[Dprglist] Compass heading using gyroscopes?

[Murray Altheim]

Hi Doug,

Thanks for the info on the smaller LiDAR and the YouTube video, which I just
watched. If I'm trying to measure distance, the Benewake products look really
good, especially that smaller one.

The idea of measuring a gap was a possible approach to aiming at the first
target of the four square challenge. It'd be kinda cool to have the robot be
able to locate that gap at the beginning of the course rather than rely on
the robot's owner physically aiming it at the target, but either works: I
like the complexity of the LiDAR and the simplicity of the laser pointer.
Hacking a laser distance meter might work but it's pretty big physically for
my somewhat-small robot. By contrast, the tactical red dot laser I've just
ordered from somewhere in China is 42mm x 20mm x 24mm and weighs 28g. That's
small enough to bury under my robot's bumper. For the same price (US$13.55)
I had the choice of a class 2 or class "IIIa" ("less than 5mW") laser and
bought the more powerful one, which might be in the cat-tattooing power range.

Currently I've got that little Pimoroni VLX53L1X Breakout Garden sensor with
a range of up to 4m (though it seems more like 2.5m in practice, really) and
is about the size of a postage stamp (remember them?!). I've mounted it on a
micro servo and have a draft post on my blog that I've not finished yet;
suffice it to say that it's a very capable sensor and can do an accurate 90°
sweep in about 3 seconds. The power requirements are almost inconsequential.

David was asking me about it on our last video conference. If you mount an
ultrasonic sensor on a servo and try sweeping it that quickly you get nothing,
sound can't travel that fast, but the little laser works really well (though
yeah, the speed of light ain't what it used to be).

Another idea I had was to use one of the Raspberry Pi cameras to look forward
towards the target and locate some specifically-colored pixels. The resolution
on the cameras is probably high enough that this might work if the lighting
in the room is good enough. Or, aim the camera at some kind of point light
source. The rules permit something like that.

But if I'm not trying to measure distance, simply point at something as a
target, a small tactical red dot laser (with allen screws to adjust trajectory)
is just the thing.

I appreciate the point of conversations like this is to "advance the technology"
that could be used on our robots. So using a LiDAR rather than a cheap laser
pointer would be a greater advance and a more interesting experiment. So I'll
continue to think about this (even though I've got a menacing black laser on
its way in the mail).

Cheers,

Murray

On 18/05/20 2:57 pm, Doug Paradis wrote:
 > Murray,
 >  I don't know what size gap you are trying to detect or the speed that> the gap may appear. Hhowever if the sampling rate is slow, about once > per second, another possibility is a laser distance meter with a serial> port. You can get a 
laser distance meter board with a serial port from> Aliexpress (I have seen them listed, but can't seem to find the right> search terms, so no link), or you might look at this project
 > (https://hackaday.com/2014/03/29/hacking-a-laser-tape-measure-in-3-easy-steps/). > I own one of these meters, have brought the serial port out, and played> with it. Its cool, but a robot generally needs a faster update rate.
 >
 > Regards,
 > Doug P.
...........................................................................
Murray Altheim <murray18 at altheim dot com>                       = =  ===
http://www.altheim.com/murray/                                     ===  ===
                                                                    = =  ===
     In the evening
     The rice leaves in the garden
     Rustle in the autumn wind
     That blows through my reed hut.
            -- Minamoto no Tsunenobu