8s build help

[srislash]

what lipos do you use with this set up, I have a similar se t up now.
I have two sets of 3s 6000mah 50c that can not keep up and two have puffed up.
I have one set of 3s 5000mah 70c they do better but still see a drop in voltage to 19.0 v and amps up to 350 @ 100% throttle

How long have you been running? More than 4 mins is likely too much. This is very often the cause of puffy batteries.

[Crash]

How long have you been running? More than 4 mins is likely too much. This is very often the cause of puffy batteries.

Ok. That is a really short run time.
Would I let them cool then recharge or run them again for 4 min or lvc?

[Crash]

How long have you been running? More than 4 mins is likely too much. This is very often the cause of puffy batteries.

Would a 8s set up provide longer run times.

[srislash]

As stated above running the same prop and rpm yes. If you run the same mah. Say you have 4s 5000mah, if you go to 8s 5000mah your run time should nearly double. But you also double your battery weight so that comes at a sacrifice.
There is a balance to it.
I tend to lean toward HV stuff and therefore mostly run smaller mah cells because I can ‘pack them in’ better.
Just google HV RC and you’ll find more on it.

This understandable? I’m not too technical in lingo, I’ll leave that to Craig. Haha

Shawn

[srislash]

Oh and let me further add, weight can mean little in a boat once on plane. If a lot of start/stop and sharp corners runtime will suffer with a heavy boat. So it depends on driving style and area to run.

[madmikepags]

OK higher voltage setups are more efficeint, My 2S rigger pulls almost 6000mah in a minute and 10 second race, My 10S rigger uses a little over 3000 mah for the same race time. Also what Brand of batts are you running? 50C 70c doesn't tell me much. If you are going to be running hot setups good batteries are a must. Try Giant Power batteries, the new Graphene cells are pretty amazing, if I were you I would use 2 6S or 8S 5000'mah in paralell, If you are going to be running a 6-8 cell setup I would recommend a bigger hull, 33" gets pretty small when using 6-8 cells. The way to do it is to parallel your cells so you have double the Mah. This is not necessarily to get more runtime but to put less stress on your batteries. When you have 10,000 mah the cells dont work as hard and you have less voltage drop under load. I would recommend using NEU motors, but if its too steep for you, TP motors are a very good alternative. When I am building a new boat (and I have built many) I have a few guidelines. For any cell count 4S 6S 8S and 10S I have RPM range that I shoot for which is between 27 and 32,000 rpm. so 4S= 1800-2200kv, 6s=1250-1400kv 8s=100-1100kv and 10S=780-850kv.These are tried and true setups very safe and fast if you do your homework and use the right equipment. I also try to use a hull size to fit the power. If you use a 8S setup in a 33" boat, the correct prop for the RPM will be way too big for the size of the hull, and therefore the hull wont run properly. For 6S I would recommend a 38-40" hull and for 8s 40"-44'. And so you know you cannot just go higher voltage with the same motor and prop, you need to change either your Kv of your motor or your prop size, with all things being equal, for example an 8S setup turning 30,000 rpm will be much more efficient than a 4S setup turning the same rpm. The 8S will also be faster because you will have more power, and less voltage drop under load. There are so many diff variables though, prop, driving style, type of hull, CG, the way the boat is trimmed etc etc....

[Raydee]

OK higher voltage setups are more efficeint, My 2S rigger pulls almost 6000mah in a minute and 10 second race, My 10S rigger uses a little over 3000 mah for the same race time. Also what Brand of batts are you running? 50C 70c doesn't tell me much. If you are going to be running hot setups good batteries are a must. Try Giant Power batteries, the new Graphene cells are pretty amazing, if I were you I would use 2 6S or 8S 5000'mah in paralell, If you are going to be running a 6-8 cell setup I would recommend a bigger hull, 33" gets pretty small when using 6-8 cells. The way to do it is to parallel your cells so you have double the Mah. This is not necessarily to get more runtime but to put less stress on your batteries. When you have 10,000 mah the cells dont work as hard and you have less voltage drop under load. I would recommend using NEU motors, but if its too steep for you, TP motors are a very good alternative. When I am building a new boat (and I have built many) I have a few guidelines. For any cell count 4S 6S 8S and 10S I have RPM range that I shoot for which is between 27 and 32,000 rpm. so 4S= 1800-2200kv, 6s=1250-1400kv 8s=100-1100kv and 10S=780-850kv.These are tried and true setups very safe and fast if you do your homework and use the right equipment. I also try to use a hull size to fit the power. If you use a 8S setup in a 33" boat, the correct prop for the RPM will be way too big for the size of the hull, and therefore the hull wont run properly. For 6S I would recommend a 38-40" hull and for 8s 40"-44'. And so you know you cannot just go higher voltage with the same motor and prop, you need to change either your Kv of your motor or your prop size, with all things being equal, for example an 8S setup turning 30,000 rpm will be much more efficient than a 4S setup turning the same rpm. The 8S will also be faster because you will have more power, and less voltage drop under load. There are so many diff variables though, prop, driving style, type of hull, CG, the way the boat is trimmed etc etc....

Very good post.

[larryrose11]

The other advantage of higher voltage / lower amperage setup is on the batteries. The 30C batteries in general, have better durability than the 60+C batteries.
Another aspect is energy density, or Watt hrs / kg. The lower C ratting batteries in general have have higher energy density. I Not always true, but in general.
I made a spread sheet to calculate that *!***!***!***!** out, but I.m a nerd.

