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Thread: LIDAR-lite 360 Mirror Scanner

  1. #1
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    LIDAR-lite 360 Mirror Scanner

    This is my idea for using the LIDAR-lite sensor to produce readings in (as close to) a 360 degree view without spinning the sensor itself. I decided to start this project to give some life to my sensor which had never had a real purpose until now.

    Thanks to my 3D printer I was able to quickly produce a "rig" to hold the sensor over a mirror. The mirror is attached to a 3D printed plate that is designed to hold the mirror at a 45 degree angle. This will allow me to bend the light 90 degrees from the sensor's emitter. The mirror holder is attached to a stepper motor that will allow me to rotate the sensor's light in a 360 degree view.

    Before I go on I've presented a few issues.


    • Blocking the view. To hold the sensor over the mirror there will be an arm somewhere in the 360 degree view. I've already taken some action here and removed some of the arm material. In fact if I remove too much more the PLA plastic I've used won't be rigid enough to hold the sensor still.




    • The mirror has to be quite large. This is something I discovered along the way. When it was just an idea in my head the mirror was really small but to ensure both the emitter and receiver are 100% in view I had to use the size you see.




    • Knowing the mirror position. Because I'm only using a stepper motor for this first design I get no positional feedback. I'll have to assume the mirror position by starting the motor and firmware at a known point.




    • Reading accuracy. By bending the light alone there is going to be a small offset introduced. Then there is the ever changing distance of the mirror as it rotates. I chose to align the emitter of the sensor to the center of the mirror. This ensures the light will project in a parallel plane. When the light is received it might bounce off the high side of the mirror in one direction and the low side on the other. I may or may not concern myself with such slight offsets introduced in the readings.


    So to get back to the setup. I had a NEMA 17 motor collecting dust and a recently purchased Teensy 3.1 (it's pink!) and ordered an a4988 stepper driver from Pololu (black edition to compliment the Teensy). I put everything together today and quickly put some 'duino firmware together. What I'm outputting is the current stepper motor position with the sensor reading. I copied a little bit of the first chunks of data into Excel and it looks like I'm off to a pretty good start.

    This project was just for fun but has become pretty interesting. I'd like to make everything available to anyone who is interested so let me know if you need the files now. Once I get things polished up I'll attach the source files here.

    The idea:

    Click image for larger version. 

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    The creation:

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    The first results:

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    There is also a "live" viewer in the works.

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    And an action shot (thanks Tom)
    http://gfycat.com/WholeReliableBlackbuck
    Last edited by r3n33; 06-10-2015 at 06:19 PM.
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    Re: LIDAR-lite 360 Mirror Scanner

    More troll ideas...
    Another option for holding the sensor over the mirror that might not introduce too much distortion is an acrylic or polycarbonate tube. The only thing to directly obscure the view would be the sensor cable or motor leads depending on which is placed at 'dead' end of the tube. It would also add quite a bit of protection to everything and give the possibility of water-proofing the assembly if the ends are properly sealed. Could also try redesigning the mirror assembly with bushings and a gear system to spin inside the tube so the stepper can be on the same side of the tube as the sensor.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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    Re: LIDAR-lite 360 Mirror Scanner

    Quote Originally Posted by tician View Post
    More troll ideas...
    Another option for holding the sensor over the mirror that might not introduce too much distortion is an acrylic or polycarbonate tube. The only thing to directly obscure the view would be the sensor cable or motor leads depending on which is placed at 'dead' end of the tube. It would also add quite a bit of protection to everything and give the possibility of water-proofing the assembly if the ends are properly sealed. Could also try redesigning the mirror assembly with bushings and a gear system to spin inside the tube so the stepper can be on the same side of the tube as the sensor.
    The tube idea is great! I'll have to keep my eyes open for a piece of scrap or something I can repurpose for testing. I did a quick search and found some cast acrylic tubes on eplastics.com for about $40 a foot in a 5" diameter which is just a bit too much for this experiment (for now).

    Thanks for the ideas. It's kinda a crazy idea I know but I wanted to see it through.

    The live viewer was worked on tonight and here is the result. On the second pass you can see an indention appear around the 200 degree mark. That is me putting the laptop in the way. The 3rd pass I remove the laptop. There is a fine balance of averaging, resolution, and rotation speed that all seem to effect the end result. Anyway here is where it is.

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    Re: LIDAR-lite 360 Mirror Scanner

    Nice!

    Like Tician mention placing both sensor and stepper on same side is a better solution. Using a large thrust bearing holding the tube and a 3d printed gear on the outside of the tube. Could also be used without a tube, just a mirror bracket with a large gear coupled to a bearing system.

