Prop choice

[Tom Costello]

I am setting up a Delta Force 35 to use in both Q mono and offshore and S mono and offshore.The Q configuration has a Feigao 14xl and the S config. a Leopard 1000KV.
As a Q boat a full 6S2P but the S boat will go 7S2P. My available ESCs are Etti 150 hv with extra cap package ,Turnigy 180 and a Castle 240 lv. I am wondering where to start as far a props are concerned.

Thanks, Tom Costello

[sailr]

I run Q offshore with a NEU 1527 turning an X447/3 on 6S. Good combo. You should be able to go bigger with the 5692 on 7S, probably a 2 blade X448 or X450. Are any of the esc's you have rated above 6S? Not sure about that. At any rate, on 6S or 7S, do NOT use the BEC. You will want an onboard receiver battery.

[Fluid]

Which Leopard do you have, the 4082 or the 5692? Based on your choice of a Feigao 14XL, I assume the 4082.

The Feigao will be stressed pushing the 35" hull on 6S compared to a Neu or Leopard setup. An x447/2 may be a place to start but I suspect the Feigao may have trouble spinning that.

The Leopard 4082 should be able to spin an x452 or x455 with ease, assuming the boat is properly set up. But much depends on the setup and quality of packs. Always go easy with a new setup and run for one minute intervals (use a stopwatch) checking for heat until you are sure the combo is safe.

I have limited confidence in any of those ESCs.

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[Tom Costello]

The Leopard is a 4082. I use a receiver pack on almost all my boats over N2. The Etti 150 HV is rated to 7S.

[Fluid]

I have limited confidence in any of those ESCs.

My personal rule is to NEVER run an ESC at its maximum rated voltage. I don't burn up ESCs very often, and I run some VERY high-powered setups. My rule is one reason I don't toast them regularly.




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[keithbradley]

My personal rule is to NEVER run an ESC at its maximum rated voltage. I don't burn up ESCs very often, and I run some VERY high-powered setups. My rule is one reason I don't toast them regularly.




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I usually go by this rule as well Fluid, but do you take into consideration wattage? I have succesfully ran 6s on 6s max escs if the current draw was low. I think too many people max out the votage rating, and then max (or exceed) the current rating of the speed controller as well. Im not sure the voltage makes that much of a difference if you dont increase the total wattage...

For example, 1450kv on6s, or 2200kv on 4s...if you run both setups with the same prop, do you think the higher voltage one is more likely to fail on a 6s max esc?

[Fluid]

I used to think the same way - until Andy Kunz explained it from the point of view of a controller designer. But another part of the reason has nothing to do with wattage. If a controller is rated at 7S but you feed it 30+ volts coasting off-throttle (when the motor is a generator) you can over-volt the controller even running 7S. Many of the SAW controller burn downs I've seen happened on the slow down.

In the past I used a few controllers at max rating but in soft, moderate speed setups. The operative word here is really moderate speed, not watts.


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[keithbradley]

I used to think the same way - until Andy Kunz explained it from the point of view of a controller designer. But another part of the reason has nothing to do with wattage. If a controller is rated at 7S but you feed it 30+ volts coasting off-throttle (when the motor is a generator) you can over-volt the controller even running 7S. Many of the SAW controller burn downs I've seen happened on the slow down.

In the past I used a few controllers at max rating but in soft, moderate speed setups. The operative word here is really moderate speed, not watts.


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Yeah I understand electronic components respond differently to voltage and can only take a certain amount regardless of current. My thought is that they should be able to take the max voltage though. I do understadn this is asking a lot though, that is why I usually still run at least a cell under the max. As I said I have ran the max voltage on lower load apps (twins/low kv/ect) and never had a problem, but I suppose there could be a little more risk there as well.
As far as the generator theory, I dont expect the motor to be a more efficient generator than it is a motor, so I wouldnt assume it would "make" a higher voltage than the voltage it takes to turn at whatever RPM its at. How are you assuming a 30V back-feed? Are you saying it compounds the voltage from the spinning motor being back fed AND the input voltage from the batteries?