1.1M Cat setup help

[norbique]

Hi,

A friend of mine and I want to build a balsa cat about 1.1m long.

We want to power them by twin motor system and we were trying to figure out what motors, ESCs, batts we would need to make these boats run fast. Our goal is to reach speeds of around 100km/h.
I'd like to ask you, the experts to give us some suggestions, 'cause we have no experience with these kind of big boats, and limited experience even with smaller cats.

Please note he has limited budget.
All suggestions are welcome, thank you!
Norbert

[ED66677]

Balsa cat for 100km/h??? you need at least fiberglass or better carbon for that speed, if not it'll blow up!
limited budget? how much? 100$? 200$? 500$?that makes a hudge difference!

[DISAR]

2 Feigaos 8XL, 4s2p, 2 ESCs 150A, 2 props 42-45?mm, 2 flex 0.187, etc...That's the cheapest way you can go and maybe you can do it, but do not build the hull too heavy. Not tested though onle read here
http://hpr06.speedtoy.com/setup.htm

In the middle of the page you will see the Feigaos setup

[shockerman80]

two 8xls on 4s will push that size boat well. Ive done it with my mti. just dont place the drive out on the sponsons very far it will make it very exiciting to drive.

[Ub Hauled]

Norbert wants to go 100km/h, I think with the 8XL motors it's probably not going to happen...
I love when people say: "I have a big hull, would like to go really fast but I have no money to invest." It cracks me up. ;)
It seems that you have a huge task in front of you Norbert, there you are with a hull that I am assuming, has not a proven design (not to say it's a bad Cat), good size and a shoe string budget.
Not many things are going for you. First of all, with a hull that large, you'll need to reinforce it, if you want it to survive more then on flip over, that means weight... that means also you'll need more power under the hood... thus require a bigger ESC... not to mention the batteries... all this cannot be of a brand that will burn on the first or second run, unless you enjoy buying stuff every week and the great smell of burn electronics. Sorry, but I don't see you spending less then 450 bux + cells

Here's why:
2x 3026 Scorpion outrunners ($150) <---- good punch for the buck.
2x Etti 150 ($300)
5s2p (?) get at least 25C cells and 8000mAh

BTW, don't mean to put you down, by all means, get this puppy going!
:)

[shockerman80]

oops i skipped the 100km part. um yea aint gonna happen on 8xls. the hull design will handle a 40 plus flip without damage (dont ask how i know) just make sure everything is held down really well. biggest problem with the twins is props that work well

[norbique]

Hello everyone!

Thanks for the fast response! I wasn't expecting this, but I like it.
First of all I'll try to gather my thoughs and give some more details of this cat.
The design is Shockerman's balsa cat, I'm sure it's a proven design.

Shockerman, please tell me if I'm wrong. I've built the cat in smaller size, and it's a very robust build, thanks to the ply reinforcement. If needed I'm ready to fiberglass it.

The battery would be a 6S A123 as a starting point. I'm not new to electronics, I want to keep Amps low thus I will go up with the Volts (at a given Power). I know I will need special (and more expensive) HV ESC above a certain input voltage due to the higher voltage MOSFETs used in them. That's why I chose the 6S, since many regular ESCs can still handle that. I can add water cooling for the ESC if it's not factory watercooled. Turnigy plush series?!

Ub Hauled, :sorry: if I made you angry, it wasn't my intention. I was just asking for help. I'm not a novice scratch boat builder, and I'm precise in what I do, but I lack the experience with big boats. I made micro boats till now. The hull is a good one, as I stated earlier, I just want to enlarge (and reinforce) it, and you're absolutely right, I can't do miracles on a shoe string budget. What do you suggest as a good cat size for 6S then?
How large can I go with balsa, ply and gfiberglass?
What input power does a 1m cat need to go 100km/h?
What aproximate RPM is needed on the shafts?
Should I consider BL inrunners only? Since there are going to be two motors running in the oposite direction a big outrunner's torque roll shouldn't be an issue either, right?! Since the two (more or less equal) oposing forces cancel each other out.

Thanks!

[shockerman80]

glassing it will work ok mine is. along with the ply. if your looking for speed a single drive is way faster.

[Jesse J]

single drive, inline rudder or offset?

[shockerman80]

offset will work its a cat dont need to be inline.

