electric diving scooter

[merkhond]

I'm looking to double performance on a diving scooter. It's a seadoo scooter
It's 5kph basic and i want 10kph. The setup on standard is 300W at 12V i believe with a basic propeller.
Not looking to change a lot, i don't know what the whole deal is with the ESC and everything and gearboxes etc and whether it'll be necesarry.
Since it's already a finished product pretty much all i can change is motor and battery pack and i'm an complete noob on this board so i don't think it's a good idea to mess with gearboxes etc.
It probably already has some type of gearbox or ESC built in it i don't really know
I just want to know what kind of RPM the propeller can handle since i'm looking to buy a motor on hobbyking and the RPM is 100.000 which seems pretty ridiculous.

I think a 2000W motor should do the trick.
Running it at 48V probably.

Suggestions on inrunner/outrunner or specific recommendations with links to hobbyking for motors and battery packs are greatly appreciated.

 

[merkhond]

thanks guys.

 

[Miles]

No problem...

 

[spinningmagnets]

I don't know if anyone from around here has tried anything like this before. Perhaps if you opened up the Seadoo and posted some pics, it might be easier to see what is possible.

What are the normal RPMs of the Seadoo 12V motor at top speed?

 

[merkhond]

I don't know if anyone from around here has tried anything like this before. Perhaps if you opened up the Seadoo and posted some pics, it might be easier to see what is possible.

What are the normal RPMs of the Seadoo 12V motor at top speed?

I can't find it anywhere but a Bladefish seascooter does 500RPM but it has a larger propeller. I'd say the seadoo would be 1000RPM range
I was looking at a motor with 2100kv so maybe that's the issue since it would get up to 100k RPM at 48V.

Does somebody know a formula or sth or how much more RPM's i need? Like 5 times more or something? And a motor suggestion with kv suggestion?

 

[merkhond]

As for battery pack:
http://www.hobbyking.com/hobbyking/...ch_A_SPEC_5000mah_12S_65_130C_Lipo_Pack_.html

This is a 12s 5ah.
If i buy 4 and put them in parallel of these that would make 44V and 20ah, correct?
Any better suggestions? Maybe buy these: http://www.hobbyking.com/hobbyking/store/__18210__Turnigy_nano_tech_8000mAh_6S_25_50C_Lipo_Pack.html
So buy 6 of the 6s1p to make 12s4p so i have 44v and 32ah, correct?
I'm not sure if i add these series and parallel things up correct can anybody check?

 

[wineboyrider]

If it's a brushed motor it might be simple as increasing voltage and controller?

 

[merkhond]

If it's a brushed motor it might be simple as increasing voltage and controller?

What do you mean? When i look online for electric motors i always see the voltage it should be ran with so i don't want to run any risks and have the motor blow up.
Also do i need a new controller? I suppose i can still work with the one they have?

I was thinking of buying this type of motor: http://www.hobbyking.com/hobbyking/..._Alloy_EDF_700kv_3800w_12S_AU_Warehouse_.html

 

[torker]

You must search more grasshopper.. :lol: Sorry could not help myself.. Ok motors and most controllers will take "some" overvolting. Motors usually take a lot more, not controllers. Controllers are limited by the caps and fets by design. One thing different about your setup from a bike is that it is always under a load. Like riding a bike in sugar sand. Dogman can tell you what happens fast, heat builds.

I think you need to get your hands dirty and tear that sucker apart and get some pics and any specs you can find. Once you can see the rating on caps and fets ( some here may know by sight) Pics and more info Model # I want to know too. I have never heard of these toys..

 

[merkhond]

Yes i am a noob.

http://www.hobbyking.com/hobbyking/store/__24567__HobbyKing_30A_Boat_ESC_3A_UBEC.html

I'm going for about 1.5kW motor at 44V so 35A, so this ESC should do the trick right?
I suspect it's already programmed and ready-to-use?

In the description it says: Low Voltage Protection: None / 2.6V / 2.8V / 3.0V / 3.2V / 3.4V
what does that even mean?

And can this controller even operate when the motor is ran at 44V or do those two don't have anything to do with each other?

 

[merkhond]

I appreciate all response, my boys. So don't be afraid to post.

 

[merkhond]

I'm building a diving scooter.
Motor is going to be aroun 1.5kW, ran at 44V and 35A.
So i'm looking for a 12s4p setup which would allow 44v20ah if all packs are 5ah.
I am limited in the space i can use so i would like to know which option would take in the least amount of space.

I was thinking to buy 4 of these : http://www.hobbyking.com/hobbyking/...ch_A_SPEC_5000mah_12S_65_130C_Lipo_Pack_.html and put them all in series.

I was also thinking to buy 9 of these boys: [urlhttp://www.hobbyking.com/hobbyking/store/__16226__ZIPPY_Flightmax_8000mAh_4S1P_30C.html[/url]

Both would allow 12s4p correct?

What would be the most appropriate volume-wise and budget-wise?

 

[merkhond]

How are my boys doing?

I'm looking for a 1.5kW electric motor that can be ran at 44V and 35A.
I would like the kv to be around 450.
Recommendations of an ESC would be welcome as well.

Thanks boys

 

[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.

 

[merkhond]

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.

 

[daju]

I'm a newbie here so tell me if I'm posting in the wrong place. First thanks to all for the great info on this forum--
I'm looking to put a mid drive motor on my downhill dualie and, like any right thinking guy, am naturally attracted to big numbers: like a very pricey 3,200 W motor Versus a 1680 W motor from another.
Help me from doing something stupid and convince me that more is not the same as better.
if I seem to be hijacking thread, bump me off someplace elsewhere!

