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[DPRG] LiDAR-Lite 360 degree continuously rotating mount

Subject: [DPRG] LiDAR-Lite 360 degree continuously rotating mount
From: Paul Bouchier bouchier at classicnet.net
Date: Sun Feb 15 20:06:42 CST 2015

Hi David,

All good points, but the intended application is localization, not 
obstacle avoidance (though it may provide a partial solution to that. An 
outdoor mowing robot is most in need of accurate localization. Decent 
obstacle avoidance, particularly of things the robot might run over and 
chew up, are also important. The mower has a bumper strip, but that 
wouldn't stop it getting stuck under benches, as John Swindle noted in 
his excellent roomba/neato/mint analysis. I think the mower has 
roomba-style downward-looking cliff detectors. Any decent solution needs 
multiple defenses, but without good localization there's little point in 
working on the "easier" problems because you can't get to a working 
solution. Tackle the show-stopper problems first. The robotics world is 
missing good and inexpensive localization solutions. GPS is a partial 
solution but it will lie to your face and tell you you're somewhere 
else, with high confidence, and make the mower mow down the flower-bed, 
confident that it's on lawn.

ROS has a particle filter localization module which localizes based on 
(lidar) ranges from objects in a previously mapped space. I think a 
high-speed long-range lidar may have application as a sensor to feed 
that algorithm.



On 02/15/2015 06:38 PM, David Anderson wrote:
> 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,
> dpa
> 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.
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