[norbique]

Hi Shocker,
I wanted the twin system so I would not have to deal with torque roll. And I have never had a twin motor boat before ;)

But if I choose a single drive, how much would that offset need to be?

[shockerman80]

it tourque rolls cause your using too large of a prop. I run little props spun fast on my boats. the 26" balsa cat only runs a x432 on 3s2p (long run times) with a 2600 kv mega. its faster then an sv on 4s

[Ub Hauled]

Ub Hauled, :sorry: if I made you angry, it wasn't my intention. I was just asking for help. I'm not a novice scratch boat builder, and I'm precise in what I do, but I lack the experience with big boats. I made micro boats till now. The hull is a good one, as I stated earlier, I just want to enlarge (and reinforce) it, and you're absolutely right, I can't do miracles on a shoe string budget. What do you suggest as a good cat size for 6S then?
Thanks!

Norbert, I am not upset man :smile:, I just have seen many people that want to go really fast without paying the piper, I find that amusing, heheheh... the reality is that for now, to get bigger hulls (like yours) to go so that fast, you'll need something reliable which translates into more expensive equipment.
Don not limit yourself to inrunners, outrunners or any equipment! My theory is, if you find something that looks good, DO YOUR HOMEWORK and look what the field results are proving, don't rely in data shown by the manufacture. The Turnigy is a good example, it is a pretty good ESC for the money, not sure if it is appropriate for your situation but nonetheless.
Using 6s1p (or 2p) is probably pull too many amps still... the is a guy call Jay Turner, if you haven't heard is name you should look his threads up in this forum, he has a Striker Cat (about 40") he powers it with one Lehner 3060, Schulze 40/160 and runs on 10s2p... he runs all day long with your desired speeds, but that setup will cost you dearly... around $500 for a used 3060, $459 for the ESC (on sale) and he uses Thunder Power... which also are not the shoe string budget batteries (there are ways around the batteries, there are more accessible lipos out there).
I'd reinforce the inside of the hull with CF, juuuuust to be certain that it can take a hit and not explode on you.
I wanna help, but we have to be realistic and see what is really viable to get you going... :thumbup:

[Jeff Wohlt]

Here...if you want some meat and muscle. Well built and 6S on each would be great. I would not hesitate to push it to 8S either.

This is what I would use for big hulls. You need the mass of 44mm dia. Shaft is already reduced.

http://cgi.ebay.com/Large-B44-2000KV-Brushless-motor-for-Monster-Truck-Boat_W0QQitemZ160334552068QQihZ006QQcategoryZ44028 QQcmdZViewItem

[Brushless55]

Wow seams kinda hi ?

44k on 6s
59k on 8s

[Jeff Wohlt]

I would stay with 6S. Yes but it has the mass to spin a decent prop without loading the motor very much I think it would be a good set up. You can run 4 or 5S to start with but it does say 6S. Looks like a well built motor for a cheapo. Screwed in rear plate, etc. Numbers are not that bad either.

Not sure anyone had seen these. I owuld have said KB 45 but they seem to be big amp hogs.

[Brushless55]

6s I think will be to much on a 2000kv motor in a big boat?
44,000rpm

[Himalaya]

I personally prefer inrunners, for :

the conviniency to get it water cooled

much faster throttle response than an outrunner having similar power capability

much higher RPM capability, wider KV choices available.

much thinner motor diameter, results in less bend angle to the flex cable and stuffing tube and thus higher drive train efficiency.

[Ub Hauled]

Here...if you want some meat and muscle. Well built and 6S on each would be great. I would not hesitate to push it to 8S either.

This is what I would use for big hulls. You need the mass of 44mm dia. Shaft is already reduced.

http://cgi.ebay.com/Large-B44-2000KV-Brushless-motor-for-Monster-Truck-Boat_W0QQitemZ160334552068QQihZ006QQcategoryZ44028 QQcmdZViewItem

Jeff, that seems to be a nice find... thanks for posting.

[Simon.O.]

1.1m is close enough to 115cm which by a stroke of good luck is the length of the HPR 115.
Have a look here for some power ideas
http://forums.offshoreelectrics.com/showthread.php?t=7899

I'll help if I can.

[norbique]

Hi! Thank you all for your relpy!

