jackplanet514

Hello All,

Went flying today and had some pretty dramatic events occur.

I was flying my GreatPlanes Tutor kit, which I usually have equiped with a 370 3.7:1 gear box, a 9x7 prop with a 7.2v 1100ma battery and a Wattage 5amp ESC. The plane flies great it climbs almost at a 45 degree angle I'll do 3 loops in a row. And I get 10+ min flights.

But today, I think I did a bad thing by changing the prop to a 10x8 and putting a 9.7v battery. I think I was getting greedy for more thrust/power.

About 100+ feet up I lost all control, luckly the plane was in a nice turn so it spiraled out of the sky and crashed on top of a school (it's a good thing I am a professional rock climber) about 200 yards away. Amazingly enough there wasn't any damage to the plane its self, however the battery and ESC were completely melted and sizziling.

In my research to find out just went wrong I read this on a message board.

If I take into account the quote above, it doesn't make sense as to why my battery and ESC were fried. Shouldn't the motor be burned up instead?

Am I correct in thinking I just pulled too many amps for the ESC to handle and it fried up and shorted out the battery?

Any advice would be GREATLY appreciated!

Thanks.

Matt Kirsch

My Feedback: (21)

A 5 Amp ESC is borderline for a 370 motor on 6 cells. 370 motors are the same as Speed 300s, which typically draw around 8 Amps when they're set up for best performance. You went to 8 cells AND increased the propeller size, both of which increase the current (Amps). It was too much for the ESC to handle for sure, and depending on what size battery this was, that too...

As you've found out, you can't just willy-nilly start changing components. The results are usually bad; the plane's performance is smoking, until the plane starts smoking, or the plane's performance stinks like smoke

Generally, you can't increase cell count and prop size without using a different gearbox, one with a higher gear ratio. Instead you would need to DECREASE the size of the propeller as you increased the number of cells in the battery. Going go 8 cells necessitated a drop to an 8x6 prop AT LEAST, and maybe smaller. The point is to increase the motor's RPMs by increasing Volts (cells), while keeping the Amps (current) the same by using a smaller propeller.

Motocalc, and P-Calc at www.flydma.com, can be used to get reasonable approximations of current draw under a given set of conditions.

jackplanet514

Another thought.

What would happen if a NiMh battery were to be charged on a NiCad setting?

From what I have read NiMh batteries are a bit more sensitive and cannot be charged as fast. Is this true?

Jack.

Dr Kiwi

NEVER charge an NiMh pack on the NiCd setting or using a NiCd only charger. The charging regimes are very different so you MUST use an NiMh capable charger, and NiMh should never be charged at over 1C.

Cheers, Phil