XM+ receiver swamping.

[John Wagg]

Recently bought an frsky XM-plus receiver to go in a model but I get serious close range swamping.

Need to be about 4 feet away which is no good if I want to hand launch.

It is being used with a Radiomaster TX16S transmitter although that shouldn't make a difference really. ??

Works fine in "range test" mode as that is obviously a large reduction in transmit power. In fact range is exceptional in test mode.

Anyone any thoughts on a cure ?   Personally I can't think of anything except perhaps shortening antenna length to reduce sensitivity or somehow reduce transmitter power.

 

Cheers

John

[Graham Bowers]

Isn't that a multi-rotor Rx? If so, I don't understand the need to hand launch.

 

Anyway, my best idea to get over swamping is to experiment with Tx antenna orientation, so point the end at the model for example.

 

I don't know how tx power could be reduced, I use a TX16S with a variety of XR receivers.

 

Possibly put a cover / sleeve over the Tx antenna until you've launched and got a bit of distance between the Tx and the model.

[Denis Watkins]

1 hour ago, John Wagg said:

Personally I can't think of anything except perhaps shortening antenna length to reduce sensitivity or somehow reduce transmitter power.

 

no John, don't alter any antenna by any length, the antenna is a precise divisible length of the frequency used and is possible to loose contact all together.

transmission strength from the transmitter can be tested

and should be tested.

[Andy Stephenson]

I've seen this effect on cheaper after-market receivers but only with the Tx within inches of the receiver. Solution, buy a better receiver.🙂

[John Wagg]

Hand launch due to very small wheels when grass is too long,

Although not an expensive receiver the XM+ is a genuine frsky receiver meant mainly for small drones but in my case in a small plane. (SBUS required but no space for a normal size Rx.)

None of my "cheap" receivers or any of my others in fact have this problem.  So what would be a "better" receiver - and don't say one that works. 😜

A bit disappointed to say the least.

Unfortunately my Taranis Tx is out of commission so I can't see if that would be O.K. with the XM+.

 

Cheers.

John

[Don Fry]

I think a different Rx antenna orientation might do the trick. 
 

But I would be suspicious of the Rx. As you say, it’s genuine, but a duff factory output that escapes quality control is possible. Your plane, your decision.

[MattyB]

6 hours ago, John Wagg said:

Recently bought an frsky XM-plus receiver to go in a model but I get serious close range swamping.

Need to be about 4 feet away which is no good if I want to hand launch.

It is being used with a Radiomaster TX16S transmitter although that shouldn't make a difference really. ??

Works fine in "range test" mode as that is obviously a large reduction in transmit power. In fact range is exceptional in test mode.

Anyone any thoughts on a cure ?   Personally I can't think of anything except perhaps shortening antenna length to reduce sensitivity or somehow reduce transmitter power.

 

Cheers

John

I’m afraid the XM+ has had a few issues down the years, and it’s always been particularly prone to short range swamping. Tbh I no longer use them; there are better RXs in the range, and I never had full confidence in them as a redundant satellite (the main use I put them too).
 

If you Google you’ll find these issues are discussed at length on RCGroups, but there has never been a bullet proof fix offered by Frsky, I suspect because of limitations in the physical design or hardware. Sorry to be the bearer of bad news!

 

Edited April 11, 2023 by MattyB

[GrumpyGnome]

As has been said, XM+ is really a multi-rotor RX where 'swamping' is not usually an issue.

 

I have an RM TX16 and find it works just fine...with loads of different receivers.  

[John Wagg]

Thank you all for the replies.

I have ordered a frsky R-XSR receiver and will see how that goes as a replacement.

 

I have some replacement Rx antennas and will have a play with the XM+ and see what affect altering the lengths will have.

 

Thanks again.

John

 

 

[John Wagg]

Update - R-SXR acquired this morning. Easily bound and tested.

No problem at all with swamping and has to be literary within inches before any loss of signal. Certainly no problem for hand launching.

 

I had a play with the XM by removing the left antenna (see below) which made no appreciable difference as regard swamping.

Next replaced left and and removed the right and that certainly gave a lot less swamping so could be an answer to the problem. More testing required of course.

Another advantage of the R-SXR is it supports telemetry (RSSI) which the XM doesn't.

Need to do a range test on the R-SXR but up to now a lot happier.

Unbelievable small size of these receivers but obviously no multi-pin connector block.

Anyone want to buy a XM+ receiver. ??  🙂

 

R-SXR on left compared with XM+ on right

 

 

[Graham Bowers]

All seems positive.

 

How does one use these for servos please?

[John Wagg]

59 minutes ago, Graham Bowers said:

All seems positive.

 

How does one use these for servos please?

Basically on its own it won't connect to a servo.

The SBUS receiver output has to be fed into either a flight controller or other unit that de-codes and sorts the SBUS signal into the various outputs.

(In my case I am using it in a small plane and it's plugged into, and overrides, the onboard receiver. The onboard receiver then acts as a controller and does the sorting of the signal to each servo etc. ) (and that's another story)

I have also another plane that the SBUS receiver feeds into a stabilizer gyro unit. The gyro unit sorts the signal into its 4 parts, one for each servo.

