Messing about in boats has always held a curious appeal for the hardware hacker. Perhaps that’s because it remains an approachable way to make something that moves under its own power with a bit of speed, and barring calamities, the worst that can happen to the unwary boater is a soaking. [NASAT Channel] is a Vietnamese hacker who is a serial producer of small motorised boats, and one of his latest is a particularly impressive example.
The boat itself is a relatively conventional expanded polystyrene hull covered with fiberglass, but the motive power is something a little special. He’s taken eight of the ubiquitous 775 DC brushed motors and used them in a star configuration with beveled gears, which in turn drives a flexible shaft which goes straight to a propeller under the craft. Each motor shares a water cooling pipe serviced by a small pump, and the drive comes from a pair of cheap PWM motor controllers. We see him zipping up and down a stretch of river next to some moored boats, and if we’re honest, we wouldn’t mind a go ourselves.
We’re not entirely convinced such a rough-and-ready eight-way gearbox will be reliable for long-term use, and we’d be interested to know just how equally so many motors are actually sharing the load. But we like it for its sheer audacity, and we think you will too. Take a look at the video below the break, and if you’re inspired then grab a hammock, some friends, and have a go.
Thanks [Wouter WW] for the tip.
I like the “do what you can with what you have” aspect of it, but I think most people here could think of more reliable ways to gang those motors. The unsupported pinions are begging for a bearing support. What we must recognize though is that the person who made it could likely see the same issue- and yet they didn’t stop perfection from getting in the way of progress! I think we could all learn from this. Plus, it turned out cool, whether it lasts or not!
Yeah I was seeing those pinions walk and thinking they’d eat each other if you weren’t gentle with the throttle.
The “do what you can with what you have” is actually very good here – good boat fabrication and engine mounts on the fly and I love radial engines even if they’re like that.
All of that said, he must have gotten quite a deal on the motors because spinning through the usual suppliers, it looks like you could get a much larger motor (small Ebike etc.) for not much more than a couple of those 775s and saved a lot of fussing.
How does he stop the motors fighting against each other, limiting the power they can put out?
In general motors rigged up to one another with rigis gearing will, provided they aren’t grossly mismatched, share the load reasonably well so long as they’re all within their efficient speed region.
You see plenty of skid steer robots with one or two driven wheels per track which when going straight forward are effectively doing the same thing and that time honored configuration seems to work well enough.
They are not in speed control (something resembling torque control), so they will never fight each other.
If they are unevenly matched in back emf it will just mean some are contributing more torque than others.
I made a friction drive ebike with 1 of those motors. It will drive the bike at 12mph no pedaling and like 22mph with easy pedaling. If I push it it actually starts to be a generator, I didn’t use a speed controller just straight 12V sla battery with on/off throttle, so can’t let it be a generator. The motor I have has a smooth spindle on the end, so if you slow down it can slip and a lever to disengage it. When I made it I didn’t think the motor would last more than a few miles, but its held up for quite a few over 3 years!
Sounds cool. do you have any pictures of that ?
Nice metal to metal whine with Fairly crunchy sounding ending there. Didnt show which and what failed. Gear lubricant of some kind maybe next time. Impressed lasted that long as have noticed significant run out before demo run. Nowhere as noticeable as chuck on fancy drill press a few days ago. Interesting choices. Loved the fiberglass boat build sequence.
Glad I’m not the only one who thought they heard the untimely end of a few gear teeth there…
had to turn the volume waaaay down.
What it needs most is a second bevel gear mounted on the front, mainly to keep the motor pinions pressed against the rear bevel gear. The front gear could be used to drive the cooling pump. Some super sticky grease on the gears would help, just enough for a light coating. Any more would just get thrown off.
Good idea. The second gear would also prevent the pinions from running into each other.
Because there is a natural balancer implemented, which is the soft long axis from the pinion to the motor and the motor mount itself, however yes, this thing is far from perfect, however it seems to work quite well.
It is similar to an unsupported “flying” sun gear in a planetary to planetary stage that is centered by the force of the gears.
One minor drawback needs to be mentioned, the long unsupported axis might put a higher than rated force on the motor bearings, these are the stiffest parts in the path of the force, thus leading to an early bearing damage by fatigue.
But hey, it works, its fun, however nobody should think that this will be durable.
next time connect the motors in series instead of parallel…
Motor shafts are much too long. They flex and the beveled gears cam out. You need bearings directly behind the small gears.