7PXR Failsafe Mystery-thoughts/advice

[Jason O'Brien]

Wanted to see if anyone else has run into anything like this. Using a 7PXR, kit Rx, and the v2 Futaba telemetry GPS.

Been working on a .67 SAW boat. Finally started getting some decent speeds/passes, and the boat starts dying while at WOT, well into a pass, and sometimes within 100' of the Tx. I eventually noticed that every time it died, the speedometer read 98mph (but I chalked that up to coincidence). Sent the video to a couple of people I trust. They said "failsafe." I enabled logging, dug through the logs, talked to Futaba, etc. Logs didn't really show anything, and I was told that the timestamps aren't accurate enough for forensics. I have no failsafes enabled, other than low Rx battery. I potted the Rx power switch terminals in epoxy just to make sure they weren't wiggling under acceleration. The Rx antenna was above my tuned pipe, and the Tx antenna was vertical.

I was certain it was fuel related. Started swapping parts. I ended up swapping (one at a time) the OS needle for a stock CMB needle, replaced all the lines, sent my fuel tank back to John Steltzer for a once-over (and used a Dubro tank with 5/32 lines in the meantime). Same result. Increased the pressure line size. Same result. Swapped engines (with a practically new one); same result. I think I pretty much ruled out fuel flow.

Back to the radio. Swapped Rx, Rx battery, and throttle servo; same result. At this point, the only common item in all of those scenarios is the 7PXR, and the Futaba GPS. As a last ditch effort, I removed the 7PXR's Rx and GPS. Installed the stuff from my 3PK, and the problem disappeared. I'm not swearing this is true, because I'm old enough to know there's a lot I don't know, but it certainly appears that the Futaba GPS was killing the boat due to either acceleration or speed. Futaba tech support said this isn't possible.

Does anyone see the flaw in my logic, or what I'm missing? I know it looks like the GPS, or its communication with the Tx, was killing the system, but I don't believe it really was. I think I'm overlooking something. The one thing I forgot to test was to just leave the 7PXR, and just disconnect the Futaba GPS. That should've been OPS test #1, but I overlooked it.

 

[Buckshot]

I think the boat is so fast it’s out running the radio signal.

 

[Mike Hughes]

Years ago, I had a futaba 3PJS. Those radios had compac modules you could add to store more models in the radio. I picked one up and put it in the transmitter. I started having range issues once I did that. I went thru the boat head to tail trying to fix it. Finally grab another transmitter to see if that fixed it. It did. So went to my original and pulled the module. Range issue was gone. I think you should go back and check it without the GPS. I think that might be the problem. It is drawing down the battery and causing it to go fail safe on you.
Mike

 

[Grimracer]

What RX battery?

 

[RaceMechaniX]

Have you tried just removing the GPS unit and only running a receiver?
Is the receiver nicely cushioned inside the tub?
Pics of the radio box?

 

[Jason O'Brien]

Using a 2s LiFe, 1450ma. Logs never show the rx voltage dipping below 6.5v.

I’ve not run with the 7pxr minus the gps. That was a gross oversight on my part. Everything is packed nicely in foam. It’ll be a couple of days before I’m home, but I’ll send pics when I get back.

Speaking of logs, I couldn’t get a clear indication of what this meant, but the rx status would toggle between 3 and 0 quite a bit. It persisted for quite a few lines in the logs, but it’s a fast stamp interval, so it had to be happening pretty fast.

 

[Grimracer]

What RX.. did I miss that info?

 

[Jason O'Brien]

Sorry, no. I started with an R334SBS, and switched to an R324SBS for testing. Same result on both.

 

[Daniel's Racing]

Are you in standard T-FHSS mode ?

Not T-FHSS SR, while I believe you could use that if in SR you have to shut it off per channel that uses standard digital servo.

You are running all digital servo's ? Surely but had to ask. Lol.

Just trying to think of things that could mess with servo's like that.

A go pro session cube video camera with it looking at the throttle assembly just to see what is actually happening while underway.

Manual if anyone interested,

https://futabausa.com/wp-content/uploads/2019/12/7PXR.pdf

 

[Grimracer]

Ok.. cool.. thanks..

