electric diving scooter

Hello there!

I am planning on making an electric diving scooter, with similar performance to a seabob cayago f7. The seabob cayago f7 has a 7hp electric motor and can go up to 14 km/ hour underwater!

https://www.youtube.com/watch?v=D4buMpPup8U
The link above shows this amazing device in action. Unfortunately, this piece of technology costs 12000 euros, so i was hoping to build a similar machine for 4000 euros max.
Since it is essentially the idea to build a similar machine the absolute maximum weight would have to be 100lbs or 45 kg as it needs to be quite agile. So perfomance-efficient batteries are of great importance!

Any suggestions motor-wise and battery-wise would be extremely appreciated as it will give me an idea of how realistic this is and the price this project would cost me.
Operating time would be 30 minutes at max performance and 45-60 minutes at cruising speeds.

Since i am a noob i will need a lot of suggestions from you guys (i will also get in contact with a local mechanic).

Thanks in advance!

Looks pretty fun. He looks like a dolphin. Would be pretty sick to just do nothing but ride that thing all over the world in the waters. LOL! I have no idea how to start a project like that but would be awesome! A whole different realm for electric vehicles.

Good luck! I'd like to see what you come up with.

Well since i lack the knowledge to select the parts i desperately need help from you guys but it seems to me that this subforum hardly gets any attention.
I'm going to put a link to it in another subforum for more views.

merkhond said:

Well since i lack the knowledge to select the parts i desperately need help from you guys but it seems to me that this subforum hardly gets any attention.
I'm going to put a link to it in another subforum for more views.

Click to expand...

Sourcing electrical parts is going to be a cakewalk compared to fabricating a streamlined, pressure resistant watertight casing with precise buoyancy control, and I doubt the members of this forum have a lot of accumulated knowledge on that subject. This is a harder problem that you seem to appreciate. Figure out how you're going to accomplish the hard part first.

I don't want to scare you away from it, but neither do I want you to spend a lot of money on components and then get stuck.

Precisely.

I'm going to buy a Torpedo 2000. Costs 850 bucks.
http://www.torpedodpv.com/models.php

come on guys.. anyone??

I'm looking for an electric motor that can be able to output 7-10kW with 700-900N for an (extremely fast) underwater scooter. Ideas?

Hi merkhond,

Here's the spec. from the Cayago 7
[ http://www.seabob.com/index.php?id=69&L=2 ]

Performance up to: 5.2 kW (7 HP)
Maximum torque up to: 22 Nm
Maximum thrust up to: 734 N
Speed over water up to: 20 km/h
Speed under water up to: 14 km/h
Speed control: 10 power levels between 0 % and 100 % via piezo buttons


Assuming a similar propulsion system and objectives, it seems you need a motor capable of producing 22Nm of torque.

I'm already aware of the seabob, but thank you for clearing up the specs!

The problem is that the seabob works with an impeller system, which allows for more RPM of the motor. It's pretty dificult to construct an agile, fast machine that can fit an impeller with a large battery pack and motor.

Do you know of any motor that has similar (or better specs) than the one on the seabob?

We started a motor comparison thread here: http://endless-sphere.com/forums/viewtopic.php?f=30&t=45489

It seems like you'll need much more torque than the Seabob, then?

assuming i'm going to use a propeller in stead of an impeller, i'm probably going to need 20% more torque and power in general to match the performance.

The main problem with the impeller is that we're looking at a whole other level of design.
If i can build off of a second hand DPV with a normal propeller, costs will be lower but i'll need a bigger motor to get to 14km/h underwater.

seems like it is REALLY low efficiency. My friend has a 600W motor that does 25kg thrust ok maybe it doesnt go 20km/h. Still, such a tiny impeller seems to be not very efficient. A reduction would help a lot here. an impeller with larger dia would just produce more thrust at this powerlevel

crossbreak said:

seems like it is REALLY low efficiency. My friend has a 600W motor that does 25kg thrust ok maybe it doesnt go 20km/h. Still, such a tiny impeller seems to be not very efficient. A reduction would help a lot here. an impeller with larger dia would just produce more thrust at this powerlevel

Click to expand...

how much would the reduction help performance-wise?

