DIY Spray Paint Mixer for Custom Colors

We’re all conversant in mixing crimson, yellow, and blue paint in varied ratios to immediately make every kind of colours. This works nice for oils or watercolors, however fails in the case of 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 need to use—till now.

Again in 2018, after I first noticed skilled spray artists lugging dozens to lots of 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 approach round mechatronics.

I needed my answer to be cheap and easy sufficient to construct as a DIY undertaking and purposeful sufficient for an artist to make use of, with out breaking their move. 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 may be opened and closed in tens of milliseconds and prevents backpressure from clogging traces.James Provost

I attempted a couple of 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 sprig head. To manage the ratios, I made a decision to borrow a trick that might 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 move right into a mixing channel for a relative length that corresponded to the ratio of the bottom colours required to make a given hue. Nonetheless, this failed as a result of totally different cans by no means have the identical inside stress. At any time when two valves have been open on the similar time, the stress distinction would make paint move 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 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 move was adequate to combine the paints. Let’s say you need to produce a clementine orange colour. 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 fast tempo to immediately create the spray-paint colour you need.

The idea is easy, however making this work in observe took fairly a little bit of experimentation. First, I needed to decide the precise durations of pulses that might produce evenly combined colours, not simply their ratios. I additionally wanted to work out the dimensions of the tubing (too slim and also you’d get low spray power; too extensive 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

Regardless that the system labored, the solenoid valves I used continually 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 have been turned off, they may cease backflow provided that the inlet remained pressurized. So disconnecting a paint can from the system would trigger on the spot 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 best way 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 move 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 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 by way of 4 main prototypes of the system earlier than reaching a working model, and I had some spectacular failures alongside the best way of the type 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 move of paint is triggered by a push button positioned above the spray head, just like a sprig 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 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. Which means the complete system—which I coincidentally dubbed Spectrum—can create lots of of distinct spray-paint colours immediately. It produces lower than 8⁴ (or 4,096) colours as a result of length ratios which can be 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 varied fixtures are 3D-printed, and undertaking recordsdata and movies can be found by way of 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 price for the invoice of supplies is lower than US $150.

Engaged on and off on the facet for about seven years, I lastly completed growing my system and writing the documentation in late 2025. After I posted a video to social media, I used to be heartened by the speedy constructive response from spray-paint artists all over the world. 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!