Subject:
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RE: New list member
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 24 Jul 1997 09:09:23 GMT
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Original-From:
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John Hatton <JOHNHA@ICSPLC.CO.stopspamUK>
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Viewed:
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1284 times
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In response to David's post about using the Mini SSC 2 boards and
producing a walking robot (my aim is a 12 servo 6 legged walker) I am
writing to provide the information that I have found. I have posted a
similar question to David about the MiniSSC 2 board but as I have not
bought any hardware yet this was from a theoretical design point of
view, David has obviously encountered a physical problem I hadn't
thought of.
I have decided to use the SERVO16 algorithm mentioned in one of my
previous postings (I can give you the address of the website for this if
needed) running on a modified Miniboard. This algorithm appears to
provide a 16 servo drive unit which appears from the documentation (I
haven't finished it yet so I could be wrong) to be able to store a
variety of walking 'styles' in the board. I'm not positive on this but
even if I am wrong the SPI port appears to have a theoretical maximum
baud rate of 1MHz. I imagine this is not actually achievable but it is
definitely quicker than the SCI port used for the MiniSSC2 boards. From
the documentation of the SERVO16 algorithm all that would need to be
added to the code is communications with the HB and the HB sending the
desired servo position to the MB.
Any other suggestions would be gratefully received as I am still in the
theoretical design stage and am open to suggestions.
David also asked about IR sensors for distance sensing, I have read an
article that uses an IR Demodulator module to give an analogue reading
of the strength of the reflected signal from an associated IR
transmitter. This signal is then processed as a standard analogue input
and the desire distance can be calculated.
Hope this is of help.
John Hatton
> ----------
> From: Boeren, David C[SMTP:dboeren@uscomm.com]
> Sent: 23 July 1997 20:14
> To: 'Handyboard Mailing List'
> Subject: New list member
>
> Just wanted to introduce myself as a new mailing list member. I've been
> reading the archives for a while, but my workplace only got the mailer
> working
> correctly to external locations yesterday.
>
> Anyway, I got my HB a while ago from Digital Microsystems. I did have a
> delay for about 4 weeks, but I got mine in the mail about 2-3 days after
> he
> posted the explaination message about his absence.
>
> My first robot was made from a remote controlled bulldozer from Toys 'R
> Us.
> I removed all the bulldozer shaped pieces and the blade assembly and was
> left with a mobile platform with two differentially driven treads. I
> run the motors
> of the bulldozer off the HB motor outputs, but they are pretty
> current-hungry,
> so I leave them on about 25% power and put each motor on its own motor
> driver chip (don't know if separate chips helps or not). Currently it
> has a pair
> of photoresistors and is programmed to arc in the direction with more
> light
> if the light difference exceeds a threshold value.
>
> At one time I had an IR emitter/detector pair, but it only sensed
> objects to
> about 1/2 inch. I tried putting in a smaller resister to increase the
> range, but
> apparently that burned it out. Does anyone know how to get reasonable
> range out of IR sensors (6 inches)?
>
> My next project is legs. This is an ongoing kind of thing that I expect
> to be
> working on a long time. The first cut calls for 4 legs with 3 servos
> each. Later
> I will go to 6 legs, but 4 is OK for now and saves money. I want to use
> a pair
> of Mini-SSC 2's to do servo control. I'm having a little trouble
> getting these
> interfaced to the HB, maybe someone can tell me what I'm doing wrong.
>
> I got the serial source code from the WWW page and disable IC's use of
> the
> serial port. I have a short (6 inch) RJ-11 cable that goes from the HB
> to my
> Mini-SSC 2. The Mini-SSC 2 uses a 9-volt battery to power the
> electronics and
> an R/C style 6v NiCd battery to power the servos. My problem is that if
> I
> leave the RJ cable plugged in after a short time (a minute or so) the RJ
> jack on
> the Mini-SSC 2 starts to get really hot, and eventually the plastic
> begins to
> melt! As far as I know, I'm using the serial ports exactly the way they
> are
> meant to be used, so what's the problem? Do I need a special sort of
> serial
> cable? The servo positions OK, as long as I unplug the RJ cable once in
> a
> while to keep it cool.
>
> My initial goal is just to get something walking, but more generally I
> want to
> study legged motion and see what tradeoffs different arrangements have.
> I
> believe that a more capable 3 DOF leg will be better than the typical 2
> DOF
> "rowboat" style legs since it is more flexible and can hopefully
> traverse
> terrain better. Additionally, the extra servo enables me to change
> stance from
> a high stance that climbs better to a lower stance that has higher speed
> over
> smooth surfaces. Eventually I want an adaptable legged platform which
> can
> tailor its walking style to the task at hand.
>
> If anyone is interested in talking more about legged locomotion or the
> Mini-SSC 2, please email me.
>
>
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