What do you think about using two of these motors in the cat?
https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=4937

or this one, it's quite similar to what Jeff Wohlt suggested on ebay:
https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=4938

Simon, I hear others saying you're an expert in scratch building. ;)
I want to ask you what do you think/recommend what would be the best way to reinforce the balsa cat?
I am planning to plank hull with 2mm balsa first, then ontop of that plank again with 0.4-0.8mm birch ply. Would this suffice for this huge boat or should I even add fiberglass to the outside/inside of the hull? Glassing the inside would be much more difficult though...
Thanks!

[EPower]

Hi! Thank you all for your relpy!

What do you think about using two of these motors in the cat?
https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=4937

or this one, it's quite similar to what Jeff Wohlt suggested on ebay:
https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=4938

Simon, I hear others saying you're an expert in scratch building. ;)
I want to ask you what do you think/recommend what would be the best way to reinforce the balsa cat?
I am planning to plank hull with 2mm balsa first, then ontop of that plank again with 0.4-0.8mm birch ply. Would this suffice for this huge boat or should I even add fiberglass to the outside/inside of the hull? Glassing the inside would be much more difficult though...
Thanks!

I use KB45 motors they are great,Amp hoggers for sure but with the right prop & esc they will work fine
they are not in stock at the moment and the ETA from hobbycity is 8 to 10 weeks LOL:beerchug:

Adrian

[norbique]

Thanks Adrian!
By amp hog, you mean it needs a higher amp ESC than other motors would? Less efficient?
Would a 100A watercooled ESC be enough for the KB45-10L 1800kv on 6S2P A123?
And what ESC for the KB45-08L 2300kv with 4S or 5S batts?

[Simon.O.]

Simon, I hear others saying you're an expert in scratch building. ;)
I want to ask you what do you think/recommend what would be the best way to reinforce the balsa cat?
I am planning to plank hull with 2mm balsa first, then ontop of that plank again with 0.4-0.8mm birch ply. Would this suffice for this huge boat or should I even add fiberglass to the outside/inside of the hull? Glassing the inside would be much more difficult though...
Thanks!
Expert ?? Just an enthusiast.
2mm balsa may be sufficient if you have small frame spacing and stringers.
For a hull bottom I would go with 3mm and cover with 1mm ply expoxied on. this will be very strong. i would suggest that it would be stronger and stiffer than a lot of glass hulls.
My new 30" has 3mm bottom without ply skin but as with the 4S rigger it will get a lot of varnish laid on.
Ply and epoxy are expensive for me to use on hulls so that is why I use more balsa and varnish.

Some of my work
http://forums.offshoreelectrics.com/showthread.php?t=8008
and some reading.
http://forums.offshoreelectrics.com/showthread.php?t=7494

Enjoy. :smile:

[EPower]

Thanks Adrian!
By amp hog, you mean it needs a higher amp ESC than other motors would? Less efficient?
Would a 100A watercooled ESC be enough for the KB45-10L 1800kv on 6S2P A123?
And what ESC for the KB45-08L 2300kv with 4S or 5S batts?

they do draw allot of amps i blew a TURNIGY Sentilon100A HV on the second run on 6s brought an Etti 150 race blew the capacitors on it i had it replaced and had the capacitor module fitted to it and so far so good :huh::smile:
on the KB45-08L 2300kv 4s would be the max i would run,and start with small props x442 or similar these motors are rated at over 3000 watts
I have to say that i do push these motors to their limit but then they are cheep to replace
i gave my boat a short run about one minutelast Sunday with my new Hyperion 5500mAh/35C batt and could really feel the difference in power we will see how the motor & Esc will cope with 3 minutes runs
what esc did you want to run in it?

Adrian

[norbique]

Adrian,
I was thinking of the TURNIGY Sentilon100A HV, but replace the caps for super low ESR ones with higher capacity asap ;) Yes, good batteries are a must. I have some A123s and they're amazing. I will use only use those in my future projects. No lipo fires, not even the thought in the back of my head it might happen anytime.
A KB45-10L 1800kv on 6S2P A123 is what I am thinking about. But I don't know will the Turnigy hold up. I'd rather go for a lower KV motor and go up with the volts.

Simon,
Thanks again for your help. I was to use 2mm balsa on the bottom too, but I'll listen to you and use 3mm on the bottom and 2mm elsewhere. Also I will use 0.8mm ply on the bottom and 0.4mm ply everywhere else epoxied. I can buy the ply at relatively good price.

