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High KV in a boat?

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Old 06-19-2017, 07:47 AM
  #1
OutlawRC
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Red face High KV in a boat?

I have been on 2 and 4 wheels since the 80's but would consider myself a noob with brushless boats.
I've got the 29" Rio EP (owned for maybe 5-6 years) and runs the stock brushed set up. Now I've got the itch to make it a little faster and ordered a way overkill esc (150a).
The reason I ordered one this big is because my LHS said I could stick a car motor in it without issue, and I've got a few laying around, seriously debating on the Viper 4.5r 4500kv.
Sticking with 2s due to lack of room.

So, my question is this...Since I see mostly lower KV and higher torque motors in boats will a higher KV motor work ok in a set up such as this? It's already plumbed to cool the esc and the motor.
My other options that I know I have laying around is a stock 17 turn, a Novak Ballistic 5.5, and sure I have a few others but nothing in the 3700-3800 range which is what I would like to try.
Thoughts on the 4500?

Anyway, during the process of soothing my upgrade itch I went ahead and ordered a 37" Inception and should be here tomorrow. Already got the batteries and everything I need for it I think.
Still thinking about making the Rio brushless.
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Old 06-19-2017, 07:49 AM
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I also have the thought of placing the 150a esc into the inception (since they evidently have heat issues with the stock 90a on 6s) and putting the 90a into the Rio.

Last edited by OutlawRC; 06-20-2017 at 05:57 AM.
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Old 06-20-2017, 12:11 PM
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I believe I also have a Leopard 1900KV 550 can size. Would prefer to leave it open in case 1 of the 1/8 scale monsters need a replacement, but could consider it if my other options are not suitable.
Any motor I have on hand would use the stock wrap around water sleeve for cooling since technically they're not boat motors.

Sooooo...what do ya'll think about installing the Viper?
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Old 06-20-2017, 03:35 PM
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The Viper motor will work fine with the right prop. Try a 38mm diameter prop to start. We run motors with that Kv successfully in 27-30" boats, just watch your heat on summer days. You'll need a 120 amp ESC at a minimum, the 150 is better.




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Last edited by Got RPM; 06-20-2017 at 04:04 PM.
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Old 06-21-2017, 04:40 AM
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Great feedback, thank you for the reply. Makes me feel better about getting the 150a esc then. That think looks huge for that little boat...
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Old 06-27-2017, 06:31 AM
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High an easy way to figure out if a battery/motor combo will work is some simple math. You want to keep a mono prop around 30K ish max ideally.Hydros and cats go a bit more usually. So 4500kv x8.4 (2s LIPO full voltage) =37800. Might have to reduce end travel a bit or cavitaion could kick in depending on the prop size. But it should work

Last edited by RainClod; 06-27-2017 at 12:23 PM.
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Old 06-27-2017, 11:14 AM
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From actual, logged data: 4500 Kv x 7.4 volts = 34,000 rpm unloaded

For loaded rpm (what happens in the real world) figure around 28,000-29,000 rpm on the water. I have no idea what "reducing end travel" means. If it means running at part throttle - DON"T DO IT! More ESCs are damaged and/or destroyed by extensive running at part throttle than you'd think. Part throttle on a potent system can overheat the ESC fast. It's your boat, you've been warned.



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Old 06-27-2017, 11:23 AM
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Could be referring to end travel on the steering servo to keep the prop from rising on a turn causing it to "spin" and therefore having more cavitation? Just guessing, maybe you can clarify a bit RainClod?
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Old 06-27-2017, 12:03 PM
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Quote:
Originally Posted by Got RPM View Post
From actual, logged data: 4500 Kv x 7.4 volts = 34,000 rpm unloaded

For loaded rpm (what happens in the real world) figure around 28,000-29,000 rpm on the water. I have no idea what "reducing end travel" means. If it means running at part throttle - DON"T DO IT! More ESCs are damaged and/or destroyed by extensive running at part throttle than you'd think. Part throttle on a potent system can overheat the ESC fast. It's your boat, you've been warned.

.
End travel on transmitter throttle settings. On a good quality brushless esc with a high PWM rate running at partial throttle is no big deal, when using proper cooling. We do it all the time on rc crawler jetboats very rare to go WOT.
Brushed esc's have/had a lot more issues with part throttle, although look at rc rock crawlers, constantly at part throttle with good cooling no problem.
My boats all have extensive cooling systems, my neo brushed motors even have both brush coolers and jackets.

Last edited by RainClod; 06-27-2017 at 12:24 PM.
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Old 06-27-2017, 12:19 PM
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Quote:
Originally Posted by RainClod View Post
End travel on transmitter throttle settings. On a good quality brushless esc with a high PWM rate running at partial throttle is no big deal, when using proper cooling. We do it all the time on rc crawler jetboats very rare to go WOT.
Brushed esc's have/had a lot more issues with part throttle, although look at rc rock crawlers, constantly at part throttle with good cooling no problem.
My boats all have extensive cooling systems, my neo brushed motors even have both brush coolers and jackets.
I use full pack voltage to compute rpms so 2s is 8.4 hence the different math. I usually figure about 20% rpm loss under load on a surface drive boat but my neo magnet brushed motor barely drops.
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Old 06-27-2017, 05:46 PM
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Quote:
End travel on transmitter throttle settings. On a good quality brushless esc with a high PWM rate running at partial throttle is no big deal, when using proper cooling. ....
This is not exactly true, especially in boats which draw far more current than any highly-geared 'crawler. Boats aren't trucks. Plenty of FE boaters think that part throttle is easier on their components than full throttle - not so at all. I have witnessed burn downs several times with new club members, and it is common to hear about on the high-traffic FE boat forum. But don't believe me, here is what one of the largest manufacturers of quality brushless ESCs has to say on the topic:

