Offloading acceleration and braking to an electric motor in a hybrid configuration allows the less efficient combustion engine run in a more narrow set of RPM and torque ranges. In some cases the motor is decoupled from the mechanical drivetrain entirely and used simply as a generator, where it can run at a single speed all the time. And this concept isn’t limited to passenger vehicles, either. [rctestflight] put this premise to the test using a small knockoff Honda motor as a generator for an electric boat.
This project builds on a previous version where he used a much smaller hobby motor to see if it could generate usable power, and that system powered a small autonomous boat as a proof-of-concept. Those motors aren’t really designed to be used in this sort of application though, so this build upgrades the internal combustion engine and pairs it with an electric skateboard motor that’s configured to run as a generator. The setup is capable of producing almost 800 watts for as long as the gasoline lasts, provided that the 3D printed parts all hold together and the other parts don’t vibrate off of the assembly.
Out on the lake at full throttle, the small generator can get the boat up to seven knots (13 kph) but at this speed [rctestflight] reports that the generator is “quite unpleasant” due to the noise and vibration. Instead, he ran it on a test bench at several RPM and torque points and documented the efficiency of the motor at each one, and then operated the boat mostly at the point he found it to be most efficient. For a hybrid drivetrain, that not only decreases noise and vibration, but also maintenance and fuel efficiency.
Although the energy density of fossil fuels is much better than batteries, a fuel-free long-distance option is still available if you’d rather equip your boat with solar panels instead.
“seven knots (13 kph)”
km/h !
No reason to shout here, both options are widely understood.
km/h: The globally accepted International System of Units (SI) symbol. It is derived directly from the mathematical formula: kilometers divided by hours.
kph: A colloquial abbreviation, often used in spoken English or on older dashboards to mirror the familiar “mph” (miles per hour) format. While convenient, it is not officially recognized by standards organizations. For everyday reading or writing, both are perfectly fine and understood, but km/h is always the safest and most accurate choice.
Personally, I’m more confused about the knots. Are they the “Gordian knot”, or referring as to “Tie the Knot”, perhaps a “Knot of People”, I doubt it will be referring to “Stomach Knot”. Although I’m pretty sure the one in this article is about speed and the others are not.
It’s km/h.
you show a perfect frame of reference thing here. for YOU kph seems normal but knots is a strange form of measurement, for ME its the opposite. I never heared of kph but i know knots. typical case of n=1. for both of us.
knots are something you put in a rope, and usually those don’t move very fast.
yep. next tie that rope to a floating bucket and trow it in the water from a moving ship. count the knots during a predetermined time period and you have your knots as a speed measurement system. use it globally and it becomes a proprietary standard.
this is in brief how knots as a speed measurement came in being.
Editors writing for an international audience should always use SI units. And spell checkers should catch such errors.
So, m/s it is.
Because the hour is not a SI unit.
Sick burn! :)
We use mostly whatever units we feel like, or are appropriate for the field. Boat speeds are measured in knots. Pin spacing in fractional inches. Don’t hate the player, hate the game.
Anyway, I never get tired of plugging https://www.gnu.org/software/units/ I have it on my desktop and my phone.
It would be an error if it was factually wrong or even particularly ambiguous. It’s not, it’s just an abbreviation of the full unit name instead of the more preferred SI symbol, and one which people can easily determine to be an alternate way of writing the same unit. It’s also true that knots are the default for naval use anyway, making this even less of a big deal.
It is ambiguous, “kph” could also be interpreted as “kilopond-hours” by older readers.
Is this not the same principle as the diesel-electric locomotive?
Or even a diesel electric submarine. However, his boat doesnt seem to be able to rise again after it submerges.
Or diesel-electric ships, which is very common. Most modern ships (excluding container and oil) are using diesel-electric. Doesn’t matter if it’s a cruise ship, a tugboat, dredger, cable layer, whatever. If it needs to be able to maneuver and built in the last 30 years, it’s almost guaranteed to be diesel-electric. Companies like Kongsberg, ABB, Wartsila etc, make electric propulsion systems for modern vessels and are combined with diesel engines to generate the power for the propulsion.
I like the fact that since a BLDC motor is acting as the generator, its also acting as the starter motor and there is no need for the pull cord starting.
Its a very neat and clean system that way
“run at a single speed all the time. And this concept isn’t limited to passenger vehicles, either. ” Actually in passenger cars it has been determined that the best efficiency tends to come from building an engine that does NOT run at a single speed all the time. Using an engine as a pure generator is sometimes convenient for non-efficiency reasons, but for pure efficiency the solution that many generations of prius drivetrain have converged on is one where the engine is efficient over a wide range and is engaged as soon as the energy demand enters that range or the battery percentage drops enough, then it stays engaged going up and down in rpm to match the average demanded output, while using the battery for smoothing and for regenerative braking.
The essential point is that Toyota made the engine get substantially equal efficiency across a wide enough rpm range that you waste more energy charging and discharging the batteries than you can save by loading the engine down more and cycling it off periodically. The exception is that if you are cruising along slowly or idling with the air conditioning on, the engine might stay off a lot of the time because the efficient range does still have limits.
The reason this project is different is that the engine he’s using isn’t specially tuned like that, and anyway he doesn’t have that much need for using the load region below the most efficient operating point. However, it’s still more about convenience than efficiency versus having a direct shaft. And seriously – having a single motor use regenerative braking to set rpm and then just putting a servo for throttle control is very convenient and the right choice for the situation! It’s just not the absolute most efficient way to do it, although it’s close.
I built a similar two-stroke equivalent a few years ago. Electrical power output was also slightly higher than the engine’s mechanical rating.
https://imgur.com/a/vZX5ExT
Ah, this video makes me want to play with it again.
Letting it run at exceptionally low speeds, doing that distinctive “fump” sound. Pushing the electric motor to its limits by having it double as a flywheel.
Absolutely love the channel. It packs in a ton of technical content and findings.