help

[bigd]

i need help with a problem
i built a cat which is 23 inches long by 8 1/2 wide made from ballsa
i am running a venom fireball 19 turn modified 540 car motor with a 35 mm 2 blade prop and a 6 cell 1800 mah venom batt this is geting me about 15-20mph
but top speed only lasts about 20-30 seconds then it starts to slow and 0nly about 1.5 mins till about dead
allso the motor gets extreemly hot on y last run the wires to the motor came off cause the solder melted
any ideas

[JimClark]

too big of prop?
big time friction in the drive line?

Jim

[ReddyWatts]

Battery Mah rating (times) 0.06 (divided by) run time = average motor load in amps

1800 Mah rating (times) 0.06 (divided by) 1.5 minutes = 72 average amps

[bigd]

i dont think the drive line is binding but will go over it to check
the prop i have on is the smallest that my local model shop has
i am running direct drive should i gear down an use a bigger prop
75 amps sounds a lot
should i go for a bigger battery
thanks for all coments

[JimClark]

wouldn't it be cheaper to just order a couple smaller props that buy a gear drive?

Jim

[ace028]

If it was me, and I was running brushed, I would probably use a trinity monster or a P2K 27 turn, and a at least 3000 mah battery. I used to use the venom 3000 batterys, they arn't too bad for the price. That would keep your amp draw down, and if your temps are ok, then you can prop up. But for sure I would get rid of the 1800's and get some 3000 or higher. And order a smaller prop. Pics?

[Avanti]

venom batteries will end up making the inside of your boat smell funny
you need a smaller prop for sure

[bigd]

thanks for the info guys
i will get new batt and props next weekend to give it a try
heers some pics hopefuly

[ReddyWatts]

The prop looks to be mounted to deep in the water. I would raise the strut way up until only 1/2 of the prop is running in the water. This will lower your amp draw a lot, give more top rpm and speed.

[Avanti]

yes if you can raise your strut out of the water a bit you need to do it. your shaft should be no lower than the bottom of the sponsons.

the hull looks great, nice job on the build.

[ace028]

I would also switch to deans connectors. Do you have a hatch for it? Looks pretty nice btw.

[bigd]

raised the prop shaft to just above the bottom of the sponsons will post some pics
let me know if it looks right

[ace028]

I'm not an expert, looks better but I think it is still too low, and you might have too much down angle of the prop. Also check your center of gravity, it should be approx 30" from the transom as a good starting point.

[bigd]

hi guys i have raised the prop a little bit more so the bottom of the hub is about level with the transom. the angle is still quite steep as i am using a solid shaft .
i took it out today but going slower than before and the transom is not getting on the plain so the prop is not coming out of the watter
thanks for any replies

[Simon.O.]

My 2c worth. I build my own and run brushed too, slowly moving to BL
1800 mAh pack is not really enough.
A 19t motor and a 35mm prop are not friends.
That prop looks similar to a brand i have used and are for submerged drive, they will cause you headaches.
Octura make a line of plastic props that are a few $ each. 431, 531, 534, Grab one of each and start with the 431.
These have a 1/8 centre and I would guess that you have a 4mm threaded shaft. this will take a little to overcome.
Solid shafts can work but you will be far better going to a flex or wire setup. it give a better thrust angle and allows for a lot more adjustment options.

Trust me, I have used crap props and solid shafts and now have seen the light.
There is a lot of information here and most of the guys are keen to help.
I love seeing hom mead balsa hulls as my shelves are covered with them.