Volts -kv - and RPM

[MG1234]

Hi I read a while back a great post about KV-volts and RPM,I searched it but didn't find it ,I'm running 6s on 3 boats,2150 kv,I read where a guy ruined the transom when his flex cable let go ,I ran my Zonda on 6 s and ruined a flex cable ,ran a bunch on 5 s and did fine it was the stock cable ,have upgraded cables comming just want to make sure it's ok,other boats are a spartan and a genesis ,both on 6s with big 2150 motors ,the cat takes a beating ,both have upgraded shafts and props ,if anyone can pop up that post that would be great ,thanks

[srislash]

I would have concerns with stock cable on that Kind of rpm but a decent aftermarket should be truer and odds are a much better weld/solder joint. I run my own glued ones and have no issues.

[MG1234]

Do you know how to figure rpm? And yes the stock Zonda cable is 8$ so no wonder it broke,the others do great so long as I really tighten the coupler

[Doby]

Multiply the motor KV by the Voltage.

[Fluid]

Depends on the motor, what really matters is loaded rpm. Some motors list the Kv under load like Lehner. (2 pole). Others list the Kv unloaded like Neu (4 pole). You cannot compare the two as the actual loaded rpm in you boat will be different. Most motors today are 4-pole and list unloaded rpm.

In general terms, v x Kv for most 4-pole motors...

Sport running (not SAW) = 25,000 - 30,000 rpm
Oval racing = 30,000 - 35,000 rpm
SAW racing = 40,000 + rpm

These are general ranges not absolutes, but if you keep within these ranges you are less likely to get into trouble.




.

[MG1234]

So my Zonda has 2150kv motors,what I was told,so on 6 s I'm turning 41000 rpm at full throttle ,? Wow ,

[grsboats]

41000 unloaded......there is a big difference under load!

[TRUCKPULL]

You must also remember that it is not just the KV under load that is lower.
Your Voltage under load is lower also.

Better quality, Larger mAMP packs, Higher "C" rating packs, all add up to higher Voltage under load.

Larry

[ray schrauwen]

A good read: http://www.rcuniverse.com/forum/spee...ere-first.html

[Shimpa]

2150kv x 24V (that's the "half full" lipo voltage - I personally don't go below 3,7 per cell) = 51600 rpm unloaded, not 41k.

[MG1234]

Yea under load is much slower,only as fast as the motor has power to spin