Trex ? Anyone?

I did search, but did not find anything.

I’m a lapsed R/C helicopter pilot (haven’t flown in a couple of years , but used to fly mild “3d”). I have several Align Trex’s (600n, 500, and 450), and all this new, awesome UAV stuff has got me thinking about picking up an APM and throwing it in a few of my machines.

I’m hoping that there are others on this forum that have done this already, as I have a few questions:

  1. What’s the smallest size “traditional” heli a 3DR APM can be put in?
  2. I’ve read (vaguely) about an “assist” mode - does this exist for “traditional” machines? I’m assuming this would allow the machine to self stabilize if it received (or did not receive) the correct inputs - this would be very helpful for ramping up on the significant learning curve that is R/C helis
  3. Anyone run an APM in a 50-sized glow machine? The thought of a large smoker flying itself does scare me, but I’m also curious.
  4. Is the APM capable of piloting any aerobatics?
  5. Any other advice?

The UAV stuff really has renewed my interest in this stuff - really cool.

It seems we “traditional” heli pilots are in the tremendous minority when it comes to APM.

I too am very interested in what APM/Pixhawk can do for the traditional heli. This tread doesn’t answer your questions head on…but covers some of the ground you are interested in. This website seemed to recommend a 450 sized heli for a test platform. Enjoy this read:

Hi guys, sorry it took a while for me to get on this forum.

  1. I don’t think there technically is a “smallest” helicopter. You could put it on a Blade Micro if it will lift it. Randy has used it on a 250, but that’s pretty small. I have a 450, and it fits, but it is still kinda hard to squeaze it on. It depends on what you want to do. If you just want to put APM on a heli, it works. But if you want to load it down with FPV cameras and a whole bunch of stuff, I think it’s too small. IMO, a 500 is a nice size. I also have used it on 600 and 700, nothing wrong with that, though they are more intimidating. I do recommend learning the system on something small and cheap before putting it on something bigger.

  2. I think what you’re talking about is Stabilize mode, which is self-leveling. It makes helis extremely easy to fly. You also seem to be asking about lack of inputs… we do have a radio failsafe that you can set up to just land it automatically if the radio goes dead.

  3. Not that I’m aware of, no.

  4. You can also get lots of info and see what’s been done over at However, we are going to be trying to transition the main support forum to this website.

The APM and Pixhawk sure have made traditional helis very interesting.

I have a Mikado Logo 400 with an APM2.5, telemetry and FPV including a MinimOSD. The heli is powered by a 4S lipo (and an extra 2S lipo for the FPV) and it has more than enough power to fly very well carrying all of the gear. Importantly vibration levels are very low and the AMP controls the heli very well.

You can set what ever level of control you want on the heli. In Acro mode you get no assistance, in stabilise it will stay upright but will drift in the wind, in alt hold it will drift but stay at a set altitude while in loiter it will stay pretty much exactly where you leave it in three dimesional space. You can still move the heli round with the sticks but when you let it go in loiter it will stay exactly where you left it.

One of the things you need to remeber is that FPV on a traditional heli is hard because the heli won’t have a tendancy to keep flying forward and its hard to know where you are in space if it starts drifting backward for example. You will need to practice with a buddy box and spotter for a while to make sure you know where you are.

Also, if you want to do aerobatics than you don’t want a controller, you want to be in control. So using an APM is for a different reason. You will however see that there is increasingly the ability to do aerobatics with an APM and there is a recent post in DIYDrones by Rob on that.

For me the APM has opened a whole new world of flying that really suites what I’m looking for. I’m a technology nut and so its what I want and the open source nature of this equipment gives insight into the technology that no other platform offers.

So go and enjoy…

Thanks for the nice post.

Your comments about FPV are interesting. This is something I want to get into and am just collecting parts at this point.

Loiter can actually work pretty well for some styles of FPV, you just need to turn up the Loiter speed. I have done it as high as 20 m/s and it’s fine, the only issue is that it does not accelerate as fast as I’d like. It’s actually an issue in the code but Leonard and Randy can’t find it.

Another option you could try is “Drift” mode. It has quasi-position holding when you release the sticks (not on collective/altitude though!) It will resist movement, but is not a true position hold. Flying forward is pure-manual speed control. You turn with the “roll”, and it controls the roll and yaw at the same time, such that it always tries not be sliding sideways. You basically have manual control over yaw, and then it automatically tries to cancel out any “skidding” with automatic roll input.

However, I caution not to push it too hard. It is designed for slower speeds. Going over 15 m/s may turn up some undesirable properties.

I had also previously worked on a flight mode intended for FPV with helis, and I’d like to continue that. It was based on the idea of having the yaw follow the direction of travel automatically. You could rotate it if you’re stopped. And you can force a skid by inputting yaw while moving. But generally the tail will just follow. In fast forward flight, you would turn by rolling. As you roll, it will turn and the yaw will follow automatically.

I think this would feel more natural for most heli pilots.

Drift mode sounds interesting. Can you explain how you set it up in more detail please.

For me the challenge in FPV with a traditional heli is that it does not have a natural tendency to keep flying forward which, as a pilot, then allows you to just make small adjustments to direction or altitude. If you let the sticks go while hovering in stabilise mode for example, the heli will drift off unpredictably. If you apply forward cyclic it will begin to fly forward and then you can release the sticks and it will continue to fly forward but again, not predictably; particularly if you then turn by banking and as it begins to sink you apply a little up-elevator instead of increased cyclic - it will come to a screaming stop or even start flying backward. All of this is difficult to interpret while wearing FPV goggles.

If the heli could be set up to keep flying forward with no inputs at a fixed altitude it would make FPV a whole lot easier. Then if you add directional control by either aileron or rudder with the other control being automated it would allow the pilot to focus on the view rather than the continuous panic of trying to keep the beast flying.

Setting up drift is pretty easy. Once you have a succesful Loiter, that’s pretty much it, Drift should be good to go.

It sounds to me like what you want for FPV is actually flying in Loiter, with a very high Loiter speed, like 20 m/s. I have done this, and it works very well other than starting and stopping is like a freight train. It’s a bit slow. This is actually a problem in the code, but nobody has found it yet.

It won’t “cruise” with hands-off, but you can just hold the stick in position and it will move at a set speed, proportional to the input.

You also don’t have to worry about rising and falling.