Change in binding behavior with Futaba 9C and Nano Rx

[flyingw]

Jim,

I observed yesterday a new and different behavior when binding a Nano Rx to an XPS Futaba transmitter module in my Futaba 9C transmitter.

I configured the Nano for binding with its LED blinking fast.  Then I turned on the transmitter while holding the PROG button.  When I released the PROG button the bind did not occur.  At the time I had the transmitter located about two or three feet from the Nano Rx.  It finally completed the binding when I moved the transmitter antenna to within two inches of the Nano.

I have a second Futaba Tx module and I put it in the same transmitter body and repeated the test with the same Nano Rx.  The binding process completed immediately with the Nano even when the transmitter was several feet away.

After performing another "two-inch" bind with the suspect transmitter module, I performed a range test with the program button pressed for low power and went more than 150 feet away without any loss of control.

In my experience, XPS transmitter modules (both Futaba and JR) seemed to always successfully bind with XPS receivers when located several feet away.  This working distance is typical during bench testing and setup.

What I have now is a transmitter module that won't bind with a receiver until it is located two inches or closer.  This same transmitter module and receiver pair delivers good range in a range test.

I'm grounding the transmitter module, and in the meantime kindly want your opinion about it.

Thank you,

Paul

P.S.  Just opened the module and checked the u.FL connection - it was seated well on the internal RF module

[XPS]

You typically want the module more than 3 feet away from the receiver during the binding process. Did you try moving it further away instead of up close? Make sure you are 10+ feet away from any other source of 2.4GHz, such as Wifi routers, Bluetooth devices, and microwave ovens (that are actually cooking something).

[flyingw]

Good point! I turned off the wifi nearby router in the room and repeated the tests. I performed a binding procedure with the suspect Tx module and it still took awhile several seconds to bind while I moved the transmitter in closer starting at about three feet - it binded when it came within a foot of the receiver. I repeated the test again with my other non-suspect Tx module and it binded to the same receiver almost immediately and from distances up to 12 feet away in the room. That's what I remember with typical binding - almost immediate and from distances of three feet or more.

The suspect Tx module takes several seconds to bind after releasing the transmitter module button, and only at close range (one foot or less), during which time the receiver LED blinks a few times before going solid and then off.

[XPS]

The binding isn't actually immediate. There is a bug in the firmware that randomly interrupts the binding process due to a timing delay that is based on the Mac addresses. However, it was found that this was a good way to insure that the signal was good enough to overcome the random delay (which results in retries when there is an interruption). Some transmitter modules give different results with different receivers as well. You may find that another transmitter module binds instantly with the transmitter.

As always, if the range test passes then there is no problem with the transmitter module.

[flyingw]

Ok, thank you for the explanation. The Tx module in question actually had a very good range test.

Now I'm intrigued by the binding process. I reckon that when you put the receive into binding mode, it starts listening. Presumably it can hear many devices using 2.4GHz, but it will only answer to an XPS transmitter module using some unique identifier, and a default frame size and number of channels. When it establishes a initial conversation, then the receiver gets the desired frame size and number of channels from the Tx module.

I don't need this knowledge to fly, but weather in the northeast has been lousy for weeks so all I can do is learn more about my equipment. The more I understand about how it works, I reduce the chance of making a mistake with it while flying.

[XPS]

The binding is interrupted constantly due to an oversight in the firmware (discovered right after the very first release). There has to be 100 frames in a row that are successfully sent to the receiver where the receiver also ACK's the reception of the packet. If all 100 in a row occur without a single error then the binding completes. If there is a retry then the process is started over. The bug is that the transmitter module's PPM interrupt is still left in place, so that interrupts the transmission of the data and depending on many factors can cause a retry. The interrupt was left enabled to give some actual time to see the LED flicker indicating a bind was occurring. This worked but also allowed for interruption in the ACK portion of the response packet. Eventually it goes through.

The transmitter's ID, frame rate, and number channels are stored in the receiver during the binding process.

[flyingw]

Interesting, and thanks. Be well.