SeamusG

Just sharing ...

I'm (finally)adding a new step in my preflight - a battery load test. Guess I've been lucky for the last 3 years. Ifound out that a 6.0 v battery that drains to 3.5 v in 2 seconds of "load" will NOTsustain flight.

Great day, 65 degrees 3-7 mph, no clouds. Got the LT-40 charged to nearly 7 v at the house. During the 2nd flight there was a sustained turn (practicing figure 8's) and the plane held the aileron &throttle settings and spiralled in from 150 feet or so. Helpless feeling - no radio control.

Good news. Nylon 1/4x20 wing bolts sheared. Nylon 1/4x20 landing gear bolts sheared (tail dragger). Fin &stab need fixing. Both wing tips need fixing (cartwheel). Alittle wing leading edge breakage / crack points, maybe a rib. Not bad given the alternatives.

So all you beginners, have a volt meter in your radio box with a load test and (oh yea)use it before each flight. Yea, 99% it'll be a yawner but maybe it will save your plane. Just maybe.

Lnewqban

Sorry about the mishap, SeamusG.
Sure you will have it back in the air in no time.

Great advice!

Batteries and switches are the two first points of failure statistically.

More about those batteries:

http://www.hangtimes.com/redsbatteryclinic.html

MetallicaJunkie

ive made it a habbit to check my batteries before every flight... it just takes a small effort to avoid a potentially dangerous situation or complete model loss

CGRetired

My Feedback: (1)

I have preached this for several years now. What I use as a quick check is the Voltwatch2. It is no replacement for a voltmeter, but is a very good tool for checking the battery condition before and after each flight.

CGr.

LargeScale88

I'm starting to get into full scale airplanes (getting my private pilots license), and every little detail is on preflight. Of course, your not watching it fly from the ground, your flying it in the air, so you want to be cautious.

Anyway, I check my RC planes like I check the full scale during preflight.

Pre flight can save all your airplanes, and save you from taking home pieces at the end of the day. You never know, landing gear screws, engine mount screws, servo screws, anything, could have came loose during the last flight, then the next flight goes bad.

Jason

CGRetired

My Feedback: (1)

Absolutely. That's the very first thing my RC instructor drilled into me. He would say "Alright Captain... What are you going to do to start this session?"

Of course, it was always the same answer.. for the first flight of the day, preflight, starting before I mounted the wing, starting at the rudder and working my way forward to the prop. This included checking the battery for charge condition. Then, assemble the plane.. mounting the wing... he would count the rubber bands on my Tower 40, then on the NexStar, watching me bolt it on. He would shake, rattle, and roll the thing and then have me do the same thing.

When it was ready for flight, it was indeed ready and I was assured that nothing would fail in flight.

I still do that. That may be why I've not had many crashes over the years. Those that I DID have were due to my failure to do something or doing something stupid.. all of which I've documented here on RCU, and that has not been many... I contribute that to my instructor drilling the preflight into me from week one, day one, hour one, and minute one.

Now, I rely on my voltwatch for most of my pre-flight inspection. All but the very first flight of the day, when I check the battery, batteries on two planes because I have two planes with parallel battery packs. For the first preflight, I check the batteries with the loaded voltmeter. After that, I rely on Voltwatch2 to keep me honest.

CGr.

SeamusG

The voltage looked good (not great - but good) until I put a load on it. Then if fell flat.

I've been a crew chief for a multi-car SCCAnational team. The pre-weekend, pre-day, and pre-session check lists were very detailed. Just haven't smelled to coffee (until today) to apply a similar approach to an RCairplane. Past lives I had a Class Alicense. Ditto for a tractor trailer.

Phoenixangel

I keep one of these in the flight box, its simple and effective. Easy enough that my 7 yr old can test my batteries for me while I drink coffee and watch others fly. http://www.horizonhobby.com/Products...105#reviewsTab

CGRetired

My Feedback: (1)

What's nice about Voltwatch2 is that it gets plugged into a vacant channel on the RX or Y cabled to share a channel. Because it is connected to the receiver and "see's" the voltatge as the receiver would see it, well, it's a loaded measaurement and you get the reaction on the LED's as the receiver see's the voltage.