" A speed controller controls power to the motor by turning full throttle current on and off really fast, 11 to 13 thousand times per second (Pulse Width Modulation or PWM). The percentage of each on/off pulse that is off compared to the part that is on determines how much power the motor sees. I.E. With a pulse that is 50% off and 50% on the motor will see 50% power. Because each on pulse is 100% of full throttle current, a system set to pull 20 amps at full throttle through a Phoenix 10 will not last if you are throttled back to the point where you only see 10 amps on a wattmeter. The ESC in this case is still switching 20 amps, which it can’t do for long. Actually it is worse than the simple example above. Because an electric motor will always to try to pull as much power as is available to get to its rpm (volts times Kv), when you are running the motor below its Kv speed by switching power on an off, each on pulse will actually be way over the full throttle amp draw... Castle Creations"


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Old 06-27-2017, 08:23 PM
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Quote:
Originally Posted by Got RPM View Post
This is not exactly true, especially in boats which draw far more current than any highly-geared 'crawler. Boats aren't trucks. Plenty of FE boaters think that part throttle is easier on their components than full throttle - not so at all. I have witnessed burn downs several times with new club members, and it is common to hear about on the high-traffic FE boat forum. But don't believe me, here is what one of the largest manufacturers of quality brushless ESCs has to say on the topic:

" A speed controller controls power to the motor by turning full throttle current on and off really fast, 11 to 13 thousand times per second (Pulse Width Modulation or PWM). The percentage of each on/off pulse that is off compared to the part that is on determines how much power the motor sees. I.E. With a pulse that is 50% off and 50% on the motor will see 50% power. Because each on pulse is 100% of full throttle current, a system set to pull 20 amps at full throttle through a Phoenix 10 will not last if you are throttled back to the point where you only see 10 amps on a wattmeter. The ESC in this case is still switching 20 amps, which it can’t do for long. Actually it is worse than the simple example above. Because an electric motor will always to try to pull as much power as is available to get to its rpm (volts times Kv), when you are running the motor below its Kv speed by switching power on an off, each on pulse will actually be way over the full throttle amp draw... Castle Creations"


.
My setups use brushless heli esc's with very high pwm and 12 pole motors. My jet sprint which has an water cooled motor mount with an ntm 2836 2700kv outrunner on 3s runs on a 60A heli esc that is potted and water cooled .You can draw 80A through it no problem all day with water cooling. On jet boats water cooling comes from the compression section of the nozzle so it is fast and consistant. Neither my motor, esc and battery (graphene) ever get even slightly warm.
My brushed bby ovalmaster offshore mono runs 05 lightning man neo 13/3 motor it has brush coolers and can coolers. The motor get prop wash pickup cooling and the esc (vintage rc hydros (6-12nimh) 60A esc) gets rudder pickup cooling.
This boat will still give brushless boat a run for their money. It runs on 6-8 cells and the motor held several world records at one time. This boat get wide open throttle treament it is insane on 7 cells with an x437.
Rc jet boats get run typically throttle .Setup properly nothing gets warm ever.

Last edited by RainClod; 06-28-2017 at 07:37 AM.
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Old 09-15-2017, 03:43 AM
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Quote:
Originally Posted by OutlawRC View Post
I have been on 2 and 4 wheels since the 80's but would consider myself a noob with brushless boats.
I've got the 29" Rio EP (owned for maybe 5-6 years) and runs the stock brushed set up. Now I've got the itch to make it a little faster and ordered a way overkill esc (150a).
The reason I ordered one this big is because my LHS said I could stick a car motor in it without issue, and I've got a few laying around, seriously debating on the Viper 4.5r 4500kv.
Sticking with 2s due to lack of room.

So, my question is this...Since I see mostly lower KV and higher torque motors in boats will a higher KV motor work ok in a set up such as this? It's already plumbed to cool the esc and the motor.
My other options that I know I have laying around is a stock 17 turn, a Novak Ballistic 5.5, and sure I have a few others but nothing in the 3700-3800 range which is what I would like to try.
Thoughts on the 4500?

Anyway, during the process of soothing my upgrade itch I went ahead and ordered a 37" Inception and should be here tomorrow. Already got the batteries and everything I need for it I think.
Still thinking about making the Rio brushless.
My experience for select Motor KV is calculate How many cells of battery are using. i.e. 3700kV using 3 Cells, Simply 3700x 11.4 x 80%(Motor Efficiency) = 33733 RPM
Normally, I will use the Range from 32000-45000 RPM depends on what kind of Boat Hull. Like Mono Hull around 25% efficiency will use higher RPM like 45000. and Outrigger have higher efficiency 10% will use 33000. Max. Speed will never higher 50000RPM it cause serious over heat and damage the Bearing.
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