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Old Aug 14, 2006, 07:05 AM
Watts Rule, Glows Drool
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Orlando E-Zone Squad Version XVII

Once again we have come near the limit of thread size and the old thread is now unsafe and must be closed.

here is a link to the E-zone V XVI thread:
http://www.rcgroups.com/forums/showt...34#post5903063
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Old Aug 14, 2006, 07:19 AM
Watts Rule, Glows Drool
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orlando, FL
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aerowizz,

Have you seen FMAdirects safe Lipo system?
http://www.fmadirect.com/products.htm?cat=38&nid=4

The system includes a charger that automaticaly detects the cell count, and will not allow you to accidentally change the setting. the batteries have a special connector for this charger and the cells (when used with this charger) are rated at a 3C charge rate, so you can charge in 20 minutes.

a unique part of this FMA system is that every model gets a discharge module, that connects between the battery and ESC and will not allow the battery to ever be over-discharged (it automatically lowers the throttle as the battery gets discharged).

The price of the battery and charger are a little more than most, but not outrageous. buying a discharge module for each model can get expensive though. I have never seen anyone use one of these systems, but the ability to charge at 3C seems nice.
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Old Aug 14, 2006, 08:39 AM
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Fine tradition during new thread creations!

Word.............Word........................Word :d
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Old Aug 14, 2006, 10:07 AM
Aerowizz
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[QUOTE=dogon1013]aerowizz,

Have you seen FMAdirects safe Lipo system?
http://www.fmadirect.com/products.htm?cat=38&nid=4 QUOTE]

This FMA lipo system looks promising. Definately a step in the right direction. However A123 systems seems to have an even better Lithium ION Battery solution which was concieved at MIT using the latest in nano-technology materials and processes.

Most of the Lithium is extracted once fully charged and according to their site "A123Systems uses patent pending laser-welded multi-plate tubular construction that is vibration and abuse tolerant. This design offers unsurpassed hermetic sealing with the lowest internal resistance, a key benefit for mission critical and medical devices or applications requiring extreme calendar life such as Hybrid Electric Vehicles."

Take a look at thier nail penetration test, quiet impressive. They have data and risk reduction testing that backs up their statements. I will keep a careful eye on their development and hobby use in the near future.


http://www.a123systems.com/html/tech/safety.html

http://www.a123racing.com
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Old Aug 14, 2006, 10:51 AM
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Yep
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Old Aug 14, 2006, 11:39 AM
Watts Rule, Glows Drool
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orlando, FL
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I don't plan on putting a nail thru any of my packs. I think those cells were under development for power tools. the construction buisness is more likely to see a nail go thru a pack?

those A123 cells have been in development for some time, but those are hard cell Lipo's if I remember right, which don't offer much benefit for RC flight, over Ni based cells.

the risk of overcharging can be eliminated by the use of smart chargers, and the risk of over discharging can be eliminated by the use of proper setups (testing amp draw), and electronics in the power system. This is how cell-phones and laptops charge and discharge safely.

No matter what power source you fly with there is always the potential of fire after a crash due to damaged power source.(I would imagine a crash of a gasoline or kerosene powered model would be the worst) Those A123 cells, as well as Nimh, Nicd's, and Lipo's can ALL get shorted out by a crash. all it takes is the connector or wires to get crushed together and you have a short which will create LOTS of heat and could set something on fire.


