What size or how many mAh

[Buoyhunter]

Hey guys I have a 31" ML Hydro. Planning on running it in a p limited race. setup for 4S with a mild prop. how many mAh am I going to need to complete the heats? I want to balance the boat out properly too...

[CraigP]

Need more info... What's your motor and prop?

[Buoyhunter]

Its a ProBoat stock 1050 kV motor and a ABC 1817

[CraigP]

I run a 1050kv on 8s. That would be real slow on 4s... you want to shoot for about 36,000 to 38,000RPM. So your motor would be closer to a 2500kv for competition and 2200kv for sport boating. You'll get lapped twice running that slow a motor! Most people are running 7000-10,000mah packs, running 4s2p packs. Hydros like some weight up front.

[Buoyhunter]

Craig, are you a NAMBA or IMPBA member? IMPBA has a voltage cap at 16.92 V for P class hulls. So I guess what you're saying is i need to up the kV?

[CraigP]

I'm not a member, but I'm really good with the electrical components... the reason I don't race is because it is centered around low voltage setups. That drives amps up, and amps is what breaks parts. But let's get back to your project... So with a 4s, 14.8V is the general value to apply to kv. So, 1050 X 14.8 = 15540rpm's, very low. You could turn a huge prop to compensate but here's the catch, larger props create more prop torque handling problems. Also, when large props cavitation then bite, they pull huge current surges, which can easily break parts. So, most have found, thru experience and school of hard knocks, that a prop speed of 30,000-38,000 yields a good compromise between these factors. Fast enough to run smaller props, less prop torque issues and the smaller prop has more manageable current surges. Also a smaller prop tends to stay in the water better, because you really want to avoid cavitation. But there's always rough water to deal with... I hope that helps you decide how you would like to proceed!

[klloyd67]

I'm not a member, but I'm really good with the electrical components... the reason I don't race is because it is centered around low voltage setups. That drives amps up, and amps is what breaks parts. But let's get back to your project... So with a 4s, 14.8V is the general value to apply to kv. So, 1050 X 14.8 = 15540rpm's, very low. You could turn a huge prop to compensate but here's the catch, larger props create more prop torque handling problems. Also, when large props cavitation then bite, they pull huge current surges, which can easily break parts. So, most have found, thru experience and school of hard knocks, that a prop speed of 30,000-38,000 yields a good compromise between these factors. Fast enough to run smaller props, less prop torque issues and the smaller prop has more manageable current surges. Also a smaller prop tends to stay in the water better, because you really want to avoid cavitation. But there's always rough water to deal with... I hope that helps you decide how you would like to proceed!

Good information, why does NAMBA rules limit 1/10 scale to 1500kv motors?, will speed be adequate on a light weight modern hull, 6-7 pounds? on 4S as rules require

[oscarel]

Its a ProBoat stock 1050 kV motor and a ABC 1817

Assuming you're in NAMBA, the only Proboat motor legal for limited from Proboat is a 1500kv motor unless your club allows for others. Does Proboat make one that's 1050kv?? Your best bet is to use whatever batteries you have and time a run to see where you are with your setup. Make sure to leave a good +20% left. It's been a while since I've run a p-limited hydro but a guess would be in the 6-8k mah range.

[fweasel]

Does Proboat make one that's 1050kv??

The stock motor in the Zelos 48 is 1000kV

[CraigP]

Assuming you're in NAMBA, the only Proboat motor legal for limited from Proboat is a 1500kv motor unless your club allows for others. Does Proboat make one that's 1050kv?? Your best bet is to use whatever batteries you have and time a run to see where you are with your setup. Make sure to leave a good +20% left. It's been a while since I've run a p-limited hydro but a guess would be in the 6-8k mah range.

I didn't realize that they limit prop rotation speed that much! 1500kv at 14.8v is only about 20,000rpm's loaded. So you have to spin a big prop... so that is where the big amp draws comes from?