The impeller is very limited in diameter because it needs to be cased within a tiny hose to use it efficiently.
It's pretty interesting because the Bladefish 5000:http://bladefishdirect.com/bladefish-5000-turbo.html has a relatively large propeller and can attain speeds of 4MPH underwater with a 250W motor, i couldn't even imagine what it would give with a 4kW motor.

As you know, I wanted to start the same project but I have so many other projects so maybe you are interessted in my Sea doo underwater scooter.

It's the one like this:
http://www.veilnu.nl/NL/veiling/24002-Onderwaterscooter

If your project will work I will buy another one.

Re: battery pack

Sent: Fri Jan 24, 2014 5:54 am
by merkhond

I'm going to run maybe 50-60 amps throught it. If i have a 88V pack= 88x50= 4400W.
I'm going to need at least a pack of 20ah to get some kind of respectable range

Re: battery pack

Sent: Thu Jan 23, 2014 5:27 pm
by LockH

Ah ha! A "diver propulsion vehicle"! Re "boat", a quick search on the Spheroid Planet (Endless) for your name turned up maybe two threads about electric propulsion ON the water (so, no hills to speak of), but I didn't read those threads. So, a "DPV", but UNDER water? Not far off, but lead batts can "sink like a stone". No buoyancy involved maybe? (eg an air filled balloon, EVen for temp/sometimes use?) So, some flavour of Li I guess. I still wanna suggest ya need to concern yourself with AMPs, as much or more than VOLTS.
L

Re: battery pack

Sent: Thu Jan 23, 2014 4:34 pm
by merkhond

the battery pack is supposed to support a 4kW motor for a diver propulsion vehicle.
What do you mean with the whole boat thing?


Re: battery pack

Sent: Thu Jan 23, 2014 4:26 pm
by LockH

Hey merkhond! Much better to ask the experts here! Me, I only hope to preach the gospel of the ebikes (Chapters by Saint Justin, St.Luke, etc, etc) Not sure why you want such high voltages? (Hint: Watts = Volts x AMPS.) Also, if you put your questions to the congregation (it's kinda huge, and growing), maybe indicate how large (heavy) a pack you want (and expandable?) and watt distances you typically ride, plus watt might be the loooongest distance ya might want to go between "refills" (batt recharges). And, how heavy is your steed now, and how well can ya pedal (to extend distances between refills, help smooth out "peaks" on startups, up hills, etc etc.

Cheers
L
PS Give up on boats did ya? Sad, sorta. I have some pieces of "Sunbrella" cloth, to use as a cover for my rusty steed (electrmaterrific trike) on shore, and will add pockets to take bamboo battens, and the whole thing I can hoist up and use as a sail (when a fair wind)


battery pack

Sent: Thu Jan 23, 2014 2:03 pm
by merkhond

Hi

I have a question, i want to make a battery pack of 88-100v with 20ah. My question is, if i take a 6s 5000mah battery pack (with 4.4v per cell, so 6x4.4=22v) and get 4 of those in series, i would get 88v at 5000mah, right?
Can i then buy 4 battery packs of 1s (4.4v) with 5000mah in parallel to get 25ah (the 5000mah from the 4 6s in series and 20000ah from 4 1s in parallel?)
And would my total voltage be 88v + 4.4v from the 4 packs of 1s in parallel?

Kind regards

so this is a series of pm's from that guy? he doesn't wanna ask those questions on the board? wonder where he got the 4.4V? so bulk charging lipo to an average 4.4V/cell and no BMS so he can make something big happen?

merkhond said:

I'm going to run maybe 50-60 amps throught it. If i have a 88V pack= 88x50= 4400W.
I'm going to need at least a pack of 20ah to get some kind of respectable range

Click to expand...

Keep in mind it's going to have some voltage sag, too, so the actual wattage you can get will be lower than that, plus losses in your controller and motor, so you probably won't get as much as you expect at the mechanical output itself.

I highly recommend putting links to your actual vehicle and use information here in this thread, so people can help you better.

I also don't recommend PMing members directly for things like this, because then only that member can help you, and if you PM multiple people then some of them are wasting their time duplicating information. Also, if it's all done by PMs, no one else learns from it, or can use the information for their own projects later, and has to ask the same questions all over again, wasting more time of theirs and everyone else's.

