electric diving scooter

[John in CR]

So you say it needs 8 times the power, but that can change when i use a more efficient propeller i suppose?

If you end up with the same efficiency as Seadoo's prop and rpm. I'd think a watercraft company should be pretty good at that, so duplicating theirs is unlikely. Slower bigger props tend to be more efficient, and you're unlikely to go much bigger, so to produce 8 times the power that means higher rpm and longer pitch, and unfortunately probably more slippage which means lower efficiency. More than likely you'd end up needing 9-10 times power from the motor to double your speed.

You are likely to end up using a more efficient motor, but that wouldn't change the power requirements at the prop, it would mean longer run times for the same amount of battery.

Again, the starting point is better efficiency through the water. I wouldn't be surprised if you could pick up close to a 50% increase in speed simply by making everything more sleek and increasing the prop pitch. You don't see hoses, dangling belt, squarish lead weights and other protrusions hanging off a dolphin do you? Get all that tidied up and sleek. Another item of really poor hydrodynamics is that flat bottomed scuba tank, so come up with a smoothly tapered cap for that. Get 50% more speed in that manner, and then you only need to double the power and the proper prop to get to 10.

To get exited first hand about the difference it can make, do a speed comparison in a swimming pool with full gear and then also with nothing but your mask and fins. That won't show the full potential, because it won't include the higher speed prop the motor can swing when you have less drag in the water.

John

 

[merkhond]

So you say it needs 8 times the power, but that can change when i use a more efficient propeller i suppose?

If you end up with the same efficiency as Seadoo's prop and rpm. I'd think a watercraft company should be pretty good at that, so duplicating theirs is unlikely. Slower bigger props tend to be more efficient, and you're unlikely to go much bigger, so to produce 8 times the power that means higher rpm and longer pitch, and unfortunately probably more slippage which means lower efficiency. More than likely you'd end up needing 9-10 times power from the motor to double your speed.

You are likely to end up using a more efficient motor, but that wouldn't change the power requirements at the prop, it would mean longer run times for the same amount of battery.

Again, the starting point is better efficiency through the water. I wouldn't be surprised if you could pick up close to a 50% increase in speed simply by making everything more sleek and increasing the prop pitch. You don't see hoses, dangling belt, squarish lead weights and other protrusions hanging off a dolphin do you? Get all that tidied up and sleek. Another item of really poor hydrodynamics is that flat bottomed scuba tank, so come up with a smoothly tapered cap for that. Get 50% more speed in that manner, and then you only need to double the power and the proper prop to get to 10.

To get exited first hand about the difference it can make, do a speed comparison in a swimming pool with full gear and then also with nothing but your mask and fins. That won't show the full potential, because it won't include the higher speed prop the motor can swing when you have less drag in the water.

John

Thanks for the reply!

I don't really plan on using the scooter with diving gear nor do i even have gear. It's just for recreational purposes at a nice beach with clear waters. The only thing i will have on is a boardshort and swimming glasses.

 

[torker]

Is yours a Seabob? Looks like they have a bump in voltage for every bump in speed. Did you say yours is 12 v now? That is low. Is it a earlier model?

 

[John in CR]

I don't really plan on using the scooter with diving gear nor do i even have gear. It's just for recreational purposes at a nice beach with clear waters. The only thing i will have on is a boardshort and swimming glasses.

If it's designed to pull a diver with scuba gear and not just a pool toy, then since it's designed for a different load it should be able to handle a significantly longer pitch prop that's likely to get you most of the way there. Those results will give you a better idea of how much more power and prop you need to add, which will add back much of the static thrust lost in the initial prop change.

Depending which model you have, stripping away much of the protective cage could help tremendously too. That would allow you to measure the profile stock nozzle and determine how different it is from a Rice speed nozzle. Some don't even appear to be a proper Kort nozzle, and definitely don't have the right props for a good nozzle/prop combo. That means a bit of research combined with good fiberglass or carbon work to create a proper nozzle could pay back bigger returns than doubling motor power. Doing these kinds of things could also relieve enough motor stress that you could something as simple as increase the motor voltage for extra power and little to no risk.

 

[wesnewell]

I never factor in the burst C rate, as even the continuous C rate is questionable. Max amp rating is AH times C rate, so 20AH times 20C = 400A. The burst amp rating would be 600A. I've pulled close to 40A on a 5ah pack of 15C lipo (75A rating) before without any problem other than a huge voltage sag (from 98V to 88V) and the pack getting a little warm after a while.With a 20ah pack your sag will be minimal.

 

[merkhond]

where can i find a propeller with a longer pitch that will fit?

 

[dogman dan]

Do some math, aiming for 40 amps. That's 5 amps past the max you can pull with the controller.

