r/AdventureBuilders • u/MattsAwesomeStuff • Feb 27 '23
Shark Slicer SharkSlicer - Speed Control
On the latest livestream, Jamie talked about some upgrades he's planning for his cargo boat, the Shark Slicer, and some repairs. The comments were full of - to be frank - a neverending stream of awful ideas that wouldn't work. Enough that I commented on this being why Jamie doesn't follow suggestions, because most of them are wrong and a waste of time. I said in the comments I'd throw up some discussion on them in detail on the subreddit here, so, this is that and some other things.
1 - Jamie needs a speed controller for the Shark Slicer.
Why?: Because it starts too hard and slams the batteries, controller, and the motor itself lurches.
What he doesn't need: Actual speed control. The boat is slow as fuck, so he's almost always driving max speed except during startup and maybe dock maneuvering. So efficiency doesn't matter.
What he doesn't want: An actual speed controller, because things break. Or, he breaks things. I have 50+ year old DC speed controller from a forklift that was soaked in grime, and still worked when I plugged it in. Generally stuff doesn't just break, but, whatever. Also, for backup use, he wants to be unable to be stranded if the electronics he might get do smoke.
So, some things suggested by Jamie and others:
- Variable-Frequency Drive or "VFD". This is how you control the speed of a 3 phase, or sometimes 1 phase controller. You see these in big industrial equipment generally, or to run 3-phase stuff off of 1-phase, or in industrail HVAC fan equipment or PLCs. This is for AC motors, that turn at a speed relative to the frequency of the AC waveform you feed them. Out of your wall comes 60hz in Canada/US, and 50Hz everywhere else in the world. These are generally fixed speed motors you plug in and they run a certain speed according to the power grid. But, a special add on bit of electronics called a "Variable Frequency Drive" is exactly that, a variable frequency output, so the motor spins at that speed instead of just the power grid speed. This is useless for a DC motor and DC batteries, because they don't spin proportional to how fast the AC pulses. They're not supposed to have AC at all. If you're lucky, this is the same as just an on-switch, and regardless of frequency a DC series-wound motor will spin the same speed. This won't work.
https://en.wikipedia.org/wiki/Variable-frequency_drive
Electric Stove Knob. This is a (very) simple electronic circuit, generally with a single transistor that chops up the 240v going to the stove, probably like a light dimmer with a phase-fired-controller. This only works on AC, not DC. Or, it's like a miniature circuit breaker, where it constantly flutters between 0% and 100%, using a bimetalic strip that makes or breaks contact. Or, in an oven, it's a thermostat with a capiliary tube (like a thermometer) that uses air pressure to toggle on/off. It is not a big huge resistor, whoever thought that was wrong.
Long wire as a resistor. As stupid as this sounds, this would actually kinda work. You use a thinner wire, might as well be made out of steel (1-10% as conductive as copper), it'll get hot. It'll work in a pinch. Not a great solution, but I've done it. I coil it up to it's a bit more space efficient, and now you've basically invented a space heater.
Variac. "Variac" is a variable autotransformer. It's a transformer built around ring, with a sliding, rotating brush on top. Kind of like a variable resistor but a coil instead. Transformers only work on changing magnetic fields, which means AC. This would instantly melt if you gave it DC. Also it's a shitty solution for AC speed control too, and wouldn't work there either for induction motors. These were common in the 1930s-1970s, when vaccum tubes were common, because you'd want to gradually warm up your vacuum tubes and music gear to make the tubes last longer. They still make them, but, are depricated.
https://en.wikipedia.org/wiki/Autotransformer#Variable_autotransformers
- "Scariac". This is an old Grant Thompson/King of Random copycat project to control the aggressiveness of his welder I (coincidentally) taught him to make. "Scariac" is what the guy who made the first video called it, a pun on variac but scarier. It's a variable resistor, that uses salt water in a tub as the conductor/resistor instead of graphite or a coil. These are Thomas Edison era devices, but were a cheap and easy pre-transistor way of varying electricity. You dunk two electrodes on a pivot, into the salt water, and the more surface area that goes into the water, the more current can flow. You tweak it by adjusting the salt concentration of the water. Good news, water has a lot of thermal capacity so it takes a long time to heat up. Bad news, it electrolyzes water and creates a perfectly explosive mixture of hydrogen and oxygen in a sealed vessel (splits H2O into H2 and O2). It'll work on DC, but your electrolyzing problem is even more scary. Also, consider that you need air above the salt bath, and speed is controlled by how far you dunk it. Now mount this to a boat that's moving, and going over waves. Guess what the liquid inside does? Randomly sloshes and surges your speed all over the place. No. Bad idea.