[CraigP]

Larry is dead on! I’ve got 1700kv motors in my 6s boats.

This is not correct, I have 1400kv motors in my %6s dual motor hydro and 1450 in my 6s Cat. I tried a 1700 in the Cat, but the hull liked the slower speed/bigger prop combo rather than vise versa. Sorry for the confusion. I agree with MadMike’s design targets very much and use the same.

[Crash]

OK higher voltage setups are more efficeint, My 2S rigger pulls almost 6000mah in a minute and 10 second race, My 10S rigger uses a little over 3000 mah for the same race time. Also what Brand of batts are you running? 50C 70c doesn't tell me much. If you are going to be running hot setups good batteries are a must. Try Giant Power batteries, the new Graphene cells are pretty amazing, if I were you I would use 2 6S or 8S 5000'mah in paralell, If you are going to be running a 6-8 cell setup I would recommend a bigger hull, 33" gets pretty small when using 6-8 cells. The way to do it is to parallel your cells so you have double the Mah. This is not necessarily to get more runtime but to put less stress on your batteries. When you have 10,000 mah the cells dont work as hard and you have less voltage drop under load. I would recommend using NEU motors, but if its too steep for you, TP motors are a very good alternative. When I am building a new boat (and I have built many) I have a few guidelines. For any cell count 4S 6S 8S and 10S I have RPM range that I shoot for which is between 27 and 32,000 rpm. so 4S= 1800-2200kv, 6s=1250-1400kv 8s=100-1100kv and 10S=780-850kv.These are tried and true setups very safe and fast if you do your homework and use the right equipment. I also try to use a hull size to fit the power. If you use a 8S setup in a 33" boat, the correct prop for the RPM will be way too big for the size of the hull, and therefore the hull wont run properly. For 6S I would recommend a 38-40" hull and for 8s 40"-44'. And so you know you cannot just go higher voltage with the same motor and prop, you need to change either your Kv of your motor or your prop size, with all things being equal, for example an 8S setup turning 30,000 rpm will be much more efficient than a 4S setup turning the same rpm. The 8S will also be faster because you will have more power, and less voltage drop under load. There are so many diff variables though, prop, driving style, type of hull, CG, the way the boat is trimmed etc etc....

Thanks for all that great information very helpful
The batteries are HRB 6000MAH 50C THAT puffed up.
With this boat I like the way a 50mm prop. Throws this hull around, the amp draw is 350+ which is hard on the lipos
The smaller props 45mm + are working too hard and going slow 40mph range.

[madmikepags]

what is your average amp draw for your run? it cant be 350 amps? you would only be able to run for less than 2 minutes on 6000mah? If you pulled 100 amps continuous you would get max runtime of 6 minutes on 6000mah cells. at 200 amps only 3 minutes of runtime, and if you use Peukerts law of battery efficieny (which gives you more accurate calculations) it would be even less.

[Alfa Spirit]

Your setup is a typical Enduro range/category setup made for long time runs and speed near 80 km/h, if you want to run faster you need a big propeller so look at the ESC and the battery, be careful.

[Crash]

what is your average amp draw for your run? it cant be 350 amps? you would only be able to run for less than 2 minutes on 6000mah? If you pulled 100 amps continuous you would get max runtime of 6 minutes on 6000mah cells. at 200 amps only 3 minutes of runtime, and if you use Peukerts law of battery efficieny (which gives you more accurate calculations) it would be even less.

true, the average is not 350 . 350 is its max draw at 100 % throttle for just a few seconds. The rest of the time say below 80% throttle the amps are down near 100 amps
thanks for all your help guys. I will test run it today and get a data log for us to kick around and see what it tells you guys....
also, going to run my smaller props to see if it still bangs the amp draw still. I have a 645 from Dasabota to try

[madmikepags]

There are a couple of things to do when changing props, when going to a smaller prop there is less prop and more hull in the water, you should try to run your boat a little looser with the smaller prop and you should see your average amp draw drop. Also if you're doing a lot of stop and go the small prop will draw more amps at start up b/c its working harder to move the same hull, but overall amp draw should be less w the smaller prop. Something to keep in mind when running at 1/2 to 3/4 throttle your boat is not up on plane and therefore more boat is in the water and therefore more parasitic drag, so running as close to full throttle as possible in the straights is most efficient, you will spike amp draw in the corners.

[Crash]

There are a couple of things to do when changing props, when going to a smaller prop there is less prop and more hull in the water, you should try to run your boat a little looser with the smaller prop and you should see your average amp draw drop. Also if you're doing a lot of stop and go the small prop will draw more amps at start up b/c its working harder to move the same hull, but overall amp draw should be less w the smaller prop. Something to keep in mind when running at 1/2 to 3/4 throttle your boat is not up on plane and therefore more boat is in the water and therefore more parasitic drag, so running as close to full throttle as possible in the straights is most efficient, you will spike amp draw in the corners.

I raised the strut to get the font end up and get some air. today went pretty good in comparison to past runs although in a 5 minute run I did hit the 255 amp mark again. the boat ran 55 mph but, it is handling really bad since I raised strut. on top speed the boat starts dancing on the tail side to side, i bet there is more speed left on the table due to the fact I am shutting down before it wrecks. I only brought one set of packs so, didnt lower the strut yet.
I really wanted to get a fresh data log with one of my smaller props for a fresh look at data it logs
the brief 255 amp draw is at 1833.00 seconds.

255ampdraw29krpmwtf.jpg
255ampdrawwithrpmdata.jpg
august27.jpg
votageadded.jpg