40 amps from 20 ah is 2c discharge rate. This is ok for the cheapo 20c packs, you won't see any drastic voltage sag under load.

So I think whatever you choose, the c rate will be fine. Concentrate on which type will take up less space. Typically, zippies are physically smaller than regular turnigy packs.

If you buy 5ah 6s packs, you need 8 packs to make a 12s 20 ah battery. Buying 9 makes sense, so you have a spare. One cell in one pack may die early, then when you need a replacement, guess what's out of stock at HK at that moment.

 

[merkhond]

Do some math, aiming for 40 amps. That's 5 amps past the max you can pull with the controller.

40 amps from 20 ah is 2c discharge rate. This is ok for the cheapo 20c packs, you won't see any drastic voltage sag under load.

So I think whatever you choose, the c rate will be fine. Concentrate on which type will take up less space. Typically, zippies are physically smaller than regular turnigy packs.

If you buy 5ah 6s packs, you need 8 packs to make a 12s 20 ah battery. Buying 9 makes sense, so you have a spare. One cell in one pack may die early, then when you need a replacement, guess what's out of stock at HK at that moment.

Thanks for the reply!

What do you mean 5 amps past the max with the controller? Probably because of my original post? It was just a calculation 44Vx35A=1540W. I don't have a controller atm and if i'm going to buy one i'll make sure it's 40A+.

Would buying 8ah 4s turnigy packs make up less space? It would require 9 of them to make 12s24ah.

 

[merkhond]

oh hai guise

 

[torker]

I haven't heard a model number? Maybe I missed it :? Need the diam. and pitch. Also is it using lead battery now? If so @ 12 v now just pick up a 4 or 5 s better start with 4s to be safe. A 4s would be over 16 volts off the charger and less sag. and lighter. If you could find a forum for water toys maybe somebody has already modded one and know how much voltage it can take. Our stock controllers for bikes @36v can usually take 48 easily and some run 60 volts like me

 

[dmwahl]

Simply increasing the speed/power won't necessarily correspond to performance increase. The prop is going to be designed for a given speed range, and running it higher may not work or may cause damage. Rather than jumping from 300W to 2000W, you might want to see how smaller increases perform before spending a bunch of money. Wikipedia has a good page on propellors, with more equations than you'll need. You will find that the relationship between prop speed and forward speed is not strictly linear.

Thanks!
And i am of course aware of the fact that a 200% increase in prop speed does not automatically mean the speed is going to double. That's not what i claimed i don't get where you get that from.

I was simply stating what John said later, that there's more to this than just increasing power. Another thing to consider is that if you're replacing a lead acid battery (heavy) with a light weight lithium pack, you may need to add some weight to make the thing nuetrally buoyant again (or whatever it started at). Wouldn't be much fun if you can't keep the prop below the surface.

 

[parabellum]

Thanks for the reply!

So the only thing you changed was the battery, correct? You took it out of the seadoo scooter and replaced it by a 4s lipo pack.
How do you know the motor would be capable of putting out 533W in the first place? It probably couldn't hence the reason it all melted down?

Did the buoyancy really change that much because of the Lipo's? Keep in mind i'm going to try to fit 9packs of 4s in there for 12s4p (don't know if it'll fit though, could you tell me?) so the weight difference from Lipo will be evened out since i will be using more.

It was not that simple, trial and error first.
Mod 1)I took LA out and could fit 4 of hard case 5Ah 4s1p LiPos, wich made 4s4p 20Ah.
error 1)Reed(magnetic) switch vent kaput almost instantly, starting current at higher Voltage was to high apparently.
Mod 2) New reed switch controlling Automotive 12V 80A relay. So switch it self just sees mA.
error 2) buoyancy. It was to light and I could not get under water with it.
Mod 3) Installed 2 rocks. I believe 1 under the front cap and other in little flat space left behind the battery inside.
error 3) Charged up and gave it for testing in swimming pool to ~40kg(80lbs) girl, drinking beer just in front. In under 10 minutes in got very lame, barely turning the propeller.
Taking it apart I noticed burned winding smell, measured current and it was way to high. Found similar motor in my junk pile (it was in some power tool before). at disassembling transmission in order to get the old motor out I found the housing of transmission melted and deformed.
I got disappointment and trow it to trash.

The end.

 

[999zip999]

These are lipo packs that need a bms or balance charger and power supply. You understand the need to weed out the bad cells before making a pack, that's why one extra pack if needed. Sometimes from hobby king a new pack can have a wonkie cell. How about a pic. so we can see the size ? No controller yet ? What's the plan ?

