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In lugnet.robotics, Mark Tarrabain wrote:
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Could someone explain to me technically why this sort of of problem with
the rotation sensor occurs?
I know how quadrature shaft encoders are supposed to work, and I can’t
see why this sort of thing should happen in the first place.
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They do work! But they are usually used with two quadrature outputs (hence the
name), while on RCX only one wire is used and the 4 states are encoded as 4
voltages levels.
(Image courtesy Michael Gasperi)
The sequence (clockwise) is Level0 -> Level1-> Level3 -> Level2 -> Level0.
Unfortunately it is possible that RCX sampling occurs during transition L1 to
L3, while the analog voltage value is near L2 (this transition takes some time,
as can be seen below)
This can also happen in L2 to L0 transition, through L1.
When this occurs, counting is perturbated...
On top of that, there is a hardware problem (insufficient filtering) which at
low speed increases greatly the probability that the transition occurs at the
wrong (sampling) time. For more details, see
http://www.philohome.com/sensors/legorot.htm
Philo
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