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1/8 Scale rules question


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#46 raptor347

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Posted 17 April 2018 - 10:18 PM

The current IMPBA rules allow S and T power, so 7-10 cells. 10S is likely an artifact of the conversion from round cells to LiPo. It's the power level boats were historically built to.





#47 Don Ferrette

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Posted 18 April 2018 - 04:31 AM

I understand that, Brian.  I'm just trying to understand why Terry says they HAVE TO RUN 10S.  I know what our, as some have called them, "spec" boats can do, just curious as to why those in IMPBA see the need to run bigger packs?  It might be something that NAMBA or R/C U might want to look in to if the reasoning is sound

Mark go back and re-read Doug's last post. Do we HAVE to run 10S? No. Why do we do it? Simple and the point I made twice earlier that keeps getting "ignored" - with FE a given application takes a certain amount of wattage to get the job done. With the number of FE scales I have built or helped build I have found for them perform reliably and with decent speeds we need to be in the range of 2100- 2500 watts. You have 2 choices how to get there volts or amps as the formula of volts x amps = watts DOES NOT CHANGE. Higher volts (like 10S) will mean a lower overall amp draw. Higher amp draw means more heat, heat is the number one killer of electronics. A properly set up 10S scale will run in the 60s, not break a sweat temps wise and can get it done on a 1P battery set up at 5000-6000mah with a 65-70C rated pair of packs.





#48 RaceMechaniX

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Posted 18 April 2018 - 06:57 AM

Don did you finish that carbon Velasco scale as an FE?
-Tyler

#49 LohringMiller

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Posted 18 April 2018 - 08:32 AM

It's true that current is the limiting factor.  A higher voltage requires lower current for the same power.  However, how are you going to regulate the maximum current?  KV, voltage and prop size pretty much set the current in an indirect way. Also anything over 8S requires an HV speed control. 

 

These days either the motor or the speed control is the fuse.  At the point of maximum efficiency, motor torque is pretty much proportional to motor weight.  Motor power is torque times rpm.  Motor can size could be a somewhat inaccurate stand in for motor weight.  The list of available motors is going to be very long.  The only way I can think of to make the process of power train design simple is to test several suitable motors and make their use required.  The list will need to be updated frequently.

 

Lohring Miller



#50 Doug Smock

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Posted 18 April 2018 - 10:33 AM

The only way I can think of to make the process of power train design simple is to test several suitable motors and make their use required.  The list will need to be updated frequently.
 
Lohring Miller

 

I agree FWIW. ;)



#51 LohringMiller

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Posted 21 April 2018 - 07:24 AM

My apologies if my comments offended anyone.

 

Lohring Miller