Subject:
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Servo Control Documentation Clarification...
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 14 May 1999 00:35:47 GMT
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Original-From:
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Andre Philippi <(philippi@)Spamless(earthlink.net)>
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Viewed:
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807 times
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Hi,
While I was trying to produce .85, 1.35, and 1.85 millisecond pulses with the
Handy Board (with *and* without the expbd.), to control Team Novak's
(http://www.teamnovak.com/products/esc/super_r/super_ro.htm) "Super Rooster"
Electronic Speed Controller (ESC), I found the following discrepancies
regarding servo control documentation:
1) First, in regards to servo control, according to
http://turbine.kuee.kyoto-u.ac.jp/staff/onat/servobasics.html, "The ON time of
the pulse indicates the angle to turn to; 1ms = 0 degrees, 2ms=max
degrees(about 120) and anything in between gives a proportional output angle.
1.5ms is generally considered to be the "center". The 1~2ms limit is
manufacturers' recommendations; you can usually use a wider range around 1.5ms
for grater throw."
So I called Novak, and they gave me "Super Rooster's" limits as following:
0.85 milliseconds - Maximum Reverse.
1.35 milliseconds - "Neutral".
1.85 milliseconds - Maximum Forward.
So far so good...but...
2) According to the "Dual Servo Routine" for the HB
(http://el.www.media.mit.edu/groups/el/projects/handy-board/software/servo.html
) we have the following:
a) Value Range: 400-4800 units...
b) Time Range: 0.2-2.4 milliseconds...
c) Default: 2560...
d) 1 Unit = 0.5 microseconds...
e) 3040 units = 1.52 milliseconds pulse length, "...which is just in the
middle of a typical servo's range...".
So, if 2a-2e are true, why wasn't the default set to be 3040 (instead of
2560), which is supposed to be the middle of the servo's range ? What was the
purpose of setting the default above the middle of the range? And, is there a
way to change the default value ?
Also, if the middle of the range *on this routine* is really 3040
(1.52milliseconds)...; Will 3040 units, be the middle of the range for the
expbd servo routine too? I could not find the "middle of the range" (in units)
for the expbd servo routines... :(
3) According to the Expansion Board servo documentation
(http://el.www.media.mit.edu/groups/el/projects/handy-board/hbexp30/software.ht
ml), we have the following:
a) Value Range: 0-3000
b) Default: 2540
So, if the range in this routine is 0-3000 units, why is the default 2540 ?
Why isn't it 1500 units ? How many milliseconds 2540 units correspond to ? Are
there any practical reason on why we would want to set the defaults so much
"higher" (longer) than the middle of the servo's range ? Why wasn't the middle
of the the range in units mapped to the middle of the range in milliseconds ?
How many *microseconds* do each unit correspond to, on the expbd servo control
routines ?
Is there a linear relationship between the unit range and the pulse length
range ?
The reason I'm asking all that, is so I can properly program the ESC,
hopefully making my car go a little slower (now is going tooooo fast...:)...
And since I don't have an O-Scope to measure the pulses coming out of the HB,
I had to ask all the above... :)
Thank you in advance,
Best Regards,
Andre Philippi.
=================================================================
Andre Philippi - Applications Developer | Phone: 626-296-5016
philippi@corp.earthlink.net | Fax: 626-296-5113
Earthlink Network, Inc. | 3100 New York Drive
http://www.earthlink.net | Pasadena, CA 91107
=================================================================
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