It was a nice early evening at the flying field. Not too much wind and a bit of lift early on.
I was moving the sticks and it just did its own thing. I was stupid enough to do it twice; just to prove there was a problem; yep, confirmed.
I got one good long flight in with one climb and lots of gliding. I then decide to plug in the radio variometer. This just plugs into a spare receiver channel and transmits beeps back to one of my 433MHz tracking receivers.
Launch was good and it flew off towards the golf course. Well above the trees I noticed that it wasn’t responding. A bit confusing at first but not to panic just yet. There was plenty of room and it was flying nice and level in a straight line. Control returned and I turned for home then it was lost again. A bit more of this, turning away from a large tree and a normal glide in and landing.
As this was the first sign of trouble I suspecting something to do with the variometer, maybe the 433MHz interfering with the 2.4G RC receiver. So I relocated the variometer well away from the two RC antennas and tried again. I didn’t suspect the variometer of causing a BEC problem as it only draws about 15mA.
I launched again and did a long slow climb out down the field at half throttle. A slow turn and large figure-8 and control was lost again, as it flew off towards a row of trees. Much lower this time so there was less room to move. Control returned in time and just long enough to turn back onto the field. A large uncontrolled turning descent into the ground and a wing tip caught the grass.
The only damage is to one wing, right where the dihedral changes, so it’s quite a clean break and should be easy enough to repair.
The ESC and BEC
After doing a few tests, I’m pretty sure that the BEC in the ESC got hot and shut off momentarily. I was cruising on about 1/2 throttle (worst ESC heat generation) before the lockout, combined with the heat from 4 mini digital servos drawing about 0.8A with a small load. The heatshrink on the ESC is split along the edge as sometimes happens when it gets too hot.
There is a plastic vent on each side ducting air into the fuselage just ahead of the ESC, but it seems not quite enough.
The ESC/BEC should be easily able to cope with the current but only with enough ventilation. It’s called a 3A BEC, but that is only very short term as it’s a linear regulator with almost no heatsinking. 0.8A in a closed space with little or no ventilation and it gets very hot.
In the picture, the silver thing is a fishing weight and the EPP foam forms a battery compartment for the 2200 3-cell Lipo.
Was it a Radio dropout?
I wondered about that but there is definite evidence of heating on the ESC/BEC. I’ve got thin black heatshrink on it which splits when overheated. The motor wires are soldered directly to the ESC.
The radio is Corona DSSS 8-channel long-range with diversity antennas installed in the fuse at 90-deg to each other. They state a range of 2.5+ KM. I have read a couple of stories about these dropping out but in all my range testing etc. I’ve not seen a problem. I have the matching 4-channel receiver on the Flitter and had no problems in the same area.
I was being cautious up near the road during the first flight as that’s where all the Wifi is; but no problems there. It failed over the golf course and over the range between the 400 and 500 yards.
When control was lost I had plenty of time to hold the transmitter up and try different antenna angles, on both occasions with no detectable improvement. The first event was quite leisurely with the glider flying happily on it’s own straight and level.
The receiver takes a second or so to re-lock on finding the signal, so you have to allow for this.
What to do about it
I’d recommend to anyone else to use a UBEC, but I don’t have one and am not going to buy one.
My solution will be to increase the heatsinking on the BEC regulators to bring them up to a reliable 1 to 1.5 amps with little or no forced air cooling.
I guess the moral of the story is to test thoroughly and don’t assume there’s enough BEC capacity or ventilation.
Here’s the solution I implemented Increased heatsinking on the ESC/BEC, with the same airflow through the fuselage.
It’s flown successfully a few times since making the heatsink mods with no sign of any problems.