EDIT: Thanks for the balsa build thread link. Now I'm afraid ;) All my bulkheads are from 5mm hard balsa. Except for the last one where the shafts will go through, that one is 5mm ply.

I must build my boats extra strong, but not only because of speed. Last weekend I ran across a bough floating on the surface of the water with my Hydromite. It threw the little boat half a meter out of the water. Luckily I only bent the turn fin, nothing else was damaged.

[EPower]

Adrian,
I was thinking of the TURNIGY Sentilon100A HV, but replace the caps for super low ESR ones with higher capacity asap ;) Yes, good batteries are a must. I have some A123s and they're amazing. I will use only use those in my future projects. No lipo fires, not even the thought in the back of my head it might happen anytime.
A KB45-10L 1800kv on 6S2P A123 is what I am thinking about. But I don't know will the Turnigy hold up. I'd rather go for a lower KV motor and go up with the volts.

Simon,
Thanks again for your help. I was to use 2mm balsa on the bottom too, but I'll listen to you and use 3mm on the bottom and 2mm elsewhere. Also I will use 0.8mm ply on the bottom and 0.4mm ply everywhere else epoxied. I can buy the ply at relatively good price.

You don't really have to replace the ones on your esc just add some to your batt wires and try to keep them as close as possible to the esc side of the batt wires have a look at the picture :beerchug:

Adrian

[norbique]

I mentioned replacing the ones in there since I'm going to disassemble it to add water cooling anyway. But your setup is easy to make, thank you, I'll consider it!

[crabstick]

Hi Norbique, :smile:

For your build I would recommend thin ply!! it will last a lot longer. there is a lot of load on the hull and hardware at 100k and can bend rudders and struts if they are not up to the job. I have recently finished building a 35 inch cat with ply after my previous balsa cat self destructed on a blowover... sure its heavier, but I have a lot more confidence in the strength of the boat.Ply is pretty easy to work with as long as you have a steady hand, a sharp hobby knife and a steel ruler.
From the examples I have seen and read about IMO a 40 inch'ish light twin 8xls on 4s each should be able to reach that 100k for sport or SAW runs.
The KB45 8L is a motor I am curious about and if it goes as good as the specs it might be another option, they are a bit heavier than the 540xls. power to weight to consider, also load on the hull.

IMO I think you may have to purpose design the hull, with minimal lift in the tunnel, because as the boat goes faster and faster more lift is obviously provided from the larger volume of air passing through the tunnel and then over she blows!!! lol we dont want that :thumbup:

for batteries if you dont want to spend a squillion, these could be an option
run 2p to each esc.. Obviously get the best packs you can afford, but if you are on a budget, these might be the ones to get.

https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8916&Product_Name=ZIPPY_Flightmax_2650mAh_4S1P_30C_

I have recently got some of these and am finding them good so far, they were 40degC after running my cat today and all cells were within .02 of a volt per cell of balance after running. Setup was the KB45 8xl on 4s2p for about 4 mins on m447, speed is around 70kmh in calm water, All in all im not too happy with the KB on 4s at the moment, I might get the 8L and try it. So duee to my findings I would NOT recommend the KB45 8xl for 4s, they are just too low in KV and you have to run giant props.

Those motors Jeff posted the links to look the same size as a kb45, but has detachable endbell by the looks! wonder what it goes like :beerchug:


For the Caps - checkout Shultze's website, theres a howto there

Cheers!:popcorn2::beerchug:

[EPower]

Hi Norbique, :smile:

For your build I would recommend thin ply!! it will last a lot longer. there is a lot of load on the hull and hardware at 100k and can bend rudders and struts if they are not up to the job. I have recently finished building a 35 inch cat with ply after my previous balsa cat self destructed on a blowover... sure its heavier, but I have a lot more confidence in the strength of the boat.Ply is pretty easy to work with as long as you have a steady hand, a sharp hobby knife and a steel ruler.
From the examples I have seen and read about IMO a 40 inch'ish light twin 8xls on 4s each should be able to reach that 100k for sport or SAW runs.
The KB45 8L is a motor I am curious about and if it goes as good as the specs it might be another option, they are a bit heavier than the 540xls. power to weight to consider, also load on the hull.

