4s versus 6s and runtime

[Erik Aa]

Hello.

Which set up is most likely to give me a 6 min + runtime? I run a delta force 29 with an octura x440x3.

1. 4s1p 6500 mah with a leopard 3674 2200kv motor.

2. 6s1p 5000 mah with a leopard 3674 1470 kv motor.

Any input on this would be highly appreciated.

Thanks,

Erik.

[RaceMechaniX]

It's actually very close, but without knowing the current draw of the motor it is a toss up. Both configurations have roughly the same RPM, but I believe the single 6S pack will give you longer run times.
TG

[kievyu]

6 min + runtime .... maybe 6s with 4082 2.5y or 3y

[Make-a-Wake]

If the 6s packs had the same mah as the 4s then i think you should see a 30-35% increase in runtime.

[iamandrew]

extra weight of a 6S Pack could make .... some difference ? :S

[NativePaul]

Is this for Naviga racing? The 6+mins runtime is the length of a Mono2 race and those battery sizes are up at the top or what capacitys are readily available in a 560gram pack within the Mono2 rules at the moment. (yes 6s can be the same weight as 4s,and Naviga give you a choice in voltage limiting the weight of the LiPo)

A 3674 is all you need, With those packs and that runtime the currents are easily calculated, at a maximum average amp draw of 65A for the 4s pack and 50A for the 6s pack, going up in motor size will just weigh the boat down and take more amps to spin up reducing speed and/or runtime.

If it is for Naviga and those cells are sub 560g packs I have to warn you that while being amoungst the best cells that you can get, the latest 5000mAh 3s/6s packs are overrated and are only actually putting out 4500Mah, despite the different labels in the real world Desire5000s, ETTI4500s, VB4500s, and Zippy Compact4000s all graph pretty closely to each other.

The stored energy available normally works out pretty closely between 4s and 6s at the 560g limit, but there are some efficiency gains from 6s and most folks that have the money to have switched to 6s, if I was buying from scratch I would go for a 6s setup.

While I don't know the DF29 well enough to say for sureI would hazard a guess that you will be able to get runtime with that setup, if not with that prop then a similar size 2 blader.

If it is for Naviga racing I have to warn you that the DF29 is rather heavy and draggy compared to the usual European and Chinese stepped Mono2s and it won't be as fast in most conditions, barring extreme rough water when folks are adding ballast and/or using partial throttle. I know folks with lightly built carbon stepped Mono2s running 4s 2700kv and 6s 1900kv, but there is no chance you will get 6 minutes in a DF29 with a setup that hot and a prop big enough to drive the boat well.

[Erik Aa]

Thanks guys!

Tyler's comment on 6s superiority is my hunch as well.

Paul, yes, your comments are right on the spot. I was thinking about trying to set up a Naviga legal DF29.
In particular, I was thinking about the Desire 5000s on 6s. But these are closer to 4500 you say?
I know the Exigas are lighter and faster (at least on the straights), but I was hoping to make this up in the turns.
The DF29 handles fairly rough waters and turns rather well. From what I have gathered the Exigas and other stepped hulls turn rather poorly.
But I haven't actually tried driving an Exiga, so I cannot tell how much of an advantage the DF29 would actually provide in the turns.
Any comments on this?

I guess I have to measure average amp draw on my current setup before making any further inferences.

Regards,
Erik.

[NativePaul]

Testiing by a trusted fellow racer puts the Desires, VB/ETTIs, and Nanotec Aspecs all within 100mAh of each other when new and all just on the low side of 4500mAh at a 10A discharge, the ETTI/VB cells are known for being rather fragile and the hopes are that the Desires or the Turnigy Aspecs will be more robust, but as yet they are too new to say, personally I doubt it, we are managing to squeeze a quart into a pint pot but you don't get something for nothing.

Stepped hulls have improved a lot and are still improving, I think the time has long passed now when an un-stepped hull could make enough in the corners to compete at the highest level in normal conditions, the latest stepped hulls (in no particular order) H&M Speedman, ETTI Envoy, Rauch Essenze, NB Evo, all handle pretty darned well. While there is generally a lift off the throttle before turn in, it isn't a long lift (especially for the Essenze which seems to have the brakes of a F1 car), the corner speeds are still pretty high and I have seen full throttle laps from all of them without going excessively wide.

If you have the DF29 already though don't let me put you off, whether you are competing at the front in the midfield or at the back, FE boat racing is a whole lot of fun I raced for several years before I won a race, and enjoyed every minute of it, a good fight to not come last is much more enjoyable than a clear win.

The setups you mentioned seem ideally suited to the DF29, but would be too low KV for a stepped hull if you chose to upgrade later, how about 1700kv in 4s in the DF29 with a bigger prop which the DF can handle, then if you get hooked and buy a stepped hull you can keep the same motor but run it on 6s with a smaller prop.

What is your current setup? Are you racing now? Where are you from? I guess from the way your name is spelt that English is your second language, thanks for taking the trouble to learn it and well done, your English is very good.

[Erik Aa]

Thanks, Paul, for providing more detail. This is very helpful.
My current setup is 4s1p 5000mah on 2200kv with an x437/3. The hull can clearly handle larger props, so x440/3 and x442 are on their way in the mail.
My set up does not last for 6 + minutes, however, so I think I will upgrade to 6s for next year. I am planning to measure average amp-draw on my current set up later today. I have previously measured peak amp draw on this set up, and the peak is around 112-116 amps.

I'm from Norway, and FE has not taken off in terms of racing here yet, I'm afraid. It's all about nitro and fuel boats.
But I would like to get to do some racing, eventually. Either by trying to get something going here, or by attending some events abroad.
I have also been toying with the idea of getting an Exiga in addition to the DF29.

Regards,
Erik.

