I recently crashed my QQ Yak due to two aileron servos(5945's) failing. One was totally dead, the other would only move in one direction. The elevator servos(also 5945's) and rudder (5955) servo are fine. I was running everything off of 6.0V NiMH batteries. I tested the servos on another receiver and battery with the same result. I have sent them in to Hitec, but I still wonder WHY??? Anyone have an idea? I sure don't. Dale

Sorry about your model[]

How do you know the servos were not crash damaged?

Can you describe what lead to the crash of your model?

Please list the equipment utilized and how the model was rigged.

It went wierd before the crash. There was no aileron control. This was on a QQ Yak with a DA 50. I am running a JR 10X with a JR 950 pcm receiver. Four 5945 servos, one 5955, two 605's on throttle and choke. Two 2250 NiMH with MCI superswitches and on a Batshare. This was probably flight number 13 or 14 but, the first flight of the day on a full charge. I had been up about 5 minutes when I lost it

This is a one servo per wing model, right? Were you using a flaperon mix?

Yes, and dual servos on elevator.

What’s puzzling me is that two independent channels/servos failed simultaneously. For two servos to fail like this is unusual at the very least and unlikely IMO.

Did you make sure there was NO linkage binding and end-point travel values were not allowing the servos to be over driven?

What type of radio/RX? Did all other functions work when the ailerons malfunctioned?

It was strange for me too. I am running a JR 10X and JR 950S receiver. I had done extensive pre-flights, so I am sure nothing was binding. The other channels were working perfectly. I just sent the receiver in to Horizon for a checkup. The servos were returned to me yesterday. Amplifiers in both were damaged. Damaged motor in one. Damaged gears and case in the other. One servo was replaced the other repaired. I would think some of the damage was done in the crash.
By the way, I want to thank you and Hitec for your quality and speed of service. Dale

Running 6 volt NiMh batteries could very well be the problem. At the higher voltage the current draw is much higher. Since NiMh batteries have a much higher internal resistance than NiCd batteries there is a very good possibility that you had a significant voltage drop for a very sort period of time under load. This can cause the receiver to do all sorts of strange things.

Pete

Would regulators help in that case? Dale

No, a regulator will not help. Because of the high current loads that can be needed batteries with low internal resistance should be used. Unless you have some very high end NiMh batteries and know that they can support the peak current load of your set up I would recommend using NiCd batteries for the supply. NiMh batteries have a higher internal resistance than NiCd batteries.

Pete

Note that not all NiMH cells have a high internal resistance -- some are lower than NiCds of the same capacity.

The real problem is the use of the wrong NiMH packs.

In my profiles, I regularly fly with 4x digital servos (HS5925) and a 1050mAH NiMH pack with zero problems -- despite some pretty serious throws and violent manuvers.

The NiMH pack I'm using however, is rated at 20A continuous and consists of five 2/3A cells.

Sometimes people think that more capacity means more current-handling capabilities but they're usually dead-wrong.

I've got some 1650mAH NiMH packs that start to sag with just a 5A draw -- but they're AA-sized cells. I use these with standard servos and they're fine but I'd never use them with digitals.

On a larger plane such as your Yak I'd never use anything smaller than a sub-C sized cell and make sure that you're buying a pack with low internal resistance, regardless of its capacity. In fact, the use of two packs would be a very wise move.

Note also that because they have their own processor, Hitec servos do seem to exhibit a "reboot" delay if the voltage feeding them drops below a certain level. This manifests itself as a period of up to 1 second when they simply stop responding. However, if you have your batteries and wiring up to scratch you should *never* experience this in flight so it's not usually a problem.