Subject:
|
Re: Sonar questions (technical ones!)
|
Newsgroups:
|
lugnet.robotics.handyboard
|
Date:
|
Thu, 26 Feb 1998 02:47:09 GMT
|
Original-From:
|
MAR ERICSON <mar@=StopSpammers=cooper.edu>
|
Viewed:
|
1409 times
|
| |
|
|
My sonar seems to be pretty accurate. I would notice a 25% difference.
???
Check your calculations. Maybe you missed something.
-----------
ericson mar
Master of Engineering Candidate
Project: Mobile Robotics
mar@cooper.edu
(212)353-4356
Department of Mechanical Engineering
The Cooper Union for the Advancement of Science and Art
-------------------------------------------------------
On Wed, 25 Feb 1998, Skye Legon wrote:
> Hello everyone,
>
> A few sonar questions (other than where to buy them):
>
> 1: The speed of sound has been widely quoted to be 0.9 ft/ms (274m/s),
> but my Physics text lists it as 343 m/s (at 20C/70F), which is about
> 1.13 ft/ms, or 25% faster. So why the 0.9 value (or just cuz
> the Polaroid guys say so)?
>
> 2: The sonar routines (e.g. sonar_sample()) return the distance as an
> int, meaning the greatest round-trip distance possible is 32768
> half-microsecs, or 8192 microsecs one-way. By my math, 8.2ms is
> about 3m (10 ft). Is this our max distance? Any way to improve
> this?
>
> 3: My sonar works well, but about 10% of the time it returns a spurious
> low value (around 2200 counts/8 inches), even if nothing has moved
> or changed in the environment. I have written a kludge to simply
> re-pulse if it receives such a result, which works fine, but it's
> ugly and I'm just treating the symptom, not the cause. Any ideas
> why this is? (I'm using sonar_closeup(), BTW)
>
> 4: I'm confused by the guts of the sonar routines. The start_time is
> read from the system TCNT register as a 16-bit integer (max 32768
> counts). If TCNT increments 2,000,000 counts/sec, does this mean
> TCNT rolls over every 16ms? If so, it seems quite likely that the
> counter will roll over while we're waiting for a pulse to return
> depending on when we peek it for the start_time. However, the
> routines work fine, so can someone please clear up my
> misunderstanding?
>
> Cheers! Skye.
>
> +-----------------------------------------+----------------------------+
> | Skye Legon | University of Waterloo |
> | Systems Design Engineering | __/ __/ __/ __/ |
> | Pattern Analysis & Machine Intelligence | __/ __/ __/ __/ __/ |
> | 143 Columbia St. West, Unit E-4 | __/ __/ __/ ____/ __/ |
> | Waterloo Ontario CANADA N2L 3L2 | __/__/__/ __/__/\__/__/ |
> | +1(519)888-9249 | ______/ ___/ \___/ |
> | slegon@uwaterloo.ca | DC 2620, 888-4567 x5192 |
> +-----------------------------------------+----------------------------+
>
>
|
|
Message has 1 Reply:
 | | Gear Motors
|
| I was wondering if anyone has a good source for fairly high quality, low cost gear motors that inteface well with the handy board. Right now i am using a cheap little, current hungry 3v toy bulldozer as a platform. I would love to find some nice (...) (27 years ago, 15-Mar-98, to lugnet.robotics.handyboard)
|
Message is in Reply To:
| | Sonar questions (technical ones!)
|
| Hello everyone, A few sonar questions (other than where to buy them): 1: The speed of sound has been widely quoted to be 0.9 ft/ms (274m/s), but my Physics text lists it as 343 m/s (at 20C/70F), which is about 1.13 ft/ms, or 25% faster. So why the (...) (27 years ago, 25-Feb-98, to lugnet.robotics.handyboard)
|
6 Messages in This Thread:
  
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
