Subject:
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RE: Brainstorms
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 13 Aug 2002 12:50:32 GMT
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Reply-To:
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<rhempel@bmts.comNOSPAM>
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Viewed:
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564 times
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<snipped Fred's excellent Cricket description>
> About the brain. My close collaborator on the design of the
> Cricket system, Brian Silverman, always argued for a pure brain --
> that is, a brain that has no motor drivers or sensor inputs of its
> own. But we never built one. Our basic brain (the Cricket itself)
> still gives you two motors and two sensors. It just seems useful
> to have that little bit of capability when you first get started.
Again, I need to go back to my real-world fire alarm experience and
say that this makes very good sense. Nobody gives much thought to the
alarm systems in their building. They must meet very tough specs
from UL while at the same time being very cost sensitive.
As no two buildings are the same, the industry standard is to provide
a main board with a few sensor and signal circuits, and then allow the
customer to buy additional cards to add more circuits such as smoke detectors,
dry relays, and signal power.
For our system, I developed a single master protocol that runs on RS485
(long distance) with the extra property that messsages were guaranteed
delivery from the master to the slaves and that sequence was preserved as well.
A rather complex system of message buffers got this done - there's an
incredible ammount of state information that must be saved in a fire alarm.
Before you say that we should use TCP/IP, the overhead was simply too big!
Fred, those little shrouded and keyed headers are pretty cool. Are they
not similar to standard servo connectors?
In fire-alarms, connecting adapter cards is always a headache. Some
manufacturers set up the connectors so that the pins of one card fit
the header on the next card - but this may require cable adapters if you
need to break up a line of devices.
Even with short daisy chains, the cables (actually the connectors) do end
up being a source of voltage drops or contact issues that can lead to very
perplexing problem solving....but no solution is perfect.
I need to review the docs more closely to see if I can develop a
driver for the RCX that will speak the Cricket protocol.....
> So while the Cricket system won't win design awards for raw power,
> it might stand to be nominated for usefulness and adaptability!
This kind of systems design is very difficult. The compromises that
you have made make a lot of sense to me. It must have been difficult
to keep things moving along at times, I'm sure.
Thanks for a very well presented note, Fred.
Regards, Ralph Hempel - P.Eng.
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Message is in Reply To:
 | | re: Brainstorms
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| Thanks Stef Mientki for pointing me to this great thread you guys have going. People may wish to take a look at the Cricket work I've been doing the last five years. The Cricket system a modular brain & sensors & actuators construction kit along the (...) (22 years ago, 13-Aug-02, to lugnet.robotics)
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