Explanatory movie of the mechanical work "laser show" that freely manipulates light by combining gears made by 3D printers

When turning the steering wheel, the light of the laser pointer moves quickly, the device that draws stars and Batman's symbols "laser show'S commentary on the author's movieEvanMr.Your own YouTube channelIt is open to the public. It is a perfection degree that I think that the design of the author and the state that the gear and cam made by the 3D printer move in engagement and precise creation method.

Mechanical Laser Show - YouTube


At the beginning of the movie, a green device with the combination of the green light of the laser pointer and the gear is displayed in the dark.


At the same time turning the steering wheel, the point of light starts to move quickly ...


A star shape was drawn.


Stop turning the steering wheel and change the set gear to another gear.


Set another gear.


And set the laser pointer as it was.


Turn the handle, another pattern will appear this time. What appeared was the American comic hero, "BatmanThe pattern of "Bat signal"is.


Turning to another gear, this time the "Club" of cards mark appeared.


This device, named "laser show", was designed by Evan who published the movie and outputted by 3D printer. In the movie, how to operate and design this device, and 3D printing method are told.


The basic mechanism of this device is that the laser repeats the same trajectory repeatedly to project the pattern as an afterimage.


In order to cause this phenomenon, it is said that the same pattern must be drawn five times or more per second.


All mechanisms of laser show are mechanical, all complex movements are due to a combination of gear and cam. The laser pointer on the two cams is moved according to the rotation of the cam, so that the laser beam applied to the wall draws a pattern.


All the parts are outputted by 3D printer. Since the original 3D data can be downloaded from the public page, it is possible to create laser show by using 3D printer by myself.


According to the author Evan's explanation, the laser pointer is being moved by applying the mechanism of "cam" and "follower".


The laser pointer moves so as to match the unevenness on the circumference of the cam. In actual cams, complicated irregularities are made according to the pattern you want to draw.


In an actual machine, combining two cams creates complicated laser movements.


In order to create an afterimage, it is necessary to repeat the cycle of laser light movement five times per second, so the laser show sets the gear ratio of the input gear from the handle of the crank and the gear of the cam to 5: 1.


In the movie, when you turn the steering wheel, the tip of the laser pointer draws a star-shaped trajectory.


Next is an explanation on how to design the cam itself. According to Evan, this part is the most complicated and interesting part in making laser show. The stars in the following images show the trajectory that the laser passes when drawing the shape of the star, and the number of points necessary to draw a star is "35 pieces"Has been set.


The movement of the laser starts with the arrow part of the pattern represented by the image, that is, from the top.


When we start rotation we will assume that we will go to the next point in the arrow, represented by the image, ie on the right side from the vertex.


Repeat this movement and convert the coordinates, you can draw a cam. To draw a cam, you must output the trajectory to each of the two cams and draw them.


Evan is hitting this trail by using "mathematics". In the movie, it is described very precisely by using mathematical expressions, but if you summarize easily, "The movement of the laser can be represented by a triangle that connects two cams and three points of the optical axis".


As shown in the image below, the length of the left oblique side of the triangle can be "radius of laser pen = rp", "radius of cam = rx" and the equation of the following image is obtained by right triangle equation.


Next, it is assumed that the angle of rotation of the cam is assumed to be a blue arrow, the angle at which the cam rotates is the angle "Kx", and "∠ B" can be calculated by using the arctan which is an inverse trigonometric function .


Angle "Kx" of the rotation angle of the cam is "Kx = 2π + 2π / n * i", when the cam draws down the time of zero degrees before rotation. "Θx" at zero degree can be expressed as "Θx = 2π - Kx + ∠ B".


Ultimately, unknown angles and coordinates are unknown as below, and by using orthogonal coordinate equations, all the coordinates of the points on the pattern are known and it is possible to output them as the shape of the cam. To calculate the point on the other cam, Evan explains that Evan can calculate the shape of the second cam by using some small changes and the same formula.


Next is a commentary on how to increase the completeness of the laser show.


What we will cover here is "How to avoid problems that arise when the pattern you want to draw grows."


As the shape to be projected increases, the radius and shape of the cam are greatly distorted, and large "hollows" and "distortions" are born as it is. This distortion increases the friction between the laser and the cam and makes the movement worse, so it can not be ignored.


Therefore, when enlarging the shape to be projected by the laser, the shape of the cam does not have a hollow like the image belowConvex polygonIt is better to have a form close to that.


Lastly, I will touch a little about 3D printing method.


The table below is a rough guide on how to print each part 3D.


According to Evan, it is recommended that if you can not output them in perfect form after 3D printing of parts, it is recommended to cut by knife.


Of course, to create laser show, you need to buy rubber bands and laser pointers in addition to output on 3D printers. Evan said he was able to purchase both at less than $ 10 (about 1000 yen).


About Evan himself, he is a software developer related to commercial transactions and is a person who is interested in mechanical engineering. In addition, some of the created 3D models are published on their Thingiverse account,3D model of laser showYou can download it from there too.