Concept and working prototype · Industrial design and engineering
Rayo: cold in the palm of your hand, in one, two or three minutes
Rayo is a handheld cooling device for athletes. Hold it between sets or mid-workout, and it cools your palm for a short, fixed cycle so you can keep going.
I designed the form and built a working prototype with a Peltier module. It got impressively cold.
- Role
- Form, engineering and prototype
- Prototype
- Working cooling, 20+ grip models
- Cycles
- 1, 2 or 3 minutes
Brief
Heat is what stops you first
When you train, your muscles make heat. If the body can’t shed it fast enough, your core temperature rises and performance drops long before your muscles are spent.
The palms are one of the body’s natural radiators: they carry a lot of blood close to the skin. Researchers at Stanford showed that cooling them can help the body dump heat, and the idea has spread through sports science and podcasts like Andrew Huberman’s.
Research
When does an athlete actually have a minute?
A cooling device is only useful in the moments an athlete can stop. So I watched where those moments are in real games, and sized the cycles to them.
Basketball
About 60 seconds of real recovery per player in a stoppage.
Football
Cooling breaks of about 3 minutes, around the 30th and 75th minute.
Tennis
Cold gloves held for 60–90 seconds at a changeover.
What 80 people said they’d want
I surveyed 80 people to find out what mattered. Most wanted faster cooling with both hands, three in four wanted tracking, and price mattered: competitors sell for $500 or more.
Both hands at once led to a version I explored and then dropped: two linked units, one for each hand. One device you can grab, use in a minute and put down won.
Why a Peltier, not ice or a fan
A cold pack needs somewhere cold to live before you use it, and it warms up as you go. A fan doesn’t get anywhere near cold enough.
A Peltier module makes cold from electricity, on demand, and lets you set the temperature. It isn’t strong enough to run a fridge, but for a small surface held in one hand, it’s the perfect technology.
Engineering and materials
Short cycles, by design
Cooling runs for one, two or three minutes, and those are the only options. Hold cold too long and the blood vessels in your hand tighten (from around the 4-minute mark), which stops the heat from leaving. Short cycles keep you well inside the safe range.
The temperature is held between set limits so it never gets too cold. And if it ever feels like too much, your body has its own safety: you let go.
Inside, and what it costs to make
A rechargeable battery powers the Peltier module, which cools the surface you hold. Electronics regulate the temperature, a heat sink carries the heat away, and the aluminium body moves heat fast in both directions.
Peltier module
Cools the grip through a copper spreader.
Quiet fan
28 dB, pulling heat out of the copper heatsink.
Light ring
A third, two thirds or the full ring for 1, 2 or 3 minutes, fading as it counts down.
Haptics
A small motor for feedback in the hand.
Prototype and testing
More than 20 grips, and what people said holding them
The shape had to sit naturally in the palm, stay put in a sweaty hand and work with one hand, so you can still drink or train with the other.
I made and tested more than 20 models, from sketches through 13 CAD versions to two printed prototypes people held and judged. Their comments changed the shape.
“I’m worried it might roll off the table.”
A diagonal cut so it stays put.
fixed“Where am I supposed to place my hand?”
Vents that show where the air goes, and a 1, 2, 3-minute switch.
“The smaller one just feels better.”
The final grip is slimmer and shorter than both prints.
fixed
Outcome
It worked, and it was cold
The prototype cooled for real: the Peltier, the regulation and the heat sink all worked together in a hand-sized body. Battery life is the next thing to measure.
There is real interest in this space, with products already on the market. The hard part is engineering cold that works in one hand, and that is what this prototype does.
