Zenoahphobic

I've spent some time in setting up my Thunder Tiger Desperado and I think I have verified that 6S on a 2000kV requires too small a prop, causing ventilation in cornering etc. That is: expressed another way, the motor requires too many revs (45,000 RPM) to get to power and a prop below 40mm doesn't provide the thrust to push this 1175mm Cat (I always suspected 45,000 RPM is too much).
In this process I suffered extreme heat build up until a very small prop was used.
So I don't wish to willy nilly start to change things incuring large expense on things melting without some advice.
Myquestion is that if I drop the 6sbatteriesfor 4s and used a larger prop to get back the speed from the resultant reduced RPM, would the current increase significantly (bringing back former over heating problems)? I,m asking do these brushless motors via the ESC make the same power at lower voltage? Is there a voltage level where power is maximised?.
The 4072 2000Kv Ace is rated for higher than 6s use, the ESC is a 200A Swordfish- the 120A Swordfish even when used at slow speed setting always shutdown although motor is 150A maximum rated.

lohring

Prop diameter and pitch determine the power required at a given rpm regardless of anything else.  Motor rpm is determined by Kv and voltage.  Loading the motor more will only reduce the rpm a little but will increase the current a lot. 

At a Kv of 2000 4S gives an unloaded rpm of close to 30,000.  On 6S it will be close to 40,000. The running rpm will be around 80% of this.  Model boat propellers in normal nitro and electric applications will usually run between 20 and 30,000 rpm.  This will help get you in the ballpark.

Lohring Miller

Zenoahphobic

Thanks Lohring.
Yes I am familiar with the table you linked to.
I think less battery voltage , ie. change 6s down to 4s will make this work but the power of the motor is also reduced.
I am now purchasing a 1360Kv to run on 6s and hope I don't need to buy yet another bigger ESC.

This project has been no end of difficulties because I had been conned by a store that were not experts at all! I bought this boat that had been repaired sponsoon crash and was set up with new components requiring only battery and radio.
Adding those two did not see the boat go! they had wired the ESC back to front and it went puff. The servo had stripped gears. I replaced the ESC with the same one correctly wired but although boat went this time it overheated and melted connectors(shop installed) and constantly shutdown.I spent more money on new wiring, connectors and bigger ESC. worked but required cooling upgrade and as mentioned smaller and smaller (inefficient) propellors. Still not good so now more money for another motor.

This saga demonstrates that one can have no end of expense, before any joy. I had no idea that electric was so difficult and that there are people selling this stuff without a clue and at least in Australia get away with it because they can con the legal system because they are regarded as the experts and I am just a stupid consumer!

*delete M i k e u p delete*

Do you have any boat clubs near by? I would get hold of them if you can for help. Did you buy using paypal or visa, they can help you get your money back!! I would!!

Zenoahphobic

Mikeup your in the right direction, I tried to post before but lost it.
Local clubs for electric don't exit.

The urge to throw this thru the store window is still very strong!
Bought thru EBay but dispute backfired, he was able to have my feedback removed and his credits restored.
Australian law is that if goods misrepresented or faulty a refund must be given but this guy was able to stall procedings and win !

*delete M i k e u p delete*

Thanks , Paul785!.

lohring

Motor power has nothing to do with rpm.  Input power is easily calculated as amps times volts. You can decrease the voltage and increase the current for the same power.  Output power for brushless motors is around .8  times this to allow for efficiencies.  Propulsion efficiency is the the amount of motor output power the propeller converts to thrust times speed to drive the boat.  This has a lot to do with propeller rpm.

Lohring Miller

*delete M i k e u p delete*

Yes it can be complicated. Example-2000kv 0n 4S = 2000 x 14.8 = 29600 rpm example 1600kv on 5S = 1600 x 18.5 29000 rpm1350kv on 6S=1350 x 22.2 =29750 rpm hope this helps. Also when going to high 6S ; weight of lipo increases, so using a 4S in parallel might be wise for sport running. Cost of lipos and your budget will be a deciding factor!

785boats

Hi guys.
Just back from holidays & saw my name thrown in the mix on this thread. Thanks for the kind words Mikeup. So, I feel obliged to add what little I can to try & help.

Zenaphobic.
Firstly, I feel for you with the dispute problems.
Unfortunately, as you've found, the motor is a bit on the small size for 4s in a boat that big & too high a KV for 6s. I've seen it work well in a Genisis cat on 4s with an M445 prop. But your hull is a bit bigger than that.
What is the actual size & brand of the 1360kv motor you've bought? Is it the 5682 size? You've picked a good kv range for that boat on 6s as you'll see in the attached table.
Your Swordfish ESC should be fine on the setup I'm sure. Just don't over prop it.
What props do you have at the moment? Just so we can see what you have to work with.

Where abouts in Oz do you live? If it's in the Brisbane area, we have a few clubs you can join.

Here's a good table for KV & Voltage on motor selection. Archive it for future reference. You'll use it often for motor selection.

