Greg and Connor Hoffman have been spending a lot of time in their garage lately. But not on your average father-son garage project.

On a Sunday in early February, Connor, a Basalt High School sophomore, was painstakingly placing hundreds of battery cells into a large, slotted container. It was part of a three-day process of building a custom battery pack for a retrofitted electric snowmobile.

For Connor, who has been fascinated with robots and electric cars since he was 5 years old, creating an electric sled will be his capstone project for school, he says. For his father, Greg, the lift maintenance director at Aspen Skiing Company, it’s also a labor of love — but one with real-world implications.

Once the custom snowmobile is complete, it’ll be used at Snowmass Ski Area (for what purpose is still up in the air). And if that works out well, the Hoffmans are game to build another one (or two), demonstrating the potential of homegrown solutions and furthering — even if just a little — the Aspen Skiing Company’s green operations goals.

“I get a lot of satisfaction from building something in my mind and then bringing it to life,” says Greg. “Connor has the same maze of ideas floating in his head and to work with him to transform his ideas into a machine that will help the environment is a privilege of fatherhood.”

Tasked with this unique, game-changing project, here’s what Connor and Greg Hoffman have learned along the way.

1. There’s no such thing as a how-to-build-an-electric-snowmobile manual.

Connor Hoffman putting his and his father Greg Hoffman’s original battery plan into action. PC: Daniel Bayer Photography

The Hoffmans got the idea to build their own electric sled after Greg, through his position at Skico, had been working with Taiga Motors to test the Canadian company’s prototype electric snowmobiles. The father-son duo pitched their idea to Auden Schendler, Skico’s senior vice president of sustainability, and “he was all over it,” says Greg.

CORE committed $3,000 toward the project, and Holy Cross Energy pitched in $2,450. Skico pledged to fund the balance of an estimated total of $15,000 (which doesn’t factor in labor).

The next step was figuring out how to build an e-sled. Both Greg and Connor had enough experience — and passion — that this wasn’t an insurmountable task. Greg, a master electrician, has been riding snowmobiles since he was 10 years old, and spends plenty of time with them on the job. “I love new technology,” he says. “Seeing all that’s new with the lifts — it just keeps you alive.”

Connor, who’s been soaking up novel vehicle technology since he watched “The Great Robot Race” on PBS NOVA as a young child, works on solar-powered radio-controlled cars through his Solar Rollers team. When he was 12 or 13, he wrote the code to create a speed-monitoring system for Snowmass’s Alpine Coaster (another one of his dad’s responsibilities).

For the electric snowmobile project, “the internet was my resource,” says Connor. He spent hours googling questions and watching YouTube videos. Finding nothing on electric snowmobiles, he devoured whatever public information he could find from the electric vehicle industry — which as it turns out was plenty.

“A lot of what we’re doing is based on electric-car conversions — it can translate to snowmobiles,” says Connor.

2. Planning and design took the most time.

Connor and Greg Hoffman contemplating the next step of their e-sled design. PC: Daniel Bayer Photography

Before they ever got their hands dirty, Greg estimates the father-son duo spent roughly 40 hours in the planning and design phase. They started talking about the project around Christmas and spent much of January deep in research.

A weekly update Connor sent to the project’s supporters illustrates the twists and turns the snowmobile design took as the research progressed. The duo initially planned on salvaging a battery from a wrecked Smart car to deliver the 120 horsepower they thought was needed to power the snowmobile, he wrote. But once they figured out that the sled would lose about 30% of its power operating at a high altitude, a series of calculations led them to settle on prismatic cells, commonly used in electric car conversation and “quite economical.” Upon further research, however, the prismatic cells turned out to be too heavy for a snowmobile, compromising performance.

“So we turned to the only logical choice anyone would make in the circumstances: We would build our batteries from scratch,” Connor wrote.

The Hoffman team also changed course on the motor, eventually settling on one that would deliver the amount of horsepower needed, fits the weight requirements, and, perhaps most importantly, has a programmable controller. Besides making the motor spin in the first place, this critical component controls the acceleration rate and the regenerative braking of the motor, among other functions they can tailor to the snowmobile’s uses.

3. Building a battery is like a very sophisticated puzzle

Closeup of the battery built by the Hoffmans. PC: Daniel Bayer Photography

Once the calculations and design were finalized, all the parts gathered, and the build started in earnest, the biggest and most complex job was assembling the battery. This involves:

  • 1,400 battery cells
  • 140 wires
  • 140 nickel strips
  • 5,600 spot welds
  • 2 battery enclosures

The wires connect a battery management system to every 10 cells, which keep them from overcharging. Nickel strips are configured to be fuses so if one cell shorts out it won’t affect the others. The battery management system also controls under-temperature, makes sure the batteries aren’t discharged too much, balances the cells to the same charge capacity, and helps track everything so that the Hoffmans don’t have to measure everything by hand. All those connections makes for a lot of up-front spot welding and soldering — 5,600 spot welds to be exact. The custom design of the battery pack also makes it flexible — capacity can be added as necessary.

“Since the battery system is such an expensive component, we want it to have as much longevity as possible,” says Connor.

4. Creative recycling was important.

The Hoffmans adding their homemade battery to the recycled snowmobile from Buttermilk. PC: Daniel Bayer Photography

For environmental and budgetary reasons, buying or building everything new was out of the question. “We want to reuse parts as much as possible and leave behind the least amount of waste possible,” says Connor. To that end, the Hoffmans were able to repurpose quite a bit:

  • A snowmobile from Buttermilk that was no longer operational
  • Many parts of the Buttermilk snowmobile, including the radiator and fan, cooling hoses, brake system and gear box, instrumentation, and wiring
  • The snowmobile’s fuel tank, which was cleaned out and repurposed as a battery pack container
  • Windows from an old Elk Camp Gondola cabin, used to build the main battery enclosure

5. Being part of the future of snowmobile technology is exciting

The Hoffmans with their nearly completed DIY electric snowmobile. PC: Daniel Bayer Photography

While there aren’t any e-snowmobiles on the market now, a few companies, including Taiga, are really close, says Greg. Which makes it even more remarkable that a father-son team from western Colorado are building their own for commercial use.

“To be able to not only see all of the parts but to put them together to make an actual working electric vehicle allows me to value the technology and research these big electric vehicle companies require even more so,” says Connor.

Because traditional snowmobiles are so dirty, even one e-sled can make a positive impact on the environment. While emissions vary by model and usage, some estimate that a two-stroke snowmobile produces as much air pollution in a day as a car will in six months.

There are other advantages with electrifying snowmobiles. Traditional snowmobiles have a well-earned reputation of constantly breaking down or needing maintenance. Without a fuel-injected engine, e-sleds are much more reliable. And much like EVs, there’s just a lot less to maintain — no oil changes, for example.

But overall, the Hoffmans’ project is inspirational and driving change. It all started when Skico approached CORE for funding to buy a couple of electric sleds, according to Marty Treadway, CORE’s program director and grants manager.

“We loved the idea as it was bringing the idea of electrification up to the hill, where people are playing, and might be paying more attention than usual,” says Treadway, who approved $10,000 as a Community Grant.

When the project morphed into the Hoffmans building their own snowmobile, CORE maintained a portion of the funding — and just as much enthusiasm.

“Home-grown solutions … We have always tried to find ways to support the DIYers, and these guys are way into it!” says Treadway.

And with that, Connor and Greg went full throttle ahead.

CORE offers energy advising and funding support for innovative, energy-saving projects like this one. Check out aspencore.org/takeaction to learn more about how CORE can help your change-driving project come to life.