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Old Jan 19, 2013, 12:53 PM
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bentech's Avatar
Canada, QC, Brossard
Joined Jun 2006
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Help!
rear stabilizer

Hi guys !!

I have a traxxas blast ''fisrt model'' and i have put a mild brushless set-up in it. it work fine but the only problem is i can't give more than 1/2 throttle because the boat bounce too much and will flip over. I dont know that much about RC boat but i think that i can fix this by addind 2 stabilizer on each side of the hull in the back.

Is some one can tell me what should i use and also what size and where exactly to put it on the hull

thanks!!
Ben.
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Old Jan 20, 2013, 04:33 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
4,955 Posts
Hi Ben,

Could you post some pictures of your set-up and list what exactly you put in the boat?

The Blast is designed for a mild brushed set-up and converting it to brushless entails more than switching the motor.

I've looked at a number of video's of this boat and it already porpoises when running the stock set-up...
Making it faster may make that worse to the point where the boat becomes undrivable, as you've experienced.

On top of that, the steering outdrive isn't really something you'd want on a fast boat, a universal coupler isn't something to use on a fast electric.

Please add some pictures showing the keelline (sideview), if there's too much of a curve, making it faster is going to end in disaster.

If by stabilizers you mean trimtabs, they reduce the porpoising, but also add considerable drag, slowing you down.

"Trimtabs are a bandaid for a poor set-up".

Regards, Jan.
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Last edited by pompebled; Jan 20, 2013 at 04:56 AM. Reason: typo.
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Old Jan 20, 2013, 08:18 AM
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Canada, QC, Brossard
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Thanks for your awnser. heres some picture of the boat. I tought by addidng 2 trim tab it would help from bouncing at higher speed !!! I dont want to made a speed demon out of this boat but only make it go a little bit faster than it was with the stock set-up. I use a 540, 2800 Kv brushless motor combine with a 2s 30c 5000mah Lipo battery. i wanted to add those trim tab:
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Old Jan 20, 2013, 04:35 PM
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Canada, QC, Brossard
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I just checked for other blast with brushless system init and i saw that there a adjustement for the propeller . I didnt know that !! Is someone can tell me how it work. i mean how to adjust it for the boat stop bouncing ?? If you look a t the picture, you can see where the adjustment screw is set. Too high or too low ???
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Old Jan 21, 2013, 08:28 AM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
4,955 Posts
Hi Ben,

Judging from the picture, there's only a very slight rocker in the keelline, I don't think that's the cause for the porpoising.

Try to lift the prop a little, so the propshaft is more in line with the keel, it's pointing down at the moment, causing lift at the transom and most likely pressing the nose down when you accelerate. Not good.

With only 7,4V, the prop has barely 19000 rpm under load, that's not much for a monohull.
If you have a smaller prop, you could try that one on 3S; 28000 rpm under load is more like it.

While you're at it, check if the CoG lies at 30% of the hull length, measured from the transom forward.
Not having the balance of the hull right also causes porpoising.

As you may know (or not) I'm no fan of adding brake tabs to a boat, it's better to get the set-up right.

In that department, sharpening the trailing edges of the transom reduces drag and porpoising, the water creeps up the rounded edge, until gravity wins and the game starts over, causing the hull to start bouncing...

Regards, Jan.
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Last edited by pompebled; Jan 23, 2013 at 05:30 AM. Reason: typo
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Old Jan 21, 2013, 11:30 AM
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Vancouver, BC
Joined Aug 2009
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Jan has some good advice there, it seems to me like the CoG part might be your main problem. Try moving the battery forward, (toward the bow) a bit at a time until the porpoising stops. If you go too far forward though, the hull will run "wet" and be a fair bit slower than it would with a correct CoG.
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Old Jan 23, 2013, 09:42 PM
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Canada, QC, Brossard
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thanks !! I'm replacing all the drivetrain, shaft, seal, drive cup etc.... during the winter season !!! temperature outside is -36 F today near montréal, not the right time to run RC boat . I will check the COG when all the parts will be back in the boat !! I will make a new post in a fews weeks when the river will be free unfrozen and let you know if the boat run good !!!
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