25" brushless mono motor and esc questions!

[manfish]

Hi all, new here so not sure if this is the right section to post?! anyhow i am after some suggestions which might help me stop cooking stuff!
Got a small shallow v mono running surface drive on 11.1 5000mah and i will admit still struggle understanding motor and speedo numbers! if i put a 4800 kv motor and a 70a speedo everything cooks i dont know how you pair motors and speedos! make sense?! any info appreciated, thanks, Dave

[electric]

Yep that will cook it. Here is some math
11.1volts * 4800kv = 53,280 rpm. This is WAY to high.
7.4volts * 4800kv = 35,520 rpm. Now that is a much better number, but a 3800kv - 4200kv motor would be even better.
Here is the deal for a 25" mono.
You need 11.1volt * 2600kv motor = 28,860rpm. This is a great target rpm number.
I would also get a slightly higher amp esc 100amp - 120amp. This leaves you some room and should be more than adequate for a boat that size. If the 70amp still works then I would just use that.
What size prop are you using?

[manfish]

Aha, now you sound like the person i am looking for! ok so thats a great help as i didnt have a target rpm either! i did do the calculation for the rpm/v at 11.1v i get that bit but now i know a target rpm i am going the right way, so do i need to know the amps i am going to draw at max rpm to choose a speedo that will cope? i dont understand how you get to a 100-120a esc and a 2600rpm/v motor?!!, cheers

[manfish]

Oh, and not sure exactly on prop but very small brass 2 blader!

[Make-a-Wake]

Consider these for 3s:

9L - http://www.offshoreelectrics.com/pro...i-540L&cat=116

ESC - http://www.offshoreelectrics.com/pro...=hef-sword-120

[electric]

The amp thing is a little bit of a combination of things. I am going to try and take a run at it with no electrical engineering degree. The bottom line is the bigger the prop the more load you will put on the motor. The more load you put on the motor the more AMPS you will pull. AMPS = HEAT Watts(Power) = Volts x Amps.

The trick is, from experience, I know with that size boat, with a good target range on the battery/motor combination, you will draw a certain range of amps. For a hull that size 120amps will be plenty. Actually, if you want to push your luck you could drop to 80amp range, but then you have to watch your prop size. The best thing you can do for youself is to get a tool so you can actually see how many amps you are pulling when you run the boat. As you put progressively bigger props on you will see the speed go up and the amps go up with it.

I have tried a bunch of different tools and will recommend a few to you in a later post. Once I started "seeing" what amps I was pulling (along with a lot of other good data) then I could prop up and KNOW that I was not pulling to many amps. Since amps= heat, a lot of people measure the heat of the motor and esc and if they are within a normal range then the assumption is they are not pulling to many amps for the equipment they have. That is a less accurate way, but does give you a reasonable "feel" for how loaded up the motor and/or the esc is. By the way, the other thing you will see when you really look at the amperage draw is that it jumps all over the place. The biggest load is when you are accellerating from a dead stop. Once you are going along at full speed it is much less. Makes sense, as you step on the gas on your car it load the engine and drinks lots of gas. Same for electric motors, but the gas is amps/volts.

Some one can correct me, but an easy thing to remember is no more than 160F for the motor,batts, esc. Not exactly a perfect number, but a good rule of thumb.

By the way the 9L motor and esc recommend above are spot on for that boat running 11.1volts. That would be a nice sport set up.

[electric]

First, you need a accurate way to measure the heat. This is a great tool for that and not to expensive. I still use this tool all the time. After the run, you just point at the battery,esc or motor and you know how warm they are.

http://www.offshoreelectrics.com/pro...od=dh-DTXP3100

Nice basic tool for measuing amps and battery usage etc. It will give you the peak amps you pulled during a given run.

http://www.offshoreelectrics.com/pro...?prod=dh-wu100

Wow, the prices have come down on this solution. This little guy will give you EVERYTHING you will need. With the right add on's it can give you speed, amps, volts, gps location, heat of your motor, esc,....blah blah blah... data overload. Seriously, the nice thing about this tool is you run your boat and then plug it into your computer and can play back the entire run. Has neat gauges and graphs and you can show each run on your PC for the entire day.

http://www.offshoreelectrics.com/pro...PRV4-LEADS-100

There is another one that is more expensive that will handle more amps. All depends on price sensitivity and if you intend to run bigger boats down the line. I can also tell you my 150amp read amperage up into the 180amp range(Peak) with no troubles.

