DIY Spray Paint Mixer for Custom Colors

We’re all aware of mixing purple, yellow, and blue paint in numerous ratios to immediately make all types of colours. This works nice for oils or watercolors, however fails relating 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 coloration they need to use—till now.

Again in 2018, once 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 method round mechatronics.

I needed my answer to be cheap and easy sufficient to construct as a DIY venture and purposeful sufficient for an artist to make use of, with out breaking their movement. 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 could be opened and closed in tens of milliseconds and prevents backpressure from clogging traces.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 sprig head. To regulate 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 movement right into a mixing channel for a relative period 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 inner stress. At any time when two valves have been open on the identical time, the stress distinction would make paint movement 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 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 movement was enough to combine the paints. Let’s say you need to produce a clementine orange coloration. 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 fast tempo to immediately create the spray-paint coloration 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 will 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 pressure; too huge and also you’d have paint accumulating within the tubes). Finally I settled on a most pulse period of 250 milliseconds and a tube diameter of 1 millimeter.

Inventing A New Valve

Regardless that the system labored, the solenoid valves I used consistently clogged up. Designed for water purifiers, the valves didn’t forestall paint from coming 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 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 movement 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 hooked up 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—purple, yellow, blue, and white—with the colour combine managed by 4 knobs hooked up to an Arduino Nano and a small show. The movement 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 hooked up 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 coloration’s paint valve could be open is one among eight values between 30 and 250 ms. Which means the whole 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 period ratios which are a a number of of one another will produce the identical coloration—for instance, 2:3 and 4:6. I added a pressure sensor to the push button, which permits for a gradient: Two coloration mixes could be dialed in, and as I improve my thumb’s stress on the button, the paint combine shifts from one coloration to the opposite.

Spectrum’s numerous fixtures are 3D-printed, and venture information 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 full value for the invoice of supplies is lower than US $150.

Engaged on and off on the aspect 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 world wide. I’m now creating step-by-step directions in order that nontechnical individuals can construct their very own Spectrum paint sprayer. I look ahead to seeing what creations artists out within the wild make!