Sentry water gun (lidar tracking!)

This high tech water gun will track persons with the lidar sensor and fire several shots of water

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Engineering is not always about solving world problems. Engineering is also about having fun, this is especially important for getting younger people enthiasastic about technical education. In Europe it's becoming more and more dramatic to find the right skilled technical people.

This high tech water gun will track persons with the lidar sensor and fire several shots of water
The idea is to build something that's relatively easy to replicate, therefore the project is constructed as much as possible with standard available components. So anyone interested can just get the parts and start replicating. The construction is made of 125mm PVC drainage pipes and aluminium extrusion profiles. Mainly 3D printer parts are used, like steppers, Minitronics V2.0, belts and axis.

Movies first!

What is it?

Its just an advanced toy :)
The gun will detect targets if it will appear closer than configured threshold. If the target moves away from the gun, the gun will be moved upward so that water will likely hit at greater distance. If the gun has reached the XY position of the target, the 4 water valves will be acivated one by one, only one valve will be active each time. This will give a nice effect.

What features does it have?

  • 180° viewing angle, 12 meter range RPlidar A1 sensor
  • 4-way water valve with nozzles having around 10 meter range
  • The steppers are controlled by Arduino AccelSteppper library to increase, decrease smoothly and prevent mechanical stress as much as possible
  • It looks frightening

The electric diagram:

More details will follow soon!


The original Sketchup drawing of the Sentry water gun, have fun!

SSEYO Koan Play File - 25.15 MB - 07/05/2020 at 09:26


The source code for anyone interested

x-zip-compressed - 4.50 kB - 06/24/2020 at 18:35


  • 1 × Minitronics V2.0 3D printer pcb with oneboard stepper drivers and end switch connection, arduino compatible
  • 1 × NEMA 23 Used for the x-axis
  • 1 × 4-way solenoid water valve You can buy on any of the Chinese platforms
  • 1 × RPLidar A1 Lidar sensor
  • 1 × 125 mm drainage pipe Only 1 meter

View all 22 components

  • Kill switch added

    Marcel06/29/2020 at 18:01 0 comments

    I added a cool kill switch, useful when persons are passing by that should not be shooted at :)

  • Additional pictures of RPLidar A1 mounting method

    Marcel06/27/2020 at 18:41 0 comments

    I noticed I didn't placed any pictures of the RPLidar A1 mounting method:

    I removed the original screws of the RPLidar and inserted new ones that will dissapear in the lasercuted plastic panel. The thickness of the plastic panel is 8mm, this is a critical thickness because the laser eyes of the lidar sensor should not be covered by the plastic panel. Maybe I will still have some negative influence with the reflection of sunlight on the panel.... but for now just give it a try.

  • Slowmotion shooting

    Marcel06/14/2020 at 11:56 0 comments

  • First test with water and moving targets!

    Marcel06/13/2020 at 19:54 0 comments

    First test of the Sentry watergun, now with water and moving targets :)

    Still some room for improvement, the movement is still a bit slow, also some elastic effect in the belts of the x-axis. The belts will be replaced by chains, also the stepper speed will be increased significant in next update.

    But even with the current setup, there is already a lot of fun :)

  • First movements without water

    Marcel06/07/2020 at 17:40 0 comments

    First movements, still a bit shaky.... I need to optimize the hysteresis boundaries.

  • Mounting everything together

    Marcel06/05/2020 at 18:59 0 comments

    Installing stepper driver, water valve, lidar sensor:

  • Nema 23 mounted including 9mm belt

    Marcel06/04/2020 at 20:36 0 comments

    Today I succesfully mounted the Nema 23 motor, everything worked as expected :)
    Next step is mounting everything back together for first test and see if force has been improved over the Nema 17 with 6mm belt:

  • Making the water nozzles from simple bolts

    Marcel06/02/2020 at 19:42 0 comments

    For shooting water I drilled some 3.2mm holes in standard M5 bolts. With real life test it seems that this was a good size for shooting more than 10 meters away

  • The water supply and 4-way electric valve

    Marcel06/02/2020 at 19:39 0 comments

    Installation of the 4-way electric valve. The valves are controlled by the relay board, I used standard 8p netwerk cable for connected them together.

  • Mounting the NEMA 23 and 9mm belt (big improvement for x-axis!)

    Marcel06/02/2020 at 19:37 0 comments

    The NEMA 17 motor for the x-axis was not strong enough (missing steps), also the 6mm GT2 belt was causing some elastic effect due to the installed mass on top of it. Therefore I'm now switching to 9mm belt in combination with NEMA 23 and TB6600 stepper driver. This will be a more powerfull setup for moving the x-axis.

View all 10 project logs

Enjoy this project?



Lucy wrote 11/28/2020 at 14:53 point

Does the liar work well in different daylight conditions please? If it's sunny is it worse than overcast? Have you tried it at night?


  Are you sure? yes | no

Marcel wrote 06/25/2020 at 20:49 point

Haha, everyone has their own preferred targets in the garden :)

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lisa788 wrote 06/25/2020 at 05:35 point

I'd love something like this to keep the geese from pooping all over my pier.... :D

  Are you sure? yes | no

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