Alt-BEAM Archive
Message #03606
To: "Jakub Pietracha" whraven@free.com.pl
From: Wouter Brok w.j.m.brok@stud.tue.nl
Date: Mon, 24 May 1999 10:34:07 +0200
Subject: [alt-beam] Re: Suspended master-slawe bicore walker.
Hello Jakub,
No, as you describe it it isn't a suspended bicore anymore. Actually it's a
normal bicore (i.e. a ringlike structure of two Nv-neurons) but with one
restiction: the resistors (of the two neurons) are dependent on eachother
in such a way that the total resistance will be constant (if one resistance
is made bigger by turning the pot the other one is made smaller by the same
amount).
The resulting behaviour from this replacement is quite different from the
behaviour of the original master suspended bicore. For example, now it will
be possible to control the duty-cycle in a better way (and thus the swing
of the legs).
By saying this I realise that I suggest that the suspended bicore has a
dutycycle, different from 50%, which is harder to control then in the new
situation. This might raise some questions, because I think most people
believe that the duty-cycle of the suspended bicore is 50% by defenition.
This however is not generally true, although one would expect the average
dutycycle to be 50%. The duty-cycle of on period of oscillation does not
need to be 50%. Actually it can differ quite a bit from that because of noise.
For a suspended bicore with equal capacitors and inverters which have
threshold-voltages approximately Vcc/2, the moment of switching states is
very likely to be caused by noise. And if this is so the circuit can switch
state in the first half a period, for example, earlier than in the second
half of the period, which results in a duty-cycle for that period,
different from 50%.
One would expect that the average duty-cycle is 50% since noise is (thought
of to be) stochastic and doesn't favour one particular part of the period
of oscillation. However if it does favour one paricular part of the period
the resulting average duty-cylce differs from 50%. Is this possible I
wonder ... Yes, I think it is (although perhaps not the reason for the
nonsymmetric leg-swing in your question) because maybe the noise produced
by the motor is different in amplitude for the two different directions. If
the noise influences the master suspended bicore this then will result in
an average duty-cycle not equal to 50%.
A couple of weeks back somebody posted the same question to the list ...
same problem. Maybe what I described above is the reason of the problem;
any comments from other people on the list?
Jakub, the solution you choose is a good one to really control the
duty-cycle, but I don't know if it is what you want. Like this the circuit
is less sensitive to noise and maybe you actually wanted it to be
sensitive. If so I would suggest that you connect springs to the legs, so
that they will not turn all the way around eventually and accept the fact
the the walker doesn't walk in a straight line.
If what I described is the reason (maybe you will get more reactions later
proving me wrong (which I would like to know)) then I you could make the
circuit less sensitive to noise by using capacitors decoupling
power-supply-lines and by choosing different-valued capacitors in the
master suspended bicore.
Come to think of it ... it is the moter connected to the master which turns
non-symmetrically is it?
Regards,
Wouter Brok.
------------------------------------------------------------------------
eGroups.com home: http://www.egroups.com/group/alt-beam
http://www.egroups.com
- Simplifying group communications
Home