DIY Spray Paint Mixer for Customized Colours

We’re all acquainted with mixing crimson, yellow, and blue paint in varied ratios to immediately make all types of colours. This works nice for oils or watercolors, however fails with regards to cans of spray paint. The paint droplets can’t be blended as soon as they’re aerosolized. Consequently, though spray cans are nice for making use of even coats of paint to giant areas in a short time, spray-paint artists want a separate can for each coloration they wish to use—till now.

Again in 2018, after I first noticed skilled spray artists lugging dozens to tons of of cans to their work websites, I used to be impressed to begin noodling on an answer. I’ve labored at Google X, Alphabet’s “moonshot manufacturing unit,” as a {hardware} engineer, and I’m now constructing a startup in mechanical-design software program. I’m no painter, however I do know my manner round mechatronics.

I wished my answer to be cheap and easy sufficient to construct as a DIY venture and practical sufficient for an artist to make use of, with out breaking their stream. So I started prototyping a system that mixes base colours whereas they’re nonetheless in pressurized kind from off-the-shelf cans.

This new rotary pinch valve will be opened and closed in tens of milliseconds and prevents backpressure from clogging strains.James Provost

I attempted just a few approaches the place pres-surized paint from the base-color cansfed by way of tubes right into a mixing channel, earlier than rising from a twig head. To manage the ratios, I made a decision to borrow a trick that may be acquainted to anybody who’s ever needed to management the bright-ness of an LED utilizing a microcontroller: pulse-width modulation. Initially, I used electronically managed solenoid valves to launch the paint from the cans. The paint would stream right into a mixing channel for a relative length that corresponded to the ratio of the bottom colours required to make a given hue. Nevertheless, this failed as a result of totally different cans by no means have the identical inside strain. At any time when two valves have been open on the identical time, the strain distinction would make paint stream backward into the lower-pressure can.

In its place, I eliminated the blending channel and tried making the paint pulses from every can sequentially converge right into a tube in order that no multiple valve would ever be open at a time. Surprisingly, this labored completely. The backflow was eradicated, and it turned out that the pure turbulence of the stream was adequate to combine the paints. Let’s say you wish to produce a clementine orange coloration. This requires yellow and crimson paint in a ratio of 1:2, so the yellow valve opens for a time period, after which the crimson valve opens for twice as lengthy. The system then retains repeating this cycle of pulses in a speedy tempo to immediately create the spray-paint coloration you need.

The speculation is easy, however making this work in follow took fairly a little bit of experimentation. First, I needed to decide the precise durations of pulses that may produce evenly blended colours, not simply their ratios. I additionally wanted to work out the scale of the tubing (too slender and also you’d get low spray drive; too broad and also you’d have paint accumulating within the tubes). Finally I settled on a most pulse length of 250 milliseconds and a tube diameter of 1 millimeter.

Inventing A New Valve

Despite the fact that the system labored, the solenoid valves I used consistently clogged up. Designed for water purifiers, the valves didn’t forestall paint from getting into the mechanism, the place the paint would harden. Furthermore, when the valves have been turned off, they may cease backflow provided that the inlet remained pressurized. So disconnecting a paint can from the system would trigger instantaneous leaking. Different off-the-shelf valves I attempted couldn’t cycle quick sufficient and have been too costly.

I had some spectacular failures alongside the way in which of the kind that solely pressurized paint can present.

So I created my very own mechanism: a high-speed, electronically managed, rotary pinch valve. It has a stepper motor that rotates a lever with a rolling bearing to constrict fluid stream inside a versatile tube. This idea isn’t new—there’s one thing like them in each peristaltic pump. However I added a spring to firmly maintain the lever within the closed place towards any again strain when the motor isn’t powered, making it a usually closed valve that isolates the connected can. Moreover, the valve is quick sufficient to be open for as little as 30 milliseconds.

I went by way of 4 main prototypes of the system earlier than reaching a working model, and I had some spectacular failures alongside the way in which of the kind that solely pressurized paint can present. The ultimate model makes use of 4 base colours—crimson, yellow, blue, and white—with the colour combine managed by 4 knobs connected to an Arduino Nano and a small show. The stream of paint is triggered by a push button positioned above the spray head, just like a twig can’s nozzle.

Cans holding base colours (A) are connected to valves (B). An Arduino-based management panel (C) opens and closes valves to combine paint earlier than it’s aerosolized (E). By shortly opening and shutting valves with various durations in sequence (D), you may combine paint in particular ratios to create desired colours.James Provost

The size of time a base coloration’s paint valve will be open is one among eight values between 30 and 250 ms. Which means the whole system—which I coincidentally dubbed Spectrum—can create tons of of distinct spray-paint colours immediately. It produces lower than 8⁴ (or 4,096) colours as a result of length ratios which might be a a number of of one another will produce the identical coloration—for instance, 2:3 and 4:6. I added a drive sensor to the push button, which permits for a gradient: Two coloration mixes will be dialed in, and as I enhance my thumb’s strain on the button, the paint combine shifts from one coloration to the opposite.

Spectrum’s varied fixtures are 3D-printed, and venture information and movies can be found by way of my web site at https://www.sandeshmanik.com/tasks/spectrum. Preprints of technical descriptions of the rotary pinch valve and mixing methodology can be found on TechRxiv. The whole price for the invoice of supplies is lower than US $150.

Engaged on and off on the aspect for about seven years, I lastly completed creating my system and writing the documentation in late 2025. After I posted a video to social media, I used to be heartened by the instant optimistic response from spray-paint artists around the globe. I’m now creating step-by-step directions in order that nontechnical folks can construct their very own Spectrum paint sprayer. I look ahead to seeing what creations artists out within the wild make!