If you go with this solution, I would also recommend :
1. This LCD screen enables you to see the results after each run without a PC when you are out at the pond.
http://www.offshoreelectrics.com/pro...tr-power-panel
2. Of course you want to know how fast you are going!
http://www.offshoreelectrics.com/pro...rod=etr-GPS-v4

Of course if you just buy the basic item for 50 dollars or so, you will have amps,volts and some other stuff. You can get the rest of the stuff whenver you want to.

[manfish]

Awesome! now we are getting there! you have given me a good idea for rpm and running temparature so i'm well on the way, i have a watts up meter but hav'nt got that involved yet, also got a point and squirt temp gun as i run ic cars and now i have an idea of what temp range i should be in i can use it! i do have an rc log data logger for the pc which does all that blah blah blah but again one of those things you buy because it will be useful and don't have any idea what information i should be looking at if i did use it! will check out the 9l motor and esc thanks for all info, i feel as though i have a very good starting point now, will keep you guys posted on testing! cheers, Dave

[electric]

Good luck Dave, sounds like you have a pretty good background and knowledge already so you should pick it up fairly quickly. There are a lot more people on this forum with a great deal more experience than I, so keep asking and people will answer. There are some slick charts some people did on rpm's and other items, but I never can seem to find them when I need them. Also, take a look at the "Tips and Info" section outside of the forum page. It actually has some nuggets of good information here and there.

We kind of stuck with your 11.1 volt battery in your example because that is what you have, but just so you know there are more options. A common setup tends to be a 14.8volt (two 7.4volt batteries) and then a 1800kv to 2200kv motor. You will see several good motors for this (SuperVee Motor,UL1 Motor) both from aquacraft. I have run it in boats simliar in size to yours and they are fast. Generally they go in boats in the 25" - 30" range.

[manfish]

Yea, well sort of got some idea, but ofcourse my only knowledge with brushless/lipo stuff comes from racing 1/12th pan cars and the gearbox tends to keep the melting to a minimum with the cars! Thanks again for all your help, i am happy i can put it back together now and should run cool! as i said atleast i know what i need to achieve now! i'll let you know how it goes!

[Make-a-Wake]

Glad you are on the right track now!! Keep all temps below 135*f.

[manfish]

Hi guys, As i said i would keep you posted on testing so here goes! Have managed to set up with 120a esc and 2600kv and temps are staying down, still on 11.1 with a 30mm 3 blade prop although to get it going anywhere near fast i have had to go up to a 37mm prop and the motor (at wire, can end) is getting too hot, the lipo is staying as low as 25 deg C the esc is running around the 35-40 deg C mark but the motor getting up to around 85 deg C i am gessing this is over propped but thought also if it was, the esc and lipo would be getting hot aswell?! i do have a new cooling jacket so going to try that but could anyone suggest a prop (dia and pitch) that would be suitable for this setup please, maybe even a few in close range? By the way, although the motor is a little warm i hav'nt fried anything yet so onto a winner!! Thanks, D

[Make-a-Wake]

Did you end up buying a Feigao............540L? Do you have seperate cooling lines? If you have one cooling line how is it routed? Is there good flow from the water exit? Any binding in your driveline? Are your connectors of good quality and large enough(4mm min.)........??????

[manfish]

Hi sorry, not been on for a few days, Ok no i didnt buy a 540 as i am using 28mm can dia 380-400 size? anyway cooling is up through the rudder straight to the motor, motor jacket to motor mount to esc then out with good constant flow from outlet, even at low speed, so i think cooling is o.k?! i have since started to run the boat on the 30mm prop and its not getting so hot, but ofcourse its not so quick!, however i have found the data logger and instructions now so will continue fiddling with it and get some info so i can tell you guys some actual details and we can go from there!! looking forward to finding out what its actually doing under load! Oh driveline free as a bird and im using 4mm banana plugs esc-motor and deans plugs lipo-esc