FrSky released an update for its very popular ACCST protocol, ACCST 2.0 . They strongly recommend that all users make the upgrade, but some are not too happy with it. Here’s what you need to know.

What’s in the Upgrade?

There are two main improvements to this update, according to FrSky:

  1. Fixed the channel output error (uncontrolled servo movements) under certain conditions.
  2. Strengthened correction and verification capability.

The first item fixes an issue where channels could become “stuck” for a short time even if a good radio link were established. The second item add encryption which makes it harder for 3rd parties to interrupt the signal link and take over control.

What’s the Problem?

ACCST 2.0 isn’t backwards-compatible with earlier versions. FrSky offers updated firmware for many of its receivers, even some discontinued models. However, it’s no simple task to update receivers built into many flight controllers. Since built-in receivers are the norm in micro quads, you won’t be able to fly your “tiny whoops” once you update a transmitter with the new version.

Anything Else Important?

Not all of the radios that FrSky has released have available update files to switch to the new protocol version. Notably, the popular Taranis X9D is absent at this time.

What’s This Really About?

A number of pilots are upset that the encryption prevents other manufacturers from making equipment compatible with FrSky radios and breaks a lot of what already exists. ACCST isn’t an open standard, so FrSky is free to do what they please with it. New radios have come out that undercut FrSky’s position in the market and this could be seen as a move to fight back. It comes at a time when the community is already suspicious of FrSky since the ACCESS protocol made the same move.

Is FrSky trying to protect its intellectual property? Maybe. But that’s not the only issue at play here. The stability improvements are real and can cause a crash even when the radio link is strong. You can read a detailed posting about the issue to get a better understanding. ACCST is an older protocol and FrSky is moving toward their newer ACCESS protocol instead. If locking out other manufacturers was the primary goal, they put in a lot more work than necessary to accomplish that result.

Perhaps one of the biggest losses for FrSky is that users will no longer know whether equipment is compatible or not. ACCST now means two different things which aren’t compatible with each other. That’s going to confuse the market and make FrSky equipment less desirable.

Should You Upgrade?

Whether ACCST 2 makes sense for you depends on your equipment and how you use it.

  • If you have a Taranis X9D (including the 2019 edition), there isn’t an update yet that will work.
  • If you fly Tiny Whoops or other craft with built-in receivers, you won’t be able to update them yet.
  • If you’re in the United States, the issue that causes the channel freeze is much less likely to occur.

How to Upgrade?

Flashing a Radio

Most radios follow a fairly similar process. First, update your radio firmware.

  1. Find and download the correct software for your radio, linked from the ACCST 2 announcement.
  2. Extract and copy the .FRX file to an SD card, and put it in the radio.
  3. Make sure your radio has a charged battery or is plugged into AC power.
  4. Turn on the radio and enter the system menu (Usually, by holding down the “Menu” button for 2 seconds.)
  5. Find the “SD Card” page in the menu.
  6. Use this page to navigate to the FRK file on the card. Long press Enter until you get the option to “Flash internal module”
  7. Wait for the process to complete

Flashing a Receiver

The process for a receiver takes a radio and a specially wired servo cable. FrSky has a video detailing the process.

Easing the Transition

If you’re at all concerned about making the transition, consider picking up a multiprotocol module. You can install this to have a radio talk with many different receivers. This can ease the transition to the new ACCST by allowing you to use older receivers with the module while the main radio is on ACCST2. Or, if you decide to move away from FrSky altogether, you can keep all of your FrSky equipment after you move.

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