder them to a two-pin header and cover the soldered
connection in heat shrink for protection. Now you can plug
the ducted fans into their appropriate receptacles.
Drive Fan Circuit
Unlike the lift fan circuit, the drive fan circuit uses both
sides of its DPDT relays. Like other H-bridges, it requires two
input pins to operate each drive fan. Two input pins permit
four combinations of outputs. When both input pins are set
• Five 1N4001 diodes
• Five 2N3904 NPN transistors
• Five 1/4W 1K ohm resistors
• Wire (#24 gauge stranded)
I also recommend getting a single row receptacle that’s
11 or more pins wide. Using receptacles allows you to plug
the components of the HoverBot together, rather than
soldering everything together. Note that there are two
ports in the lift fan circuit. The first — the ducted fan port
— is where the ducted fan plugs into the circuit. The other
port — the battery port — is where the four AAA battery
pack plugs into the circuit. Note that if after you plug
everything together and the HoverBot sucks itself to the
ground at take-off, you plugged the battery pack in
Just a typical relay circuit. The robot controller saturates
the base of the 2N3904 with 4. 3 mA of current so the
transistor will let current flow to the relay coil. The closed
contacts inside the relay then route current to the lift fan
without a voltage drop to the fan. Note that the schematic
only shows the normally opened side of the DPDT relay; the
normally closed side is not used.
SERVO 11.2010 47
