Pololu Sample Project: Simple Hexapod Walker Manuale utente
Sample Project: Simple
Hexapod Walker
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Materials and Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Sequencing the Hexapod Gait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Using a Script for Obstacle Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. Suggested Modications and Improvements . . . . . . . . . . . . . . . . . . . . . . 20
7. Conclusion and Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
Page 1 of 21
1. Introduction
Six-legged locomotion is a simple, robust system of walking that is very popular both in
the animal kingdom and among robotics hobbyists. Robot hexapods range from simple one-
motor toys to advanced platforms with 18 or more servos. This tutorial shows you how to
build a very simple autonomous hexapod robot using just three servos. The 2"-high hexapod
is capable of walking forward and backward, and can turn left and right. Two forward-
looking distance sensors provide obstacle avoidance. The brain of the hexapod is the Pololu
Micro Maestro [http://www.pololu.com/catalog/product/1351], a 6-servo controller that can read
inputs and play motion sequences in a stored script.
See the Micro Maestro User’s Guide [http://www.pololu.com/docs/0J40] for complete
documentation on the Micro Maestro.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
1. Introduction Page 2 of 21
Parts you will need to build the hexapod robot.
2. Materials and Tools
Parts list:
Quantity Part # Part Notes
1 1351
Pololu Micro
Maestro Partial
Kit
Get the kit version so that you can solder in your
own wires for the most compact possible robot.
3 1053 Sub-Micro Servo
3.7g Generic
These generic servos provide the lowest
possible cost and weight, but you may substitute
other servos, such as the Power HD sub-micro
servo HD-1440A, to customize the design.
2 1134
Pololu Carrier
with Sharp
GP2Y0D810Z0F
Digital Distance
Sensor 10cm
This is a tiny distance sensor with a long enough
range to keep your hexapod out of trouble.
1 1171 Battery Pack: 4.8
V, 150mAh
This battery pack will provide enough power at
about 5 V to power the hexapod for ve or ten
minutes.
1 1168
2.5 mm Shrouded
Male Connector:
2-Pin, Right Angle
The polarized connector lets you connect the
battery pack safely to the Micro Maestro.
3 – “Jumbo” paper clip Used to form the legs of the hexapod. These
should be 6" long when unfolded.
Tools required:
• Soldering iron and solder
• Hot glue gun
• Wire stripper
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
2. Materials and Tools Page 3 of 21
• Long-nose pliers
• Diagonal cutter
• Some wire for connecting the parts
Most of these parts are available in the Tools [http://www.pololu.com/catalog/category/5] section
of the Pololu web site. A hot glue gun is available at most craft stores for a few dollars.
Update: The case for sub-micro servo 3.7g generic [http://www.pololu.com/catalog/
product/1053] has changed slightly since this sample project was written. Versions
shipping now have solid black cases instead of transparent blue ones and a portion
of the top plane on the opposite side of the output shaft is now slanted rather than
completely at, but they still work as simple hexapod robot actuators as described
in this project. The pictures below show the two version side by side, with the old
version on the left and the new version on the right.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
2. Materials and Tools Page 4 of 21
3. Construction
Step 1: Attach the battery connector.
Using a pair of pliers, ip the leads on the battery connector to the other side.
Bending the leads on the battery connector to
the other side.
Verify that this allows you to plug in the battery as shown below, with the black wire
connected to ground and the red wire connected to BAT, then solder in the connector.
Soldering a power connector to the Micro
Maestro.
Step 2: Set up the Maestro for self power.
With your battery disconnected, attach a wire (red) from the positive terminal of the battery
connector to VIN. Take care not to short or damage any of the components on the board.
Now, with the battery plugged in, your Maestro should be powered-up and slowly ashing its
yellow LED, indicating that it is waiting to detect the baud rate on the serial communication.
You will not be using serial communication for this project, so you need to disable baud rate
detection in the next step.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
3. Construction Page 5 of 21
Self power and a battery connector on the Micro
Maestro.
Step 3: Verify that the Maestro and servos are functioning.
The Maestro Control Center is used for conguration and control of the Micro Maestro,
for testing, debugging, scripting, and more. See Section 4 of the Micro Maestro User’s
Guide [http://www.pololu.com/docs/0J40] for complete instructions on using the Maestro
Control Center.
Launch the Maestro Control Center and congure your Maestro for “USB Dual Port” mode.
The yellow LED should now be mostly o, ashing very briey about once per second. On
the Status tab, enable servo ports 0, 1, and 2, and the yellow LED will start double-blinking,
indicating that some ports are active.
