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Author Topic: What does 22ms mean? (in Spektrumspeak)  (Read 49 times)

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Offline Deerslayer

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What does 22ms mean? (in Spektrumspeak)
« on: March 16, 2019, 07:05:14 AM »
When you Bind a model, your Spektrum radio (most of them, I think) will show and announce (if Bitchin' Betty is available and awake) the protocol being used (DSM2 or DSMX) and a time (11 or 22 milliseconds). So what? Well, for the curious, here is the explanation of what the numbers mean and how the Spektrum folks pack the available channels into the available slots. For most of us, this would never matter. However, for something of extremely high performance, such as a jet or 3D monster, one does care, as you don't put an critical item that demands extremely quick response to commands onto one of the upper channels.

The following a response from Andy Kunz, the Lead Developer from Spektrum, in answer to a question from a viewer (like me). This had to do with converting a model from one transmitter to another.

The Spektrum protocol puts out a packet of data every 11ms. The packet holds 7 channels.

In 22ms mode, that means there are 7 x 2 slots available, 14 channels total. The first 6 of each packet are channels 1-12, and the last slot is used for the X-Plus channels (which makes it very obvious why they are up to 88ms latency).

In 11ms mode, there are 4 channels that are sent every time, and the remaining 6 channels come in 3's. It sends out 4 channels + 3 channels, then the next packet has the same 4 channels + 3 different channels. 4 + 3 + 3 = 10 channels max in 11ms mode.

The DX18 generates its data as 12 channels + 8 channels, where channels 11 & 12 are the same as X+1/2.

The DX20 generates its data as 12 + 8 also, but channels 11 & 12 are configured independently.

This is what the "DX18 Compatibility Mode" option is for. It lets you pick 10+8 or 12+8 mode.

Because the iX12 can import files from either one, or from a lower end DX, it can generate either mode as well. It's important to understand what you are getting the configuration from to know how it will behave. If you import from a DX18 or lower, it will most likely be in DX18 Compatibility Mode, generating channels 1-10 normally and using X-Plus data for 11 & 12. If you import from a DX20, if it's in 20-channel mode then channels 1-12 will be as you expected. It is done this way because the purpose of importing a file from another type of radio is to make it so that the new radio controls the old model exactly the same way. You want your new radio to fly the plane the same way as the old radio, not change channel assignments on you.

Opalix didn't understand that part and assumed that the DX8 file he imported would automatically go into the 20-channel mode. It doesn't do that because a DX8 works in DX18-compatibility mode for channel generation (but you can't get there on the menu). He's got it all straight now (we've been working with him for several weeks through Product Support and PMs).

Andy
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