Cheers.
Paul.

Zenoahphobic

Thanks you're confirming I am on the right track. That is a good table.
Like often in life sometimes we get ourselves caught up the wrong path. With hindsight I perhaps should not have bought this. Thought  I was spending wisely but maybe I'm throwing good money after bad because in the end I may get satisfactory performance but the boat won't visually from the outside reflect the money spent.
The motor I have now bought is a Leopold 5682. Of course now I also need a new coupling and mount as well!
I have numerous plastic props of known/unknown actual pitch, and Prathers 215,220,230 and bigger that would probably be too big.
I'm in Melbourne, and I know I should speak ill of anyone, but I will not recommend WirelessHobbiez Melbourne

*delete M i k e u p delete*

I apologize to Paul 785 for typing your name in this mix. Now it won't happen again but you are the most knowledgeable boater in that region of the world who would know the answers, SORRY!

785boats

No No No Mike.
You've got the wrong idea there. Don't apologize. I'm quite humbled that you put my name forward. What I said was sort of 'tongue in cheek'. It is I who should apologize if I made you feel bad. It's all good. Really.

Zenophobic.
When I saw the 1360kv I realised that it was a 56 series motor & that you would need to change the mount.
It's probably too late now but this motor would offer the same power & KV with the original mount.
[link]http://shop.rcboatbitz.com.au/index.php?main_page=product_info&cPath=47_45&products_id=984[/link]
Rc Boat Bitz are a good company to deal with here in OZ. Have a look through their products.

The Prather 230 would be a good prop to start with.

Don't worry pal, a lot of my boats don't look worthy of the investment in them. Either time or money. It's the same the world over.
Cheers.
Paul.

*delete M i k e u p delete*

Paul785- don't worry about. You're still the BEST for info and a real person in my books. I've read and seen on forums where you've gone overboard on info and almost see people are all ears. I'm not trying to make your head real big, just telling what's what. You're like Mr. Pompbled of Sneed,Netherlands who help so many people and glad you do. Take care.

Zenoahphobic

Thanks 785boats.
I have renewed enthuasium, nice to see shop like rcboatbitz with a large range of goodies here in Australia which have been available at overseas countries, although world shopping is becoming more and more acceptable.
230 OK to start with and go bigger from there?
Now to destroy the collet with the broken allen key piece - does anyone know how to get this out so that a new key can be used? tapping, lightly heating and strong magnet no go. The grub screw probably too stuck, have also a seized grub screw in prop collet. I used to swap all these with stainless steel screws from local bolt shop - why can't all collets come that way!
Maybe a topic for a thread.

785boats

I've got the same sort of problem with a coupler myself. I'm going to have to try & drill it out. You might have to do the same but it might ruin the thread in the coupler. If that happens, I'll just tap a larger thread & use the next size up grub screw.
That's all I can think of, so if anyone else has a good idea I'd like to hear it too.

With the prop size, if the heat & current draw is OK then yes try another slightly larger prop.
It also depends on your batteries. If they aren't big enough to supply the power required, then that 230 prop can be considered to be too big. What brand, capacity & C rating are you running & is it a 1P or 2P set up?
I think you will need at least 5000mah at 45C minimum if 1P.

Joe at rc boat bitz is good to deal with. Although some prices may look high, you have to remember that the shipping costs into the country from USA, Europe or China etc have been included. So the prices are only a few bucks more than buying from overseas ourselves. I can live with that.

Cheers.
Paul.

Zenoahphobic

Drilling out grub screws Ok if they are soft but the "store' left a piece of allen key inside the screw - can't imagine drilling that without going off centre and/or burning out some drill tips.
My Lipo's were cheap imports from HongKong. 2 X 5500 mah 35c. I've had LCV problem on last use afterwhich batteries expanded! Recharging still put 5000mah back in, however left fully charged in boat in car and discovered them covered in water and fatter!! Never seen this wetness before and I expect the 60c temperatures in the closed car (30 plus degree days lately) has caused some sort of condensation issue. Bit worried now that these might have ruptured, or are about to and oozing toxic stuff, and might explode. Another expensive cost to replace. Will discharge them,let cool (maybe put in fridge) and check capacity with recharge. Currently on 24.5volts each.

srt10

My Feedback: (20)

sounds like you ran your packs to low
something to watch out for on these high amp boats

siberianhusky

I don't think I'd mess with those batteries anymore, dump them in salt water, let them totally discharge that way for a few days and throw them out!
If you put 5000mah back into 5500mah packs they are finished, the puffing is telling you that.
I'm not sure what collected on the outside of the packs but they would have been at the ambient temperature in the car, they would have to be much colder to cause condensation. Unless seriously abused lipos have some way of cooling themselves due to some chemical reaction. I've never heard of what happened to yours.
Don't risk it, get new batteries. If they were mine I wouldn't even have them in the house.

Old Sloppy

Gather them all up and sell them at the next swap meet.
You don't want plastic props.

Harry