Subject:
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Re: 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 03:01:52 GMT
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Original-From:
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Nick Taylor <ntaylor@iname.com>
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Viewed:
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969 times
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Andre:
You're right about the HandyBoard & expansion board documentation not
being correct in its servo entries. I don't recall what values I found
to work properly on the bare HB, but on the expansion board the default
of 2540 comes close to centering the dozen or so servos that I've
tried. The +/- 90 degree points are typically 1040 and 4040. Since
I don't have a 'scope either I don't know what the actual pulse widths
are ... but these same servos have typical ranges of 1050-1950 us
when used with a PIC.
Hope this helps,
- - - Nick - - -
Andre Philippi wrote:
>
> 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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Message is in Reply To:
| | Servo Control Documentation Clarification...
|
| 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 ((URL) "Super Rooster" Electronic Speed Controller (ESC), I found the following discrepancies (...) (25 years ago, 14-May-99, to lugnet.robotics.handyboard)
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