IMO I think you may have to purpose design the hull, with minimal lift in the tunnel, because as the boat goes faster and faster more lift is obviously provided from the larger volume of air passing through the tunnel and then over she blows!!! lol we dont want that :thumbup:

for batteries if you dont want to spend a squillion, these could be an option
run 2p to each esc.. Obviously get the best packs you can afford, but if you are on a budget, these might be the ones to get.

https://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8916&Product_Name=ZIPPY_Flightmax_2650mAh_4S1P_30C_

I have recently got some of these and am finding them good so far, they were 40degC after running my cat today and all cells were within .02 of a volt per cell of balance after running. Setup was the KB45 8xl on 4s2p for about 4 mins on m447, speed is around 70kmh in calm water, All in all im not too happy with the KB on 4s at the moment, I might get the 8L and try it. So duee to my findings I would NOT recommend the KB45 8xl for 4s, they are just too low in KV and you have to run giant props.

Those motors Jeff posted the links to look the same size as a kb45, but has detachable endbell by the looks! wonder what it goes like :beerchug:


For the Caps - checkout Shultze's website, theres a howto there

Cheers!:popcorn2::beerchug:

4s for that motor is not enough juce m8 i have some 6s 4500 mah zippys you can have, might not be able to handle the power LOL

[Brushless55]

they do draw allot of amps i blew a TURNIGY Sentilon100A HV on the second run on 6s brought an Etti 150 race blew the capacitors on it i had it replaced and had the capacitor module fitted to it and so far so good :huh::smile:
on the KB45-08L 2300kv 4s would be the max i would run,and start with small props x442 or similar these motors are rated at over 3000 watts
I have to say that i do push these motors to their limit but then they are cheep to replace
i gave my boat a short run about one minutelast Sunday with my new Hyperion 5500mAh/35C batt and could really feel the difference in power we will see how the motor & Esc will cope with 3 minutes runs
what esc did you want to run in it?

Adrian

The rating of 3000 watts is on 10s I believe

[norbique]

If I decide to go with the HV ESC. I can up the voltage and choose a lower KV motor.
Same power, more volts, less amps. :)
What KV motor would I need at 9S A123 = ~28V ?

[EPower]

The rating of 3000 watts is on 10s I believe

i did not say that they produce 3000 watts on 6s
The rating on these motors are
KB45 8XL :3528Watts @36V
KB45 8L:3439watts@36v
These ratings are totally over the top:w00t:
We all know that a 10s pack fully charged will put out more then 37 volts
these motors are rated at 36v max so a 10s pack would fry this motor in 30 seconds or less :rofl: I have a good friend that ran an 8L on 8s in a ducted fan jet the thing got that hot it melted the fan unit
I ran my lizard on 8s myself for less then a minute and the motor was so hot you could not touch it
My opinion 6S max and don't run them parallel I like these motors but lets not forget they are cheap :thumbup1:

Adrian

[EPower]

If I decide to go with the HV ESC. I can up the voltage and choose a lower KV motor.
Same power, more volts, less amps. :)
What KV motor would I need at 9S A123 = ~28V ?

Forget the KB or Feigao at 9S, get yourself an A class motor :beerchug:

Adrian

[crabstick]

id agree, 9S you will need an A Grade motor...

I wouldn't run either a Fiegao or KB over 6s

[Brushless55]

What about this version?
http://www.offshoreelectrics.com/proddetail.php?prod=fei-580-L

[crabstick]

sorry i should re-phrase, I wouldnt run a Fiegao 540 series on over 6s

the 580 yes I would run on 6s

[Brushless55]

I wonder how much better the new 580s are over the 45s

[EPower]

I wonder how much better the new 580s are over the 45s
The 580s are supposed to be a better motor but who knows, i haven’t seen any feedback so far on their performance

[Brushless55]

I wonder how one 580 would do in my Mean Machine? :thumbup:

[EPower]

I wonder how one 580 would do in my Mean Machine? :thumbup:

I would say it would go great what are you running at the moment ?

[Brushless55]

I would say it would go great what are you running at the moment ?


I will be putting my SV27 motor and esc in it this weekend..

[EPower]

I will be putting my SV27 motor and esc in it this weekend..

