Check my math please...

[tsenecal]

Okay,

here is the situation.

I have an old MRP budweiser electric tunnel hull (22" vacform version) running with the following setup: Aquacraft EP1 outboard, Feigao 540s 8t motor (4700kv), CC hydra 120, hyperion 3s 2200 mah x2, in parallel (11.1 volt @ 4400mah), octura x430. this boat is pushing 50mph when it stays on the water.

it does pull OVER 120 amps, however, so i want to change things around a bit.

my thinking is to go with a Feigao 540s 16t motor (2400kv) and switch the batteries from parallel to serial (22.2 volt @2200mah).

according to FEcalc this will drop me down to 66 amps, but increase my speed from an estimated 49mph to 52 mph.

having said all that, which ESC should i go with? I would no longer need to spend $180 for a CC hydra 120, but what is there in the 70-90 amp range with good quality?

thanks

Tim

[Steven Vaccaro]

The 8 turn doesnt overheat on that setup? How long are your runs?

[domwilson]

Too high on the RPM's on both setups. Feigao motors will not last long hitting those kind of rpm's. You want your rpm's around 27k to 31k give or take. Go with a setup in that range. You should be able to increase your prop size, lower your amps and get better run times and definitely be easier on you drive system.

[tsenecal]

guys,

I am aware that this is the bleeding edge for the motor, the lower unit, and the hull, as well as the ESC.

I am using a cooling jacket on the motor, and water cooling the ESC. heat is not a problem. I am not using the built in BEC on the ESC either. motor and ESC are warm after a run, but not hot.

120 amps is the max during acceleration, but the average is only 60-70. I get 3-4 minutes on a run. I am using 120amps as my spec, because I believe in building this to handle max amps, not average.

as far as props go, because its the EP1 outboard, I can't go any bigger than a x432. the cavitation plate and length of the propshaft wont let me go with a x435, or with a x632.

all I am asking is whether or not I am sane in my assumption that by swapping volts for amps, I can get an ESC that doesn't cost $180+

thanks

Tim

[Simon.O.]

I'll see if I can help here, I have a tunnel that is similar and all of the other power components that you mention.
My tunnel is fine with the 8S (mine is 4400kv) on 2 cell lipo to a 531 prop.
My little rigger loves the 3 cell feed to the 8S motor with a 431 prop.

Back to your boat.
3S to a 8S motor is out there but not outrageous.
You are limited by prop size (dia) so you can up the pitch.

You are correct that trading amps for volts is the way to go.
I am not sure how you have arrived at your Amp figures but I can say your setup should pull 100-110A easily.

If you have the room then drop in a Mystery 200A esc and run it as is out of the packet. They are great and my big rigger will clear 105kmh consistantly with one in there.

My small rigger has the 100A mystery that sits a hair over 50mph consistantly.
That is 2cells fed to a 7S can on a 632 prop.

After all of this I can say this. You do not need a $180 esc to go quick or for what you are after.
Search the bay and you shoul fine some reasonable cost esc's. I have.

[tsenecal]

Simon.O

thanks for the info...

I will look into these mystery 100a and 200a ESCs...

the data comes from both an eagletree data logger, and a garmin GPS used in the current setup, and FECalc to compare with the hypothetical new setup. I entered in the settings for the current setup into FECalc, and got pretty close results for what is really happening, so I assume that the real data for the new setup should also be close.

whose 531 prop are you using?

[Simon.O.]

Simon.O

thanks for the info...

I will look into these mystery 100a and 200a ESCs...

the data comes from both an eagletree data logger, and a garmin GPS used in the current setup, and FECalc to compare with the hypothetical new setup. I entered in the settings for the current setup into FECalc, and got pretty close results for what is really happening, so I assume that the real data for the new setup should also be close.

whose 531 prop are you using?

Eagletree.. Nice to have real world data
The 531 is the purple plastic from octura. They lasted about as long as the flex shaft in my Academy / mrc OB unit.

If I run this tunnel again I will do it with a conventional inboard drive and make a dummy OB to look right.

[tsenecal]

I had similar issues with the original MRP outboard, it too was a flex cable, which would break about every fourth run. I was simply forcing too much energy through it to get to 35-36 mph. the EP1 is two shafts with a bevel gear. It has already outlasted the original in every conceivable measurement.