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We Dyno'd a Horse: Measuring True Horse Power with Donut Media

Motivo and Donut Media team up to answer an age-old engineering question



About the Project


Here at Motivo, we love working on cool projects with awesome people. Many of us are gearheads at heart, fascinated by fast cars, motorcycles, and other vehicles, and we're all about the amazing science and engineering behind them. So we were thrilled last fall when the folks from Donut Media, a YouTube channel about all things cars, reached out to us with an idea for an experiment on measuring horsepower. Then they told us whose horsepower they wanted to measure.


Enter Big D.


A large black horse standing next to the Motivo x Donut Media horse dyno.

We set ourselves to a little bit of historical research, and it turns out James Watt had never actually measured the horsepower of a horse. Best we can tell, he more or less made it up. Although equine transportation is a little outside of our comfort zone of planes, trains, automobiles, and robots, Jeremiah and the Donut Media crew were asking a question that needed answering. Motivo would rise to the challenge.


Casey Iwasaki, a lead mechanical engineer who has been working at Motivo since 2021, was on the project team. We caught up with Casey this spring for a behind-the-scenes look at what it was like to measure the horsepower of a horse. 


Lead engineer Casey Iwasaki leans against a horse dyno made by Motivo and Donut Media

Q&A with Casey Iwasaki


How did you get involved with the HRSPRS project?  


I’m a lead mechanical engineer here at Motivo. My background, both personally and professionally, lies largely in the automotive realm. Between that and my experience at Motivo developing lab-grade measurement and data acquisition systems, this project was right up my alley – in our initial engagements with the Donut team, they had me at “dyno.” Then they had me a little more at “horse dyno.”


What was your favorite part about the project? 


Working with the creative team at Donut was a really unique experience for me. Their team was super flexible and collaborative, which smoothed out the process of balancing technical feasibility (and schedule) with their vision for the final product.


What was the biggest challenge of this project? 


This project came with the typical schedule and cost challenges, but beyond that, the biggest difficulty was working with the number of unknowns involved in collecting the data. We began this project without good data on expected power from the horse, dynamometer characteristics, or transmission losses in the donor vehicle. Since we only had one shot to get everything right on camera, we worked strategically to reduce these risks by incorporating flexibility into our designs (both of the rig, and the experiment) and conducting unconventional research (digging into research papers from the 50’s and watching horse pull competitions frame-by-frame) to inform our design choices.


How did the timeline compare to the client projects you've worked on?


From our first engagement with the Donut team to shoot day, I think it was 3 or 4 weeks. This project was certainly on the quicker side of things for us, and that shaped the way that we approached it. Short timelines like this mean that we can’t rely on specialized parts that take weeks to arrive, and we can’t test as extensively as we might like to. We have experience working in these timeframes though, and always work to maximize the time and resources we have available to us.


How did you make sure the results we got were accurate and scientifically valid?  


Accuracy and precision were challenges with the equipment we had to take these measurements. Because the dyno is designed for cars, which develop a lot more power than a horse, we weren’t exactly working in its sweet spot. While one of our goals was to read power from the dyno, we didn’t want to sacrifice accuracy or precision in the process. To make sure we still got good numbers out of the experiment, we instrumented our steed with GPS and a load cell measuring the tension in the rope. These sensors gave us force and velocity measurements, which were then used to compute the horse’s instantaneous power output throughout the pull. These sensors, due to their placement, were not subject to the same inertial and frictional losses that affected the dyno’s measurement, giving us more confidence in this data than what we could gather from the dyno itself.


Was there anything about this project that you learned, or got to experiment with, and have used on subsequent projects for clients? 


Funnily enough, a few weeks after we shot the video, we repurposed the same data acquisition setup for a test on parts we were developing for an electric aircraft. 


A team of five men from Motivo and Donut Media working together on a Honda Civic to engineer a horse dyno.

Is that the end of the story? 


Well  – maybe. We still have the Civic with a horse-dyno attachment sitting under a cover in our parking lot. 


What should we do with it?


A horse dyno engineered into a Honda Civic sitting in the Motivo parking lot.

If you’ve got a great idea, submit them in the form below. If your idea is crazy enough, we might, just might, actually do it. 



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