I know there is no substitute for horsepower but 580s in a SV27 that's a total overkill LOL:just-kidding:
This is also a very nice motor

●Input voltage:DC11.1-22.2V 3-6cell Li-Po
●Max continuous current:70A/85A(60sec)
●Max output power:Approx. 1600W/2000W(60sec)
●KV value:1650KV
●Dimension:spindle 5x65x43.3mm
●Weight:Approx. 300g

i will run one of these when i kill my KB45:rofl::beerchug:

Adrian

[crabstick]

I know there is no substitute for horsepower but 580s in a SV27 that's a total overkill LOL:just-kidding:
This is also a very nice motor

●Input voltage:DC11.1-22.2V 3-6cell Li-Po
●Max continuous current:70A/85A(60sec)
●Max output power:Approx. 1600W/2000W(60sec)
●KV value:1650KV
●Dimension:spindle 5x65x43.3mm
●Weight:Approx. 300g

i will run one of these when i kill my KB45:rofl::beerchug:

Adrian

Adrian, I think Brushless55 was saying he is going to put the sv27 power plant in... not a 580 into a sv27 :rofl:

[Brushless55]

Yep a Mean Machine Cat..
That Align motor on 5s in my MM would be killer! :w00t:

[Brushless55]

I wonder what would be a killer setup in my MM that has nutso speed and good run times on 4s or 6s?

[EPower]

Yep a Mean Machine Cat..
That Align motor on 5s in my MM would be killer! :w00t:

Sorry M8 My mistake must be old age :rofl::beerchug:

[EPower]

Yep a Mean Machine Cat..
That Align motor on 5s in my MM would be killer! :w00t:

Yeah can't wait to try one :thumbup:

[EPower]

I wonder what would be a killer setup in my MM that has nutso speed and good run times on 4s or 6s?

I guess you have to compromise somewhere you can't get the best of both words
I always go for SPEED :rockon2:

[Brushless55]

I guess you have to compromise somewhere you can't get the best of both words
I always go for SPEED :rockon2:

Well I was thinking if I went with a 14XL to a 12XL on 6s that way it pulls fewer amps (longer run times) than a faster motor but would rip on 6s.. :thumbup1:

[norbique]

This is also a very nice motor

●Input voltage:DC11.1-22.2V 3-6cell Li-Po
●Max continuous current:70A/85A(60sec)
●Max output power:Approx. 1600W/2000W(60sec)
●KV value:1650KV
●Dimension:spindle 5x65x43.3mm
●Weight:Approx. 300g

i will run one of these when i kill my KB45:rofl::beerchug:

Adrian

Where did you find this motor Adrian? How much does it cost?

Another question, and to get back to the original purpose of this thread. :olleyes:
We're talking about X number of series Lipos and motor KV's but what I want to know is: What should be the target free-run RPM for a 1.1m twin motor cat? What RPM range should I consider? After some research, I am thinking that somewhere between 30-40K, am I right?! Cause if I knew this it would help me in choosing the right motor and the number of series connected A123's.

I made some calculations with th KB L's. The XL's are too much for this boat I think, also very heavy, so I left them out for now. Correct me if I'm wrong.

Batteries are A123's NOT lipos. I calculated 3.2V / cell

KB45-8L 2300kv @ 4S = 29440
KB45-8L 2300kv @ 5S = 36800 *
KB45-8L 2300kv @ 6S = 44160

KB45-10L 1800kv @ 4S = 22040
KB45-10L 1800kv @ 5S = 28800
KB45-10L 1800kv @ 6S = 34560 *
KB45-10L 1800kv @ 7S = 40320

KB45-12L 1400kv @ 5S = 22400
KB45-12L 1400kv @ 6S = 26880
KB45-12L 1400kv @ 7S = 31360
KB45-12L 1400kv @ 8S = 35840 *
KB45-12L 1400kv @ 9S = 40320

(I marked what I think are good setups with a "*")

And here's what some of you have advised me so far:
(Lipo batts - I calculated 3.6V / cell)

Feigao 540 8XL 2084KV @ 4s = 30009
B44 ebay 2000KV @ 6S = 43200
KB45-08L 2300kv @ 4s = 33120

[EPower]

Where did you find this motor Adrian? How much does it cost?

Another question, and to get back to the original purpose of this thread. :olleyes:
We're talking about X number of series Lipos and motor KV's but what I want to know is: What should be the target free-run RPM for a 1.1m twin motor cat? What RPM range should I consider? After some research, I am thinking that somewhere between 30-40K, am I right?! Cause if I knew this it would help me in choosing the right motor and the number of series connected A123's.