So, if you use it, when you turn on your RX, and move the TX sticks, the current draw shows a direct relationship to voltage that Voltwatch2 sees, and you get immediate feedback as to battery condition. It has several green LED's, followed by a couple yellow LED's and a red LED. Moving the sticks will cause a draw and the LED's will flicker down a bit, depending on how the battery deals with the load. It's a great way to track binding linkage, by the way.

Anyway, if you get a flicker into the red, well, it may indicate a problem or just that you need to charge the battery.

It's a great way to monitor your voltage "on the fly" and keeps the warm-and-fuzzy's around.

CGr.

SeamusG

Thanks for the endorsement CGRetired. Will definitely look into them.

CGRetired

My Feedback: (1)

They are by no means a replacement for a good ESV (Expanded Scale Voltmeter) but a great and inexpensive addition to your glow powered planes. As I said, all of my glow planes have one installed.

CGr.

jester_s1

Another option if you don't want to buy a voltwatch for every plane is making a servo connector for your standard electrical multimeter. You can plug it into an extension on your receiver the same as you do the voltwatch and get a digital reading of your voltage. You can even grab a control surface and move it to nearly stalling the servo to simulate a worst case scenario in flight condition.

jetmech05

Just add a thought here....make sure the volt meter you are using puts a load on the system....most digital voltmeters for commerical use like Flukes will not put a load on the batteries...all it tells you is the voltage...not whether the batteries will last under a load....as said above an expanded scale voltmeter will load the batteries as will some digitals for RC use...mine has a selectable load .5, 1, or 2 amp load.....Plus they're cheaper than commerical voltmeters

batdog

My Feedback: (1)

Is it possible in a 40 size plane to run a back up battery? Does anyone do it? I think I have read the larger planes do.

Lnewqban

batdog,

Read the "Parallel Operation = Reliability & Flight Time" in the link I have provided above.



There are visual and audible alarms offered by Tower:

http://www3.towerhobbies.com/cgi-bin...&I=LXHDJ2&P=RF

http://www3.towerhobbies.com/cgi-bin...&I=LXSZ87&P=RF

The second one saved one of my planes that developed an electric problem in the air, which was associated to vibrations.

Since then, I check my Voltwatch's lights while moving the sticks and with the engine running.

batdog

My Feedback: (1)

Lnewqban Thanks for having me look at the link yo provided. Thats a easy fix but will the weight be a factor in a 40 size (I don't think it would be) but want your opinion please and what about in a smaller plane say 25 size? I like to have back up systems in place if possible.

CGRetired

My Feedback: (1)

For smaller size aircraft, the load on the battery pack is not as great as it is for larger, even 40 size planes. Where the redundancy comes in is with larger aircraft with 5 or 6 servos and a good load on the control surfaces while doing maneuvers.

I have two 90 size pattern planes and use the parallel battery approach. Both have OS 1.20AX engines... weight change from one to two battery packs in negligable. I have spare channels on the receiver so one battery goes to the battery port and the other goes to a spare receiver slot. Or, you can always use a heavy-duty Y cable and paralled them that way. Each battery has it's separate switch.

Ok, that's the basics. Weight wise, well, as you said, smaller, say 25 size planes are probably not good candidates for parallel battery packs because and added several ounces might make a difference on how that smaller plane flys and handles. As you move up in size and power available, that amount of weight becomes less and less of a concern so it becomes a point of experimentation. If it works, go for it. If you don't like the way it handles with the added weight, well, remove it and go to a larger battary pack.. say from 1200 to 1800 mah pack.

CGr.

pmerritt

My Feedback: (118)

Couldn't have said it better. A volt watch or volt meter will only tell you registered voltage. Get a load tester and run it two or three times. My habit is as soon as I get the charger unplugged and putaway(always are charging on the way to the field) , Irun the load test a couple of times and watch for any significant drop in voltage. For about $25.00 you can get a good one and that's a small insurance policyprice from losing a plane due to abad battery nearing failure!

CGRetired

My Feedback: (1)

It seems that I have to explain this every time Voltwatch2 comes in during these discussions.

First of all, the voltwatch is not a replacement for a good LOADED voltmeter. Everyone should have a decent ESV in their flight box.

Second, the voltwatch, by design, IS a loaded voltmeter. It is in the circuit when everything on the plane is powered up. By that definition, it is measuring the load on the battery during operation and gives you an instantaneous indication of battery load.

