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Starmoon
12-12-2005, 04:36 PM
I'd like to put one on the pico stick w/fuselage....will this work??? I like the idea of 30 min flights......

rcers
12-12-2005, 04:46 PM
Yes but it will have to be small and light. LiPoly is much better for duration.

Mike

Matt Kirsch
12-12-2005, 05:03 PM
Number of cells only determines top-end power, not duration. The capacity of the cells, in mAh, is what determines duration.

That pico stick will have better performance, but duration will be the same, or even shorter, with a 7-cell pack that's light enough for the plane.

If you're looking for 30-minute flights, you'll need a 2S (two cells in series) LiPoly pack with approximately 1000mAh of capacity. The highest-capacity NiMH that won't be too heavy for the pico stick has only about 400mAh of capacity, and will only give you about 10-12 minutes.

Starmoon
12-12-2005, 05:04 PM
http://www.greathobbies.com/products/productinfo.php?prod_id=HIF075L3


How about a HIF075L3??

3 cell, 750 mah...

rcers
12-12-2005, 05:46 PM
You will want 2s for that motor. It will burn up on 3s unless you prop down considerably.

That is the right capacity however. With 700-750 mAh cells at 2amp draw (typical of the ips drives) you will be at 40+ minute flights easily.

Mike

Starmoon
12-12-2005, 05:54 PM
You will want 2s for that motor. It will burn up on 3s unless you prop down considerably.

That is the right capacity however. With 700-750 mAh cells at 2amp draw (typical of the ips drives) you will be at 40+ minute flights easily.

Mike


is 800 mAh too high on a two cell?

rcers
12-12-2005, 05:56 PM
As long as the weight is OK for the aircraft it is fine.

You will not need the extra capacity, 40 minute flights are well, long!

Mike

Starmoon
12-12-2005, 06:01 PM
As long as the weight is OK for the aircraft it is fine.

You will not need the extra capacity, 40 minute flights are well, long!

Mike



it is 67 g or so....

rcers
12-12-2005, 06:10 PM
67g is heavy, very very heavy. Most cells of that weigh around 15-18g each. So for an assembled pack I would shoot for 30-40g (2s).

Mike

qban_flyer
12-12-2005, 06:22 PM
http://www.greathobbies.com/products/productinfo.php?prod_id=HIF075L3


How about a HIF075L3??

3 cell, 750 mah...

I am using a T/P 860 2 cell pack with mine spinning a 10X4.7 orange propeller. With proper throttle management I get in excess of 57 minute use out of each charge. I take the plane and one pack with me to the field, I fly on and off all day long, about ten flights of five minutes each and still have power for one more if I so choose. :)

AEAJR
12-12-2005, 09:04 PM
is 800 mAh too high on a two cell?

I can see you are a little confused about batteries. Maybe this will help.

This note is intended to clear up a few terms and concepts around electricity
as it applies to electric airplanes.


Think of electricity like water. Volts = pressure Amps = flow

Volts is like pounds per square inch, psi. Says nothing about how much water
is flowing, just how hard it is being pushed. You can have 100 psi with zero
water flow.

Amps is flow, like gallons per hour. You can have flow at low pressure and
you can have flow at high pressure.

Amp hours is how much flow can be sustained for how long. It is used as a
way of measuring how much electricity is in the battery. Like how many gallons
of gas in your tank. It is a capacity number. Says nothing about flow or
pressure, it is about capacity.

Amps and mili amps? We are just moving the decimal point around.

1 amp (short for ampere) - 1000 miliamps (mili means 1/1000)

Examples

So a 7 cell NIMH or NICD pack provides 8.4V (pressure).

The motor will draw electricity from the pack at a certain flow rate, or amps.

If you have a have a 650 mili amp hour pack, it can deliver a flow of
.650 amps (650 miliamps) for one hour. If you draw it out faster, it doesn't
last as long. So your motor might pull 6.5 amps for 1/10 of an hour, or about
6 minutes.

A 1100 mah pack has double the capacity of the 650 mah pack, so it should
last "about" twice as long but it won't make the motor run any faster just because it has more capacity. A bigger gas tank on a race car does not make it go faster.


What is C in relation to batteries?

C ratings are simply a way of talking about charge and discharge rates for
batteries.

1C, = 1 time the rated mah capacity of the battery. So if you charge your 650
mah pack at 1C, you charge it a 650 miliamps, or .650 amps.

1C on a 1100 pack would be 1.1 amps.

2 C on your 1100 pack would be 2.2 amps

Motor batteries are often rated in Discharge C and charge C.

So a 1100 mah pack (1.1 amp hour) might be rated for 10C discharge, so you can
pull 11 amps ( flow ) without damaging the battery.

Then it might be rated at 2C charge rate (flow), so you charge it at 2.2 amps
(2200 mah)

How did I do? Things clearing up?

If you have a 500 mah pack - any kind - and it is rated at 16C that means it
can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 8C that means it
can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 12C that means it
can deliver 12 amps

If you have a 1500 mah pack - any kind - and it is rate at 8C that means it
can deliver 12 amps

If you have a 1500 mah pack - any kind - and it is rated at 20 C that means it
can deliver 30 amps.

If you have a 3000 mah pack - any kind - and it is rated at 10 C that means it
can deliver 30 amps.

So, if you need 12 amps you can use a pack with a higher C rating or a pack
with a higher mah rating to get to needed amp deliver level.


One last point. Motor batteries vs receiver batteries

Some batteries can sustain high discharge rates. Others can not.

Those used as transmitter/receiver packs typically are made for low flow/amp
rates while those made for motor packs can sustain higher rates.

So, having a 600 mah pack does not tell you if it is a motor pack that can put
out 6 amps, or if it is a transmitter/receiver pack that would be damaged if
you tried to pull power at 6 amps. It is enough to say that they are
different.

Clearly a motor pack could be used for a transmitter/reciever job, but a
transmitter/reciever pack should not generally be used as a motor pack.

Basics:
http://www.modelaircraft.org/mag/FTGU/Part8/index.html (http://www.modelaircraft.org/mag/FTGU/Part8/index.html)

Lithium Batteries
http://www.rchobbies.org/lithium_battery_breakthrough.htm (http://www.rchobbies.org/lithium_battery_breakthrough.htm)

New Electric Flyer FAQs
http://www.ezonemag.com/pages/faq/a105.shtml (http://www.ezonemag.com/pages/faq/a105.shtml)

More
http://www.wattflyer.com/forums/showthread.php?t=1933 (http://www.wattflyer.com/forums/showthread.php?t=1933)

qban_flyer
12-13-2005, 03:26 AM
Great post Ed. Easy for everyone to understand and with links to boot. :)