BR said:
The best I can do is give a description of the apparatus. It
involves three RC servos mounted on a rotating ring used to form a
gripper system. Each gripper pad is located equidistant about the
outside rim of a small 5" dia. hemispherical bowl containing water.
The opening of the 5" bowl must be in full view. The 5" bowl is
floating in a larger bowl filled with water. All three servos are
connected to one signal output of an EZ servo 1 chip (a pre-
programed controller). A problem occurs when the bowl is released.
The gripper releases the bowl as fast as it can when the signal
pulse width changes abruptly from 1725µs to 1650µs. However, the
differences between servos always causes the bowl to drift slowly
away from the lagging servo. This is determined by releasing the
bowl while the ring is stationary. Adjusting the servo mounting hw
only reduces the problem. So, I'm looking for a way to fine tune
the release and minimize linear motion of the bowl. If this can't
be done with delay lines I would appreciate any suggestions.
You are going to try to slow down the signals to each individual servo,
I'm guessing, using some kind of RC delay. That sounds like a tuning
nightmare. The RC delay will probably be temperature dependent. Anthony
Fremont already pointed out that the servos may be voltage dependent,
which means that they could be interacting in funny ways if they are all
powered from the same battery.
I wonder if somehow slowing down the servo action would work? It is
probably the quick snap which is imparting energy to the bowl. The
energy that is imparted by the faster servos is damped by the final servo.
Another possibility would be to use a clear string (like fishing line)
to hold the bowl in place. The servos would hold the line, rather than
the bowl itself. If the line had no tension on it (it was just used to
anchor the bowl in place), it would not be possible for the servos to
impart any energy on the bowl by releasing it (depending on their
position, they may splash the water, causing motion). The line would be
invisble in the water (hopefully).
On the other hand, a simple delay using a microprocessor would be easy
to cook up. Using the internal clock of a PIC, for example, you could
easily get repeatable delays of 1 ms within about 40us. A single $2
microprocessor could sequence the three servos in arbitrary and
repeatable ways, using trimmers to set the relative delay (so you can
tweak it in the field). I can do this for you if you are still
interested in persuing the delay scheme. email me if you are interested.
rc<surname>@comcast.net (replace <surname> with my last name)
--
Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.