 

[bearing]

If you increase battery voltage, you probably need a current limiting controller. Or at least one that ramps up the speed slowly so that it doesn't instantly put a very high current into the motor when it switches on while the motor is not moving. I believe that is what killed the transmission, not the load at higher RPM. If you buy a simple controller without motor current limit, you can probably make it ramp speed slowly by putting an RC filter in series with the throttle. And then put a diode across the resistor to make it ramp speed down faster for safety.

I don't think you need to mess with the prop until you have increased speed enough for your liking. If you increase the voltage/RPM, the propeller will maybe move a lot of excessive water. Like, if it pulls two persons as fast as one person, you can change the prop for better efficiency with one person. Make the chord of the blades smaller, in that case. But I would only do it if I could buy a new propeller if that fails.

 

[dogman dan]

I thought you meant that you had purchased a 35 amps controller.

Only once you know your controllers amps, will you know what potential max wattage you will be feeding your motor. What the motor actually pulls in reality will depend on the weight of the diver, the drag of the stuff he's wearing, and the type/size of the prop the motor is turning.

But save enough to say anyway, that 20 ah of 20c battery should not sag too much under load. If you load it at 5c, 100 amps, it's still only 25% of the rating they put on the battery, which is a lie. In any case, it will run a 40 amps controller just fine.

12s, call it 46v for calculation purposes, X 40 amps controller is 1840 watts. So if you want to hit 1500w max, use a 30 amps controller. But chances are, if you run your motor on 40 amps controller, it will pull 20-30 amps when in use, cruising. So I see no particular problem with using a 40 amps. If it's pulling all 40 amps all the time, you need a smaller prop to lessen the load. Or a bigger motor.

 

[John in CR]

I like the buoyancy problem of going lithium. Don't use rocks though. Use a bigger, heavier, more powerful motor and switch to direct drive as part of that improvement.

OR

Just DIY a whole new thing. I have these yet to fully focus visions of 2 very slightly buoyant battery+motor+ducted prop rigs strapped to my body for hands free operation and really flying through the water. I have some tiny 4kw inrunners that are up to the task, and while the high rpm might be noisy, 10hp combined peak input could be tremendous fun.

 

[merkhond]

I like the buoyancy problem of going lithium. Don't use rocks though. Use a bigger, heavier, more powerful motor and switch to direct drive as part of that improvement.

OR

Just DIY a whole new thing. I have these yet to fully focus visions of 2 very slightly buoyant battery+motor+ducted prop rigs strapped to my body for hands free operation and really flying through the water. I have some tiny 4kw inrunners that are up to the task, and while the high rpm might be noisy, 10hp combined peak input could be tremendous fun.

I'm way too much of a noob to be developing a whole new thing lol.
And all these comments about Lithium and buoyancy, i'm going to use way more packs than the one pack of lead acid which is like 12V10ah or something so the 9 packs of 4s8ah lithium will even the effect out my boys

 

[merkhond]

Thanks for the reply!

So the only thing you changed was the battery, correct? You took it out of the seadoo scooter and replaced it by a 4s lipo pack.
How do you know the motor would be capable of putting out 533W in the first place? It probably couldn't hence the reason it all melted down?

Did the buoyancy really change that much because of the Lipo's? Keep in mind i'm going to try to fit 9packs of 4s in there for 12s4p (don't know if it'll fit though, could you tell me?) so the weight difference from Lipo will be evened out since i will be using more.

It was not that simple, trial and error first.
Mod 1)I took LA out and could fit 4 of hard case 5Ah 4s1p LiPos, wich made 4s4p 20Ah.
error 1)Reed(magnetic) switch vent kaput almost instantly, starting current at higher Voltage was to high apparently.
Mod 2) New reed switch controlling Automotive 12V 80A relay. So switch it self just sees mA.
error 2) buoyancy. It was to light and I could not get under water with it.
Mod 3) Installed 2 rocks. I believe 1 under the front cap and other in little flat space left behind the battery inside.
error 3) Charged up and gave it for testing in swimming pool to ~40kg(80lbs) girl, drinking beer just in front. In under 10 minutes in got very lame, barely turning the propeller.
Taking it apart I noticed burned winding smell, measured current and it was way to high. Found similar motor in my junk pile (it was in some power tool before). at disassembling transmission in order to get the old motor out I found the housing of transmission melted and deformed.
I got disappointment and trow it to trash.

The end.

how many amps were you running

 

[parabellum]

how many amps were you running

There is no underwater CA available. And outside water numbers are invalid.
SEA-DOO® Seascooter Classic Pro ZS01. Cant find W specs now but I have the impression of believing then it was 300W. Its 3 years old experiment and was not documented since I believed that it will be just swapping batteries and fun thing and not trashing fully functional scooter.
Rest is made up with calculation and can be considered imaginary numbers but truth magnitude and relation. :wink:

 

[merkhond]

hope to see you baby