feihu-RCU

I have the graupner (GR3306) Speed 300 6v motor w/ 5:1 gear ratio and 8x6 prop. On 9.6v Nicads, it draws 10 amps for 15 oz thrust.
How do I make the voltage adjustment for lipos?
Do I go to 2s (7.4v) and a larger prop?
Or should I go to 3s (11.1v) and a smaller prop?
Or what would you suggest in order to get the max efficiency?

Would appreciate your comments.

feihu

SitNFly

My Feedback: (54)

If you want to draw roughly the same 100 watts as you are drawing now, you would have to pull about 15 amps using a 2S lipo. This would probably kill your motor is short order. 100 watts on 3S is a more reasonable 9 amps. You just have to make sure you prop accordingly. Typically, the tradeoff is more power, shorter duration with 3S and less power, more duration with 2S. Plane weight has a lot to do with your selection. A 12 oz plane would fly quite nicely on 2S, a 20 oz would not.

Time Pilot

I've not done it, but I have yet to hear of anyone who flys a speed 300, to recommend flying them with a 3S lipo. The motor is not designed for that high voltage--the higher the voltage, the faster the motor spins.

I have heard of people flying a ball bearing 280 on a 3S lipo though.

Read through the specs of the plane:
www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJCC2&P=ML

Maybe the manual will give you more information on the power system.

Here's the motor:
www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJEV8&P=7

Hmmm... Ran the numbers through pcalc at
http://brantuas.com/ezcalc/dma1.asp

and according to that, the 280 BB on 3S Lipo with that system sure isn't efficient.

If you need 100 watts out of a small motor, you should start thinking brushless....

feihu-RCU

Thanks sitNfly, and thanks Time Pilot for your replies.

Looks like the speed 300 is not practical with lipos, so I'll just stay with what I got.

feihu