flybyjohn

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All right, this evening I lost my 4 star forty. You can check it out in crashes and rebuilding forum page. Well the short and skinny of it is I took off with full batteries and in full control. Flew for at least 8 minutes and doing different manuvers and then right when I go to line it up for a landing, I slow the throttle down and then I get full up elevator with no control input. then the engine goes reving again and then cuts again and then full up elevator again. I may have had a little control but only for fractions of a second and then no response. but the servos were doing all sorts of things because the plane was going haywire. I was flying in a soccer field adjacent to a freeway in Montana. After the crash I pluged in the battery that was laying on the ground and the servos were twitching with little control. I assumed interferance in the area but when I got home did the same test and the servos worked for a few seconds then started twitching again. Checked receiver battery and all was good, 4.98 volts on a 4.8 volt 2100 mAh pack. the radio is airtronics rd8000 and the receiver is an older, old style plugs airtronics dual conversion 6 channel.

I want to rule out radio interference because I would like to fly at this location again.
I think that if it was interference then I may not still be getting interference now.

I would like to rule out my tx. It has a full charge.

Maybe the rx antanea has broken somewhere in the plastic sheathing?

Maybe the rx is just old and years of vibration has caused it to malfuntion.

Any Ideas out there that may pinpoint my problem or allow me to rule out any components.

Thanks
John

BuschBarber

My Feedback: (2)

Were you using an ESV to measure the battery voltage and if so, does the ESV put a load on the batteries? Unloaded voltage may appear OK, but put a .5a or 1a load and what does it read. The reason I ask is that some flyers still use a standard multimeter instead of an ESV designed for RC batteries, with a selectable load.

flybyjohn

My Feedback: (2)

no, I wasn't using an ESV. I have heard of testing them under a load but don't have that equipment right now. I think I can dig up some information on how to put some resistance in the circut and try and measure it again.

The funny thing is that I took the receiver and battery out of the plane now and set it up on the kitchen table and all works good without any glitches.

Campgems

Is there a flying field close to where you were flying? A week ago monday, we caught some guys flying within 2500 feet of our field. Interference from another TX goes both ways. That is a possibility.

A question, when you put the battery back in and the servos were dancing, was the TX still on? If not, that could explain the jumping servos.

We had a case a few years back that involved a Highway Patrol relay tower that was putting out a dirty sighnal and feeding into our frequencys. Paging towers are a great source of interference. Our club has a good spectrum anylizer and it shows a paging freequency snuggled up to the Ch 11 end of the band, In our case, it is a clean signal, I took the anylizer to Savannaha when I visited my son because the guys at his field were complaining about hits. They had a paging tower next to ch 11, but it was spilling out wide on both sides of the base fequency.

At our field today, one of the guys was flying one of the RTF foam texan, one that came with TX and all the electronics already installed. It was on CH 19. Well after a few mintutes, he was making a low pass near the end of our runway and the plane went nuts for just a second or so, then straighten back out. The next pass over the same area and it took another hit. 3 our of four times when he flew over that end of the runway, it would shudder and shake then straighten right out. We got out the spectrum anylizer and I sat an watched it while he flew that pattern agin and again 3 our of 4 times he took a hit, but the spectrum anylizer showed no interference. What we think might be happening is that the barbed wire and woven wire fence around our fild may be the problem. He was coming right over the corner of the fence when he was taking the hits. One thing I did find though was that his TX was not on frequency. It was slightly of to the low side of CH 19. That coupled with the fence may, and it a big may, have caused the problem. He is going to put a Spectrum RX in and not take the chance of loosing the plane. By the way, more than one other guy has complained about the same area. Who knows???

If you can, join a club and fly at their field. They will probably have equipment to detect interference and will probably know of Dirty Channels to stay away from.

Good luck

Don

flybyjohn

My Feedback: (2)

Campgems, thanks for the reply. My tx was on before I plugged in the battery to test it after the crash. The nearest and only flying field in the Helena Valley is over 5 miles away. My plane was straight out to the corner of two fences when this happened also. Another thing I was thinking about also is that I may have had my tx antanea pointed straight at the plane when this happened. I have heard that this is a no no and I know better. Whether this was the problem or not I do not know. The first approach for landing I made was the same pattern with my tx in the same position with reguards to the plane as the second and there were no problems with that pass although with the second pass, I was about half as high as the first.

BuschBarber

My Feedback: (2)

I am sure this applies to batteries used for all purposes, but with regard to the batteries we use in RC equipment, you need to test the batteries under load. You can get a reading of 5v, with a 4.8v pack, using an ESV with NoLoad, and when you apply the load, the voltage can shoot down to 4.3 and below in a matter of seconds.

I can take a fully discharged Rx pack and put a 5 minute charge on it and it may read 5v when I first turn on the ESV, but it will start to drop, after a few seconds. I check batteries Before and After each flight. If the voltage is close to what I consider the Cuttoff point, I will field charge, to Top Off, and then fly. I have had battery packs fail as I was taxiing out for takeoff, even though the voltage looked OK in the Pits. It happens very infrequently, but it can happen anytime.

If I am not sure I am getting the Capacity out of my batteries, I will Cycle them. I try not to Cycle more than once a month as it does wear down the batteries.

If you fly several times a day, with the same batteries, you get a feel for how much the voltage is dropping after each flight. It is usually the first flight of the day that I am most worried about because I have no reference point other than the ESV tells me the battery voltage is OK

Most of the new Tx's have reliable voltage readings and not just RF needles

I use a .5a load for NiCad/NiMh batteries and a 1a load for Lithiums. I tend to use Lithiums for all my Rx and Tx packs. They are so rock solid, charge quickly, and hold their charge for a long time.

flybyjohn

My Feedback: (2)

BuschBarber, Thanks for the info on the ESV. I looked it up and found out how to make a simple one with a flashlight bulb. I do not know how many amps I am drawing from the bulb but the side says 6v lanterns/ 4.8V - 0.75A 3.6W . I took the two batteries that I was deciding between that day I flew and the one that I decided not to use showed 4.8V before plugging in the bulb and the other was just above 5V. I used the 5 volt one. Now with the bulb as a resister, the 5 v pack drops to below 1.1 volts in 5 seconds and the 4.8V only drops to 4.5 and slowly goes down from there but it is very slow. The 5 V pack does not even keep the bulb lit beyond 3 seconds. but then as soon as it has 5 - 10 seconds to rest it is up to 5 V again.

I guess this means I can chalk this up as a failure due to battery pack. Its is a electrical/mechanical failure not pilot error, however in this hobby, the pilot is usually the mechanic so I guess it was the pilot after all.

Thanks again for the help,

John

BuschBarber

My Feedback: (2)

Good luck!! I love RC. If I have a crash, I like it to be one where no one gets hurt and I could not have prevented it. It seems that the day I lose a battery is the one day I forget to check it, even if I do it every day for the previous 364 days. The same is true for selecting the correct Model Memory and making sure the Control Surfaces are moving in the right direction. Fortunately, on 2.4, I do not have to remember to Extend the Antenna.