Graupner

[Matt C]

Hi All,

I'm a bit of a newb so excuse the question:)
Could someone explain what the difference is between a graupner 700 8.4 v and 9.6v apart from the name:)?

Thanks

[Steven Vaccaro]

Depending on the model, there is probably a difference in rpm.

[Joe Friars]

The RPM difference would help explane what was told to me:
the 9.6v would give you longer runtimes than the 8.4v, but would be slightly slower.
I'm new at this too, but I went for the 8.4v in interest of speed.
I won't know much more until the boat is finnished!
Joe

[Eodman]

Pictures of the build man ... post em as you go!

[Matt C]

Guys,

Been surfing the old net and found some stats:
700 9,6 v 15000rpm
700 8,4v 14700rpm

bit more confused now:s

Thanks

[Dr. Jet]

The key factor here is rpm per volt, commonly referred to as the Kv of a motor.
15,000 rpm at 9.6 volts = 1562 rpm/V
14,700 rpm at 8.4 volts = 1750 rpm/V

The 8.4 motor has a higher Kv (1750 rpm/V) and correspondingly less torque per volt (Kt, usually expressed as inch-ounces per volt).

[Matt C]

Thanks Dr Jet, thats cleared it up:)

Whats the max number of cells each can run on?

Thanks

[Dr. Jet]

Maximum voltage (number of cells) is not as important as maximum watts (volts x amps). You can get away with 16 round cells if you keep the prop small (low amps). Try to keep the motor below 500 watts until you resolve handling and cooling issues on your particular hull. Generally, these motors are run on 12 round cells or 4S LiPos. Keep a close eye on temperatures as it is easy to smoke one of these motors. Don't ask how I know.

[lonewolf]

Been there done the 9.6 hmmmm 1st bought 1st smoked....

[Matt C]

Guys,

Thanks for the info.

Should tell you a bit about my projects. The first is a 28" outrigger and the second is an old super hawaii. Wanted to start someone sensible and then build up so this is why i'm looking at the Graupner 700. Dr Jet, you mentioned props, what would you recommend for the outrigger?
Also just trying to work out the maths:s say if i was running 12 volts would this mean that the watts would be 150 watts based on the motor running running at 12.5 amps max drain?
Guess will start to think about water cooling judging by the smoking of motors issue:)

[Dr. Jet]

With a rigger running an 8.4V 700 motor, I would start with an X640, then gradually work up to an X642 then an X645. There are others that would work, but the X-series seem to have fewer issues with cavatation and fine-tuning.