Alt-BEAM Archive
Message #08098
To: beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Thu, 2 Dec 1999 18:54:02 -0800
Subject: [alt-beam] Re: D'oh! Head Revelation
Ooops! once more for those who can't read MS OUTLOOK email with embedded
graphics.
Brilliant Richard! and a good time resurrect the old servohead project.
The attached schematic works with unmodified hobby servos and can be used
with an umbilical connection to move the motor or the shaft with respect to
the base. In first case the umbilical requires a 2 conductor cable for power
and in the second case, the cable is 3 conductors for the eyes. The power
required for this circuit is a few ma but the servo continuously draws
50-100ma and more when stalled. A 74HC240 can be used instead of the 74HC04
shown. In that case, up to 4 servos can be proportionally controlled with
analog voltages from a photo bridge or other source like microcore outputs
(hexapod), temperature (green house vent), differential sound level
(security camera aiming), potentiometer ( 2 wire remote control), etc).
<>
In the uCrawler V2.0, I did what you suggested and replaced the circuit
inside the servo housing with the crawler circuit which also uses the servo
pot (P1) for feed back to pump the crawler legs. As shown in the attached I
changed the time constant from .3 ms to 30ms and that circuit will control a
head exactly as you described but power efficiency is not great (ie similar
to a bicore). A PS head version should be quite easy to do.
<>
> -----Original Message-----
> From: Richard Caudle [SMTP:rwcaudle@hpamonon.com]
> Sent: Thursday, December 02, 1999 12:28 PM
> To: BEAM
> Subject:
>
> Hey all,
>
> I just thought of something...I had proposed using a head controlled pot
> to drive a +Phototropic robot body a couple of weeks ago. Inside of a R/C
> servo is a gear train, positioning pot, circuitry, and a motor. The
> driver circuit could be removed and a BiCORE (or PSH) circuit put in it's
> place and the pot leads going out to the robot's body circuitry. The
> whole thing could be housed in the box for the servo! The "eyes" are the
> only thing that needs to move. Why mess with the weight of the entire
> head. It dosen't have to go all the way around because it's mounted to a
> mobile body. I have something like servos at home (gleaned from an old
> "Teddy Ruxpin") and I'll give it a shot tonight, if I can find my
> 74HC240. I left it right over there...
>
> Wondering Aimlessly,
>
> Richard
Attachment: hservo1.gif
Attachment: uCrawlerhead.gif
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