FrSky Taranis - spiritual successor to the Multiplex 4000?

There's been a lot of interest in the FrSky Taranis recently. In fact it must be one of the most eagerly anticipated R/C system in recent years.

The reasons are not hard to find. First there’s the price - just $175 / £139.99 (Tx only). Second, it offers the kind of capabilities you'd expect to see in a high end set. 

It's sure going to ruffle a few feathers over at Futaba and JR, not to mention the boys at Bretten-Gölshausen.

And there's the operating system. FrSky have taken the bold decision to power their new radio with OpenTx, an open source o/s with which you can build complex recipes using simple building blocks. OpenTx opens up some very interesting possibilities for controlling complex or off-beat models.

FrSky Taranis

OpenTx

OpenTx allows you to define mixers, assign curves, control mixers with switches, and wire up mixers in all kinds of weird and wonderful ways. If this reminds you of the philosophy behind the Multiplex 4000 then you'd be right (although there also are some significant differences).

Companion9X

Fortunately it's not necessary to own a Taranis to try out the programming, thanks to the open source Companion 9X software. If you're thinking of purchasing a Taranis then please do yourself a favour and install it now - it's a good way to familiarise with the programming and when you eventually purchase a transmitter, you can upload your setups.

Companion 9X - basic setup for 6 servo F3F glider using cascading mixers on Ch 07,08 (work in progress)

Programming

When evaluating a high-end radio, I like to check out the programming by replicating the F3F setup on my Multiplex 4000. This is a challenging test as it demands some pretty sophisticated mixing, three flight modes, a reflex option, and in-flight adjustment of snapflap volume, snapflap expo, camber, and differential. A single 3-position switch is used to select the flight modes, with the appropriate mixers switched in automatically.

I'm attempting to program all this in Companion 9X. Familiarisation is well under way. Will I be able to program all the functionality? Will the program be easily maintainable? The answer is... I have yet to find out, but I'm enjoying the ride!

Companion 9x: curve definition screen 

OpenTx v. MPX 4000

OpenTx and the Multiplex 4000 show considerable similarity in their programming model, and many MPX 4000 owners will be interested in some comparisons. So here are a few notes I've made. Remember that I'm using Companion9X, not an actual transmitter - I think it reasonable to assume that the final Taranis will work much the same way.

• Like the 4000, mixers in OpenTx can have multiple inputs. Unlike the 4000, there is no limit to the number of inputs per mixer.
• Mixers can be cascaded, just like the 4000.
• Mixers are more flexible than the 4000. Individual inputs can over-ride or multiply those higher up in the list. 
• Mixers in OpenTx are displayed in a concise 'list' view. One niggle is that you can't assign a meaningful name to a group of related inputs. This makes it a little tricky to navigate through cascading mixers. [edit: please see developers' response below - seems this is just an issue with Companion9x]
• Like the 4000, OpenTx offers sophisticated switch functions. There is no direct equivalent of attenuators ('analog switches'). However there is a workaround using a 'multiply' mixer mode.
• OpenTx does not have a Controls layer, for conditioning the inputs. How easy it is to emulate this functionality will become clearer with use, however I feel this is something which 4000 owners will miss. (To give you some idea of how the 4000 differentiates between different controls, see my 4000 Controls Reference). 
• On the 4000, curves are unique to each usage. With OpenTx, curves are shared. The OpenTx approach ensures consistency if a curve is used in more than one place, however you have to keep track of which curves are used where [edit: curves can be named].
• OpenTx programs can be constructed and managed on a PC using Companion 9x.
• In conjunction with FrSky modules, OpenTx can use telemetry data to trigger actions like voice commands, servo movements etc. This is very powerful indeed, for example, you can cut the throttle when a certain altitude is reached, with voice confirmation!

In summary, OpenTx provides great flexibility. However it is also quite challenging to program especially when venturing beyond simple control setups. So, if you're expecting the functionality of a 4000 with the ease of programming of a Cockpit SX, you'll be disappointed. But if you enjoy programming, and have the skills, then OpenTx may well be just what you're looking for. And if you want to do clever stuff with FrSky telemetry, OpenTx plus the Taranis opens up some exciting new avenues.

Final word (for now)

OpenTx is a great initiative, and it's interesting to see it being adopted by a manufacturer. OpenTx developers are active in the forums and are helpful and receptive to ideas.

So it seems that two decades after the launch of the 4000, we've finally come full circle with a radio with some similarities, and a very affordable price tag. With a well tried RF link and sensor ecosystem, the Taranis promises to be an fascinating proposition and I look forward to testing it.

A final assessment on the programming will await my experiences attempting an F3F setup on the Companion9X simulator, see more Taranis-related posts.