(The stabilizer/gyro can be switched in or out as needed.) 

https://www.radiolink.com/bymea

 

So if you just want to control servos and/or motor ESC then a normal Rx will be better. 

 

Edited April 12, 2023 by John Wagg

[Ron Gray]

Or use an sbus to pwm decoder

[Ace]

7 minutes ago, Ron Gray said:

Or use an sbus to pwm decoder

Sorry about the hi-jack  - will that decoder work with any manufacture receiver with a S-bus out put?

[Graham Bowers]

18 minutes ago, Ron Gray said:

Or use an sbus to pwm decoder

I have seen these and am considering one for the wing of my "60" sized BlackHorse Chipmunk so four analogue standard servos.

Is it possible to use the receiver to drive servos and one of these as well, do you know?

And any views on the capability of using it in that application please, from the perspective of passing enough current?

The FrSky instructions don't give much away 😉

[John Wagg]

I wouldn't have thought there is any problem with current as it only has to handle very low "signal" currents.

The "driving" current for a servo will come direct from the battery, via the connector pins and servo plug, to the servo.

The electronics on a servo accepts the low signal current from the decoder and then amplifies this to drive the servo motor. So it's the servo electronics that has the limitation regarding current.

 

Quite often a receiver will quote a working current but it's usually only mA. This is not what it will handle but what itself requires to work.

 

 

 

Edited April 13, 2023 by John Wagg

[Neil R]

58 minutes ago, Graham Bowers said:

I have seen these and am considering one for the wing of my "60" sized BlackHorse Chipmunk so four analogue standard servos.

Is it possible to use the receiver to drive servos and one of these as well, do you know?

And any views on the capability of using it in that application please, from the perspective of passing enough current?

The FrSky instructions don't give much away 😉

I'd suggest doing your homework on the analogue servos aspects. My understanding was that these converters require digital servos, and I think I remember confirming this with my own checks, admittedly with some low spec analogues. I think I've even read that some low end digitals might not work. On first buy of any such converter it's also likely you'd need to buy the channel changer gizmo. 

 

I've also been meaning to properly check how the fail-safe aspects work: on a recently completed model with a mix of both SBUS-converted and normally connected servos, only the SBUS ones twitch if I accidentally switch the Rx on first.

 

I do like and use these converters by the way!

[Graham Bowers]

1 hour ago, Neil R said:

I'd suggest doing your homework on the analogue servos aspects. My understanding was that these converters require digital servos, and I think I remember confirming this with my own checks, admittedly with some low spec analogues. I think I've even read that some low end digitals might not work. On first buy of any such converter it's also likely you'd need to buy the channel changer gizmo. 

 

I've also been meaning to properly check how the fail-safe aspects work: on a recently completed model with a mix of both SBUS-converted and normally connected servos, only the SBUS ones twitch if I accidentally switch the Rx on first.

 

I do like and use these converters by the way!

I guess where there's a compelling reason to use them, it's worth ascending the learning curve.

 

For a 4 servo wing I think a simpler solution is a multi way connector, and that's the way I think I'll jump. e.g. https://www.4-max.co.uk/maxloc-connectors.html

 

Probably more spaghetti to deal with - I can do that 😉

[Graham Bowers]

1 hour ago, John Wagg said:

I wouldn't have thought there is any problem with current as it only has to handle very low "signal" currents.

The "driving" current for a servo will come direct from the battery, via the connector pins and servo plug, to the servo.

The electronics on a servo accepts the low signal current from the decoder and then amplifies this to drive the servo motor. So it's the servo electronics that has the limitation regarding current.

 

Quite often a receiver will quote a working current but it's usually only mA. This is not what it will handle but what itself requires to work.

The absolute nub of the matter is in your first sentence. Does it, or does it not only handle signals, with power coming from elsewhere?

 

Anyway, driving a 4 servo wing is probably easier overall with a multi plug.

 

 

Edited April 13, 2023 by Graham Bowers

[Richard Wills 2]

I use the frsky ones in the wings of my BF-109, one in each wing driving 3 digital servos each.  I wondered about current but then realised there is only 1 wire the same gauge coming out of the switch which drives everything so stopped worrying and its been fantastic, one servo plug per wing.  Well 2 actually, they are digital only and my electric retracts didn't like the short pulse width but 2 is better than 4 per side.

[John Wagg]

52 minutes ago, Graham Bowers said:

The absolute nub of the matter is in your first sentence. Does it, or does it not only handle signals, with power coming from elsewhere?

 

Anyway, driving a 4 servo wing is probably easier overall with a multi plug.

 

 

Under normal expected conditions the power from the battery would go to the receiver first then via the SBUS lead to the decoder.

On both the receiver and decoder there will be the common + & - connections on their respective circuit boards.(pins).

So the weakest point will be the SBUS connection lead.  In this case it would have to carry all the current required by the servos.

Another possible case would be if using a BEC supply from a speed controller that is plugged directly into the decoder. The SBUS lead would only need to carry the very low current required by the SBUS receiver circuit.

As Richard notes, as long as the wires (plus & negative) are thick enough then there shouldn't be an issue.