dca386da

PID: SoupGate-Win32 v1.05
On Fri, 21 Dec 2018 21:17:08 +0000,
real-not-anti-spam-address@apple-juice.co.uk (D.M. Procida) declaimed the
following:

>
>I see that they come in two basic types: continuous rotation (their
>speed of rotation is determined by the pulse width) and fixed travel
>(usually 180 degrees, sometimes a bit more).
>

 Continuous rotation servos are basically ones in which the comparator
(may have a different name) has been disabled. The comparator is the
circuit that matches the integrated pulse (visualize charging a capacitor,
the longer the pulse, the higher the voltage on the capacitor) to a voltage
obtained from the position (visualize a potentiometer on the servo shaft).
When the voltages match, the servo stops turning. Replacing the
potentiometer side with a divider network (so it always reads "mid-point")
means longer pulses move one direction, shorter pulses move the other way.

>They come in various standard (not sure how standard these actually are)
>sizes - micro, sub-micro, standard.
>
>And they can have plastic or metal gears.
>
>What else should one be aware of? I have an application in which I'd
>like reasonable accuracy and precision, and for a 5-degree command (say)
>to have a 5-degree output.

 How many servos? For the most part, the RPi only has one readily
accessible PWM output module. Any more and one has to program their own
timing logic for digital GPIO (and mixing periods for multiple such is an
even greater headache) -- and this logic will be subject to the OS tasking
preemption.

https://learn.adafruit.com/adafruits-raspberry-pi-lesson-8-using-a-servo-motor?
view=all
"""
If you want to control more than one servo, then the easiest way to do this
is to use something like the Adafruit I2C 16 channel servo / pwm
controller. This tutorial explains how to use it.
"""
https://learn.adafruit.com/adafruit-16-channel-servo-driver-with-raspberry-pi?v
iew=all

 Probably cheaper than using an Arduino UNO (I'm presuming you aren't
going to be wiring up a bare AVR chip) to gain its 6 PWM outputs; not to
mention you won't have to program a command protocol over the serial port.

 Avoiding the Arduino, but also swapping out the RPi -- a Beaglebone
Black has 7 pins that can be configured for PWM (two are normally the SPI
pins) and runs Debian (on which Raspbian is based) -- so is a single board
solution, and (if using Python) the code is practically the same (import a
different IO package).


--
 Wulfraed                 Dennis Lee Bieber         AF6VN
 wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

--- SoupGate-Win32 v1.05