    Have fun!
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  5. #5

    Re: LIDAR-lite 360 Mirror Scanner

    Very impressive! Looks like you are having a lot of fun!

    this also looks very promising. Sure looks like you find lots of great ideas to use your 3D printer for!

    At some point I may have to try to add my Lidar to the Hexapod. My earlier thoughts were to mount it on the same Pan/Tilt as camera. But I would not be able to get 360 degrees (unless the robot moves). Also not sure if it would give the same resolution that you are getting with the stepper motor.

    The one idea I had was throw a second lidar on the backside of the turret... But that is probably cheating

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    Re: LIDAR-lite 360 Mirror Scanner

    Quote Originally Posted by Zenta View Post
    Nice!

    Like Tician mention placing both sensor and stepper on same side is a better solution. Using a large thrust bearing holding the tube and a 3d printed gear on the outside of the tube. Could also be used without a tube, just a mirror bracket with a large gear coupled to a bearing system.

    Have fun!
    I'll ponder the idea but I think the biggest limitation of all is the sample rate of the sensor. Then again it depends on what sort of resolution the application may need. Because it can scan quite fast but will miss a lot of points along the way. We are playing a little with some ways to keep the rate up and interpolate points. You can see a little of that in the video where the points are altered slightly just after scanning to try and make a best guess as to what might be between the samples.

    Quote Originally Posted by KurtEck View Post
    Very impressive! Looks like you are having a lot of fun!

    this also looks very promising. Sure looks like you find lots of great ideas to use your 3D printer for!

    At some point I may have to try to add my Lidar to the Hexapod. My earlier thoughts were to mount it on the same Pan/Tilt as camera. But I would not be able to get 360 degrees (unless the robot moves). Also not sure if it would give the same resolution that you are getting with the stepper motor.

    The one idea I had was throw a second lidar on the backside of the turret... But that is probably cheating
    It could be promising for certain applications. Though the cost could be argued with using something like a continuous rotation servo with position feedback. There is also the option of doing a 180 scan and using two sensor setups. Or even a structured light sensor. Just depends on what you need I suppose. I'm not even sure what I'm going to do with this thing when I'm "finished". Hah, finished
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  7. Re: LIDAR-lite 360 Mirror Scanner

    This is a fascinating project! I'm really interested to find out how it turns out. Have you considered pointing the sensor upwards, mounting the mirror above it and spinning it with a gear or a belt? Conceivably, you could avoid any obstructions to the beam.

  8. #8

    Re: LIDAR-lite 360 Mirror Scanner

    you could avoid any obstructions to the beam.
    Right -- you'd spin the whole mirror/post setup, using a lazy Susan type bearing (or slip ring.)
    Apparently, the "nicer" lazy Susan bearings are called "slew bearings."
    Another option (as I suggested in the other thread) is to use the post as the zero marker in the measurements.
    Last edited by jwatte; 06-14-2015 at 11:46 AM.

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    Re: LIDAR-lite 360 Mirror Scanner

    Quote Originally Posted by tigakub View Post
    This is a fascinating project! I'm really interested to find out how it turns out. Have you considered pointing the sensor upwards, mounting the mirror above it and spinning it with a gear or a belt? Conceivably, you could avoid any obstructions to the beam.
    Thank you! I have been considering different ways to accomplish this but so far haven't taken action. I like the idea of removing the obstruction but (somewhat embarrassingly) haven't been able to form the image of a simple way to accomplish this. I have a few "half" ideas in my head and probably would benefit from some time at the whiteboard for some drawing or playing in Sketchup.

    Quote Originally Posted by jwatte View Post
    Right -- you'd spin the whole mirror/post setup, using a lazy Susan type bearing (or slip ring.)
    Apparently, the "nicer" lazy Susan bearings are called "slew bearings."
    Another option (as I suggested in the other thread) is to use the post as the zero marker in the measurements.
    This still is an option I like since I could improve on the design and use a single post rather than a hollowed out post. Being able to home the mirror position is a great solution to not using an encoder or extra hardware which keeps the cost down. Plus I like the overall simplicity of the current design since it doesn't require extra hardware and virtually no assembly.

    Spinning the whole mirror/post setup would include spinning the sensor? That's something I wanted to avoid because of the wires.

    ...

    I'll likely try both, using the current design to home the mirror and make a new model that spins the mirror and post.
    Last edited by r3n33; 06-14-2015 at 09:44 PM.
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  10. Re: LIDAR-lite 360 Mirror Scanner

    I've actually been knocking this idea around in my head for the past week, too. Here's a crude (really crude) mock up to illustrate what I'm thinking:

    Click image for larger version. 

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    Or maybe a belt instead of gears?

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