Have a couple of questions

[mtnbikefreak]

I'm setting up a ep rigger. size is about 26"

Need to know the common config to get it running fast.

a) Some people using outrunners, some inrunners. I'm concerned with heat issues, so will an outrunner do without cooling ?

b) What kv of motor do u guys use typically ? Been seeing people using 4200kv on youtube with about 30amp esc. But won't that generate more heat since the torque is less running at so high kv ?

c) Prop dia and pitch ? The prop shaft is 5mm, so what size of prop is a good start ?

[Doraemon]

I'm no EP expert but you can check out the motor/esc/drive/prop set-ups that Adrianli and Frank have used on their Cats for guidance (see their 30" Cat thread). They have a lot of "R&D experience" with high power and high amp BL set ups

[Adrianli]

U should be looking at 540XL size type of motors. The motor KV depends largely on the number of cells u wana run it. Amp draw depends on ur type of prop.

[mtnbikefreak]

I went to JH today, saw the prop as listed below :

http://www.jethobby.com.sg/cgi-bin/ezsite/prod/manager.cgi?action=show&pid=857&cid=48&idx=41

Think it's an Ocura 825 prop

Looks pretty big. I'm pretty concerned about the amp draw. Say, if i use a 550 motor 2600kv for a 26" outrigger as shown below, with that prop, what's the current draw going to be like ?

I feel that i am going to burn that motor with such a large prop, but the drive shaft is using a m5, and the one at jh is meant for gas engines.

Any suggestions ?

[Adrianli]

As per previous post, u need a 540XL BL motor or 700 or 800 size brushed motor to have sufficient torque to push the boat.

A 550 motor will burnt in no time.

Prop size is trial n error, go for small prop n work ur way up.

[Adrianli]

Hi,

Went n help u do a little research, here is wat I would suggest for a 26" rigger :

1) Feigao 9L 2731KV brushless motor n need a water jacket

https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=4882

https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=4887

Alternative : tis one comes wif water jacket

https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5146

2) Octura X432 or X632 prop and work ur way up the dia.

3) At least a 70A ESC

4) Get a 1/8" prop shaft wif flex cable hardware like tis : http://www.offshoreelectrics.com/pro...t-oc6str-130da



As per PM, u wanted to run on 3S lipo, this above setup should give u 40mph as fast as my Cat. Tis above setup will draw at least 50-60A easily, so do use a good lipo pack. A single 3S1P 2200mah 20C lipo will be smoked big time.



Thatz all the advise I can give, its all up to u now. Happy building.

[mtnbikefreak]

Thanks.

Yeah the 5mm drive dog would have to go or else i would see another motor in fumes. I'm dropping to a 3mm for now. The 3rd motor with the inbuilt water jacket looks familiar, u were using that right ?

One more question, If i use a smaller prop compared to a bigger prop to drive the 26", a smaller prop would mean that the rpm is higher when in the water right ? Would i suffer from a significant speed loss than running on a bigger prop at lower rpm ? Taking into assumption that the motor and esc are within ratings, and amp draw is not an issue.

[Adrianli]

Big or small prop, rpm is the same!!! RPM is determined by ur motor n batts.


Big prop = more thrust

Small prop = less thrust


Big or small prop, depends on the type of boat n size of boat. Always start wif a small prop. Learn to walk b4 learning to fly. Pitch of prop also play an important part too.

More reading up for u................


Yup, that motor was sucessfully used in the 26" Yamaha boat wif 3S2P lipo batts running wif a 80A ESC. Sold it off after I had my fun.

[mtnbikefreak]

Erm the link below says that it does affect the rpm a little depending on the dia and pitch of the prop.

http://www.a1discountprop.com/propinfo.htm

Now i am confused. Is it a very small difference ?

[Adrianli]

That site refers to real boats.


For fast r/c boats, I'm toking abt 30,000rpm range till very high speed 50-60,000rpm range. U want the required rpm, increase the throttle, the prop will still turn at that rpm. However ur amps will increase also lah. According to the site u posted, difference is 200rpm. 200 : 30,000 = 0.006666667 difference. Can u tell the difference??? (I need a vomit blood emo-icon)

U want, u can also get a governor n set the rpm u want. Tis one, really professional liao.