DIY Spray Paint Mixer for Custom Colors

We’re all accustomed to mixing purple, yellow, and blue paint in numerous ratios to immediately make every kind 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 massive areas in a short time, spray-paint artists want a separate can for each colour they wish to use—till now.

Again in 2018, once I first noticed skilled spray artists lugging dozens to a whole bunch of cans to their work websites, I used to be impressed to start out noodling on an answer. I’ve labored at Google X, Alphabet’s “moonshot factory,” 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 means round mechatronics.

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

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

I attempted a number of approaches the place pres-surized paint from the base-color cansfed via 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 will 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 circulation 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 completely different cans by no means have the identical inside stress. At any time when two valves had been open on the similar time, the stress distinction would make paint circulation backward into the lower-pressure can.

Instead, I eliminated the blending channel and tried making the paint pulses from every can sequentially converge right into a tube in order that no a couple of 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 circulation was enough to combine the paints. Let’s say you wish to produce a clementine orange colour. This requires yellow and purple paint in a ratio of 1:2, so the yellow valve opens for a time frame, after which the purple 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 colour you need.

The idea is simple, however making this work in apply took fairly a little bit of experimentation. First, I needed to decide the precise durations of pulses that will produce evenly combined colours, not simply their ratios. I additionally wanted to work out the dimensions of the tubing (too slender and also you’d get low spray power; too large and also you’d have paint accumulating within the tubes). Ultimately I settled on a most pulse length of 250 milliseconds and a tube diameter of 1 millimeter.

Inventing A New Valve

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

I had some spectacular failures alongside the way in which of the type 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 circulation 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 in opposition to any again stress 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 via 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 type that solely pressurized paint can present. The ultimate model makes use of 4 base colours—purple, yellow, blue, and white—with the colour combine managed by 4 knobs connected to an Arduino Nano and a small show. The circulation of paint is triggered by a push button positioned above the spray head, much 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 rapidly opening and shutting valves with various durations in sequence (D), you possibly can combine paint in particular ratios to create desired colours.James Provost

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

Spectrum’s numerous fixtures are 3D-printed, and challenge information and movies can be found via my web site at https://www.sandeshmanik.com/projects/spectrum. Preprints of technical descriptions of the rotary pinch valve and mixing methodology can be found on TechRxiv. The overall value for the invoice of supplies is lower than US $150.

Engaged on and off on the facet 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 quick constructive response from spray-paint artists all over the world. I’m now creating step-by-step directions in order that nontechnical individuals can construct their very own Spectrum paint sprayer. I stay up for seeing what creations artists out within the wild make!