Subject:
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Re: design alternatives: servo control and power source
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 16 Apr 1999 07:41:17 GMT
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Original-From:
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Mike Jones <michaelj@&avoidspam&wt.net>
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Reply-To:
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michaelj@wt.net%nospam%
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Viewed:
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1129 times
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> Hello,
>
> I am planning to build a robot based on the Lynxmotion Hexapod II
> and Big Grip kits. There will be 12 servos for lego control, 2
> servos for the manipulator, and 2 more for a camera pan/tilt
> unit. Everything appears fairly straightforward, but:
>
> 1) I am trying to decide on whether to use two mini SSCs or the
> Ferrettronics chips to control the servos. Does anyone have
> any info/experience that might sway me one way or the other?
> Is anyone aware of documentation or tips for using either
> of these with the handy board?
I don't have the Ferrettronics chip datasheet in front of me but some off the
cuff calculations:
2400 bps/10 bits per byte=240 bytes per second
each servo will require at least 2 bytes (servo # and position)
16 servos * 2 = 32 bytes for each position update (if the protocol also has
a chip address then 16 * 3 = 48 bytes!)
if you can talk with 2 different chips simultaneously then 32/2=16 bytes per
update
240/32 = ~7 so your leg position updates will only happen every 1/7 second which
is pretty slow and the legs would move like driven by stepper motors (stop,
start, stop, start)
I think the ssc will communicate faster than 2400 bps so updates can happen
faster.
>
> 2) I am wondering if I can run the servos from the handy board
> batteries or if I need to have a separate battery pack for
> the servos. Obviously the HB batteries won't last very long
> if they are also running 16 servos, but would this work?
You should be able to run from the same battery as long as to drop the voltage
down to about 6V but definately be sure to use the same ground or the servos
won't operate correctly. If you do decide to use separate batteries make sure
the grounds are also connected.
On a different subject, you may want to join the legged robots mail list. Just
send an email to
legged-robots-subscribe@egroups.com
It will respond with a message of instructions. This list has been pretty active
and can help you with all sorts of issues related to walking robots.
Mike
(moderator of the legged robots mail list)
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