New World SAW Record 148mph

[shoboat]

Charles,

I agree that is a really nice lake.

On a different subject the ABC propellers that were used in the record run

were not special at all. Basically stock propellers just sharpened and balanced.

Believe it or not they only had a 1.4 pitch ratio.

Thanks,

Mark Sholund

 

[Charles Perdue]

Charles,

I agree that is a really nice lake.

On a different subject the ABC propellers that were used in the record run

were not special at all. Basically stock propellers just sharpened and balanced.

Believe it or not they only had a 1.4 pitch ratio.

Thanks,

Mark Sholund

Turning at a ZILLION RPMs

 

[RaceMechaniX]

They are probably spinning them 42-50k, but with 40hp per prop!

TG

 

[shoboat]

Tyler,

I heard approximately 62,000 RPM with about 45 to 50 HP per engine.

Amazing Set Up,

Mark Sholund

 

[RaceMechaniX]

It could be. Marko was running pretty big motors and those usually don't like being spun that high but then again this is SAW where anything goes.

I heard outrageous power numbers close to 100hp total at peak acceleration. Simply nuts.

 

[lohring]

Input power is a simple calculation. Watts = volts x amps. Horsepower = watts / 746. If the record was set with a 6S battery, the nominal volts are 22.2. The maximum under load might be 25 volts for a short period. From an article I wrote in 2007:

The theoretical peak burst current of a power supply equals 1/2 the rated voltage divided by the internal resistance. This is what you can use for the 3 to 5 seconds needed in a SAW run, but chemical batteries may not be able to deliver electrons at that rate. LiPos are rated at 3.7 volts per cell and some have internal resistances .003 ohms per cell or lower. For prewarmed Polyquest, Thunderpower, or similar 20C 5000mAh cells the 3 to5 second limit is known to be over 300 amps (60C).

These days I bet 600 amps might be possible with a custom speed control. That would give around 20 input horsepower on 6S. The same current would give over 30 hp on 10S. If bigger packs were used the current could be higher. What can even the best possible ESC that will fit in a model handle? The speed control we used in the full size electric boat was rated at 2000 amps, and we ran around 900 amps maximum.

Lohring Miller

 

[Christian Lucas]

Hi Lohring ,

that's right what you wrote . Chemical batteries do not stay this high amps at 1/2 of the free running volts . Only fuelcell do that .

And the 600 amps are history . You note the straight mono record boat from Ralf Moser ? The Lehner 3080 suck this amprate during acceleration some peak show 1200 amps and there are some smaller motors that handle this amprate .The esc is a brick . But the biggest problem is that it is realy not easy to load this amps in to the windings . The Inductivity of the coil limites the max amps a coil can be load . In high class motordesign the engineer used it to limit the max amp draw of the motor naturaly .

If next year a Munich SAW will be held . You are All welcome to visite . By the way the Munich rawing lake has no water in and out ,it is simple the deepest point of at Munich and groundwater feed. So to get such in your backjard you have only to dig deep enough and water will self fill the lake.

 

[Ralf Moser]

Phase peak amps the mgm measuring, dc load on the lipos is 600-700a (300-350a/pack)

Point with this high currents is inductance, there are only a few options on motors, which are low inductance, proper revs and enough mass to handle the ohmic heat.

We speak about input power, the power on the shaft is mostly significant lower than what expected with pure ohmic calculations. Reactive current lowers the rpm without increasing torque

 

[lohring]

I carefully talked about INPUT power, a simple calculation with a DC power supply. The output power has to take into account all the above factors and is something like 80% to 90% of the input power with brushless motors. I just wanted to point out the upper boundaries of what was likely. Forty to 50 horsepower seemed extreme. Of course if you could really pull 1200 burst amps, my figures would double. That's why electric motors are great for acceleration. (language NSFW)

Lohring Miller

 

[Ralf Moser]

Sounds a little bit aggressive, maybe language

I wanted to clarify what peak Christian spoke of, phase or acceleration peak measured on the cells. And what problems occur with the motors in our size.

myself thought when speaking about 40-50hp it is the 14s2p cat by marko where 500a during acceleration were measured on the batt side. For each lipo package since each controller in his boat can withstand this amps shortly.

 

[lohring]

Thanks for all the information and clarification. It seems that motors and speed controls have caught up with the potential of lithium polymer batteries. That makes the power available to electric model boats greater than that in any internal combustion class.

Lohring Miller

 

[Darin Jordan]

Ralf or ??. Just curious. At those amp loads, what are the cells pulling down too??

 

[Andy Brown]

Congrats on the new records and speeds!

Amazing technology guys!

I'm still learning how to burn nitro.

 

[Ralf Moser]

Darin, do not know what the cells delivered in markos cat. Myself sits around 3,5v on the esc input @350a each package. So the single cell directly measured is slightly higher normally.

 

[Darin Jordan]

Darin, do not know what the cells delivered in markos cat. Myself sits around 3,5v on the esc input @350a each package. So the single cell directly measured is slightly higher normally.

Thanks, Ralf. That's better than what I had expected at those loads. Will be good to know for calculations in the future.