I made some calculations with th KB L's. The XL's are too much for this boat I think, also very heavy, so I left them out for now. Correct me if I'm wrong.

Batteries are A123's NOT lipos. I calculated 3.2V / cell

KB45-8L 2300kv @ 4S = 29440
KB45-8L 2300kv @ 5S = 36800 *
KB45-8L 2300kv @ 6S = 44160

KB45-10L 1800kv @ 4S = 22040
KB45-10L 1800kv @ 5S = 28800
KB45-10L 1800kv @ 6S = 34560 *
KB45-10L 1800kv @ 7S = 40320

KB45-12L 1400kv @ 5S = 22400
KB45-12L 1400kv @ 6S = 26880
KB45-12L 1400kv @ 7S = 31360
KB45-12L 1400kv @ 8S = 35840 *
KB45-12L 1400kv @ 9S = 40320

(I marked what I think are good setups with a "*")

And here's what some of you have advised me so far:
(Lipo batts - I calculated 3.6V / cell)

Feigao 540 8XL 2084KV @ 4s = 30009
B44 ebay 2000KV @ 6S = 43200
KB45-08L 2300kv @ 4s = 33120

KB45-10L 1800kv @ 6S = 34560 *This probably the setup i would go with should get you aroun 50 to 55Mph i would not want to run more then 6S with a KB45 8S setup would be fine with the 580S
but running times would be fairly short around 3 to 3 1/2 minutes with a 5000mAh batt
Lipos are 3.7v per cell
Those motors are made by Align helicopters they are a Hybrid outrunner

[norbique]

Why are you all saying you would not go up with the voltage?!

Why do you think electricity is transformed up to hundreds of thousands of volts in energy transfer? To lower the currents, (thus the loss) at a given power.

If you use a lower KV motor you can have the same RPM, same power, the only difference is higher volts, less amps, (less heat) correct me if I'm wrong.

P = U * I
P - power
U - volts
I - current

For example lets suppose we have 2KW of power.
1st case: 20V * 100A = 2000W - here you need as monster ESC
2nd case: 50V * 40A = 2000W - here you can live with a smaller (current wise) ESC which has higher voltage capable MOSFETs, aka: HV ESC.

I dont' get it?! :frusty:

[Brushless55]

I know there is no substitute for horsepower but 580s in a SV27 that's a total overkill LOL:just-kidding:
This is also a very nice motor

●Input voltage:DC11.1-22.2V 3-6cell Li-Po
●Max continuous current:70A/85A(60sec)
●Max output power:Approx. 1600W/2000W(60sec)
●KV value:1650KV
●Dimension:spindle 5x65x43.3mm
●Weight:Approx. 300g

i will run one of these when i kill my KB45:rofl::beerchug:

Adrian

I think this motor could work great.. low kv and run 5s or 6s :banana:

[EPower]

Why are you all saying you would not go up with the voltage?!

Why do you think electricity is transformed up to hundreds of thousands of volts in energy transfer? To lower the currents, (thus the loss) at a given power.

If you use a lower KV motor you can have the same RPM, same power, the only difference is higher volts, less amps, (less heat) correct me if I'm wrong.

P = U * I
P - power
U - volts
I - current

For example lets suppose we have 2KW of power.
1st case: 20V * 100A = 2000W - here you need as monster ESC
2nd case: 50V * 40A = 2000W - here you can live with a smaller (current wise) ESC which has higher voltage capable MOSFETs, aka: HV ESC.

I dont' get it?! :frusty:

that is all true all i'm saying is that all the KB i have seen running at high voltage never lasted more then a couple of runs

[EPower]

Hi,

A friend of mine and I want to build a balsa cat about 1.1m long.

We want to power them by twin motor system and we were trying to figure out what motors, ESCs, batts we would need to make these boats run fast. Our goal is to reach speeds of around 100km/h.
I'd like to ask you, the experts to give us some suggestions, 'cause we have no experience with these kind of big boats, and limited experience even with smaller cats.