I have a question, i want to make a battery pack of 88-100v with 20ah. My question is, if i take a 6s 5000mah battery pack (with 4.4v per cell, so 6x4.4=22v) and get 4 of those in series, i would get 88v at 5000mah, right?
Can i then buy 4 battery packs of 1s (4.4v) with 5000mah in parallel to get 25ah (the 5000mah from the 4 6s in series and 20000ah from 4 1s in parallel?)
And would my total voltage be 88v + 4.4v from the 4 packs of 1s in parallel?

Click to expand...

I hope I am just misunderstanding the above, but in case I am not, some advice:


Series packs/cells: voltages always add, capacity and current always stay the same.

Parallel packs/cells: capacity and current always add, voltages always stay the same.

I think you need to get your calculator fixed, too, because 6 x 4.4 = 26.4, not 22.

Also, unless I am completely misunderstanding your description above, you're not going to get anything like what you want out of that math. If you want 25Ah, you have to parallel 25Ah of the same total number of series cells. If you have 6s of 5Ah, then to get 25Ah you must use 5 parallel 6s 5Ah packs.

You cannot parallel a 1s with a 6s, unless you like fire. Even if it wouldn't burn or otherwise destroy the cells, it will not work.

If you are going to series the 1s 25Ah with 6s 5Ah, you only get 7s 5Ah out of that. The other 20Ah of the 1s is unusable because you do not have 20Ah more in the 6s part to match it.


I don't know what cells you want to use, but if it's RC LiPo as the description suggests, 4.4V is overcharging, and you're probably going to damage the cells, and with cheap stuff probably going to have a fire at some point because of it.

I strongly recommend you look at the wiki for the various RC LiPo articles, and all of the various noob / newbie / beginner threads about them in the forums, for how to set up, use and charge them, or you may well end up destroying your project (and maybe your vehicle, house or other storage/charging areas) in a fire, either because of charging them incorrectly, or because of hooking them up incorrectly and shorting them out, overdischarging them, etc.


EDIT: I PM'd Merkhond with a link to this thread, so we can help him avoid a fire, and get his project working.

Actually what i was trying to do is get the voltage to 88v from getting the 4 6s packs in series (all packs 5ah so the 24s pack 5ah) and add 20ah to that by putting 4 1s packs (with each 5ah) in parallel.
Does that work?

I had a hard time following all that. If I understand at all, you want 24s 20 ah.

4 6s 5 ah packs in series is 24s 5 ah.

8 packs, 4 sections of two parallel connected 6s packs is 24s 10 ah. And so on. Each section is two packs, the pair is 6s 10 ah.

so a 20 ah pack you want will take 16 of the 5 ah 6s packs.

4 packs in each parallel connected section, then series connect the 20 ah 6s sections.

And there is a shitload more you will need to learn, if you don't plan on burning the house or garage down.

Thanks for your response.
I had no idea that it would take 16 packs of 6s to get to 88v at 20ah. I'm not going to be able to fit 16 packs of 6s in a DPV in a million years.
Good night sweet prince.

There you have the problem we have all had, in a nutshell. The range we want takes more than we can afford, or carry sometimes.

dnmun said:

so this is a series of pm's from that guy?

Click to expand...

Yup.

he doesn't wanna ask those questions on the board?

Click to expand...

That was my question to the poster. Many Ebike Masters aboard here with waaaaay more tecky know-how about the electramaterrific thingee than I. Myself, I am only satisfied the tech works (and I hope will continue to improve - though I can't imagine any more giant leaps, but instead a steady roll), and seek to stamp out last remaining (local) pockets of resistance. RESISTANCE IS FUTILE.

merkhond said:

Thanks for your response.
I had no idea that it would take 16 packs of 6s to get to 88v at 20ah. I'm not going to be able to fit 16 packs of 6s in a DPV in a million years.
Good night sweet prince.

Click to expand...

I will be installing a 12S 30Ah pack, made from 4S 5Ah bricks, for my commuter conversion.
That's 18 bricks all up.

Not sure what a DPV is, but they'll fit in the triangle on my hardtail.

Rutiger said:

Not sure what a DPV is

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That's in the first post, in the quotes by LockH of Merkhond's PMs to him.

Ahh, thanks AW. I only quickly breezed through the first post, found it hard to understand.