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Cosmos:

Projection Analog Clock

Cosmos (September 2020) is my sixth collaboration with Guy Marsden and as always the completed  Clock exceeded my expectations. Cosmos works by projecting the image of a 12 LED NeoPixel ring onto a round frosted acrylic screen and thereby tells time to the nearest 5 minutes.  Hours and minutes are denoted by blue and red LEDs, respectively. When the hour and minute LEDs overlap the color seen is purple (blue + red). The time lapse video below shows the clock at work. The NeoPixel ring is located in the base and above it sits a 50mm Pentax camera lens (circa 1971) resting atop a set of extension tubes. The lens focuses the images of the LEDs onto a mirror that is set at a 45 degree angle to the optical axis of the lens. The mirror then projects the image of the NeoPixel ring onto a round frosted screen. The electronic clock mechanism and coding is identical to that used in Mushroom Zoom except it runs backwards given that the mirror introduces a left to right flip of the NeoPixel ring image. Thanks as always to Guy for providing the professional photo-documentation at each step during the build and for photos/videos of the finished clock.

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Clock showing 7:20

Shows time advancing at approximately 100X actual speed

Blue dot = hour and Red dot = minutes

Time changes every 5 minutes

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Final 3D rendering Used to Guide the Engineering and Fabrication

Guy and I went back and forth through several iterations (see below, "Evolution of Cosmos Design"), as we do for all our collaborations, until settling in on the design shown below. We do our best to nail down the essential design elements before fabrication begins. Getting to this point can often take several months of conversations about critical design specifications, materials to use, and overall aesthetics. Once fabrication begins Guy makes additional aesthetic and engineering recommendations. For example, Guy elected to round over the edges of the base in order to visually reference the curved shape of the dome, modified the shape of the mirror and screen stands, and employed black Delrin, rather than glossy acrylic, for the 3 black cylinders holding the stainless steel posts. Each of these modifications had a tremendous impact on Cosmos' final design.

The Build

(Find all the details at Guy's Cosmos Page)

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Key Components

 

1) Lens

50mm f1.4 lens attached to 3 extension tubes. I've had this lens since 1971 when I got my first new camera-35mm SLR Asahi Pentax.

 

2) Mirror and Stand

Plymor Round 3mm Beveled Glass Mirror (4" diameter) from Amazon (https://www.amazon.com/gp/product/B07T56PPLZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1)

An adjustable (up/down) vertical post (5/16" diameter stainless steel) is fixed to a "floating base" (1/2" thick Black Opaque Chemcast Acrylic; TAP Plastics- https://www.tapplastics.com/product/plastics/cut_to_size_plastic/acrylic_sheets_color/341). A horizontal post (5/16" diameter stainless steel) extends from the vertical post and is linked to the mirror assembly such that that the mirror can be moved forward/backward and rotated in order to establish the correct 45 degree angle between the mirror surface and optical axis of the lens. All posts made of 5/16" diameter stainless steel.  

4) Projection Screen and Stand

Frosted Satinice clear acrylic disc- 4.5" diameter and 1/8" thick (TAP Plastics).

 

An adjustable (up/down) vertical post (5/16" diameter stainless steel) is fixed to a "floating" base (1/2" thick Black Opaque Chemcast Acrylic). 

 

4) 12 LED RGB NeoPixel ring (Adafruit; https://www.adafruit.com/product/1643). The ring is controlled by the same electronics used for Mushroom Zoom although in this case chip is programmed to run counterclockwise given that the mirror flips (left/right) the image of the ring. 

5) Glass Dome

8" x 12" from Collecting Warehouse (https://www.collectingwarehouse.com/)

6) Base

Comprised of two layers of 1/2" thick Black Opaque Chemcast Acrylic.

The Projected Image of the NeoPixel Ring

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In order to achieve the proper projected image (3.25" outer diameter and striped appearance of each LED) it was critical to correctly set the distances between all the components (NeoPixel ring to back of lens; center front of lens to center of mirror; center front of lens to center of projection screen). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Multiple prototypes were built using Legos and an adjustable mirror support. Adjustments were made until the desired projected image was achieved. Measurements were taken and a final prototype (no more Legos) was then constructed and sent to Guy.

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Final Prototype

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Evolution of Cosmos Design

Several different cases were rendered in 3D before settling in on the general form designated by the asterisk(*).

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Determining Size of the Glass Dome

I placed the final prototype on an image of concentric circles and determined that everything would fit perfectly inside a dome with an inside diameter of  8". Fortunately I was able to purchase a dome that was 8" (ID) x 12" (H).

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Optimization of Clock Accuracy

Accuracy is adjusted by altering the number of fixed length delays programmed to occur during a 5 minute interval. This is an iterative process and each time the code is adjusted a time lapse video is used to measure accuracy. Below is an example of such a video (it runs backwards because it is not being viewed through a mirror). When viewing the time lapse at 0.25x one can readily determine the time elapsed between each hour and measure the accuracy over a 12-24 hour period of time. The elapsed time on the clock is compared to the elapsed real time shown along the bottom of the video.

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Determining Elapsed Time for Each Hour on The Clock

The elapsed time was determined for each hour interval on the clock. The data sheet shows that the clock is running very consistently over the 12 period examined.

"DABs Clocks is a unique business that focuses on finding ways to display time in unconventional ways. The goal is to create time pieces that are both functionally and aesthetically pleasing. Working collaboratively with Guy Marsden, over the past several years, we have produced 14 one of a kind clocks. Please explore the gallery and contact me if you have any questions.

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