Please note he has limited budget.
All suggestions are welcome, thank you!
Norbert

This was your original post saying he has a limited budget 100 k is possible on a 6s setup :thumbup1:

[norbique]

You're right EPower and sorry, it was a typo. I meant "we have limited budget" and not "he has limited budget". :sorry:

What I try to say is you can save on battery costs by not buying 2x 6S packs (12 cells altogether) wire them in parallel and use a higher kv motor. But to buy 8-10 cells and wire them in series and go with the lower kv motors.

What do you think why did the KB's on higher voltages last only a couple of runs? Magnet wire insulation problem or why?
Or did they use higher voltage on higher kv motors, thus forcing them beyond their current and RPM limits?!

[Brod]

I think this motor could work great.. low kv and run 5s or 6s :banana:

Those Align motors are nothing special,i fly helis mainly,they are fitted as standard in the Trex 600,seen a few burn up on 6S lipo and not flown hard either.
Most of the Trex 600 guys change then for better quality motors.
Brod...

[norbique]

Those Align motors are nothing special,i fly helis mainly,they are fitted as standard in the Trex 600,seen a few burn up on 6S lipo and not flown hard either.
Most of the Trex 600 guys change then for better quality motors.
Brod...

What are those better quality motors? Could you name some of them?

[Brod]

NeuMotor 1515/2.5D/F on 6S,
I run a Tango 45-07 on 10S in my Trex600,comes down cold after 6 mins of hard flying.

Not cheap but both superb motors.

I like many,just cant put these expensive motors in boats,we only get 1 or 2 visits to the lake every week.
My helis get flown much more often,so warrant a big chunk of cash on the power systems.
I just ordered 2 Medusa motors for 2 of my FE boats,i will report when i get them fitted.
Brod..

[Brod]

2 of these motors would make a great twin setup in a 1.1M cat,good quality motors.
I have a couple i run in hulls,they are tough, long lasting motors
http://www.astecmodels.co.uk/catalog/product_info.php?cPath=24_48_77&products_id=725

http://www.megamotorusa.com/
Brod..

[norbique]

After a lot of research and lots of PMs (thanks for your help and patience Jay!), I decided on the Feigao 540XL as the motors for this boat. Battery will be a lipo, contrary to my liking. But I can't afford to pay $500 for a set of A123's. So lipos 6S 5000mAh and modified (water cooling / waterproofing) cheap 100A ESCs off ebay. Strut still undecided...

[Brushless55]

Awesome, keep us posted!

[norbique]

Another question: I decided to go with wire drives instead of the flex shafts.
Will a ɸ2 mm diameter steel shaft do tho job? Motors Feigao 540XLs.

[norbique]

I decided on the setup.

Motors: Feigao 12XL
Batts: 6S 4500mAh lipos
ESCs: 100A Mystery modified - watercooled and waterproofed, 5 more 1000uF low ESR caps added
Wire drive: ɸ1.5 mm steel wires
Props: K45, x447 L+R, or K51

Thank you all who helped me to decide!
Link to the build thread:
http://www.rcuniverse.com/forum/m_8820353/mpage_5/tm.htm

A pic of the motor hatches I finished yesterday:

[norbique]

OK, I stumbled across this: (Scorpion and Hyperion joined their forces)
http://www.scorpionsystem.com/files/i785_popup_image.jpg http://content.aircraftjapan.com/prod/HP-HS3026-XX.jpg
and now I can't decide whether to stay with the 12XL's or to switch to these.
I was told these scorpion motors have higher power than the 540XLs do. Can someone comment on this?!
What also makes me go for the outrunners is, that they have stator laminations not only copper like in the Feigaos and if it burns up it can be rewound. And it has 10 magnet poles VS the 2 poles of the Feigao.
Only con of the outrunners I can think of is a bit troublesome cooling.

[Himalaya]

Steven of OSE is going to carry a monster 63mm outrunner with water cooling. I looking forward to that to power my 1.4m mono project.

[norbique]

Are you referring to the littlescreamers motor?

[Himalaya]

Yes. I would call it a Bigscreamer instead. :banana: still have a bit worry about it's cooling effect though.

[norbique]

At the end I went for the T600 1400KV Turnigy outrunners. They are good quality motors.
Batteries will be A123's. 7S2P times two, one for each motor. Roughly equal to a 6S 4500mAh Lipo pack. A little bit low capacity, but I don't want to go with Lipos, nor can I fit 3P setup in the hull. :)
ESC still just a plan, SkyWing 150A heavily modified. (watercooling, waterproofing, cap banks)