[Erik Aa]

Quick update: average amp draw for 4s1p 5000mah on 2200kv and x437x3 was measured to 86,4 amp.

Regards,
Erik.

[NativePaul]

Crikey, that is a thirsty hull, is it running wet? A boat ploughing water will pull more amps than one skimming it, can you move the CoG any further back while maintaining enough stability?

Id the answer to the above is, "no its setup fine.":-

A 2 bladed X438 should get you close to 6 minutes on 4s 6600mAh or 6s 4500mAh, and the remainder would be achievable by cutting it a little, IF it is still enough to push the hull. You are looking to prop up though and I doubt the x438 will be any faster than the x437/3, I would expect you to lose the advantage of the little extra pitch from having more slippage from the lower blade area.

Do you not think it is not fast enough as is? At 86.4 Amps average you are using around 1280 watts at the moment (based on a nominal 3.7v/cell) and getting a 3.5 minutes run time on your 5000mAh cells, with the extra energy of newer cells a 6s 560g setup will net you an average of 1000 watts for a 6 minute run, add a generous 5% for the extra efficiency of the higher voltage, lower amp draw 6s setup, and you are still only up to the equivalent of 1050 Watts. Or if you were to carry on using the same power you are using now it would still net you less than 5 minutes run time.

Going 6s may get you a bigger prop if you go lower than 1470KV enough to drop your total RPM significantly (as would staying on 4s and going lower than 2200KV), and that bigger prop may cavitate less and improve acceleration especially out of the hole, but as you are spinning it slower it would probably lower your top speed unless your getting bad high speed cavitation at the moment, with 1470kv you would still have to prop down to get runtime.

[Erik Aa]

Thanks, Paul, for your insightful comments.

Yes, the hull is running a little wet. I will try to lower the strut a little before my next run. The hull is also rather heavy at around 2,8 kg with the 4s setup (it has a cast in flood chamber that adds additional weight). Regardless, I am becoming more and more convinced that I will have to go for a stepped hull if I want to race competitively under Naviga rules.

I am contemplating an Exiga on 6s 4500mah and 1700kv with 40-42 props...

From what I have gathered, such a set up will make the 6 + min runtime.

Any input on this set up or choice of cells?

Kind regards,
Erik.

[NativePaul]

That was the most popular boat and setup competing at the front of the field around here this year, ETTI Exiga, ETTI/VB 4500, Leopard 3674 1700KV, Tenshock CNC 40-42mm.

Other hulls and setups are capable of being just as competitive.

I listed the top hulls and cells earlier, 36mm 74mm/XL motors from Leopard, Lehner, Mega, Neu, Plettenberg, Tenshock (and Turnegy, if you pick the wheat from the chaff) are all competitive. 100 amp+ ESCs from Castle, ETTI, Himodel, Shulze and YGE are all pretty popular and competitive, I would shy away from Swordfish as they have the reputation of not giving the RPM that the others do, and some have had poor throttle response as in a lag when you lift off but the ESC doesn't for half a second or so, I have had swordfishes myself and not suffered the throttle lag, but have noticed better performance when upgrading. Almost everyone runs Tenshock CNC alloy props and most of those that don't run Graupner carbons, I have heard that Tenshock cloned the Graupner shape so there is little difference in the way they run, but dont know either well enough to confirm or refute this, I only know 2 people still running BeCu props, but while pretty shabby out of the box I firmly believe that if you know what you are doing and are willing to put the work in, you can cut/tweak a BeCu prop into being as good or better and they are tougher than either. I think it would be hard to beat an ETTI ballraced wire drive for propulsive efficiency and they are very popular for sure. Opinions differ on water pickups some using rudder, some through hull and some propwash, there is such a mix up in the results that I don't think its a big enough difference to worry about. I see many different rudders in use, usually from the hull manufacturer but sometimes a generic Chinese one, some have a favoured maker that they use on all hulls, and some make there own. The turn fin is usually homemade, maybe they bought one then used the bracket but changed the blade for one that suited there driving style more than the bought one, carbon is probably the most popular then alloy, glass and stainless. Trim tabs, if you need to fit these you bought the wrong hull or screwed up putting the hardware in, rip it all out and have another go. Servos, digital and very harge mini or standard size speed isn't as important as torque, .15 seconds is fine, popularity is probably Hitec, Savox, Futaba, generic Chinese, JR. Radios are personal preference and budget really, most popular is Futaba then Spectrum take most of the rest, a few use Sanwa/Airtronics, frsky, HK, Traxxas, I don't know anyone that uses it for boats but the Hitec/multiplex 2.4 system is basically the same as FASST so it should be up there with the best for boat use, in if I ever break my Futaba set UN-reparably I will seriously consider switching, on RX cost and TX quality grounds, the only one i would say steer clear of is Acoms, as the only one I have seen had hideous range, couldn't make the back straight or far end of the oval.

[Erik Aa]

Thanks again, Paul. Your inputs are indeed very helpful. I run an etti 150 opto esc with additional caps.

I have one more question regarding 3 vs 2 bladed props.

From what I have gathered, 3 bladed props generate less torque roll and makes the hull more stable in turns (at least for non-stepped hulls) compared to 2 bladed props. Is this the case with stepped hulls as well? However, are 3 bladed props heavier on the amp draw? Do anyone race 3 bladed props, or is it only 2 bladed props that count?

Kind regards,

Erik.

[NativePaul]

Yes 3 bladers limit torque on stepped hulls too, and are used sometimes, but we normally run much higher KV setups than they do in the states, which require smaller props to keep the amp draws in check, and the smaller prop size usually limits torque enough that 3 bladers are not necessary. Prop design helps too, a Graupner or Tenshock has a lot less blade area than the same size Octura has out of the box.