strange electrical gremlin. help!

[jebster]

So I have a 6x6 ( jebster's 6x6 ) that acts up. After about 10 minutes of running he steering servos go haywire. They start randomly swinging right and left, not responding to command. Throttle still responds normally. Not sure what to make of it so I'm looking for suggestions. Here is all the equipment involved. The rig has lights and a servo winch but this happens when neither of those are running.

- Novak Goat 3s w/ 18.5 novak Crawler brushless motor
- 3 solar servos for steering
- Castle pro bec powering front axle servos; separate CC bec for rear axle
- 4000mah 2s lipo (25c I believe)
- airtronics mt-4 tx and 461 4ch rx

Bec's are tapped off direct from the battery at the connection point to the esc. Esc lead carries the power to the rx.

I've pulled the battery when this happens and it still has plenty of juice. If it was a draw issue I would have thought it would occur all the time, not after running for awhile. Could he bec's get hot and have problems? Since the throttle seems fine it doesn't to be an issue with the esc or rx getting enough juice.

I'm open to all inputs on how to diagnois this. A little frustrating to say the least.

[OFFROADRCKOREA]

Using the bec have u removed the main esc red power wire? also are ur servos warm at all? Something has to be heating up after that run time and then causing the issues.

Thanks,
ORK

[Meatwad]

Which hole on the servo horn are you using? They could be overdrawing and heating up if the leverage is too great from the outermost holes.

[jebster]

The bec's are direct to the servos, not through the rx so the esc powers the rx.

I was thinking heat might be an issue. I'll have to feel a few parts next run. Just odd that all 3 servos act up when there are two separate circuits.

As far as second arms go they are 1" long and I'm using the outer hole.

[Charlie-III]

Sounds like you have a decent set-up.

Does the issue show up with any battery pack?

Do you have a ground from the servo/BEC connection back to the RX? (Spektrum needs the grounds, other set-ups are finicky on if they need it).

[jebster]

Originally Posted by Charlie-III

Sounds like you have a decent set-up.

Does the issue show up with any battery pack?

Do you have a ground from the servo/BEC connection back to the RX? (Spektrum needs the grounds, other set-ups are finicky on if they need it).

I have only been running one set of packs (both the same 4000mah size). I will try some of the smaller packs I have just to mix it up.

I only have the signal line running back from the servos to the rx. They do get jumpy if I switch off the esc since they still have power but otherwise they work fine until the mystery issue comes up.

I did think of another experiment. I have the system set up to run front only / rear only / crab / opposing for the axles. Maybe I'll run just front then just rear to see if I can isolate the source.

Keep the ideas coming guys. I hope I can get this solved.

[jebster]

The plot thickens. Took the cab off so I could test temps and ran it hard for 20 minutes today. No issues. The hottest and component of the system got was the motor and it only reached 98 degs. Battery, servos, esc, becs were all cool to the touch. I'm stumped as to what has caused the issue. From today's test heat doesn't seem to be a factor. Even with the cab on I'm sure there is enough cooling air getting in.

Could it be some kind of interference? My kids were running their rigs the other day. Both are using traxxas 2.4ghz tq systems.

[OFFROADRCKOREA]

Originally Posted by jebster

The plot thickens. Took the cab off so I could test temps and ran it hard for 20 minutes today. No issues. The hottest and component of the system got was the motor and it only reached 98 degs. Battery, servos, esc, becs were all cool to the touch. I'm stumped as to what has caused the issue. From today's test heat doesn't seem to be a factor. Even with the cab on I'm sure there is enough cooling air getting in.

Could it be some kind of interference? My kids were running their rigs the other day. Both are using traxxas 2.4ghz tq systems.

Hmmm.. I like this one haha. Do u have another rx u can try? Did u test the rx temps? Funny that multiple things are going wrong and not one. Kinda points to the rx. Also what ur radio voltage at?

Thanks,
ORK

[jebster]

Originally Posted by OFFROADRCKOREA

Hmmm.. I like this one haha. Do u have another rx u can try? Did u test the rx temps? Funny that multiple things are going wrong and not one. Kinda points to the rx. Also what ur radio voltage at?

Thanks,
ORK

That is one thing I don't have a replacement to swap out for. The power to the rx is being supplied by the esc so I assume it is at 5v but I haven't measured. Given the problem didn't occur today I'm not sure what to pursue next. Maybe a few more hard runs to try and see if I can consistent cause the issue.

I do agree it seems to be associated with the rx but I have to keep working this.

[Charlie-III]

Have the kids run their Traxxas radios again and see if the issue comes back.
Also check your TX batteries.

PS, do all the servos get twitchy or just 1 or 2? Do any share a RX channel? If so, are they the only ones that twitch?
Just wondering if a single servo is creating an issue with the others (through a shared RX channel).

[jebster]

Originally Posted by Charlie-III

Have the kids run their Traxxas radios again and see if the issue comes back.
Also check your TX batteries.

PS, do all the servos get twitchy or just 1 or 2? Do any share a RX channel? If so, are they the only ones that twitch?
Just wondering if a single servo is creating an issue with the others (through a shared RX channel).

i will get them out to try running all the rigs together again.

i have it setup for the front two axles to share a single channel (and the cc pro bec) for their two servos while the rear axle servo is a different channel (and a cc bec). it seemed like all the servos got twitchy but i need to confirm. if it was the pair of front axles only could controlling two servos be too much for a single rx channel?

[Charlie-III]

Since the BEC handles the load, I see no issues with multiple servos off a single channel.

[SunnyUSAF]

How long are the cables for the BEC's including any extensions. You might be picking up some RF noise and it could be causing the servo driver IC inside the servos to glitch. One way to find out would be to install these. I know its a radio shack item but they do work. Snap Choke Core - RadioShack.com
Any time you make a cable longer it acts like an antenna and picks up any extraneous noise. Which could be causing the issue. Worth a 3.00 experiment, good luck.

[jebster]

Originally Posted by SunnyUSAF

How long are the cables for the BEC's including any extensions. You might be picking up some RF noise and it could be causing the servo driver IC inside the servos to glitch. One way to find out would be to install these. I know its a radio shack item but they do work. Snap Choke Core - RadioShack.com
Any time you make a cable longer it acts like an antenna and picks up any extraneous noise. Which could be causing the issue. Worth a 3.00 experiment, good luck.

that is a thought. bec power lead to the servo is probably 2 inches. signal lead from that connection point back to the receiver might be 5-6 inches. may have to try an experience like you suggested.

[Calderwood]

I would start by grounding the servos.

[rhett314]

What voltage are your bec's set to? If they are set too high you might not be supplying enough voltage after 10min of run time causing them to glitch. Any chance you can try a 3s on it?