Let's Make Robots!

AX-12 Robot Arm

Draw numbers of the winners of the LMR Donation


This is my competitor for the LMRv4 Donor Appreciation Robot challenge. Using 5 Dynamixel AX-12+ Servos and an Arduino Mega. Programming has been done through Pypose, part of the Arbotix project.


5 Dynamixel AX-12+ servos has been used to build the robot arm and gripper. The arm has 4DoF and the gripper 1DoF. An Arduino Mega board has been used to control the servos. Only UART1 (RX1,TX1) are needed to control all servos. No external hardware is needed to attach the servos. The gripper is made by a claw from the local home depot. The idea has been lent from the Make project Teleclaw.


There is no real programming needed. The Pypose sketch from the Arbotix project has been used without any modification. You can create poses very easy using the Pypose editor. Also sequences (running different poses time controlled) can be created with a few mouse clicks.

Update 2012-04-30:

This is my actual setup. Nothing has changed on the robot arm. A bowl with 140 wooden dowels has been used for a sample drawing. Each dowel will get a unique number from 1..140 or whatever the actual number of contributors is. No detection of invalid drawing so far (if the gripper gets none or more than one dowel). The robot arm is doing some kind of stirring now, before the drawing. But it doesn't work well, the bowl is moving more than the dowels. The 2nd video shows a sample drawing 5 out of 140. It takes 7 attempts to complete. 2 failed attempts.

Sample numbering of a wooden dowel.

Update 2012-05-04:

The winners of the LMRv4 donation marathon has been drawn. I couldn't show the drawing live at the RobotParty, but a prerecorded video has been showed during the hangout. Spacial thanks to Andrew 'inoblegnome', Erin 'RobotGrrl', Nils 'NilsB' for their efforts and all others that gave me great tips to complete this challenge.

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Nice gripper (remaind me on mine a while ago) and robot arm :)

Thank you, Markus. I have lent the idea for the gripper from the Teleclaw robot. Just saw your gripper with the light barrier. That brings up a new idea to sense that the gripper has caught a dowel.

Maybe a small potentiometer could do the job as well. If the gripper moves out of the bowl and is still in a certain opening position, it has caught a dowel.

we made a arm too buddy but it was awesomely powerful and less comples using servo motors


Will you participate in the challenge?

Thats a good looking arm! Some suggestions:

  • open claw before digging into bowl
  • add some sort of feedback to you know you have hit something.

The whole thing shakes a bit while moving. Perhaps you could benefit from NilsB's "Smooth Head Rotation" tip here http://letsmakerobots.com/node/31697

Thank you for the tips, mogul. The claw is very limited in the range between open and close. It is opened, before digging in the bowl. Would need a longer lever to open it wider.

Yes I think about of using a feedback mechanism. The servo is intelligent, you can read back the current. Will see if I can get this work.

At the moment the arm follows only a pre programmed sequence. I can only change the poses and the time lapse between the poses. The servo itself  is doing the movement by the given parameters (time and destination angle). After shooting the video, I realized, that one of the servos has shut down because of overcurrent. Maybe that was the cause for the shaky movement.



Nice arm!

To use it to select winners from the LMR fundraising donors, would you number the pegs 0 through 9 and select a three digit number one digit at a time? Or what?

No I have more than 200 wooden dowels, each will get a unique number.