September 23, 2015

3GX MR on the T-Rex 250

I've had a T-Rex 250 DFC since a few years. I flew it a few times when it was new but after a while the gyro starting acting all weird and tilting uncontrollably. It came with a 3GX which I used. I tried setting it up over and over again to no avail. I even took it apart completely to check everything. Didn't help.

The thing is, the installation of the gyro is very tight. Most likely I had vibration issues and even additional damping tape wouldn't work. A potential issue could have been the tight cable installation. Anyway, that's all history now. I was certain I took a picture of the cabling, but cannot find it right now.

When I crashed the CopterX 250 I decided to retire it and reuse the 3GX MR from it. I installed it in the T-Rex. It made the entire installation much better. Less cables and no external receiver. After installation I was in for a great surprise. It just worked. It even flies well just like that!

The MR is actually a great solution for a helicopter that it fits in. Since almost all parameters are pre-configured in the MR there's not much to do but follow the installation instructions to the point. You cannot place servos the way you want and you must install the gyro in the given direction. The setup the present for the helicopter size and adjust servo centering and endpoints. Thats it! And it's enough!

September 13, 2015

Longer legs for the Trifecta

Last week I noticed that HobbyKing had started selling longer legs for their Trifecta frame. From the early discussions on rcgroups and by my own opinion the short legs was one of the shortcomings of the frame. Pilots fitting a small battery on the frame would be satisfied with the short legs. But even a 1300mAh battery would be nearly too big and many users use bigger batteries. The frame itself is capable of fitting quite large motors and props and many takes advantage of this and the battery that comes with such a setup.

Personally I use a 2200mAh battery. I didn't intend to in the beginning but I can use that size without compromising flight performance. Such a battery means I always belly land and take off. It comes with a few risks such as imbalance at takeoff and lipo damage at touch down. Worked fine so far but those legs will help alot in the future.

Arms legs. Old and new.

Tail leg. Old and new.


I ordered them right away and HobbyKing made a surprise delivery in only 8 (non-working) days. With el-cheapo shipping, this was a big surprise. I took the baby in the stroller to pick up the package and he was sleeping once I got back home. Perfect!

It took only a few minutes the change the legs. I had some issues with getting the old pins out to remove the old legs. But then, perfect! It doesn't look as bad as on the HobbyKing website, which gives the configuration a spidery look.

Arm with short leg.
Arm with long leg.


Tail with short leg.

Tail with long leg.

Trifecta with the new extended legs.

September 4, 2015

WLToys A979 worn out differentials

I got my WLToys A979 almost a month back. I wanted a cheap, small truggy to play around with the few times I get the opportunity. The car is really worth its price. But still, being cheap means it surely has its flaws.

I only managed to squeeze through three batteries before it started behaving badly. It had a hard time running through the grass and did make some funny noises. I quick inspection determined that the rear differential was nearing the end. But only in one direction, backwards it was working just fine. At the time, I took the differential apart and by inspection I couldn't really see any damages. But I ordered new ones right away.

I got the new differentials today. Replacing them is easy. It takes maybe 5 to 10 minutes. You'll need to loosen up 9 small screws and detach the camber links. The diff can then easily be popped out and back in its position again. I managed to do it during day time and the wife didn't even notice, now that's something!

I took the old diff apart and cleaned it up. It is now obvious that the gears are worn on one side. I tried my best to take a photo of the wear but you can't see the details really.

It is clear that the differentials on this car is one of its weaknesses. I haven't been crashing the car yet and have no idea what will break under those conditions. But even the careful driver should stock up on differentials as they obviously wear out quickly! Wltoys is probably making business out of this, since the differentials is fairly expensive in relation to the price of the entire car with radio, battery and charger included.

I got my differentials at dx.com but you'll also find them at banggood, aliexpress (cheapest atm.) and ebay.