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Old 21-11-2018
Yorkiebar Yorkiebar is offline
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Default Chasing a runaway car - BEC, servo, ESC or RX?

No, not literally!

Been having issues for the last few months where at random times my XB4 will just sod off of it's own accord. It's getting so bad I'm always driving it on tenterhooks expecting it to happen at any time and not really progressing during racing as I'm tending to take it easy.

First - original setup:

Flysky GT3B TX/RX, Savox 1258TG, HW Quicrun 120A ESC, SP V3 7.5 sensored.

The Savox I got with the buggy so it stayed in almost throughout. Quickly realised that the GT3B was a bit parp and I wanted to change to sticks anyway, so I got an Sanwa Gemini II and converted it to 2.4 using the FrSky hack mod and bought a bunch of V8R4-II RXs.

Everything was gravy with the stick setup, until a few races passed and it started running away again. I even thought it may be my Fitbit interfering (Bluetooth and HR monitor) so tried taking that off, to no avail.

Made a glitch buster using a 16V 4500uF electrolytic, same problems

Changed motor to a Trackstar 8.5, and an LRP 7.5 and still have same issues.

Upgraded ESC to a Corally Cerix 160A which has a 5A BEC - still have same issues!

Ruling out some things - Cells are the same used in my truck and 2WD, no issues. TX same for truck and 2WD so rules that out. Same model RX in all 3 vehicles so possibly not issue unless RX in the XB4 is faulty.

Suspected it may be the Savox 1258 so swapped it for a 1256 which I had as a spare - was better but still had 2 runaways!

The failsafe is set correctly on the RX but it takes 2 seconds for it to drop inputs to zero, hence the runaway.

I used the servo tester on my Corally progbox and it shows a current draw of 4.9A in swing test with no load!

So that leaves me with one last thing to swap - the RX. I know many folk use the V8R4-II and have no issues in varying buggies, some with silly wind motors in and the others have no issues at all. I don't like the silly short antenna but one chap I know has removed it completely and has no issues, and some of the flying chaps get 2Km range out of them.

I'm loathed to add an external BEC as it's more hassle and limited to space to do a neat install in the XB4.

The only other spare servos I have are LP ones for my lad's Yoke, but other than ditch Savox altogether I'm running out of ideas - and to a point patience.

Any pointers from anyone who has chased a similar issue?

Cheers.
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Old 22-11-2018
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cutting42 cutting42 is offline
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You have identified the problem already, its the Savox.

Been down this route before with Futaba and Savox. On some cars it worked fine, on other installs for some reason the 1256/57/58 range all glitch and with many different ESC.

Also saw a similar problem with Spectrum servos as well that needed a glitchbuster to fix. I have used Corally servos for the past 3 years with no issues.
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Old 22-11-2018
Yorkiebar Yorkiebar is offline
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Ta Gareth, I had already in my mind come to that conclusion but others at my local club are running Savox without any of my problems, so was maybe trying to look for a solution that doesn't exist!

Might slap in the lo pro trackstar I have and see how that turns out just to draw a line under it.
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Old 22-11-2018
mattr mattr is offline
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Yup, savöx.
Terribly power hungry, add it to a slightly weedy RX or BEC and you'll get problems.

My Savöx/Spektrum set up would quite regularly go dead, whenever you went WOT or tried to steer lots pretty much. Makes races start interesting. Got rid of them all. Now have no issues (also got rid of the spektrum, but for a different issue.)

Now use a combination of KO Propo, Futaba, Highest, MKS and Trackstar.
None of which have caused me any issue.

Last edited by mattr; 22-11-2018 at 12:37 PM.
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Old 22-11-2018
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I would say Savox although one bit is missed out in all the info? Are you running a PT( personal transponder) in either of the cars?
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Old 22-11-2018
Yorkiebar Yorkiebar is offline
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Hi Kevin, yes to PT - although I have two and have tried both so don't think there's an issue there. Current draw has to be in the region of 100mA at a guess for something so small, and it's mounted the complete opposite side of the car to the RX so don't think it's an interference problem.
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Old 22-11-2018
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it'll be the savox servo. 1258's are very hungry servo's and most bec's will struggle with them. fine in an 1/8 car where you have a seperate battery but not that good with esc's. have seen several problems with this at meetings and at club, with the cars cutting out, losing binding and killing cheaper esc's. try running a seperate ubec unit powering the servo only, or a ko/futaba servo. a 4wd buggy puts quite a load on the servo with the amount of grip they produce, especially if you are using a centre diff which allows the car to unload to the front wheels.
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Old 22-11-2018
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frsky v8r4 receivers have a very good range, when i started using them i tested the frsky system and spectrum system on a futaba 3vc, range was more than double that of the spectrum, ran to limit of line of site with frsky without cutting out.
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Old 23-11-2018
mattr mattr is offline
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Don't think the PT would be an issue, I've done a direct swap before now, savöx to highest between two test runs and the difference was immediate and obvious, only thing I changed was the servo, still had PT and aux fan (running off the Rx).
And that was a *very* grippy car. Used to pull the carpet up on fast corners. (Slicks, soft inserts, traction compound and the car set up very specifically for that sort of driving.)
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