 

[merkhond]

I'm a newbie here so tell me if I'm posting in the wrong place. First thanks to all for the great info on this forum--
I'm looking to put a mid drive motor on my downhill dualie and, like any right thinking guy, am naturally attracted to big numbers: like a very pricey 3,200 W motor Versus a 1680 W motor from another.
Help me from doing something stupid and convince me that more is not the same as better.
if I seem to be hijacking thread, bump me off someplace elsewhere!

Yeah i'd say you're hijacking the thread.
Just make a new thread.

 

[wesnewell]

12 of these would be the cheapest route for 20ah of 12s. Configured as 12s4p, that's a 400A rating.
http://www.hobbyking.com/hobbyking/store/__18631__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack_USA_Warehouse_.html

 

[parabellum]

I converted 1 of those guys to 4s lipo, which are 16,8V fully charged. I melted transmission and motor all together in less then 10 min of operation. Those 4 volts are almost doubling power of the scooter and heat loses it cant handle. Motor is brushed type and reed switch can not handle current rise related to V, I added relay . You will need some space for rocks or lead bricks because LiPos are not as heavy as original Lead batteries. Motor and transmission must be changed or cooled in some way.
Little math.
300W/12V(under load fully charged LA)=25A
12V/25A=.48Ohm motor resistance
16V(those are even more under load LiPo fully charged)/.48Ohm=33.33A current on motor
33.33Ax16V=533W Power consumption on 16V

 

[John in CR]

As parabellum's results demonstrate, it's more difficult that made to seem in earlier posts. You're talking about moving through water where virtually all of the power required is determined by the resistance of the water, and power is proportional to the cube of speed. That means to double your speed it will require 8 times the power.

Props are optimized for a narrow range, so even if you managed to increase power 8X, you'll need a different prop, and figuring out the new optimum prop isn't a trivial manner. At that kind of power I think you'll have to go to contra-rotating propellers like on torpedoes, because the torque trying to force you and the scooter into a spin along the props axis will be far greater.

It an interesting project for sure. If you pull it off, I want to build one too. Seadoo's cheap model, under $200, goes 3kph, and the $1,250 version goes 7kph. Getting to 10 won't be easy and you probably don't want to be in the prop wash to do it, so start thinking along the lines of something you ride partially in like the DPD's the military has.

If doubted the 8X power requirement, look in the DPD info. Their speed model has double the power and is only 33% faster. If you want faster, then start with making you and the vehicle sleeker through the water, and then increase power.

John

 

[merkhond]

I converted 1 of those guys to 4s lipo, which are 16,8V fully charged. I melted transmission and motor all together in less then 10 min of operation. Those 4 volts are almost doubling power of the scooter and heat loses it cant handle. Motor is brushed type and reed switch can not handle current rise related to V, I added relay . You will need some space for rocks or lead bricks because LiPos are not as heavy as original Lead batteries. Motor and transmission must be changed or cooled in some way.
Little math.
300W/12V(under load fully charged LA)=25A
12V/25A=.48Ohm motor resistance
16V(those are even more under load LiPo fully charged)/.48Ohm=33.33A current on motor
33.33Ax16V=533W Power consumption on 16V

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.

 

[merkhond]

As parabellum's results demonstrate, it's more difficult that made to seem in earlier posts. You're talking about moving through water where virtually all of the power required is determined by the resistance of the water, and power is proportional to the cube of speed. That means to double your speed it will require 8 times the power.

Props are optimized for a narrow range, so even if you managed to increase power 8X, you'll need a different prop, and figuring out the new optimum prop isn't a trivial manner. At that kind of power I think you'll have to go to contra-rotating propellers like on torpedoes, because the torque trying to force you and the scooter into a spin along the props axis will be far greater.

It an interesting project for sure. If you pull it off, I want to build one too. Seadoo's cheap model, under $200, goes 3kph, and the $1,250 version goes 7kph. Getting to 10 won't be easy and you probably don't want to be in the prop wash to do it, so start thinking along the lines of something you ride partially in like the DPD's the military has.

If doubted the 8X power requirement, look in the DPD info. Their speed model has double the power and is only 33% faster. If you want faster, then start with making you and the vehicle sleeker through the water, and then increase power.

John

Thanks for the calculation you made there as a noob i had no idea! Again a very helpful reply!
So you say it needs 8 times the power, but that can change when i use a more efficient propeller i suppose?

Any sites where i can buy light-weight propellers with a similar diameter to the one they use in the seabob?

 

[merkhond]

12 of these would be the cheapest route for 20ah of 12s. Configured as 12s4p, that's a 400A rating.
http://www.hobbyking.com/hobbyking/store/__18631__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack_USA_Warehouse_.html

The '400A rating' you said, does that mean i could run 400 Amps through it?
I see in the details: max discharge 30C.
So that would be 30x12=360A at a max discharge.

I didn't even know you could add those things all up, it probably has to do with the fact that the current is being distributed over all the 12 packs so you can just add the max discharge all up?

 

[999zip999]

That's what hobby would led you to believe. Try 80 or maybe 120 amp. Plus most motors would melt at some point. Or 17,000 watts ? You wouldn't be able to use it from the boiling water as steam coming off it.
Can we see a pic. Of your scooter ?

 

[merkhond]

That's what hobby would led you to believe. Try 80 or maybe 120 amp. Plus most motors would melt at some point. Or 17,000 watts ? You wouldn't be able to use it from the boiling water as steam coming off it.
Can we see a pic. Of your scooter ?

I know 400A is a ridiculous number. But it's nice to know that i can buy 12 packs of 4s and pick the 20C ones which would easily give me a nice max discharge. I'll only use 50A max so that's great.

I'll put up some pictures tomorrow!