[oscarel]

The stock motor in the Zelos 48 is 1000kV

Zelos 48 motor isn't used for P-limited, completely different size motor.

d. P-Limited Approved Motors
i) The motors shall be used as shipped from the manufacturer, with the
exception of creating a drive shaft flat spot, adding water cooling, and
allowing the motor to be connected to the ESC by any means.
ii) Currently approved motors
Brand Model Description
AquaCraft AQUG7000 L36/56 7.2-18V – 6 pole brushless
AQUG7001 36-56-2030 – 6 pole brushless
AQUG7002 36-56-1800 – 6 pole brushless
Himax HB3630 1500 brushless – 6 pole brushless
ProBoat PRB3310 A3630-1500 – 6 pole brushless
PRB4017 A3630-1800 – 6 pole brushless
DYNM3835 A3630-1500kv – 6 pole brushless,
water cooled, marine motor
DYNM3830 A3630-1800kv – 6 pole brushless,
water cooled, marine motor
iii) In addition, the CD has the discretion to allow the following:
(a) An aftermarket motor that is a re-labeled and exact copy of any
approved motor.
(b) Any generational change of an approved motor, or a motor that
is used in a Ready To Run (RTR) offering from a manufacturer
that produces over 100 units of said offering, as long as there is
no more than a 5% increase in any of the following
manufacturers specifications as compared to any single
approved motor: Kv, maximum constant amperage rating,
mass, and MSRP.
(c) The race flyer shall list additional allowed motors for the event

I didn't realize that they limit prop rotation speed that much! 1500kv at 14.8v is only about 20,000rpm's loaded. So you have to spin a big prop... so that is where the big amp draws comes from?

There only pulling in the 100 - 120 amp range at max. These little motors can only handle so much. We've run limited OPC tunnels here and they're only using a 5000mah lipo, same with the riggers. Again, the 6-8k was a guesstimate and probably more suited for full P than limited.

[CraigP]

Oscar, what's the voltage specs in P-Limited? Can my 34" Vortex Hydro qualify for this class? I'm currently rigged for about 3000W average, peak 5000W on prop cav recovery, and the boat weighs about 10lbs. Thanks!

Is there a P-Limited Sport and if so, how much different is that class?

[T.S.Davis]

Are you planning to race? You need to find out what the venues you plan to race at are allowing.

NAMBA has a list of approved motors in their rule book for P limited. The trouble is that the list hasn't evolved. The NAMBA 10th scale motor list is different than the P limited motor list. Looks like it's been posted since I started typing.

If you're running IMPBA you need to see if there is a local club running a form of limited. IMPBA has no such limited classes despite them being the most popular FE classes in the history of FE racing. IMPBA fights the very notion that these classes should exist. IMPBA clubs and venue have to work around the book and create their own parameters. The typical spec for IMPBA clubs and some NAMBA clubs that are progressive is a simple size limitation. So it's 34" max boat length, 4s batteries, and a max motor size of 37mmx62mm in our club. Allows for some manufacturing flux but still is a limit. Any kv is allowed. Looks like you're in MI so I would go with the size spec.

The 31" ML is and was designed for 4s power. If you truly want to have the option to race it at some point a number of known setups exist. Makes a killer spec boat.

Aquacraft 2030 on an Octura X445
Proboat 1500kv on an Octura X450
Proboat 2000kv on an Octura X447
TP 3630 1950kv with an Octura X445
Raider 1850 (not sure on the prop for these yet)
Raider 1750 on an X450 give or take.
Promarine's smaller motor works too but I never found the exact prop to put on it. I was so sure this was going to be THE motor that my optimism baked ours.

I've raced all but the 1850. I leaned conservative on the props. You might run more dia once you have the boat figured out and running free. The Aquacraft is the least forgiving of that bunch. If something is wrong it will give up the magic smoke the soonest. As always, run 2 laps the first time and check for heat. Then next run, do an extra 2 laps etc. Don't go out and run until it quits. You wont learn a thing about the setup as everything will be hot.

[oscarel]

Oscar, what's the voltage specs in P-Limited? Can my 34" Vortex Hydro qualify for this class? I'm currently rigged for about 3000W average, peak 5000W on prop cav recovery, and the boat weighs about 10lbs. Thanks!

Is there a P-Limited Sport and if so, how much different is that class?

Craig, P classes are 11.10 - 16.92 V. 10,000 mah max and hull is max 34” with the p-limited's having to have an approved motor that I posted above. The rule book is here. The class we're discussing here is the P-Limited Sport class. The guys down in HOTMBC race them quite a bit.

[T.S.Davis]

P limited sport by NAMBA rules is/are a 34" full bodied hydro, 4s batteries with up to 10k mah, and a motor from the list.

There are dimensional limitations on a sport but I'm 99% certain the Vortex meets them. Not sure about the length though. Is it truly 34"? I can't remember. Haven't seen one in a couple years.