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Old Oct 09, 2013, 11:05 AM
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I feel the need... the need for MORE speed

Topic say it all, i want more speed on my Joysway Bullet now that i've got it running again. I'm a n00b in the RC world so i would appreciate all help given here. I would also like to keep the current ESC and not go to extreme

The current setup in my boat are: water cooled 50A ESC with BEC (no brand name), water cooled 2815 out-runer brushless motor, 11.4V 2200 mAh 3S battery, stock plactic propeller

It has been suggested to switch to 4s battery but not sure how many mAh, what do people suggest? Also it have been suggested to upgrade the propeller to metal and maybe also 2 -3 mm larger.
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Old Oct 10, 2013, 06:08 AM
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Old Oct 10, 2013, 11:12 AM
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I could not find anything in detail about the motor, especially about the KV of the motor, which made it hard to know if the boat would work on 4s. I think the motor is 1900kv which will be fine in terms of RPM to go 4s. That would be the first way to get more speed. I also couldn't find the actual size/pitch of the stock prop, which would be the starting place for a better prop. I am sure the right prop will add 5 to 10 mph to the boat, even on 3s, but I just don't know what to recommend.

As for Mah - you will probably still be around the 3000mah range. I imagine the biggest issue will be to make sure it fits in the boat. Some kind of 4s, or pair of 2s ... 30c or so... The amp draw will go up a bit with the same prop on 4s, so having a bit more capacity in the battery will offset some of that for runtime. Usually the stock props are conservative enough that cranking them up a bit more is still within the limits of the electronics.

But without more details it is hard to know for sure.
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Old Oct 10, 2013, 01:25 PM
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Thanks cyber... yeah the parts used in my boat is a big mystery. On the reseller's website they recomend 11.2 V 2200 mAh 25c battery it's not listed how many cells.

This is a link to the replacement prop. Sadly it do not tell the pitch only the diameter as you see Link The manual for the boat say the prop are: P1.4X40... so maybe 1.4 is the pitch ratio giving a 56 mm pitch according to THIS calculator? The diameter of the prop are 40 mm.

I sent a e-mail to Litlehawk asking them about the motor KV, i will post the reply as soon as they send any. Their Challenger boat has the same motor as my Bullet.
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Old Oct 10, 2013, 02:02 PM
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Maybe...!

Quote:
Originally Posted by viceguy View Post
Thanks cyber... yeah the parts used in my boat is a big mystery. On the reseller's website they recomend 11.2 V 2200 mAh 25c battery it's not listed how many cells.
Hey Viceguy, maybe you need to read up a little on Lipo's, 11,1V means three cells! 4S means 4 cells which amount to 14,8V, each Lipo cell is 3,7V nominal.

This is your boat: http://www2.ripmax.net/Item.aspx?ItemID=B-JS-8301, you could probably can get away with 2 - 3mm more on your prop which is the cheapest way to increase speed, without increasing weight. More cells (speed) and more amperage (runtime) will increase weight which is again detrimental to your goal. Be sure to get temperature readings (when tweaking your boat this way) in between short runs until your sure you won't burn anything when running a full load on the batts. Boo
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Old Oct 10, 2013, 02:53 PM
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Well what can i say Boo that i haven't yet said... electricity isn't something i know a lot about as long as my PC work, my car start and my boat run i'm a pretty happy viking

Ahh yes, ripmax.... one of the many that had my rudder in back-order and i see it still is :/ Actually the boat is sold under a lot of different brands and names: Joysway, 2fast2fun... even HK has it but renamed it Quanum Aquaholic

Anyway Litlehawk did suggest i could run 4s as all the electronix in my boat are identical to their Challenger.
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Old Oct 10, 2013, 03:12 PM
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Quote:
Originally Posted by cyberhoops View Post
I could not find anything in detail about the motor, especially about the KV of the motor, which made it hard to know if the boat would work on 4s. I think the motor is 1900kv which will be fine in terms of RPM to go 4s.
According to Litlehawk: it's a 28mm motor (the shaft i assume) should be in the 1850 to 2000KV range. if upgrading I would go with a 4s capable setup in the same or slightly lower KV range
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Old Oct 10, 2013, 05:13 PM
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Given a 40mm prop, and I think you are right about the 1.4 being the pitch factor. 28mm should be the length of the motor, which is pretty short - but an outrunner generates a bit more torque than a similar sized inrunner.

