Horror Story

Since no one has yet, I will. ESV stands for Expanded Scale Voltmeter. This means that, instead of the 0-150 or even 5000 volt range of many meters, this meter reads a very narrow band, usually within 10 volts or less, and it does so with great accuracy, since the scale is so small, and "expanded" over a standard meter face. ESV's may be analog or digital, and may or may not have a switchable "load". This load mimics the servo drain in the airplane. Dr.1 Driver "There's a Hun in the sun!"

If you cycle you batteries a couple times a season, and chart them, the chances are low of having a problem. As long as you know where you are on the discharge cycle, there is a good safety margin.

-- Jim in NC

And the expanded means you can read finer than tenths of a volt.

What are commercial ESV loads? I use a home-brew digital with a 350ma resistor in line.

-- Jim in NC

Even a very simple thing such as having an inexpensive VoltWatch built into the model is a quick and easy way to find at least some potential battery problems between ESV checks.

If that was a brand new pack, and there is no gross or obvious physical damage form the crash, I wonder if there's product liability there. Dr.1 Driver "There's a Hun in the sun!"

What is the color code on a 350ma resistor Jim? ;>)

Ah...red and green pokadots? Dr.1 Driver "There's a Hun in the sun!"

While we were having lunch Sunday, I joking asked him if he had considered that. He said that since this fiasco was mostly his fault, he was going to pick up the tab. Normally, it would be quite refreshing, someone actually taking responsibility for his own mistakes, but for this guy, it's par for the course. You would have to know him to really appreciate it.

That was the first thing everyone thought. Watching the video, when the pilot declared that he didn't have it, he started that he was on channel 17. Everyone who had a transmitter on that channel, including the camera man, hurried to check that they didn't have a transmitter left on. None found.

If I manage to get it posted, I'll let everyone know.

That what made this so unusual. In most cases, the plane goes right in, especially a big twin. The fact that it flew around so long was simply amazing. The video is of really poor quality because the camera man, in his elevated excitement, had a hard time following the plane. The panic conversation the sound track picked up is quite interesting. The pilot actually power cycled his transmitter at one point in an attempt to re-establish control. As the plane drifted further out, pretty much doing the same kind of 45 degree loops until it finally spiraled in. If I hadn't seen the video, I would have had a hard time believing that the flight really lasted seven minutes.

Sounds like a minor case could be made for a failsafe setting that would at least close the throttles. In this case it sounds like the throttle springs on the carbs would have to do the work if indeed the battery went completely away.

I had weird problems after installing a new battery in my chopper. I bought a new JR 1400MAh 4.8v nicad pack, charged it at 140MAh for 20 hours, then cycled, and repeated 4 times. I have an on-board battery monitor, and my governor also has a voltage monitor w/failsafe (and I have my PCM programmed for failsafe). Anyway, about 2 minutes into the second flight (after checking the voltage before take-off), the chopper would stop responding, then about 1 second later, respond again. Trying to bring it back in, it started again, but while I still had servo control, I didn't have throttle response since the governor was going into failsafe. On the ground, everything checkout out OK, and battery voltage seemed OK. I swapped out the pack with another JR 1400MAh battery I just purchased and cycled as well and had the same problems. After more head scratching, I noticed the voltage indicators would suddenly drop to below 3.8 volts, then spike back up to

4.8-5.4 volts. While moving all the servos, it would drop to below 3.8 volts and go into failsafe. I bought a new battery pack (NOT JR), and have not had this problem. The LHS told be that I charged the batteries wrong and that is why I had problems, but I charge and cycle my true-blue Futaba packs and my 2 no-name packs the same ways without any problems. I am having problems with my 2 new JR packs (also, I had a JR pack in my airplane last year and about 2 months into the season, it would no longer cycle). Needless to say, I am done with JR packs.

Unless he's using coreless servos, or has a great mechanical advantage built into the linkage, the throttle spring would have a hard time closing the butterfly against the servo gearing. ANY fail-safe device may "fail-safe" at the most inopportune time. It could instruct the servos to put the plane into loops, right over the crowd. It could put the plane into "straight and level" when it's in a 45 degree dive towards the pit area. The BEST fail-safe device is continuous checking and rechecking. Dr.1 Driver "There's a Hun in the sun!"

I built the thing from some plans in a RC mag many years ago. I think it was called the milliamp wizard, or something like that.

Mine has a variable resistor in it, which reads through a meter, and can read from 0 to 1 amp., and on another scale, higher. It has a switch to use it as a load, and also a way to pass juice from the battery to the receiver to check for servo binding, ect. All that is left to do to use it as an ESV, is to put the digital volt meter with it, then dial in the load and read the voltage.

Thus the question of how much load commercial units use.

I'm not an electronics whiz, but I understood the article enough to build it, at one time.

-- Jim in NC

If the packs were tied directly together (paralleled) then the good pack would try to charge the bad pack and you would still end up with low voltage. If you added some charge protection diodes (not in the packs but in the cabling in the plane) you could prevent one from charging the other. However, the plane would need to be able to run off of just one pack at a time (i.e., you are using two packs for protection or to extend flight time, not to allow more current to be drawn).

Just my opinions as an electrical engineer, I'm very new to the hobby (

Time again I guess to point all to the Article on the subject of parallel packs at the Battery Clinic. . . . ".Parallel Operation = Reliability and Flight Time" this should answer most of the questions.

-- Red S. Red's R/C Battery Clinic

us out for "revolting" information.

added some charge

could prevent one

off of just one

flight time, not

Interesting article. I have never worked with NiCads. My experience was with using lithium batteries in parallel in a project at work. We have to use blocking diodes to meet Underwriters Labs' criteria for using the batteries in an approved product.

He doesn't mention Nimh or Lithium Ion cells in the article, just Nicads. I wonder if they are different. I would suspect the Nimh's are similar to Nicads and the Lithiums are similar to my Lithium experience at work. I guess I could check the data sheets.

Bob W.

The behaviour noted is consistent with an intermittent high resistance contact in the pack.

A hogh resitsnace pack can do weird things - as teh sevos draw power, teh vlots go down below what is necessary to operate the reciever and/or other servos. Sometimes they just don't work, sometimes they drive to endstops.

Failsafes won't work if the power to the failsafe fails.

I disagree with some of what Red Schofeld says, but the absolute dependence of our models on 100% rock solid battery power to the avionics is not an area of disagreement. How to achieve that is...more open to discussion.