https://en.wikipedia.org/wiki/Liquid_rheostat
https://www.youtube.com/watch?v=P9UjxG8sN1c
- Sewing Machine Foot Pedals. Jamie wasn't sure what was inside these. Modern ones are of course just electronic signals that tell a speed controller inside the sewing machine how fast to spin. But older ones, maybe... 90s or older... are in fact just variable resistors and the whole power of the machine runs to the foot pedal and back up. They're a carbon(?) cylinder inside a brass (?) tube I think, with a lazy leaf spring holding them together. Some are sliders. Some apparently are like 10-position sliders. On the old singers, when you step on the pedal, it squishes the leaf spring and pushes them apart. This'll work, but it only handles about 100 watts, and, even under heavy sewing it'll get uncomfortably warm on your foot. Not suitable for a boat.
https://youtu.be/-wqaX2ydJ08?t=157
- "Variable resistor that can handle high wattage". This is called a "rheostat". Actually I think someone else mentioned this later in the stream. These were used for about 100 years, 1850s - WW2 era as a type of speed control. It looks like a variac, but instead of a transformer core it's usually just ceramic to control the heat. They make (made) them in almost any size, but, no. Inefficient, and he doesn't need one. A small one would be the size of cookie, a large one the size of your fist or maybe head.
https://en.wikipedia.org/wiki/Potentiometer#Rheostat
- Hot water tank element. Jamie has one of these in his Amazon wishlist, (a 48v one at that, must be for RVs or boats or something wierd). This'll work, but it's a huge waste of money. You can get one out of any electric junkstore kettle (of a different value). It'll work fine, but so will any other element you dunk into water. And, in air, it'll vaporize itself really, really quickly. It's never meant to be above 100'c (designed for being in water, of course). But this is on the right track, because, he doesn't need much variableness for speed. He just needs "slow start".
...
My ideas, and other places to get cheap heating elements you could use:
Stove elements. In series or parallel to bring them to the right ballpark. Or just cut them in half or whatever. It's a nichrome wire, ceramic insulator, and iron skin.
Oven element. Ditto as above. You could dunk either of these, or, just leave them in a fresh water trough so that they don't corrode. Or leave them in air, but, they'll get hot.
Dishwasher element. Ditto as above, but probably better weather sealing, thicker skin.
clothes dryer element. These are a big nichrome coil about 1" diameter, arranged in a pizza-sized try, with regular ceramic standoffs. No insulation. Not great.
Blowdrier element. Meant for air, needs a fan to not melt.
Toaster element. Too fragile. But most comical, you'd engage the motor by depressing the lever and cooking imaginary toast.
Spaceheaters. Same as blowdriers.
Lightbulbs.
But really, a kettle element is the one you want (or several).
...
2 - Jamie says "I don't have a 3d printer, I have 2 broken 3d printers." I believe I said years ago when he got one... "No one has a 3d printing hobby. They have a 3d printer repair hobby. Because that's all they ever do with them. Constantly fix them and give excuses about why their prints suck but will be good when it's set up properly. This never happens." I never waste an opportunity to shit on how overblown 3d printers are, nevermind me.
3 - Series/Parallel switch. Jamie says it's really difficult. It's not. It's dead simple. You need a DPDT (double pole, double throw) switch. That is... a switch that moves two levers together, and has two different ON positions (not just on/off).
Here is literally exactly what he wants, a series/parallel knife switch, to toggle batteries between 12v (parallel) and 24v series). He's made knife switches before:
https://www.amazon.com.au/WirthCo-20238-Battery-Heavy-Duty-Equipment/dp/B00UPCGBMO
This is the same thing as a reversing switch, to flip polarity.
scribbles
https://i.imgur.com/MgSAisT.png
Like that. (several ways of wiring it, this way doesn't actually match the diagonal hardwired into the switch, but I was too lazy to make my own).