Next, using a piece of male header (included with the Maestro), temporarily connect a servo
to port 0. Make sure to connect the wires correctly, with the brown or black wire connected
to ground. You should hear a short high-pitched whine as the servo activates, moving to and
holding a position in the middle of its range. After a fraction of a second, when the servo
has reached its position, it should be silent. Move the slider from 1000 μs to 2000 μs to test
the motion of the servo. Test all three ports and all three servos before continuing with the
assembly.
Congure each of the servo ports to “Go to” 1500 μs on startup. This will make it easier to
align the legs later on.
Congure ports 3, 4, and 5 to be inputs. This is important, since you will be connecting
sensors later and want to avoid shorting them out!
Disconnect the battery before continuing.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
3. Construction Page 6 of 21
A sub-micro servo with mounting
tabs clipped o.
Step 4: Construct the body by gluing the servos
together.
Remove the mounting tabs from all three servos with
diagonal cutters. The tabs are not needed for this project and
can interfere with the motion of the servos.
Next, join the servos with a few dabs of hot glue as shown
below. You do not need much glue to hold them securely! Try
to align the corners precisely to make at surfaces for
mounting the other parts.
Try to align the corners.
Clip the servo cables, leaving at least 2" (more if you are less experienced with soldering).
Strip a small amount of wire from the end of each cable.
Cut and strip the servo leads, leaving about 2” of wire.
Step 5: Solder the servos and sensors to the Micro Maestro.
This step requires patience and care. A second pair of hands could be very useful.
Use solder to tin the leads of the servos so that they can be connected initially without
additional solder. Looking at the pictures below for reference, place the Maestro on the back
side of the body and place the middle wires over the front of the Maestro and into the holes
for channel 1. Holding the wires in these holes, pull the Maestro away from the body, then
touch the soldering iron to each connection so that the small amount of solder on the wires
melts and holds them in place. You should now be able to add more solder to each of the
connections, until the holes are lled and the wires are held securely. Check carefully for
loose strands of wire, which could cause shorts.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
3. Construction Page 7 of 21
Digital distance sensors with
trimmed carrier boards.
Continue, soldering the right servo to channel 0 and the left servo to channel 2, so that the
servos are arranged in the same relative positions as the ports.
Connecting the servos to ports
0, 1, and 2 on the Micro Maestro.
Cut the sensor boards with a rotary tool, grinding wheel,
diagonal cutters, or a jeweler’s saw, removing the part
containing the unneeded mounting hole, so that they are as
small as possible. (Make sure you do not cut any traces.)
Then solder them to a cable so that you can connect them to
the Maestro. The example below uses a 4-wire ribbon cable,
sharing the power and ground connections for the two
sensors. Ribbon cable makes the assembly relatively clean,
but you can use whatever wire you have available. Look
ahead in the instructions to see where the sensors are going
to go, and make sure that you have a long enough cable.
Think about how to keep the wires close to the body and out
of the way of the legs and servos.
Soldering the sensors to a four-pin cable.
Solder the sensor power and ground to +5V and ground on the Maestro, and connect the
outputs of the right and left sensors to channels 3 and 4, respectively. Note that we use +5V
instead of the battery voltage so that the Maestro channels will never see higher voltages
– and another benet is that the sensors will work under USB power, without the battery
plugged in.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
3. Construction Page 8 of 21
Soldering the sensor cable on to the Maestro.
You now have a complete electrical assembly. Plug in the batteries, and the sensors should
become active, turning on their red LEDs whenever they detect an object within 10 cm. With
the Maestro control center, you should be able to see the input value change from 255, when
no object is present, to a low value of 40 or so, when an object is detected. If the LEDs are
always on, you probably forgot to set the ports to inputs in Step 3.
Step 6: Construct the legs.
Unfold the paper clips into straight pieces of wire. Pliers make ugly dents in the metal, so
try to use your ngers and the edge of a table to do this.
Straighten the paper clips as much as possible.
The wires should be six inches long. To make the front and back legs, fold two of them into
1.5" sections, with 90° angles between the sections, like this:
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
3. Construction Page 9 of 21
The front and back legs of the hexapod. The segments at the end
should be 1.5” in length.
Fold the third piece into an M shape, with sections of length 1.25", 1.75", 1.75", and 1.25",
like this:
The middle legs of the hexapod. The segments at the end should
be 1.25” in length.
Hot-glue the legs onto servo horns. Use a straight horn for the middle legs and cross-shaped
or round horns for the front and back legs.
Sample Project: Simple Hexapod Walker © 2001–2010 Pololu Corporation
3. Construction Page 10 of 21
Indice
