Sunday, July 7, 2013

Open Source Controllers

A rundown of the controllers for which open source firmware is available.

Spektrum DX6i

I can hear people scratching their heads from here: The DX6i can run open source software? Cool! Hook me up! Unfortunately, that's not the case (otherwise, I might still have one). However, it's a very popular entry-level controller. It's capable enough that you may never need a new controller, and if you do, it's probably for more channels rather than missing functionality in the controller. You can probably find one at your local club or hobby shop. Reviews range from good value for the money to garbage, so I suspect it's middle of the road. I'm using it as a baseline that I expect you might be familiar with, if you haven't seen any of the others.

Walkera Devo

These are very capable controllers. All the ones you're liable to find come with the latest features the DX6i doesn't have - a backlight, a real speaker instead of a buzzer, vibration warnings, and telemetry. They run the deviationTx Open Source firmware, but without manufacturers support.

These controllers do not have a module system for exchanging transmitters to use different protocols. However, the CPU in the controller actually controls most of the protocol outside the transmitter itself, which means the authors can add protocols - if the radio transmissions are correct - just by adding software. deviationTx supports numerous Walkera protocols, Spektrum's DSM2 and DSMX protocols as well as the Nine Eagles J6Pro controller protocols without further hardware modifications.

You can add a transmitter by soldering it into the controller. deviationTx has support for FlySky (used by some WLToys ultra-micro copters, among others) and Hubsan X4's protocol by adding a module. The next release should have support for FrSky and SkyArtec protocols with an additional transmitter, and support for yet more transmitters and protocols - including the one used by newer WLToys V2x2 quads - is in the works. At the present time, you can only have two extra transmitters in a controller.

This level of control also allows the controller to emulate behaviors that are done at a very low level in transmitter, such as the WLToys extra functions.

Devo 7E

Street price is around $80 at this time. This is an unusual controller, in that it's not much bigger or heaver than the cheap controllers included with most RTF craft. However, it's a fully computerized controller capable of running deviationTx. It's not quite up to the feel of the DX6i - the gimbals don't seem quite as good. Replacing the cheap plastic sticks (it takes Futaba style sticks) goes a long way towards making up for that. It does have two issues:

  1. Lack of controls. It comes with two two-position switches. There are mods to add either two more such switches, or a three-position switch if you're running deviationTx. That firmware also allows you to use the six configuration buttons as three pairs of trims for extra analog inputs, and the next release will allow them to be used as momentary buttons, toggle buttons, or even on/off pairs of buttons, which will help a lot.
  2. The radiated signal is low power. There is a published mod that increases the output power, but it's probably illegal in most jurisdictions.

In spite of those two problems, I think the Devo 7E with deviationTx is the best buy for a first controller, but you will outgrow it if you stay in the hobby any length of time.

Devo 10

The Devo 10 is a full-features, full-size controller. It costs about twice as much as the Devo 7E, but - well, it's more than twice the radio. Better quality, smoother gimbals, and like the DX6i this is a controller you might not outgrow. It's more capable than the DX6i, and generally better quality.

Devo 6s

This is another small form factor controller, like the 7E. Not only does it sport a color touch-screen, but it doesn't suffer from the low power transmitter of the 7E, and has more available controls. Not as many as a full-size controller, but you have to give up something to keep the size down. With the additional controls the next release of deviationTx will make available, it'll have more controls than the DX6i. It's build quality and gimbals are similar to the Devo 10.

The downside is that it costs as much as the Devo 10. Unless the small size or the color touch screen are must-have features for you, the Devo 10 is a better buy.

Devo 8s

Similar to the Devo 10, but with a color touch screen interface at an extra cost. I'm not convinced color touch screens are a good idea for RC controllers: hard to read in direct sunlight, and possibly a bit fragile for something that's going to be dragged to and from flight fields on a regular basis.

Devo 12s

The top of the line. Better build quality, more functionality, better screen - though it is a color touch screen. It still manages to weigh less than the Devo 10. The downside is that it costs about twice as much as the next most costly Devo, the 8s.

Other variants

Some older Devo controllers you may run into.

Devo 6, Devo 8, Devo 12

These are identical to their similarly numbered brethren, except they have no telemetry support. You may be able to add a module to get that, but those are even harder to find than the controllers.

Devo 7

This is not in any way like the Devo 7E. It's more like an early version of the Devo 10. Most importantly, the architecture is sufficiently different that deviationTx hasn't been ported to it. So unless you're looking to do the port, don't get suckered into buying this thinking you're getting the Devo 7E.

TH9X et al

This is a much more complicated set of controllers, because they are made by more than one company, and have numerous aftermarket modifications available.

