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e-Electric Batteries & Chargers > Help with older Logo 20 & cell count
 
 
karlk
Heliman
Location: Petaluma, CA

I'm buying a older Logo 20 from a friend, and need some help deciding on how many cells to run. He just hovers & does FF, while I'm going to use it for basic aerobatics with a few flips & some inverted stuff. It has a Kontronics KBM 67-7 motor with their 25-14-32 heli controller. I think they have both been discontinued, but this was a recommended combo when the Logo 20 first came out. Nobody on Ezone seems to know anything about this motor & esc. I've seen the heli fly several times.

Anyone have advice on 20, 22, or 24 cells? I'm concerned about the 25A rating of the esc, so I don't want to push it hard. I know with 24 cells I can run less current for the same power, at the expense of the weight of 4 cells. Is this the way to go, or will the added weight kill any benifit since I have to be conservative? Eventually, I'll probably get a new motor & esc, but for now I just want to get it in the air.

Thanks

-Karl
12-26-2002 Over year old.
 
 
FlyinBrian
Veteran
Location: USA

Hi,

"I know with 24 cells I can run less current for the same power"

Not exactly true, power is power (or watt's). Raising the voltage will mentaly get you around the amp rating but you'll still be pushing the speed controller past its rating (which does work in some cases).

The following #'s are from me aka an idiot when it comes to electricity, they are what I believe to be correct but I am sure someone will prove me wrong but they will wait till I post to say anything Power is watt's, watt's are volts * amps. Its just a lot easier for people to understand # of cells and amps is why manufactures rate them that way.

These #'s assume the same amperage and we know that will not be the case as the volts go up (but you'll hit these points in the air, plus the xtra weight will help increase the amp draw) Most speed controllers can handle a pretty large spike in current for a short period of time, just depends on how it was rated and how long the spike is.

1.1volts under load per cell.....

20 cells * 1.1 volts = 22v * 24amps = 528 watt's
22 cells * 1.1 volts = 24.2v * 24 amps = 580.8 watt's
24 cells * 1.1 volts = 26.4v * 24 amps = 633.6 watt's

I'm not trying to say you wont get away with it, try 22 cells out and see how it goes, check the motor and esc tempature through out the flight. Take your time and work up to abusing the new found power. Both the motor and esc will be at risk and either can burn up. Jump in head first and find out, there really is no one out there that can answer wether or not it'll work (too many varibles... flying style, heli weight, blades, tempature, on and on).

How is the sceadu doing?
12-27-2002 Over year old.
 
 
karlk
Heliman
Location: Petaluma, CA

Uh, yeah, I learned the whole P=V*I back in the few EE classes I had to take in college. My point was, ignoring the extra weight of tacking on 4 more cells, if the heli requires 400 W to hover, less current will be required on 24 cells than on 20. You're right, though, that weight can't be ignored, and the motor is most efficient at a certain rpm, etc, etc.

I'm actually going to start with the recommended 20 cells I found in the original Logo manual for my motor & esc. Though it also states to run a 1100 rpm main rotor, and I'm looking more for 1500 or so.

The friend I got it from ran it on 20-24 cells, with different pinions, and said the motor or esc never got too hot to touch. He didn't do much to load the heli, though.

The Sceadu is doing great. It's the heli I take every weekend.

-Karl
12-27-2002 Over year old.
 
 
FlyinBrian
Veteran
Location: USA

Hi,

What I was kinda hinting towards is: If 20 cells @ 24a (528w) is what the esc/motor were rated at then 24 cells @ 20a (528w) is the max you could run and stay near its rating.

The period of time is important as well, if its rated at 20 cells @ 24a for 10 minutes you can probably get away with 20 cells @ 35 amps for 5 minutes or 24 cells @ 30 amps for 5 minutes.

Check the input capicitors for heat as well, if they burn up the esc will keep working but the voltage spikes that now get through will burn the esc up sooner or later.

I allways heard electric were simpler than gas models
12-27-2002 Over year old.
 
 
E-gpeden
Senior Heliman
Location: Lake Louise, Alberta, Canada

"I allways heard electric where simpler than gas models "

Hi Auger,

They are if you buy a suggested system, or "what works". The system in question was one of those, but pre-dates most of our experience. I have no direct experience with this combo, so have not offered any opinions, but I think that recommended stups back then were based on 20 cells. I am going to throw this question out on the E-Heli mail list, where I first got recommendations on the LOGO by European modelers a few years ago.....

Cheers!

Cheers!
Glen
12-27-2002 Over year old.
HOMEPAGE  
 
 
karlk
Heliman
Location: Petaluma, CA

Yes, 20 cells, 9 tooth pinion, with a 1100 head speed. Of course, all the motor/esc combos were for a 1100 head speed on the chart I found. I don't think I'll be doing any flips at 1100

Thanks for the help

-Karl
12-27-2002 Over year old.
 
 
ecranage
Senior Heliman
Location: West Yorkshire UK

Karl,
How did you get on with your set up?

I have just bought a Logo 20 with a Kontronik KBM 67-07 with a Kontronik 3SL-26-14-32 speed controller.
Evan
05-04-2003 Over year old.
 
 
rscamp
Veteran
Location: Ontario, Canada

Karl.

I did a search for "KBM 67-7" and found a reference to a Logo with 22 cells. My guess is this motor is a 600 to 700 RPM/Volt motor so it will be VERY sluggish on 20 cells - especially with a Kontronik controller. Kontronik controllers are smooth-starting but tame - if you go to a Schulze controller you can probably get significantly more RPMs.

I would be inclined to try 24 cells as I think current will be the issue with the controller rather than power. It should work fine unless it has bad FETs or something. I had the high step-frequency version of this controller with a Tango 45-06 in a heavy Shuttle and it never failed. It is now my emergency backup controller You might want to limit collective throw a bit to help reduce peak current draw.

Also, I suggest you run the governor at no less than 80% or so and size the pinion for, say, 1700 RPM. (Perhaps 1600 RPM is more realistic if the motor is only 600 RPM/Volt.) This should also help keep the current to a reasonable level and be easier on the controller.

Rob
05-04-2003 Over year old.
HOMEPAGE  
 
 
karlk
Heliman
Location: Petaluma, CA

I'm not sure how this thread ended up in the battery section, but anyway...

I got a hold of Mikado directly, and they suggested 24 cells with the 8 tooth pinion. That's what I've been running for a few months now, with a 1600 rpm head speed (80% in govenor mode). The power is about like a 30 size heli on 15% fuel. Loops require full power with a good run to build up speed. I think I'm using 8.5-9 deg pitch. I've been getting 5 minutes of "spirited" flight, with another 1.5-2 minutes of hovering after. You can see a few pics of it in my gallery.

Blades are MS600. I've tried a set of SAB 600, but they slowed the cyclic rate down too much for my tastes (stock paddles)

I'm going to try upping the head speed a bit to see if it improves the loops. I may try running a little more pitch, but I'm still concerned about the 25A limit on my esc.

Overall I'm pretty happy with the little guy. I'm building a Joker to keep it company. Next year I'll either get some of the new lithium batteries, or a newer motor/esc. I suspect the older motor will have terrific performance with the weight reduction offered by the lighter packs. Maybe I'll build a pack using scr1700 (43g vs 60g per cell) in the meantime.

-Karl
05-04-2003 Over year old.
 
 
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