Posted in: SERVO Blog (09/14 at 09:24 AM)

Working Droid Caller

R2-D2 Builder, Bob Ross responds to the Mind/Iron editorial in the July 2011 issue of SERVO Magazine about his experiences with voice recognition.

I’m a member of the R2-D2 Builders Club and also an electronics engineer.  My R2, although not 100% finished cosmetically, is a working engineering platform used in an attempt to duplicate many of the movie version’s features.  He is currently one of the more full function droids with the capability to go from 2 leg to 3 leg (2-3-2), can tilt (look down and up) when in 2 leg mode, has servo controlled dome panels, holoprojectors (HPs), etc.

The e-mail below is one I posted to the R2 club in May describing a voice recognition device based on a Droid Caller prop used in the first Star Wars movie.  The C-V that’s mentioned refers to Celebration V which was a huge Star Wars convention in Orlando last August.  DroidCon was a meet in Indianapolis this past May for R2 builders.  I had given a presentation on my droids construction at that meet.


Just wanted to pass this info on to you to see if it may be of any interest to you or the Servo readers.  More technical information could be provided since the club posted version was more general in nature.

Best regards,

  Bob Ross

——- Forwarded Message——-
From: Bob Ross
To: R2 Builders Club

Sent: Wednesday, May 18, 2011 6:41 PM
Subject: [r2builders] Working Droid Caller

At the close of my presentation at DroidCon last Saturday, I unveiled my latest gizmo - a working Droid Caller.

Had actually started voice recognition for my R2 last year before C-V, but put it aside to get more critical things finished.  Once back, I continued with the project and made a change in direction.  My initial design was to put the electronics and mic into the droid and just talk to it.  Being at C-V with all the bedlam in the Droid Room convinced me that a different approach would be better.  Briefly thought of wearing a wireless mic to transmit my voice to the electronics, but that seemed clunky and expensive.  Then had a brainstorm to combine the complete electronics into a self contained handheld device and send wireless commands to the droid just as my remote does.

Did some research into Star Wars communicators and saw the storm trooper ones C3PO used to talk to Luke in the trash masher.  Was a contender until I saw the Droid Caller Luke wore on his belt at the farm.  It took an instant to decide that was the one to duplicate.

The electronic design is centered around a Tigal VRbot voice recognition module I read about it in Servo magazine.  (Note its been superseded by a newer model called EasyVR.)

The VRbot is a small module that decodes preprogrammed Speaker Independent (SI) words and self programmed Speaker Dependent (SD) words.  It has a bidirectional serial interface that receives microprocessor (uP) commands and sends word response codes.  Words are arranged in various Word Groups so the uP can tell the VRbot which group to decode from and then, depending on what was recognized, can prompt it to decode a word from the next logical group.  For instance the phrase, “hp-one-on” is comprised of 3 words (highlighted) from 3 groups per below:

SD1:  hey R2, remember, hp, mp, side panel, pie panel, body panel, dome, arm, position
SI2:  zero, one, two, three, four, five, six, seven, eight, nine
SD2: on, off, up, down, left, right, center, front, back, open, close

Once the uP collects the response string, it translates that into the same type of AT command as is done by my remote.  The data is transmitted as a digital packet to the R2 using the MaxStream RF module.

As an assembly, the electronics are packed (squashed) onto both sides of a breadboard PCB.  Used my favorite Atmel AT89C51 RE2 micro to do the processing which includes the above, plus detecting a key switch (power on, power off, phrase recognition), LED word prompting, debug display port, training (via VRbot GUI), etc.  The mic is mounted on a round right angle board that also includes the word LEDs.  A pair of 3.7V lithium batteries provide the power source.

Mechanically, the case is made from various pieces of plastic PVC pipe and aluminum fittings.  All were turned on a lathe to come as close to the Droid Caller prop as I could.  The website below has some pictures of the props and what they were made from (Kobold flash attachment) along with an article on building a non working prop from metal pipe.  As with all SW props, there are different variations.  I chose the one with the straight sided top.

This was really a neat project.  Had never worked with word recognition before and was interesting getting it to all come together.  In a quiet setting, it decodes spoken words pretty reliably.  The most fun was adding in the “hey R2” to simulate the interactive droid.  It sends a command to play the “deedlebeep” and then automatically restarts phrase processing to decode actual commands.  Of course I added in “remember” with the following word group.  Each tells R2 to play a sound and/or perform a script movement.

SD3: C3PO, Luke, Leia, Han Solo, Chewbaca, Obi Wan, Lando, Darth Vader, Jabba-the-Hut

Attached are some pics of the Droid Caller and its components.

ILM Droid Caller - Prop that Luke wore on his belt
PIC 0002 - Various electronic and mechanical components
PIC 0016 - Case top
PIC 0022 - Case parts and doo-dads
PIC 0004 - Electronics inside case
PIC 0007 - Finished Droid Caller