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[DPRG] LiDAR-Lite 360 degree continuously rotating mount

Subject: [DPRG] LiDAR-Lite 360 degree continuously rotating mount
From: Rud Merriam rudmerriam at gmail.com
Date: Sun Feb 15 21:35:52 CST 2015

Does a mower really need localization? How about just going where the 
grass is not cut? That is a vision processing problem. Or maybe you 
could use a lidar to scan just above the height of cut grass. If it 
detects grass it needs to be cut.

- 73 -
*Rud Merriam K5RUD
* /Mystic Lake Software <http://mysticlakesoftware.com/>

On 02/15/2015 08:06 PM, Paul Bouchier wrote:
> 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.
> Regards
> Paul
> 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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