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Build an Arm for Your TurtleBot

This tutorial takes you step by step through building an arm for your TurtleBot.

Build an Arm for Your TurtleBot

The TurtleBot mobile robot is designed for both academic and hobbyist researchers. The open source hardware design provides excellent documentation for adding modifications and extending the capabilities of the robot in hardware or software. The robot is available for purchase as a kit or, if your research budget is limited, this guide will help you extend your TurtleBot by adding an arm.

Steps

Step #1: Assemble the Arm Base

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Build an Arm for Your TurtleBot
  • You will need:
  • 1x Printed/Lasercut Base Plate
  • 1x F3 Bioloid Bracket
  • 1x Dynamixel AX12A
  • 8x Bioloid N1 (M2 Nut)
  • 4x Bioloid S1 (M2-6 Screw)
  • 4x Bioloid S2 (M2-8 Screw)

Step #2:

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Build an Arm for Your TurtleBot
  • Insert the servo in the base in the only orientation it will fit.
  • Next, put nuts (N1) in the bottom two holes of the servo on either side.

Step #3:

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  • NOTE ABOUT NUTS:
  • There is a special technique to getting the nuts into the servos and to stay:
  • First, push the nut in by hand.
  • Next, take a screwdriver and force it closer into the servo.
  • This will make the nut line up with the hole as shown in the last frame below, allowing you to screw into the nut.
  • A more in-depth demonstration is available here.
  • We will be using this technique throughout the assembly process: to put it briefly, any time there is a nut, put the nut in first, lock it in, and then screw into it.

Step #4:

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Build an Arm for Your TurtleBot
  • Turn the base around and put S2 screws into the corresponding 4 holes in the base plate, as shown on the right.
  • Make sure that the groove on the servo horn, showing where the center is, lines up with the red line in the picture.
  • This offsets the center of the arm in order to allow it to reach to the back of the TurtleBot, but restricts its reach to the right. This essentially makes the robot "left-handed."

Step #5:

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Build an Arm for Your TurtleBot
  • Attach an F3 bracket to the servo horn with four S1 screws as shown.
  • Now you can turn the bracket along with the servo horn.

Step #6: Assemble the Main Joints

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Build an Arm for Your TurtleBot
  • You will need per joint :
  • 4x Bioloid S6 (M2-6 Screw)
  • 4x Bioloid N1 (M2 Nut)
  • 1x F3 Bioloid Bracket
  • 1x F4 Bioloid Bracket
  • 3x F10 Bioloid Bracket

Step #7:

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  • Put the parts together as shown in the picture.
  • F3 bracket on top, F4 on the bottom, F10s in between.
  • Put nuts in 4 holes on the inside of the F4 bracket.
  • This is a similar procedure to step three, where you want to force the nuts in first so that they don’t fall out as you put in the screws.
  • However, since this is less of a press-fit, you may want to put your finger over the nut as you insert and tighten the screw.
  • Assemble two of these parts.

Step #8: Attach Servos to Joints

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Build an Arm for Your TurtleBot
  • You will need per joint :
  • 1x Joint from previous step
  • 1x Dynamixel AX-12A servo
  • 4x Bioloid S1 (M2-6 Screw)
  • 1x Dynamixel S-B screw, the BU bushing insert, and WA washer

Step #9:

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Insert the bushing (BU) into the hole on the right side of the F4 bracket, and the washer (WA) on the inside of the bracket.

Step #10:

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  • Insert the servo into the assembly, and use four S1 screws to fix the bracket to the horn and one S-B screw on the opposite side (to fix the washer and insert).
  • Repeat the process with the other joint. You should again have two of these parts.

Step #11: Assemble the Arm

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Build an Arm for Your TurtleBot
  • You will need:
  • 2x Joints from previous step
  • 1x Arm base from step 1
  • 8x Bioloid S1 (M2-6 Screw)
  • 8x Bioloid N1 (M2 Nut)

Step #12:

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  • Put 4 nuts into the 4 slots on the bottom of each servo.
  • Attach the top of the F3 bracket to the bottom of each servo and screw them in with S1 screws.
  • Note: It will take some force to snap the servos into the F3 brackets; make sure the holes on the bracket line up with the holes on the servos before you start screwing them in.

Step #13: Assemble the Gripper Pads

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Build an Arm for Your TurtleBot
  • You will need:
  • 2x 3D printed gripper parts
  • 1x Bioloid F3 bracket
  • 1x Bioloid F2 bracket
  • 8x Bioloid S2 (M2-8 Screw)
  • 8x Bioloid N1 nut
  • 8x M2 fender washers

Step #14:

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  • Attach the left side of the gripper to an F3 bracket with four S2 screws, 4 nuts, and 4 washers.
  • Attach the right side of the gripper to an F2 bracket, again with four S2 screws, 4 nuts, and 4 washers.
  • For both grippers, make sure the tabs on the brackets face the same way as the bend in the gripper (that is, the gripper is closing towards the direction the tabs are pointing).

Step #15: Attach Gripper Pads to Servo

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Build an Arm for Your TurtleBot
  • You will need:
  • 1x Gripper pad set
  • 8x Bioloid N1 nuts
  • 8x Bioloid S1 (M2-6 Screw)
  • 1x Dynamixel S-B screw, bushing (BU) insert, and washer (WA)

Step #16:

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  • Insert 8 nuts into the spaces shown in the picture.
  • Attach the right side of the gripper (with the bigger bracket) to the servo horn.
  • Insert the bushing (BU) and washer (WA) on the opposite side of the bracket as before, use four S1 screws to fix the gripper bracket to the servo horn, and finally use an S-B screw to fix the bracket to the shaft on the other side.
  • Attach the left side of the gripper (smaller bracket) to the bottom of the servo as shown below using four S1 screws.

Step #17: Assemble the Wrist

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Build an Arm for Your TurtleBot
  • You will need:
  • 1x Bioloid F3 bracket,
  • 1x Bioloid F2 bracket
  • 11x Bioloid S1 (M2-6 Screw)
  • 7x Bioloid N1 nuts
  • 1x Dynamixel S-B screw, BU insert, and WA washer

Step #18:

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  • Use three S1 screws and nuts to attach the F3 and F2 brackets together at a 90-degree angle.
  • Note: In the pictures the bigger bracket is offset on the smaller one; you should see three holes unobstructed on the smaller bracket.

Step #19:

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  • Attach the wrist assembly using 4 nuts (that should already be inserted from the previous step) and four S1 screws to the side of the gripper servo farthest from the horn so that the large bracket is centered on the side of the servo.
  • Insert the servo into the assembly using, as always, four S1 screws for the horn, the Dynamixel insert and washer, and one S-B screw.
  • The wrist servo horn should be on the opposite side of the arm from the gripper servo horn.

Step #20: Attach the Gripper to the Arm

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  • You will need:
  • 1x Gripper assembly
  • 1x Arm assembly
  • 4x Bioloid S1 (M2-6 Screw)
  • 4x Bioloid N1 nuts

Step #21:

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  • Slot 4 nuts into the bottom face of the wrist servo as shown.
  • Attach the top of the F3 bracket on the rest of the arm to the bottom of that servo.
  • Make sure that all the servo horns face the same direction.

Step #22:

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Build an Arm for Your TurtleBot
  • Attach Standoffs to the Arm Base
  • You will need:
  • 4x 6-32 2” hex standoffs
  • 4x 6-32 ½” screws
  • Screw the four standoffs into the holes on the base of the arm using 6-32 screws.
  • YOUR ARM IS DONE!