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[DPRG] LiDAR-Lite 360 degree continuously rotating mount

Subject: [DPRG] LiDAR-Lite 360 degree continuously rotating mount
From: David Anderson davida at smu.edu
Date: Sun Feb 15 19:38:38 CST 2015

Thanks Paul,

Just trying to get a feel for how this might be used.   16cm at 40m 
means 4cm, about 1 and 3/4 inch, at 10 meters.  So, unless the scans are 
jittered vertically,  nothing above or below a 1 and 3/4" strip would be 
detected at 10 meters, which is still 30 feet away from the robot.

That might work well for walls or fences or tree trunks, but would miss 
many (most?) real-world outdoor obstacles that are higher or lower than 
a strip a couple of inches wide at 30 feet.   Curbs, for example, or low 
hanging branches.  The legs of a picnic bench, but not the bench 
itself.   Chains of a swing set, but not the swing. And so on.

And that little strip then becomes even more narrow as the range closes, 
i.e., close to the robot, when you need it the most.  At 2.5 meters,  
(we're about to collide!) that strip is 1cm, about 1/2 inch, and nothing 
above or below that will be detected.   Not that useful outdoors, in my 
experience, unless your robot happens to be, you know,  an inch and 3/4 
tall.  Otherwise, obstacles that might be detected at 10 meters simply 
disappear as the robot gets closer. Not a strategy for success.

So maybe you need to have a fancier rotating mount, one that can pivot 
vertically to give a denser data set than just a thin strip of the 
environment at some arbitrary height.   But that would increase the 
sample time for a complete scan and correspondingly increase the 
response time of the robot.

If it were operating in a typical artificial indoor robot environment 
(flat orthogonal walls, "objects" that are simple cubes and cylinders 
sitting directly on the floor, etc,) it would probably work fine.   
Outdoors-real-world, I'd have a lot of questions.

I'm not sure what you can trust from such a tiny, thin-slice sample of 
the environment.    How are you planning on using this data?

best regards,

On 02/15/2015 03:22 PM, Paul Bouchier wrote:
> Excellent question David. The Tx spec says 4mrad, so if I'm operating 
> the calculator correctly, that's a 16cm spot at 40m (both horizontally 
> and vertically). Are you thinking about narrow reflectors? Or about 
> the fact that a 1 rps (60rpm) system sampling at 2kHz would take a 
> sample every 0.18 degrees (3mrad), thereby giving overlapping coverage?
> Paul
> On 02/14/2015 12:39 PM, David Anderson wrote:
>> Do you what the vertical spread of the beam is?
>> thanks,
>> dpa
>> On 02/14/2015 09:46 AM, Paul Bouchier wrote:
>>> FYI - I saw a post from the LIDAR-lite folks posting on RoboBill's 
>>> post of a similar rotating platform, and they said that in the first 
>>> quarter they'll start shipping units with a 2kHz scan rate. Here's 
>>> the URL - look for the post by Dennis Corey.
>>> http://diydrones.com/group/ardurover-user-group/forum/topics/contributing-to-giving-sight-to-av-s?commentId=705844%3AComment%3A1870054&groupId=705844%3AGroup%3A903163
>>> That's more like what we need for a scanning lidar suitable for 
>>> outdoor work.
>>> Paul
>>> On 02/02/2015 09:45 AM, Paradug wrote:
>>>> David,
>>>>       I understand your pain. I often have similar thoughts.
>>>>      The LiDAR-lite shows promise as a sensor due to its range 
>>>> outdoors (~40 meters). It only takes a max of 100 points per second 
>>>> which is slow compared to the rotating LiDARs made for indoor use, 
>>>> like the Neato XV11 (range ~6 meters indoors), which make about 
>>>> ~2000 reads per second. In the example shown in the links, the 
>>>> author is showing a successful 360 degree sweep at about once every 
>>>> 8 seconds by using 2 sensors. This is a meaningful step forward for 
>>>> using these sensors usefully in a robot, but still slow. Using the 
>>>> same idea with faster rotation and 360 points per revolution, he 
>>>> should be able to get down to about 2 seconds per revolution.  For 
>>>> a robot going less than 2 or 3 meters per second that might be 
>>>> okay. Especially for the case where no object was moving (i.e., 
>>>> people).
>>>>     I am considering an LiDAR-lite based idea that is different for 
>>>> use on my outdoor robot. The linked project has some ideas worth 
>>>> stealing ;^). However, I am still on the fence on purchasing the 
>>>> LiDAR-lite. I need to have a firmer grasp of what I have to 
>>>> accomplish in the software. The SLAM course I mentioned earlier is 
>>>> helping that situation.
>>>>     This might be a good opportunity for a group project within the 
>>>> club. I know some members have LiDAR-lites.
>>>> Regards,
>>>> Doug P.
>>>> *From:* David Anderson <mailto:davida at smu.edu>
>>>> *Sent:* Monday, February 02, 2015 9:44 AM
>>>> *To:* dprglist at dprg.org <mailto:dprglist at dprg.org>
>>>> *Subject:* Re: [DPRG] LiDAR-Lite 360 degree continuously rotating mount
>>>> Cool.
>>>> <rant>
>>>> In all my other hobbies, except robotics, when someone has a new 
>>>> innovation, they show their craft (heli, sailboat, whatever) doing 
>>>> something really cool, and then explain the technology that makes 
>>>> it possible. That's why I might be interested in the technology, 
>>>> because it allows the platform to do something interesting that 
>>>> can't be done any other way.
>>>> But that is never the case with hobby robotics. Instead, the 
>>>> technology is demonstrated as if it is an end in itself, with the 
>>>> hope that someone will eventually do something cool with it.  Just 
>>>> once, I'd like to go to a link like that posted below by Doug, and 
>>>> see a video of a robot DOING SOMETHING interesting, followed by a 
>>>> description of the technology required to do that interesting thing.
>>>> (As an aside, this same thing seems to apply in spades to all the 
>>>> hobbiest ROS robots I've come across. Surely there are some HOBBY 
>>>> robots running ROS somewhere out there DOING SOMETHING  interesting 
>>>> that makes all the pain of getting ROS to work worthwhile.   If so 
>>>> they seem to be keeping pretty quiet about  it.   Where are all the 
>>>> videos?)
>>>> </rant>
>>>> OK, I'm done, move along, nothing to see here...
>>>> dpa
>>>> On 02/02/2015 08:15 AM, Paradug wrote:
>>>>> Here is an interesting project for members with 2 LiDAR-lites.
>>>>> http://www.thingiverse.com/thing:662646
>>>>> *http://hackaday.io/project/4087-360-degree-lidar-lite-scanner*
>>>>> Regards,
>>>>> Doug P.
>>>>> _______________________________________________
>>>>> DPRGlist mailing list
>>>>> DPRGlist at dprg.org
>>>>> http://list.dprg.org/mailman/listinfo/dprglist
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