Help Appreciated with First 'Real' Boat

Help Appreciated with First 'Real' Boat
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Help Appreciated with First 'Real' Boat - 11/12/2009 4:32 AM

scott09

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From: Byron, GA, USA
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Hi all, just purchased my first 'real' boat (yes, off ebay!) - only played with China junk toys up till now.

Have been in the shadows here without joining for many months and tried to absorb all I can on lipo setups - feel stupid because I'm just not getting it!

New (used) boat details:
Shockwave 36 hull
2770 kv Brushless motor
120 amp scorpion esc capable of up to 22.2 volts (huge heatsink for extra esc cooling)
Venom two blade prop with bullet prop nut
Has all factory proboat shockwave rudder and hardware.

Seller uses 2 11.1v 3700 lipos parallel for 6-8mins of flat out run time.

I have become lost in the myriad of readings on rc electric and remain confused about what lipos to go for here as it relates to mAh and C rating.
Naturally I want the full-out he gets (claims 50+mph) but really want more run time.
Do I just need to focus on higer mAh packs or does the C rating come in to it? Stick with 3s or go 2s or what?
Have numerous 11.1v 3s 1800mAh and less lipos for aircraft that I guess would never work...or possibly run these in series?

I don't want to burn anything up - the esc/motor - and I just don't know what lipos to target for the best punch plus longest runs.
Essentially, as experienced users, if you ended up with this model, what lipos would you use?
I'll ask about the ebay lipos later

Please feel free to point me towards any threads you think may help straighten all this out in my head - chances are I've read them already
Really appreciate this community's knowledge and look forward to any feedback you have the time to offer.
Btw, feel free to suggest different props if you think it's worth it.
Thanks!
Scott

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RE: Help Appreciated with First 'Real' Boat - 11/12/2009 5:32 AM

rebuilder

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Cool................That sounds like the same exact boat i just had on my watch list on E-bay.....It was white........I shied away from that boat due to all the cracks that had been in the hull and had been refilled over and over.

GOTCHA

That is a very nice boat!! Lots of good lookin hardware and the color scheme is classy. Is the motor a feigao..........it looks like an XL size? Are you sure he ran the lipos on parallel...........seems like it would be hard to hit 54 on 3s................. You certainly dont need to run lipos any less than 4000 mah and 20c. If that motor is an XL then at 2770kv its pullin over 100 amps, in which case you need at least 20c and 5000mah minimum. Have fun!!!

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RE: Help Appreciated with First 'Real' Boat - 11/12/2009 5:12 PM

scott09

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Hehe, you did get me!
I watched it for a while in then, of course, got caught up in the bidding at the last moment.
Yes, he said parallel...and that's where I start to get confused.
2 3s 20c lipos in parallel will deliver 120amps, right? The same as a single 6s 20c?
Two 4s would deliver too many amps and burn the esc? One 4s wouldn't deliver enough, unless it was a 30c?
Then it's just a matter of how many mAh I can afford.
I'm going to end up reading some more

Thanks for the response.

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RE: Help Appreciated with First 'Real' Boat - 11/12/2009 5:40 PM

NobodyFamous

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just a quick reference for you in regards to parallel to series wiring.

When you wire batteries in parallel, you would add the amps together, and volts stay the same.
ex. 11.1V 3700mAh + 11.1V 3700mAh in parallel = 11.1V 7400mAh

When you wire batteries in series, you would add the voltage and the amps will stay the same.
ex. 11.1V 3700mAh + 11.1V 3700mAh in series = 22.2V 3700mAh

by increasing your voltage, you can decrease the amps needed to produce the same power. (volts x amps = watts and watts is like hp, in fact 1hp = 745.7watts)

The C rating has to do with how fast the LiPo's will deliver the amps. If the pack can only deliver 50amps, and the ESC can handle 120amps, you will only ever get 50amps.

beyond that I can't help. I would recommend running you batteries in such a fashion that you have 22.2 volts, and try to maximize your mAh for longer run times.

