RxMux available at Acroname Robotics

[JayFrancis]

Acroname Robotics is now the exclusive distributor of the RxMux:

http://www.acroname.com/robotics/parts/R306-RXMUX.html

They also have a connector kit available:

http://www.acroname.com/robotics/parts/C18-RXMUX-CONN.html

Jay Francis
Reactive Technologies

[zlite]

Bravo, Jay. Nice move on lowering the price and making the connectors available. It's an excellent product, now made even more attractive. Recommended.

[air]

I'd like to make a suggestion on this. It would be nice if there was some sort of keyed sequence for the changeover instead of the simpler </>1.5ms system.
If some simple sequence could be sent on the change over channel it would make a great system for ensuring that an autopilot stayed enabled in the presence of interference.
It would be unlikely that the interference would take a form that would match a simple sequence.
For example a scheme like this:

Input One:
Start channel at 1ms
Move channel to 2ms for 3 seconds
Move channel to 1ms
=> Input One selected

Input Two:
Start channel at 1ms
Move channel to 2ms for 6seconds
Move channel to 1ms
=> Input Two selected

Or something along those lines.
Just a thought.

[JayFrancis]

That's an interesting suggestion, and might be useful in some applications.

I'd love to have some user comments on this. If your autopilot goes haywire, how long are you willing to wait for a failover sequence to put you (the receiver) back in control? The current operation could be set up to work just like a buddy box (let go of a switch, and you're back in control).

As far as operation with interference, I strongly recommend the use of PCM radios or radios with intelligence that can reliably go to a failsafe mode if signal problems occur (such as the new spread spectrum radios). When using standard PCM radios, there could be loss of signal situations where it becomes difficult to distinguish between valid and invalid servo signals.

If the RxMux detects signal loss (no servo signal), or an irregular servo signal, it will default to input A. This might be your receiver or autopilot, your choice. Some of the college teams need this to be a failsafe receiver, for a controlled crash scenario if radio contact with the aircraft is lost. Others could use it for their autopilot. It really depends on your system design.

--Jay

[air]

Hi Jay, I already use a receiver (MPX DS IPD) with programmable failsafes etc, my concern is someone else using the same channel at some point along the flight path. I'm considering switching to either a 2.4GHz or 878Mhz system that supports receiver IDs for this reason.
If there was a simple sequence for switchover it would provide a good level of protection IMO as it would be quite unlikely that the other person would match the required sequence on the appropriate channel.

[JayFrancis]

The MPX DS IPD looks like a nice receiver.

If enough people would like a function similar to what you described, I'd consider adding that mode to the RxMux. However, I think the better solution is to use intelligent radio technology that limits or prevents glitches being sent to the servos, and that can discriminate between multiple transmitters.

--Jay

[clolson]

The RC world is diving head first into 2.4Ghz and in a couple years it's going to be really tough to find a 72mhz system.

I have futaba FASST system and it is able to lock the positions of all the controls in a fail safe situation (including the throttle if you want it to hold position too.)

So all you have to do to "securely" enter autonomous mode is flip your transmitter switch to activate the autopilot selection channel, and then turn your transmitter off. Nothing but your transmitter is going to be able to pull the system back into manual mode, and the activation channel is "locked" in the on position.

note: I say secure in the sense that no random signal and no other transmitter will be able to shoot you down. However, I'm sure the protocols are simple and unencrypted? So a devious person could easily build a jammer or hijack the protocol and take over, but I'd consider those chances pretty remote.

Curt.

[air]

Hi Curt,
Yes, those are my thoughts exactly.
The DS IPD 35Mhz receivers that I use claim use some sort of Tx detection whereby they recognise small differences in the received pulses of individual transmitters and therby reject other transmitters on the same channel. In practice however if the initial transmitter is turned off, another one on the same channel can easily take over.
I've used them with the picopilot for example - when I turn off the transmitter, the RX holds the autopilot output at enable for 30secs (max failsafe time) after which it outputs nothing. The picopilot stays enabled based on the last good frame received so all is good in the world. However I'm always worried about a stray signal and am considering switching to 2.4 or the 878Mhz system offered by DMD in spain for the reasons you mention.

@ Jay - yes I guess you're right and its probably something that should be handled by the receiver. I guess I was just getting frustrated by the problem and looking for a solution in the wrong place.

[kevinhines]

Acroname Robotics is now the exclusive distributor of the RxMux:

http://www.acroname.com/robotics/parts/R306-RXMUX.html

They also have a connector kit available:

http://www.acroname.com/robotics/parts/C18-RXMUX-CONN.html

Jay Francis
Reactive TechnologiesJay, Thanks! I just placed my order with Acroname for an RxMux. I am looking forward to receiving the RxMux and the connector kit.

Clear Skies,
Kevin