Servo - June 2008

servo connector so you can easily connect sensors to the docking station. The completed OEM docking station is shown in Figure 6. One of the sensors that easily plugs into the docking station is the Lynxmotion single line detector that I added to my setup to eventually create a simple line follower. These are really great sensors but have to be bent a little to fit the Mark III chassis. They easily plug into the three pin connections of the docking station. Figure 7 shows the sensor by itself.

I didn’t finish the line follower code in time for this article but you can find plenty examples of this in SERVO. I mainly just wanted to demonstrate how easy it was to put all this together and end up with an effective, low-cost robot from off-the-shelf parts and a little creativity of your own.

main:

Forward:
For x = 1 to 20

FIGURE 7. Single line detector.

servo serv1, 1200, 1
servo serv2, -1200, 1
Next

‘ Send the servo control pulse
‘ 20 times
‘ Drive the right servo forward
‘ Drive the left servo forward
‘ do it again

Pause 500

‘ Delay 500 milliseconds

Backward:
For x = 1 to 20

servo serv1, -1200, 1

servo serv2, 1200, 1

Next

‘ Send the servo control pulse
‘ 20 times
‘ Drive the right servo in
‘ reverse
‘ Drive the left servo in
‘ reverse
‘ do it again

Pause 500

‘ Delay 500 milliseconds

Goto Main

‘ Go back to the top and drive
‘ it again.

Software

Conclusion

I wanted to at least test my final creation by writing a simple program to drive the servos. This is a quick program to make the robot go forward for a short distance, then pause for a half second, then move the robot backward and delay for a half second again. The program will loop through this over and over again. This is a simple program (shown next) that demonstrates the Basic Atom servo command.

serv1 con p10

serv2 con p11

‘ Make nickname for servo1
‘ connection
‘ Make nickname for servo2
‘ connection

x var byte

‘ Create a counting variable for
‘ the servo loops

If you wonder what the final robot looks like, check out Figure 8. It’s nothing exciting but it’s simple to build without a lot of expense. We do have a few of the older docking station boards, so maybe I’ll make a kit out it for anybody that wants a one-stop source for this same kit.

As I mentioned, I ran out of time to get the line sensors working before sending this to SERVO, so I’ll consider that plus maybe wheel sensors for a future article. The off-the-shelf chassis from Junun.org works well and saves you a lot of cutting and bending of metal, plus its smooth finish prevents any sharp edges. Adding the docking station definitely simplifies connecting an OEM module of your choice. If you want to modify the design or just build it the way we have it, remember the docking station board files are available from expresspcb.com. You can use their low-cost $59 option if you don’t need silkscreen or solder mask. SV

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