They are all full-size controllers using full-strength transmitters and have a fairly complete selection of controls. They have a bay that accepts - possibly with some work - JR-compatible transmitters, which allows them to work with receivers for any protocol for which you can find an appropriate transmitter.

TH9X and clones

The original controller was the FrSky TH9X. A number of companies licensed the right to manufacture and sell it under their own brand, most notably Hobby King, under their Turnigy brand. That's the least expensive of the bunch, generally called the T9X, and the one most people think of when they think of 9X controllers. That's the one I'll describe here.

The Turnigy 9X has lower quality than the Devo 7E, much less the DX6i. The gimbals are about the same as the Devo 7E. Other manufacturers could well have used better parts, though their controllers will cost more.

It comes from Hobby King in one of two forms, either with or without a transmitter and receiver. Either retails for about $50. However, Hobby King charges shipping, and has a number of warehouses around the world, which will have a different (usually higher) price and shipping cost. The provided transmitter is also Turnigy-branded, and speaks the FlySky protocol used by FlySky receivers and the older WLToys aircraft (V911, V912, V9x9 quads; not V922 or V2x2 quads). However, the radios can't manage the extra functions of those quads with the shipped CPU. The transmitter is hardwired into the controller, and needs to be disconnected before you can use a transmitter for a different protocol in the module bay.

There are also published mods for taking the transmitter out of a MLP4DSM controller - the controller shipped with smaller RTF E-flite airplanes and Blade 4-channel copters - or similar and soldering it into the controller, allowing it to use the DSM2 protocol.

As shipped, this controllers firmware cannot be updated. That requires a hardware mod. Likewise, it's a fairly primitive controller - no backlight, a simple buzzer the only form of alert, no telemetry. There are mods to fix all of that, as well as upgrade the CPU for more performance, which might enable the WLToys extra functions, or add an SD card for extra storage. Given the appropriate set of mods, you can playback audio files from the SD card for specific warnings, meaning instead of beeping when you turn it on with dangerous switch or stick settings, it tells you about them.

If you buy a controller without a transmitter, you'll have to add one - which will push the retail price out to close to the cost of a Devo 7E, before you factor in shipping. If you buy one with a transmitter, and do an inexpensive version of the firmware upgrade mod, you might be able to get one put together for slightly less than the street cost of the Devo 7E. But adding a backlight is cheap and simple, and real sound playback and vibrations are likewise. Nothing fancy like telemetry, or a better CPU or voice playback, but you've still got fewer features (if more functionality) than the Devo 7E, and have probably paid more for it.

Fully tricked out with all the upgrades, this controller has functionality if not quality comparable to the better Walkera controllers - but you will have spent more on it than they cost you to begin with. Not to mention having to build it yourself.

The likely lower cost and more functionality with a lot less work is why the Devo 7E beats this out as a recommended entry level controller. This is the controller to buy if you enjoy modding electronics.

Turnigy 9XR

This is Hobby Kings upgraded version of the controller. It is also about $50, but is only available without a transmitter. It does have a backlight and a port for upgrading the firmware, but you'll have to buy the programmer and a transmitter before you can use it.

Quality is, if anything, worse than the original. Very few of the parts have changed, and there have been reports of problems with some of the changes that the original didn't have.

It's also the first controller that shipped with open source firmware from the manufacturer. They've released the source, as required by the license. It was dated software before they released it, and most people purchasing this controller upgrade to something newer fairly quickly. However, the community was not involved in the design of this controller, and the response has been fairly poor in spite of the excitement the announcement generated.

This can be a cost effective controller if the size or limitations of the Devo 7E bother you, and you don't want do the soldering required for the TH9X clones.

FrSky Taranis

This is a new controller, and is just starting to get into the hands of hobbyists. It was designed to run the openTx branch of the th9x software, and ships with that installed. It also ships with all the bells and whistles you can add to the TH9X - backlight, vibration, upgraded CPU, SD card, voice playback, telemtery, etc.

This controller has the same module bay for transmitters as the TH9X, so it can fly anything they can. However, it also has a built-in transmitter. You can use them both at once, meaning you could have one transmitter for controlling your aircraft, and a second for controlling an FPV camera, or whatever else you'd like, using just the one controller.

Unlike the 9XR, this controller was designed with involvement from the open source community. The initial response has mostly been positive. It's not perfect, but the problems are minor, and easily correctable if you're so inclined. Reportedly good build quality, high-quality gimbals, and a very solid feel.

It's to early to say for sure, but could well be the controller to buy if you're looking for something that's not at the bottom of the price scale. It's less expensive than the Devo 8s, or than what you'd spend on upgrading a TH9X clone or the 9XR to anywhere near it's capabilities.

Next time

Configuring a Devo 10 running deviationTx to get the most out of your flight simulator, to show how flexible this software is.

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