Amp Draw Issues...

[mars]

Hi All,

I am running the following setup in a Graupner Systems Cat:

Feigao 540 12XL
Turnigy 180 ESC
Turnigy 5000Mah 20c 6s
x440 prop
I do have a slight "S" bend in my flex shaft as a left over from my brushed power system.

I did a test run and the boat flies! I did 1-2 minute runs and checked temperatures. After the first run I was at 105F. After the second run I was at 135F. I waited for the temps to drop to 120F and did another run and got to 140F. All temps were taken on the end of the shaft.

I would like to be able to run a full battery without worrying about temps but do not feel comfortable with my temp rise numbers (ambient was 68F).

So, I can move my balance point back a bit to get the hull up a bit but will this help amp draw a lot? If so great!

I notice that I get about 6' of cavitation on startup but then the boat takes off on plane. Can I reduce my prop size to an x438 to try to reduce amp draw? Does it make sense to detounge my x440?

Finally, I notice I get no rooster tail at all when running fast. The bottom of my strut is about 1/8" up from the bottom of the sponsons and parallel to the bottom of the hull. Should I raise it up a bit? Will this help amp draw at all? Will this cause more cavitation?

Any advice is much appreciated,

Mars

[blackcat26]

6' of cavitation is alot. I'd say your either underpropped, overweighted, COG is too far forward or overtimed (pardon the G W Bush terminology). How much does your boat weigh RTR? What timing are you using? Too much timing and a small prop and an overweighed boat can make some heat. Also check your center of gravity needs to be in the 28-33% range.(measured from transom) With it too far forward your boat will run "wet" and run up some extra amps in the process.

[mars]

More Info!

Thanks Blackcat26

More info:

- CG is at 33% - I will move this back to 28% by moving the batteries.
- My RTR weight is 5.6 lb - This does not seem really high to me for a 29" cat - but I am a noob...
- I have my timing set to 15 deg. - should this come down some?
Regarding the prop - could a larger prop draw less amps or does it always draw more (my assumption is that a larger prop always draws more amps...)?

Thanks again for your help - I hope to move CG back and, if needed, change my timing tonight and run tomorrow.

As an aside, in my reading here on the forums, it seems that LOWERING my strut might make my hull run dryer. Is this right? If so, should I consider lowering my strut until the bottom of the strut is in plane with the bottom of the sponsons?

Mars

[ReddyWatts]

This hull has built in trim that is turned down in the last few inches of the sponsons. Some users have modified the hull and taken this out.

Did you water cool the motor and esc?

[mars]

Water Cooling and Trim

I have a full jacket on the motor with one intake and one outlet. I also have water cooling on the esc with one intake and two exits. When running I can see the water coming out of all three outlets.

I did not take the trim out of the hull...I have my strut set parallel to the bottom of the hull in front of the last two inches, which are angled down a couple degrees.

Thanks!

Mars

[blackcat26]

15 deg timing is fine. I think you either need a bigger prop of like reddy stated it may be hull design. Remeber that brushless motors need some load on them. If you have a 442 or a 642 laying around try that. Make a few passes and bring her in and temp her.

[mars]

Prop Size & Strut Angle

I will move the CG back to 28% and run tomorrow. If this does not bring the temps down and decrease the cavitation i will try an x642 I have on hand to see if this brings temps down.

To fine tune the strut height should I lower it or raise it to start? I notice most FE boats have a good rooster in most videos - mine has none. I assume this is an indication of something and have a hunch that whatever is wrong may be causing high amp draws and high temps...

Just a thought - I am assuming that the built-in trim on the hull tends to push the nose into the water. Can I angle the strut ever-so-slightly up in the back to counteract the wetter running the hull trim is causing? Or will this make the hull hard to control?

Thanks!

Mars

[blackcat26]

Do you have a pic to put up so we can see this baby? I have never heard of this boat before. I'd set the boat on a flat surface like a window or glass table or a good pc. of mdf. Then set the strut level with the board/glass. This should be a good starting point.

[blackcat26]

Oh sorry didn't read close enough yes prop tail up in the back will raise the bow. Down in the back just the opposite.

[mars]

Pictures

This hull is an ABS vacu-formed hull that I got when I was a kid (20+years Ago). I added carbon and kevlar cloth to the bottom and made the canopies out of painted soda bottles.

In the picture I have lowered the strut about 1/16" so it is about 1/16" above the bottom of the sponsons.

I will test again soon with the CG back and the strut down just a bit, as shown.

Interesting thing - I charged the batteries after (4) 1-2 minute runs and I only put 1600Mah back into the batteries.

Mars

[mars]

Update - Still Hot But...

I ran about 4-5 minutes and my motor shaft temp is 135F. Is this about right or should I be able to run longer before my temps get this high?

I am thinking about taking 1 cell out and running 5s - will this help keep temps down?

I was running in some pretty choppy water so I was at 1/2-3/4 throttle most of the time as if I went to full the boat was just too unstable.

Thanks!

Mars

[blackcat26]

Good question. Seems a little hot still. Looking at the pics again the water pickup may need to be lowered just a little. If that does not work you can try dropping the timing back a notch to the 10-12 range. Are you using the 642 now?

[Make-a-Wake]

Something seems a bit off, I ran the same exact motor on 6s in a 31" mono with an x640 and temps were always 110-115 max. Did you try the 642, may be a bit much, do you have a 442?

[mars]

Thanks Guys!

I am still using the x440 BUT I am not using a thrust bearing - is one required at these power levels?

I see a good stream of water coming out of the motor cooling exit so I do not think it is a cooling system issue...

Will lowering the timing make a difference - maybe I should drop it down to 10-12 degrees...

If you think a thrust bearing will help I will order one.

Any and all help appreciated...

I will try the x642 tomorrow to see if a bigger prop could help...

Mars

[mars]

Rookie Mistake

Hi All,

I finally got out to run again after doing the following:

Changing to 5s
RAISING the strut so the bottom of the strut is 1/8" above the bottom of the hulls (now I get a really great looking rooster tail!)

I did a 2 minute run and got 100F
I did another and got 130F...what the?

Then a friend pointed out that I have the motor cooling hooked up to my secondary water pickup and the ESC hooked up to my rudder pickup.

I let everything cool to about 80F and swapped the water pickups. I immediately saw AT LEAST twice the water flow coming out of the motor-side outlet! (Thanks Blackcat26!)

I ran 2 minutes and hit about 115F. I then ran 3.5 minutes and hit 120F. So, from ambient (65F) I should be able to run a good 6-7 minutes at least.

I think I am getting about 30-35mph - plenty fast for me!

This boat if finally working out! Now that I seem to be getting everything working I will make some runs as is and then start tweaking. If all is well after a few runs I will try the x642 (I am still running an x440 now).

Then, If I am feeling the NEED FOR SPEED I may try 6s again for 2-3 minute all-out speed runs!

Thanks to all for your help!

Mars