Going up in diameter is one option, but increasing diameter takes the amp draw up faster than increasing pitch.

You might try an Octura 640, or the equivalent. Going with 1.6x pitch will increase the boat speed and draw fewer amps than going with an 42mm prop. I did some dinking around with propeller math at one point per the link below...

http://www.rcgroups.com/forums/showthread.php?t=1628409

But I would get a couple props to try 640, 442, 642 - then do some testing to see what works best.

The 440 size prop should be fine going 4s, but that will change a lot about the boat with heavier batteries and way more power. 2000kv should be just fine to push to 4s, but you will have to test it a bit to get the balance/strut angle/etc right. That would be more work to get right than just a prop change.

I would go with prop changes before going 4s.
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Old Oct 10, 2013, 07:19 PM
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About 4s. Back to being a math geek here. I was reading my post again about propeller math. I should look at that more often.

Going from 3s to 4s will be similar to changing the KV of a motor - basically increasing the rpm and therefore the amp draw. The formula would imply:

1.333 ^ 3 for the power increase is 2.37x. More than double the power level from 3s to 4s when running the same prop. That is power, which is volts * amps, and the voltage did go up...so factor out the voltage and you get an increase of 1.77 for the amp draw. If that prop was drawing 25 amps it would now draw 36.

That is about the same increase in amp draw as going from a x440 to an x645
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Old Oct 11, 2013, 05:50 AM
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now you talk way above my head and iq cyber, care to break it down to something easy understandable?

Edit:

btw, doesn't this site do the same as your calculations? LINK
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Old Oct 11, 2013, 12:03 PM
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The implication of the math is to try some props, working up toward an x645. If the temperatures and such are all reasonable with a 645 then you could switch and go 4s with the 440. If things are hot with the 645, then it is also going to be hot with 4s on the 440 and you would need to prop down on 4s to something like a 437.

I have not seen the link you mentioned above, but slightly different from what I was calculating. I was playing around with what percentage increase there would be in amp draw for various prop changes.

That calculator suggests that currently your boat is at 25mph using 3s and a 440, and if you went up to a 645 it would get to 32mph. Changing to 4s and using the 440 would get you 33mph. That is even somewhat consistent with the power calculations.
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Old Oct 12, 2013, 06:18 AM
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Ok now i understood you better, this is also confirmed by a reply i got to a youtube comment i made. It's rough translation from norwegian to english (funny how i'm better at translating the other way), this is what he said

Quote:
4S lipo works great and I do'nt notice anything wrong with the electronics. I use 4S lipo at 3600mAh and 4000mAh, both 20-40c. Batteries generate some heat, but they can withstand it. These batteries are a bit heavier than 3s lipo, this changes the handling of the boat. It goes much faster, but it effect the ruddr control. The impact is on the rudder cause you to be more sensitive when you make turns. I did not try with another prop, but think that when the torque increases with 4s lipo then you may consider aluminum or brass propeller.
Based on that i would think just doing a prop upgrade would be the best choice, then again i could do battery and prop and just be a bit easier on the trottle (like that's gonna happen )

what do you think?
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Old Oct 12, 2013, 12:30 PM
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I think you try both... it is worth the experiment. Prop first - then batteries.
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Old Oct 12, 2013, 01:07 PM
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Ok.. will see what i try first but it will be next year because today we got sleet My bathtub is not big enough to do prop and battery tests in

Anyway still things to do even if the weather is bad, i wasn't happy with the color of my boat as black on water do not show really good. My idea was to re-spray the boat in the Kawasaki green color, but that color turned out to be hard to get on spray can.

So i settled for fluorescent red/orange instead, i knew the color would change a bit when i added clear coat on top but i wanted a deep shine. I've ordered some different brand stickers from a locale company, among others Lamborghini (sounds perfect for the motor lol) in gloss black... i think the boat will look much better than out of the box.

Anyway here is two pictures i took after removing the masking tape today, I’ve kept some black (below the waterline, cabin air-intakes and roof hatch as you see.



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Old Oct 12, 2013, 02:18 PM
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There you go. No more stealth boating for you! You won't miss that boat in the water. I like it.
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