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, 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, 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 , 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...

[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_W0QQitemZ160334552068QQihZ006QQcategoryZ44028QQcmdZViewItem

[Brushless55]

Wow seams kinda hi ?

44k on 6s
59k on 8s