Just more info

https://futabausa.com/wp-content/uploads/2018/09/R324SBS.pdfhttps://futabausa.com/wp-content/uploads/2018/09/R334SBS.pdf

 

[Jason O'Brien]

Just to clarify, this radio and gps are not new. I’ve run the snot out of it for a year. Buckshot and I ran 100 laps in Atlanta a few months ago, doing some testing, using this literal same equipment (different boat).

I’ve also been running it without issues in this SAW boat for 3 or 4 months. The problems started when the boat started approaching 3-digit speeds/hard acceleration. It has cut off at EXACTLY 98mph several times. Never at 50mph, or 70, or 80, and it’s never been far away.

 

[Grimracer]

Very odd.. if it was 88MPH .. I would feel better..KIDDING!

And when this happens you also loose steering?
Does it retain 'distance" information"?
When you bring the boat in.. all is fine i suspect.

Sorry for all the questions.. but man.. this is ODD!

I can reach out to Futaba and see what they say.

Grim

 

[Daniel's Racing]

... or even 68 would make more sense
...because at 69 they blow a rod.

The 98 gps thing makes it especially intriguing. Safety feature telling you your too dang fast.

Can any of the telemetry cross talk into the radio functions ? I mean can any of the sensors be programmed to make any response within the radio portion itself. I didn't think so but really don't know having not messed with the sensors on them very much.

 

[Jason O'Brien]

You’re right, it is odd! The logs show distance info.

I’m joking about 98mph (it really has been cutting off at 98, but I think it’s just an odd coincidence). And yes, boat is fine when I bring it in.

I have no idea if I’m losing steering. I’ve tried to wiggle the rudder, but the boat has no fins, so rudder input doesn’t do much at anything above slow idle.

 

[Jason O'Brien]

... or even 68 would make more sense
...because at 69 they blow a rod.

The 98 gps thing makes it especially intriguing. Safety feature telling you your too dang fast.

Can any of the telemetry cross talk into the radio functions ? I mean can any of the sensors be programmed to make any response within the radio portion itself. I didn't think so but really don't know having not messed with the sensors on them very much.

Futaba says there’s no way the gps can affect a servo

 

[Grimracer]

For the sake of argument Ok...lets go with it..(it makes ZERO sense that the GPS would cause that) if thats the case then lets track elsewise.

To me.. it would be fuel flow or air flow.. pull the plug and there is no water or grey on the plug?
Do you have the fuel line inside the tank AT LEAST 1/8 inch away from all walls?

Is there a cowl on the boat.. did you try without.

Grim

 

[RaceMechaniX]

One of the guys on IW was running a 7 or 10PX with GPS at the recent Cinci TT and he ran without issues including a measurement of 100mph on the GPS. I have run many many passes at 140mph+ with a 4PX and a R324SBS receiver without any issues. I do have the 400mm antenna's on almost all my SAW boats. Are you running the standard antenna or a longer one?

I can only suspect there is a resonance that occurs near 98mph in the boat which causes the receiver to fault. I would suggest moving position of the receiver within the boat as an easy test.

 

[Grimracer]

I have a motor that sub inducts the piston.. at a certain RPM it just light switches out. EVERY TIME! lol.. what a pain in the......... needless to say.. SHELF!

Grim

 

[Daniel's Racing]

For the sake of argument Ok...lets go with it..(it makes ZERO sense that the GPS would cause that) if thats the case then lets track elsewise.

To me.. it would be fuel flow or air flow.. pull the plug and there is no water or grey on the plug?
Do you have the fuel line inside the tank AT LEAST 1/8 inch away from all walls?

Is there a cowl on the boat.. did you try without.

Grim

Another trans/receiver fixed it.

One of the guys on IW was running a 7 or 10PX with GPS at the recent Cinci TT and he ran without issues including a measurement of 100mph on the GPS. I have run many many passes at 140mph+ with a 4PX and a R324SBS receiver without any issues. I do have the 400mm antenna's on almost all my SAW boats. Are you running the standard antenna or a longer one?

I can only suspect there is a resonance that occurs near 98mph in the boat which causes the receiver to fault. I would suggest moving position of the receiver within the boat as an easy test.

He is only 100 feet away when it occurs.

>>>>>

Maybe try setting it up on a fresh model number. This often cures many issues if something is acting crazy in one models programing it may not follow it to the new model number.

 

[John Beardslee]

Jason, does it occur in both left to right and right to left? Is the coax portion of your antenna 2 inches away from any conductor? Preferably 2” above for a SAW boat.
John