[Dprglist] [Dprg_roborama_committee] DYI 360 degee spinning LiDAR

[Chris N]

My 2 cents:

Definitely an impressive design, i.e. from an electro-mechanical point of view, but given that the cost of the RPLidar A1 (and its clones) is <$100, I’m just not sure its worth it.  Maybe it has a form-factor advantage in some situations?

Since it has 2 sensors, the effective rotation rate is actually equivalent to 120RPM, but that is still too slow!

I find that even the 300RPM of the RPLidar A1 is too slow for a robot that moves faster than a turtle – at least in my experience with the navigation stack in ROS (e.g. Gmapping or hector slam).     

I have cranked it up to almost 600RPM (10Hz), but at that rate, my Pololu Romi base was shaking quite a bit…..I suppose on a larger / heavier base this would be fine and I should probably try that at some point.

The problem with 300RPM is that the laser scan gets significantly warped as a result of robot motion, especially when the robot is turning.

I might have mentioned it already to this group, but I have actually spent significant amounts of energy on a lidar data de-warping logic earlier this year.   Got it to work, but it didn’t seem to improve the SLAM performance much – there are probably navigation stack parameters that need to be tuned properly…….That’s just one of the many complexities in ROS……

My code for the Lidar de-warping is here:  Experiments with de-warping lidar scans  
Discussion on answers.ros.org: How to deal with slow RPLidar scan rate on fast moving robot?

The code is in the form of a ROS node, but the core logic can be used outside of ROS of course.  Anyway, if somebody is doing Lidar and is finding the speed of the RPLidar to be an issue (due to warping), let me know and I can provide more details.

It was kind of fun (but exhausting) applying some math to create this de-warping logic, but if at some point I decide to get serious again about ROS and Lidar, maybe I will just pony up the $600 for a RPLIdar A3:   25 meter range,  16K samples /second,  1200RPM (20Hz).     Monitoring eBay for a good deal…..

Chris.

From: Doug Paradis via DPRGlist
Sent: Sunday, December 20, 2020 12:49 PM
To: Ron Grant
Cc: dprg_roborama_committee at lists.dprg.org; dprglist at lists.dprg.org
Subject: Re: [Dprglist] [Dprg_roborama_committee] DYI 360 degee spinning LiDAR

Ron,
     I agree about the rotation rate. I am also not a big fan of the VL5xL0X sensors, but I haven't tried the VL53L0x. I do think the project shows the issues that need to be addressed. If I were just starting out with nothing, I would prefer to just buy a RPLidar A1M8 from Robotshop.or DFRobot.  It has a scan rate between 1 and 10 Hz with 5.5 Hz used to get 1 reading per degree. 

    For indoors, this would be a good unit to have in your new simulator. For outdoors (and also indoors) you might want to allow for the Benewake line of sensors and the LiDAR-Lite. These are not scanning LiDARs, but have larger range and are usable outdoors. 

Regards,
Doug P.

On Sun, Dec 20, 2020 at 9:49 AM deltagraph--- via Dprg_roborama_committee <dprg_roborama_committee at lists.dprg.org> wrote:
Looks cool, but kinda slow rotation rate at 60 RPM vs about what 5X to 10X that speed in some of the robot vac cleaners.
Of course not bad to stop for a second, scan then move on, OR at least be aware of your position vs scan vector.

I am working on a new simulator rendition with LiDAR, looks promising and fun to play with. 
I can see useful to include variable scan rate to simulate range of available sensors low-cost units  to high-speed high dollar ...


Ron


-----Original Message-----
From: Doug Paradis via DPRGlist via Dprg_roborama_committee <dprg_roborama_committee at lists.dprg.org>
To: DPRG <dprglist at lists.dprg.org>
Cc: Doug Paradis via DPRGlist <dprglist at lists.dprg.org>
Sent: Sun, Dec 20, 2020 9:20 am
Subject: [Dprg_roborama_committee] [Dprglist] DYI 360 degee spinning LiDAR
Interesting Instructable: 
https://www.instructables.com/Project-Lighthouse-360-Mini-Arduino-LiDAR/

Regards,
Doug P.
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