(volts = speed and amps = run time, sort of)

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HP = (Volts x Amps x Eff.) / 746 [Eff.=Efficiency, 89%=.89]
HP = (rpm x Torque) / 5252

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RE: Help Appreciated with First 'Real' Boat - 11/12/2009 6:07 PM

rebuilder

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Do you know what brand motor and the size..........is it a 36 x 74 mm? I pretty sure that a high kv motor like yours on 6s (22.2v) would put it over 60,000 rpms, that would be above any product specs i would imagine..........3s is right at 30k.......still seems tough to hit 54........................Is it e feigao motor?

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RE: Help Appreciated with First 'Real' Boat - 11/12/2009 11:32 PM

rebuilder

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quote:

ORIGINAL: scott09

Hehe, you did get me!
I watched it for a while in then, of course, got caught up in the bidding at the last moment.
Yes, he said parallel...and that's where I start to get confused.
2 3s 20c lipos in parallel will deliver 120amps, right? The same as a single 6s 20c?Two 4s would deliver too many amps and burn the esc? One 4s wouldn't deliver enough, unless it was a 30c?
Then it's just a matter of how many mAh I can afford.
I'm going to end up reading some more
Thanks for the response.

In order to figure amperage output you need to know the mah of the batt first, and the "c" rating. 5000 mah 20c = 100 amps, 4000 mah 20c = 80 amps etc......... Also a battery cant deliver too many amps, it supplies only what the motor asks for up to its capability. If your motor can pull 100 amps then you would need like a 5000 25c minimum(125 amps), 30c even better (150 amps).

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RE: Help Appreciated with First 'Real' Boat - 11/13/2009 12:50 AM

scott09

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Wow, thank for the info all.
I don't know what kind of motor but will report back once it's delivered.
I have so much to learn! Lipos are so costly that I want to make the right purchase for this motor/esc the first time around.
Thanks again!

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RE: Help Appreciated with First 'Real' Boat - 11/13/2009 5:41 AM

scott09

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Been reading up, again.
Seems I need to wait for boat to determine quality of motor but I'm certainly not against burning/replacing motor. The esc is apparantly way more expensive so that's what I should protect by not getting a motor that will draw more amps than the esc can handle, eh.

Given that, running dual lipo packs in parallel will give me the longest run time because of combined capacity while keeping voltage the same.
So, if the motor can handle 4s, go for it....that would be ~41k rpm. 3s would give ~31k rpm (2770kv motor).

So considering hooking 2 packs parallel, whether 4s or 3s, I need to simply get the highest mAh packs I can find for duration.

Am I starting to get the hang of it or am I way off base?
Can typical 2770kv motors handle 40k rpm or should I keep it at 30k rpm with 3s packs?

I still just gatta ask about the ebay lipo packs man they're just too cheap, freakin 10k mAh packs...what's up with that?
Thanks guys,
Scott

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RE: Help Appreciated with First 'Real' Boat - 11/13/2009 8:54 AM

brodjack

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If your motor is 2770kv you are stuck with 3S lipo,4S would be too many rpms and would force the use of a very small prop.
Plus 4S would use massive amps and would probably ruin your electrics.
You want to run 2 of these in parallel;
http://hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10356

I run a FE Shockwave too but on 4S using a 2000kv motor.10000mah on a x645 prop,easily giving us 10 mins. run times.

Brod..

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RE: Help Appreciated with First 'Real' Boat - 11/18/2009 6:50 PM

scott09

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Boat arrived.
The motor is not labled/stamped other than a 2770kv sticker. It measures 74mm x 36mm.

Sounds like no matter what, I should get as high a mAh batteries as possible.
I still question why 3s instead of 4s? That's 11.1V vs 14.8. I don't know if the motor will handle 41k rpm on 14.8V, does anyone? 14.8 would give me longer run times...