Put one in, turn everything on, and wiggle the sticks. The LED's will flicker "down" to show what the load is during those stick movements. If it goes to the red any time, well, it is showing a couple of possible conditions.... a weak or discharged battery, a bind in the linkage, or the control surface.

It is a healthy way to monitor battery conditions immediately before and after each flight.

Mr Cox

I just want to support the use of a voltwatch. It measures the voltage under the load present in each particular plane, just want one needs. It can be mounted inside a clear canopy for instance and makes pre- and post-flight checking very easy. Well worth the money.

LargeScale88

Another system I use for checking battery voltage is the Dynamite system from Horizon Hobby. This puts a load on the battery, which its better to check with a load, and it gives voltage for "under load", because a standard volt meter may give the voltage with no load, and the battery may be close to dead, but still give a high voltage.

Jason

Lnewqban

The importance of redundancy grows exponentially with two factors:
1) The size and weight of the model (more capacity to produce harm and liability in the event of a loss of control).
1) The cost of the model (more investment to protect against crash).

Yes, you can do it for smaller and less costly models, but the price to pay is the extra weight.
As mentioned above, that is your choice, and it is not easy to find light small capacity batteries nowadays (working in parallel they can have half the capacity than one single battery).

There is an intermediate solution for small models, which is using a five cells battery and two switches.
Any radio system can work with 4.8 volts and 6.0 volts, and a battery fails one cell at a time, other than due to low charge.

Copied from

http://www.hangtimes.com/rcbattery_faq.html

"Q: Isn’t the pack the most likely thing to fail on the airplane? Why back up the switches?

A: Whups.. looks like the Wives Tale Tag Team has been busy again. The likelihood of a tested, known to be in good condition and properly charged pack suddenly suffering a cell failure in flight is unlikely. Falling short of a castatrophic weld or cell interconnect casualty the two components on the aircraft most likely to fail during flight operations are the connectors or the switch assembly; both items being very susceptible to vibration and fuel soaking damage leading to an ‘intermittent’ operating condition.. something that’s insidiously difficult to detect before it costs you a plane.

Q: What can I do to protect myself against the ‘unlikely’ event of a cell failure?

A: Cells typically fail ‘shorted’.. that means that falling short of a major mechanical failure of the battery pack cell interconnects (why you should NEVER fly a ‘soldered’ pack), electrical continuity of the system remains intact.. in other words, if a cell shorts out, the system voltage drops by the value of the failed cell. To avoid allowing the voltage drop of a failed cell to threaten the system, just use a 5-cell pack instead of a 4-cell pack. To avoid the remote possibility of a weld or battery interconnect strap failure, using parallel packs does the trick & covers all the bases."

In my experience, I have seen more crashes due to improper charging and overlooking of pre-flight check outs, than due to battery failure.
Faulty switches and loose or dirty connections (in battery, servos, receiver) have claimed another good number of victims.

Here it is, another cheap insurance against loose connectors:

http://www3.towerhobbies.com/cgi-bin...?&I=LXHVC9&P=7

Rodney

I also tout the advantages of a Voltwatch. If you could only have one (a loaded VM or a Voltwatch) I'd always take the Voltwatch. Properly used (checking before and AFTER each flight) you can be assured of the capacity for the next flight. The big added advantage of the Voltwatch is that it is almost as good as an oscilloscope in checking for bad wiring between the batttery and receiver as well as giving you a warning if you have any servos going bad and drawing high currents. When you wind both sticks around at full deflection and see those LED's drop down into the red, you can be assured you are running a risk to fly. Any momentary transient shows up warning you of bad contacts or high impedance wiring. A loaded volt meter will not do this. Now, I'm not saying not to use a loaded voltmeter as it give valuable information too, just not nearly as much as a Voltwatch will.

Lnewqban

Precious information, Rodney!

What data is more useful, the one that the Voltwach shows while moving the sticks or while holding them in full deflection for a moment?

CGRetired

My Feedback: (1)

Well, I hate to contradict information from othes, but I can tell you that I did, indeed, have a cell failure in a pack on my Venus II. I had two batteries on that plane, all was ok on take off, and I flew for about, oh, 12 minutes or so. When I landed, I checked the batteries with voltwatch.. one gave me a good reading, then when I switched over to the other battery, well, it was in the red.

I checked it with an ESV and I barely had 2 volts in a 6 volt pack. A cell failed in flight draining the battery almost completely. The only reason the plane continued to fly was because of the other battery.

CGr.