PS I believe following safety instructions is the real "step in the right direction" ALL accidents I have read about have been caused by not following the safety instructions, mostly, improper charging/discharging, or notwatching a damaged pack.
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Old Aug 14, 2006, 01:09 PM
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Quote:
Originally Posted by dogon1013
I don't plan on putting a nail thru any of my packs. I think those cells were under development for power tools. the construction buisness is more likely to see a nail go thru a pack?
How about a screwdriver? Well, about 5 months ago at Moon Port Modelers someone with a Puffed up battery who perhaps got pretty peeved about the situation attempted to hammer in an old screwdriver in and everyone backed off quickly thinking they were going to witness some action.....well, NOTHING!!!!
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Old Aug 14, 2006, 01:21 PM
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Quote:
Originally Posted by dogon1013
No matter what power source you fly with there is always the potential of fire after a crash due to damaged power source.(I would imagine a crash of a gasoline or kerosene powered model would be the worst) Those A123 cells, as well as Nimh, Nicd's, and Lipo's can ALL get shorted out by a crash. all it takes is the connector or wires to get crushed together and you have a short which will create LOTS of heat and could set something on fire.
Okay, Toby has a very good point here......

In those old threads that I posted yesterday you will perhaps read one incident that I had with my GWS Beaver at HomeDepot field and right across the WaterFord Lakes Town Mall....I slapped in a new battery and took off towards the East as this is where the wind was coming at us and I turned Left (North) and parallel to Alafaya Trail and then, I found myself in a scary state of affairs....nothing seemed to work...I turned and throttle up and nothing seemed to respond. The model seemed to freeze exactly where my last command and it floated for the BEST LANDING EVER and all by it self!!!!

I ran towards the model 300 yards inward (North) of the park side from Homedepot and found smoke coming out from the model and quickly turned it upside down to reach for the battery .....it was smoking and all the heat shrink melted and could not get the dang "JST" connector apart so, I just yanked off the battery with the connector out and threw the battery in the air and landed several feet away. The battery continued it's disintergration....and I left with the model intact.

Certainly, if this had been a Li-POLY....there would not have been anything to recover when it landed as I suspect the Foam would have melted seeing how these Li-POLY's can react. The failure analysis was that the "JST" connector failed and the two contacts made contact and acring shorted out the battery and explains the reason why the model did not respond. I was so....lucky that I turned her towards the North and long the Trail as it would have landed across the Trail in perhaps the Fountain pond area!

I quickly learned that those "JST" connectors have a limited cycle times (Connect and Disconnect)!!! Soon after this, I went to Ultra Deans on all my setups.
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Old Aug 14, 2006, 03:12 PM
Jungmeister 55
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Orlando Herndon, Florida, United States
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Agree with Toby and Carlos...I remember loosing my Homebuilt Jungmeister for the same reason. I never went back to using JST connectors on any appication that pulls more than 2 or 3 amps.

Lithium ION batteries existed before the newer Lithium POLYMERS we use today. They are tougher indeed. But they're also heavier and if not charged right they could very possibly burst with a pretty powerful and damaging reaction when the case bursts.

Lithium Polymer cells are "soft" in nature and they just "puff up" without bursting if damaged.

In two years I've only damaged on 3S1P T.P. pack and that because I flew the plane way below the cut-off voltage level...

Gerry.
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Old Aug 14, 2006, 04:23 PM
Things are looking up...
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So 50,000 views and 3300 posts is enough now to kill a thread? Or was it the sudden rush of activity when everyone wanted to talk Lipo safety?

My only Lipo - an Apex 3S1P - is treated like a baby, carried in a cushioned case, but so are my NiMH's. I've had two NiMH's go critical during charging after maybe 100 cycles each, most likely due to a bad cell, but I have not gotten the Lipo past luke warm in any full power flying of my larger FW-190's. I'm just not using the battery to capacity. Plus, I made a foam bay for the pampered Lipo in the FW-190 fuselages just in case I crash it, not so much due to safety, I just don't want to damage and lose a battery that cost 5 times more than my others. To be "safe" I charge the Lipo outdoors and keep an eye on it (what with all the lightning in the area). My Hobbico charger will only charge the a Lipo at 1 amp, which is a pretty safe level and the 12V power supply I run it on (the charger that is) is only capable of 4.5 amps at 12V. But heck I watch all my batteries after having a NiMH get boiling hot and melting the shrink wrap charging at only 1.6 amp and staying that way for 30 minutes even after unplugging it.

