Mbed-controlled Robotic Arm (1/2)


GT ECE 4180 Fall 2011 (Lab 3)

  • gvalentin3
  • ebernstein6

Note: This post was our original inspiration
We use a slightly less expensive version than the one shown in the image.


  • Hardware-only Lynxmotion AL5A
  • 3 Hi-Tec HS-422 RC Servos (or HS-322)
  • 1 Hi-Tech HS-755HB RC Servo (This servo is larger than the others)
  • 1 Hi-Tech HS-645MG RC Servo
  • Power supply
  • Object to be used as arm base
  • Mechanism to hold robot base to object base (Gorilla tape will do the trick)



Ignore any reference(s) to the Lynmotionx controller since we will be using the hardware only kit controlled by the mbed.

Discrepancy with Picture

The diagram corresponding to the mounting of the last (mini) C bracket seems to be different from the picture. (We believe the picture is correct)
Thanks to Dr. Allen Robinson for helping us figure this (and other things) out!

http://www.lynxmotion.com/images/assembly/al5a/al5a12.jpg http://www.lynxmotion.com/images/inv/ballb02.gif

Verify your Springs!

Some Lynxmotion kits contain the wrong load balancing springs. The ones required are 1.5" 1.58lb NOT 2.5" 3.61lb.

If no springs are used, the servos will be unable to fully sustain the weight of the arm and the current draw will increase substantially.


In the robo class, the servos are named in the following way (starting from bottom to top)

  • claw = p25
  • wrist= p24
  • elbow= p23
  • base = p22
  • spin = p21



The Robo Class

Import programRoboArm

Robo class for controlling Lynxmotion AL5A Arm

Movements and Limitations

Full Open = 1.5msStraight=1msForward=1msFlat=1msFull ccw=1ms
Closed = 2msLimit=1.6msFull Bac=2msLimit=1.7msFull cw=2ms

Note1: Front and back directions are relative to the springs
Note2: Some limitations might vary for different configurations


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