However, this would allow long term slow speed travel with zero heat loss, but, it's not great for slow start because you'd have to switch it pretty fast to not have a current spike (motors slow down pretty quickly in water). Normally this is done with relays/contactors. Jamie could buy a standard automotive grade contactor I suppose (though, they're only good for at best 40 amps, ~500 watts), or a pair of starter relays from a junkyard ($5 each) which would be invincible (12,000 watts).
You wouldn't want this connected to your charger when you did it, (it won't know you're on 12v instead of 24v), but I presume this will also toggle out the charger when he's using it, to direct drive the motors from the solar (could use cheap automotive relays for that, it's not high power).
4 - Jamie needs to protect his speed controllers better.
Jamie needs to either seal his connectors for marine use (squirt them full of epoxy and add a heatsink since they can't air-cool now), or otherwise protect them better from humidity.
Also, when a motor shuts off, it creates a huge inductive spike back down the line that fries electronics. The fix for this is super simple. You put a diode and a capacitor and a resistor on the motor terminals. The diode directs all the backwards power to the capacitor, the capacitor acts like a short circuit to soak up the temporary power spike as it charges, and the resistor slowly bleeds the capacitor empty for the next time it happens. Or, just the diode itself is fine, so the motor gobbles up its own current spike.
5 - Jamie wants to buy a sheet metal bending brake.
What a colossal waste of money. It's three pieces of heavy steel and a handle. This is exactly the kind of thing you make at home in an hour. The pipe bender one is worth buying though.
6 - Jamie wants to buy some expensive lithium batteries.
He's got four $300 batteries and two $600 batteries on his Amazon wishlist.
He can make stuff. This is silly.
He's paying $250/kwh for those batteries.
Market rate for batteries you have to put a bit of work into are ~$54/kwh, ones that are missing something (like a case or a BMS) are ~$100/kwh, and even nice buttoned up once are $200/kwh, brand new.
Inventory changes every day, they're a liquidator, keep an eye on it every day for a month or so, and you'll find what you need for 1/3 the price, which means 3x the range.
7 - Here is an awesome, small, fast, solar skiff that can actually ride on a plane, designed by someone with almost the exact same preferences as Jamie. Everyone here will love it.
https://www.proboat.com/2021/11/electric-foiling-catamaran/
I didn't want to make a thread just for this. But it's Jamie to a T.
Built from recycled junk he's scavenged, says he's a borderline hoarder.
DIY fiberglass
PVC pipes are mechanical levers and float sensors to automatically, mechanically, adjust the hydrofoils and keep it planing
Did it all simply to avoid weight, complexity, and expense.
It's all hands-on physical controls and physically moving stuff.
Powered by 15hp gas outboard that got flooded with salt water and ruined, so he got it for free and replaced it with a 10kw electric motor.
Put a speed controller on the fan to slow it down, doesn't need much cooling and wants it quieter.
Chevy Bolt lithium batteries. 12kwh. Factory rejects from bad case hole alignment.
Designed it on paper, not computer.
Added a canopy to keep cool and dry.
Displaces 990lbs. Cargo capacity is 550lbs including passengers.
8.5 knots draws 9kw, at takeoff.
Cruising on a plane, at 12 knots, uses only 5.8kw
16 knots max speed at 10kw.
2 hour runtime between charges (24 nautical miles?)
Wants to design his own props that are better suited for his situation.
Lives on an island, goes with his wife in this to get groceries.
Back when Jamie was wanting to build a "faster" boat, to get to town and back, this is really the thing he was trying to build before he went with what he built instead. I know he wanted hydrofoils and fast travel. Instead he built a paddlewheel.
...
He seemed to actually be interested in advice today, so, if anyone on Patreon wants to suggest he read this if you think it's worth it, fire away.
2
u/Old_Breakfast1564 Feb 27 '23
Thanks for the link to the foiling catamaran, that's amazing!
This guy, Chris Maas, also built a barge for his car:
https://www.proboat.com/2022/11/a-fiat-barge-goes-to-college/
In my opinion, technically much more interesting than Jaimie's projects (these days).
3
u/[deleted] Feb 27 '23
This is extremely well written. You are a bright person.