I'm just glad it was a cheap $12 NiMH pack I dropped on Carlos' car and not my precious Lipo. His car broke my battery. (actually it is just fine - just a bruise)

Rick
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Old Aug 14, 2006, 05:20 PM
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Quote:
Originally Posted by mechrick
I'm just glad it was a cheap $12 NiMH pack I dropped on Carlos' car and not my precious Lipo. His car broke my battery. (actually it is just fine - just a bruise)

Rick
Hey Rick,

Actually, the Pack landed on my Roof / Rear Glass panel and they do flex to some degree would explain why your battery pack still works, as I whole heartly beleive that if it would have landed on that hard asphalt driveway the battery would have been unusable.

Ain't you glad that Carlos showed up!
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Old Aug 14, 2006, 06:41 PM
Watts Rule, Glows Drool
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The forum admins have said that 3k posts is usually the max, and it helps with searching if the threads are kept relatively small. I think we had one get up to 5K posts one time.
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Old Aug 14, 2006, 08:39 PM
Robot, RC Pilot & Builder :-)
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Roanoke, VA, USA
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Quote:
Originally Posted by guapoman2000
Kevin,

That's a perfect substitute! Perhaps not in the brick configuration like the one in Aeromicro but, it will get the job done.
Hey Carlos, Thanks for the advice. I guess I will be picking up some Round 2/3A size Ni-MH's pretty soon.

If any of you guys could adivse me regarding whether I should try a higher or lower gear ratio, and/or change to a different prop (I've been flying with a GWS 1080 prop), in order to increase the speed of my current Beaver setup, I'd appreciate it.

Or, where can I read up on how to select a prop to optimize the plane's performance (i.e., speed)? Are there some good books or websites you could recommend on this topic? (Mike already told me about one RC airplane book that looks really good, and I've ordered a copy of it: ISBN 1-85486-190-5, "Model Aircraft Aerodynamics.")

I appreciate the help!

Thanks!
Newbie Kevin
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Old Aug 14, 2006, 09:14 PM
Watts Rule, Glows Drool
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orlando, FL
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I would suggest you pick up a copy of "Basics of RC model aircraft design" by Andy Lennon. It covers everything you could ask for, without spending 7 years in college, and it's only $20. (ISBN 0-911295-40-2)

It covers "practical Techniques for building better models" and includes choosing airfoils and aerodynamics, as well as CG, Wing design, Stability design, reducing drag, landing gear design, design for aerobatics, tailess plane design,.....

26 Chapters in all. Chapter 18 is "Propeller selection and estimating level flight speeds"

This book doees not go into electrics specifically, but every other aspect that you could think about is answered (Like why the C-5 Galaxy has anhedral, instead of dihedral?) I would Consider this the Bible of RC design, just because it covers so much. It's the best $20 I've spent on a book in a long time. I think I had Barnes and Nobles order it.

Toby

PS
here is a simple speed calculator someone posted. You need to know the rpm of your prop.
http://www.pponk.com/HTML%20PAGES/propcalc.html
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Old Aug 14, 2006, 09:16 PM
Watts Rule, Glows Drool
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Here is another usefull online calculator worth bookmarking:
It's often called P-calc
http://brantuas.com/ezcalc/dma1.asp


The beaver is a rather high-drag airframe. To get any speed out of it you will also need thrust. It's difficult to say what you need to do without measureing the amp-draw of your motor at full throttle.

a 1080 prop seems a little high pitched, you might be trying to spin that prop a little too fast. I would try a few different props out, or go to a lower gearing (prop spinning slower). This will lower the amp draw, which will decrease the load on your batteries and hopefully keep the voltage high enough to give you a little more rpm. a similar effect will happen by going to a lower pitch prop (APC 10*7 is a great prop). the lower pitch will put less of a strain on your motor, and it will draw less amps.

most multimeters allow you to measure current up to 10amps, I bought a cheap digital one years ago at wallmart and it still works good for amp measurements.
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