Total Newbie Questions

[rake]

Dear forum !

I hereby appologise in advance for my pure ignorance and inability to digest the plethora of information present on this and other forums with respect to the art of FE Models !

I have taken a leap of faith and indulged myself and my son in the aquisition of the Micro Hydro by the name of Small bolt and am now eager to learn the basics of how NOT to blow up motors, cells and ESC 's.

To this end may I ask to pick your brains and guide me into this sport safely ?

The Setup =

Motor: 2604KV water cooled brushless in-runner with aluminum water cooled motor mount

ESC: 50A with water cooling jacket with BEC

Drive system: collet, 1/8" flexi cable, brass tube, teflon lining, teflon washer, 30mm nylon propeller, prop nut, tail nut, aluminum strut

Rudder: 50mm aluminum

Trim Tab: aluminum with stainless steel plate

Cells I propose learning with are 2S 2450mah 30C (Intended to keep speed down while I learn, I then intend to go to 3S 2450mah 30C)

My Questions are as follows.

1) How do I work out what the current draw will be from the motor ?

2) How do I work out the run time of the setup above ?

3) How do I work out the limits of the ESC / Cells / Motor in order to avoid fires and other unwanted ocurrances !

I guess this is all pretty basic stuff but I seem to get swamped with too much info when reading on the web.

I kinda worked out that the cells will give 8.4V fully charged and
at 30C will yeild 73.5 amps

but further to that I'm pretty lost !

Any help greatfully received.

Many thanks in advance.

Rake !

[PDR447]

I'm kind of going through the same thing currently(just getting into FE). From what I've gathered the only way to estimate what you are going to pull is "FEcalc". It's an app that was written years ago from what I can tell so it's accuracy is questionable imho. Besides that the only real way to test is a either a data logger or a watt meter(http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXLMV0). The issue with the watt meter is it doesn't log data, so the best you can do is hold the boat stationary in water and hit the gas to see what it pulls. Data logger(like eagle tree) is better but it's also a lot more $$.

From my limited knowledge your setup seems fine as long as you don't have a super steep pitched prop.

[rake]

Many thanks for the reply PDR.

I see many post with basic calcs for stuff like selecting the rith cells and power for a given motor, run times etc and that what I was trying to get my head around.

Say for example if I up the cells will the ESC take it...

I probably have more reading to do !

Cheers.

[hyrulejedi86]

Hello and Welcome to OSE. There is undoubtedly a pleathera of information here as well as alot of well seasoned FE builders and racers.

Do you have some more information about the boat you got? Is it the hobbyking small bolt?
http://www.hobbyking.com/hobbyking/s...dproduct=11244

If so it looks like a fun little boat but if you read the comments on hobbykings page then people who have used it have added lots of good info there. If it is at least similar to the one you have it will still help.

as for your questions:
1) You need some stats from the manufacturer to know what the motor can do, according to hobbyking it requires at least a 30A ESC. So assuming 30A is the continuous amp draw then you can use that to figure what kind of watts the motor will put out. 30A x 11.1V (3s lipo)=333Watts. If you decide to go with a 2s battery instead of 3s then 333W / 7.4v (2s lipo)=45A. (I used the formula Watts=Volts x Amps)

2) You can use that calculator that you were talking about with this information and get pretty close to your real runtime. But of course anything can change that even the selected prop. Someone on hobbyking said with a 3s battery they were getting 5-10 minutes of runtime.

3) When choosing an ESC to go with a motor you would like to have 20% above the motor amp draw. IE if a motor will draw 100A then you want AT LEAST 120A ESC but more is always better. I would feel better if it were me and I were using a 100A motor to have a 150A or bigger ESC. Same idea applies to the batteries. You have to figure out what their safe constant discharger current is, which you did for the cells you were looking at, and make sure that they are also above the amp draw of the motor to help keep them running cooler during amp draw spikes.

Hopefully some of this was helpful and feel free to continue to ask ?s.

[rake]

Many thanks hyrulejedi86,

Thats great info. I'm sure I'll have more ?'s but for the time being thats all.

Once I get the boat through and start messing I'm sure it will provoke more questions.

Its blowing force 10 here right now so not quite sailing weather !

[Eodman]

Welcome aboard, First thing understand we were all where you are once a while ago. Hell some of us(me) are still learning!

Please do not hesitate to ask your questions, don't burn something up because of an unasked question!

I only ask ONE favor, PLEASE DO NOT SWIM AFTER A DISABLED BOAT! If you must --- put a life vest on! We don't want to read about another Father or Son having drowned because common sense was not used!

OK I will now get down off the stage and let you ask all the questions you want!

Thank You I'm here all week!

[rake]

Welcome aboard, First thing understand we were all where you are once a while ago. Hell some of us(me) are still learning!

Please do not hesitate to ask your questions, don't burn something up because of an unasked question!

I only ask ONE favor, PLEASE DO NOT SWIM AFTER A DISABLED BOAT! If you must --- put a life vest on! We don't want to read about another Father or Son having drowned because common sense was not used!

OK I will now get down off the stage and let you ask all the questions you want!

Thank You I'm here all week!

Dont worry and thanks for the sanity check !

I've been doing watersports for quite some years and I'm aware of the safety aspects :)

Boat has new arrived and figuring out the setup !

Cheers.

Ron.