A Single Axis
Robotic Arm With
by Paul Verhage
Getting a robot arm to lift up and down
is pretty easy; just connect it to a servo.
The challenge is trying to get it to pick
up an object. Taking a clue from the end
effector on the Space Shuttle’s robotic
arm, I came up with a “snare” of an
idea. Now, my CheapBot robots carry a
practical robotic arm.
The single axis robotic arm described here lifts and lowers targets captured within its end effector. The end effector
is a wire snare that wraps around targets, and is extended
and retracted by a miniature servo. Because of a momentary
pushbutton switch at the end of the arm, a robot carrying
this arm can determine when it has successfully captured and
released its target. Combined with a little logic, I was able to
program a CheapBot to follow a line and use its arm to pick
up plastic jacks at one end, and deposit them at the other.
To keep the arm practical, I selected components that
were available at local businesses, including hardware stores,
hobby shops, and craft stores. I ordered the few remaining
items from Jameco. Here are the necessary parts:
- 1 inch diameter hidden pillar*
- Miniature servo (like a GWS Pico or JR Sport Micro)
- Momentary pushbutton switch (Jameco part number
- Piano wire, 20 mil diameter, 36 inch long
- Mini EZ connector****
- 4.7K ohm resistor (1/4W)
- Heat shrink
- #24 AWG stranded wire
- 2-56 machine screws
- 2-56 nylocks (use nylocks so the arm can’t fall apart
- Connectors to your robot controller (like three-pin
*Hidden pillars are fluted tubes used in wedding cakes; I got
mine from George’s Hobbies in Lawrence, KS in their cake
**Syntra is a 1/8 inch thick sheet of foamed PVC (poly-vinyl
chloride). Since it’s foamed (filled with air bubbles), it’s softer
and easier to machine than regular PVC (which is a very hard
plastic). Syntra is available from online robot stores, local plastic
companies, and some sign companies.
***Correplast is corrugated plastic and very popular as a sign
material. I was able to purchase some from a local sign
****Mini EZ connectors attach piano wire push rods to servo
horns in model airplanes. You’ll find them in hobby shops that
carry RC airplanes.
Putting the Pieces Together
The arm is constructed in five pieces:
1. The arm core.