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RE: Help Appreciated with First 'Real' Boat - 11/18/2009 7:17 PM

brodjack

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have a look at this table for motors and cell counts for boats,you should be somewhere in the middle of the red writing.
A prop spinning at about 40000rpm will use massive amps on your boat and result in short runtimes plus possibly hot components,which will most likely not last long.
A reliable sensible set up will give much more prolonged fun and less heartache,trust me.lol
My son Jacks Shockwave runs and runs requiring little maintenance and repairs.Unlike my faster boats which have burnt ESCs and puffed the odd lipo pack.

You could always swop the motor for a lower KV one and then use higher volts for better efficiency,using this chart as good guide.
Brod.

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RE: Help Appreciated with First 'Real' Boat - 11/19/2009 1:24 AM

scott09

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Thanks for the feedback, you guys are really cool about being patient with newbs.
I still don't have it all figured out with the voltage, amps, watts, prop size, rpm been around long enough to know I should defer to wisdom on the matter.
Great little chart btw, thanks!

Will go with 3s setup like all are suggesting and that's what the seller ran. He stated 6 to 8 min runs on two 3700mAh packs with cool motor/esc after run. The freakin heatsink for the esc wieghs as much as the motor.

Now to really beat a dead horse with a newb question, are the 10k mAh packs on ebay worth getting or would you stick with brand name 5k mAh ones?
Thanks again for sharing your experience.

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RE: Help Appreciated with First 'Real' Boat - 11/19/2009 9:32 AM

brodjack

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Link needed for the 10k packs.
Brod..

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RE: Help Appreciated with First 'Real' Boat - 11/19/2009 6:54 PM

rebuilder

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You might consider getting a lower kv motor and going 4s............Like this feigao 540 8XL 2073kv........

http://www.offshoreelectrics.com/proddetail.php?prod=fei-540XL

Your current motor is pulling some major amps............like around 100 or more..........this 8XL would be more in the mid 80 range. Here is a handy chart for feigao's and would probably correlate somewhat to other similar kv motors.

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RE: Help Appreciated with First 'Real' Boat - 11/19/2009 7:36 PM

NobodyFamous

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yes, brodjack, thank you for the chart. saved it, I will be referencing that for my own nitro V conversion.

_____________________________

HP = (Volts x Amps x Eff.) / 746 [Eff.=Efficiency, 89%=.89]
HP = (rpm x Torque) / 5252

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RE: Help Appreciated with First 'Real' Boat - 11/19/2009 10:27 PM

scott09

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Again, thanks mucho for the feedback, you guys are a wealth of knowledge!

Wanting a link on the ebay batteries is well-noted, will get those choices out there for your opinions well before time to buy, but....
...you mention going lower kv motor and higher V pack. I love this, more tinkering and why not! Same esc will work and motors are not too expensive. And I'm buying new lipos anyway, so....

Why stop at 14v...what about an even lower kv motor and 18v packs? The esc is rated for 22.2V. Why not 6s packs?

Btw, the prop now is an Octura x448 and am up for any suggestions as I begin accumulating my boat hobby extras...sounds like I'll have an extra motor in the toolbox soon

In no hurry, won't hit the water till it warms back up months from now so am enjoying the tinkering.
And that gives time to try paint schemes, which we all know makes a boat run better anyway

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RE: Help Appreciated with First 'Real' Boat - 11/20/2009 3:46 PM

NobodyFamous

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I'v seen a good paint job add 5 mph!

_____________________________

HP = (Volts x Amps x Eff.) / 746 [Eff.=Efficiency, 89%=.89]
HP = (rpm x Torque) / 5252

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RE: Help Appreciated with First 'Real' Boat - 11/21/2009 1:26 AM

scott09

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Hehe, my car always feels faster when it's clean

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RE: Help Appreciated with First 'Real' Boat - 11/23/2009 6:12 PM

rebuilder

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Scott, hows the boat runnin?

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