Motor causing servo to shift off-centre?!

[Fiddybux]

Hi all,

I wonder if anyone has had this problem before?

My setup - XX4, LRP Quantum 2 ESC, Fantom Vortec 9x1, Futaba S9550 Servo.

Whilst I was going round the track recently I noticed I was unable to turn hard left. On a number of occasions this lack of steering ended up putting me on the straight with oncoming cars coming fast. So I bailed out of the race for fear of a big pile up and lots of damage.

When I inspected the car later on I did some tests, and with the motor attached it definitely caused the servo to off-set more to the right, i.e. the centre position of the servo was not in the middle any more!? The servo would move off centre when the motor was active, but was fine when the motor was stood still. If I disconnected the motor completely and turned off/on the ESC the problem went away and was not repeatable.

Later on I noticed that the middle of the brush wire had almost completely split, meaning there was only a few threads holding it together. Now it has completely snapped after I pulled it.

Also with the ESC set to higher punch levels, this seemed to increase the likelihood of the servo going off-centre...at lower punch settings it didn't happen as often.

So my question is, can a brush wire that is almost snapped off / partially disintegrated cause the servo to go nuts like this? The problem only seemed to happen with this particular motor and other motors did not affect the servo in this way.

I suppose if some of the electricity that was supposed to be going to the comm was actually finding its way to the outside of the motor can and then conducting through the graphite chassis to the servo might cause it??

Thanks in advance all.

[ashleyb4]

What cells are you using because low capcity cells or cells that are getting old some times dont put enought power throught the BEC to the reciever meaning the servo isnt getting the full voltage it needs. This may be a reason i hope you understand that. That could be why.

A

[bert digler]

Originally Posted by Fiddybux

Hi all,

I wonder if anyone has had this problem before?

My setup - XX4, LRP Quantum 2 ESC, Fantom Vortec 9x1, Futaba S9550 Servo.

Whilst I was going round the track recently I noticed I was unable to turn hard left. On a number of occasions this lack of steering ended up putting me on the straight with oncoming cars coming fast. So I bailed out of the race for fear of a big pile up and lots of damage.

When I inspected the car later on I did some tests, and with the motor attached it definitely caused the servo to off-set more to the right, i.e. the centre position of the servo was not in the middle any more!? The servo would move off centre when the motor was active, but was fine when the motor was stood still. If I disconnected the motor completely and turned off/on the ESC the problem went away and was not repeatable.

Later on I noticed that the middle of the brush wire had almost completely split, meaning there was only a few threads holding it together. Now it has completely snapped after I pulled it.

Also with the ESC set to higher punch levels, this seemed to increase the likelihood of the servo going off-centre...at lower punch settings it didn't happen as often.

So my question is, can a brush wire that is almost snapped off / partially disintegrated cause the servo to go nuts like this? The problem only seemed to happen with this particular motor and other motors did not affect the servo in this way.

I suppose if some of the electricity that was supposed to be going to the comm was actually finding its way to the outside of the motor can and then conducting through the graphite chassis to the servo might cause it??

Thanks in advance all.

i reckon the gears are shagged in the servo and are slippin

[PaulRotheram]

checked everything for stripped parts mate? steering arm splines, servo horns (both of them) faulty servo? possibly the gears.. every metal gear servo has at least 1 plastic gear.

have you skimmed, rebrushed and cleaned the motor? I know what your like for not doing that often enough

[Fiddybux]

Hey all (and Paul),

I know you know me and nope I didn't clean the motor up, new brushes etc before hand....but it was freshly skimmed and the brushes were cleaned up real good.

The cells were fully charged, GP4300's - been fine on everything else I've run.

Checked the servo hard by applying resistance to the arm when it was moving. You know, held it and tried to make it slip...but couldn't do it...it pushed against me all the time in both directions. Servo seems ok from my testing in non-race conditions around my living room and outdoors on the road with a different motor.

Checked all the other possibilities, like the servo arm slipping, the steering arm, the ball-cup threads (XX4 has some on the steering arm from the servo and they were holding and not stripped).

It's weird cos it really seems to be this particular motor, which now has a totally split brush wire.

I just wanted to know if a partially split brush wire could cause this weirdness? Could this happen??

I'll put some new brushes on it soon and see if it does the same thing anyway...and report back of course.

Cheers.

[PaulRotheram]

take a picture of the motor arm and endbell and post it up.

Try another motor and or servo and see where it goes from there.. if it is either of these.. then its time to replace one unfortuantly.

[Fiddybux]

Here's a pic of the broken brush wire, which I suspect was shoving volts into the outside of the can and messing up my servo (via conduction through the graphite chassis). Bear in mind that the brush wire used to be connected up, albeit with only a few strands of wire connecting it together which I didn't actually notice until after I'd run the race and experienced the problems.



And here's the pic of the comm (all a bit burned after about 6 laps)....doesn't look good does it!?! The comm was freshly skimmed and golden (honest!) before racing...now it appears to be a bit burned.



All other tests with other motors so far suggest that the motor is at fault.

Cheers.

[bert digler]

Originally Posted by Fiddybux

I'm not entirely sure of the point of uploading the image, especially of the comm was freshly skimmed and golden (honest!)...now it appears to be a bit burned.

Anyway here's a pic of the broken brush wire, which I suspect was shoving volts into the outside of the can and messing up my servo (via conduction through the graphite chassis).



And here's the pic of the comm (all a bit burned after about 6 laps)....doesn't look good does it!?!



Bear in mind that the brush wire used to be connected up, albeit with only a few strands of wire connecting it together which I didn't actually notice until after I'd run the race and experienced the problems.

All other tests with other motors so far suggest that the motor is at fault.

Cheers.

to be honest mate i bin racin for for 26 years dodgy motors dont shag servos i reckon its the gear set

[Fiddybux]

So how can I test for a knackered servo gear, other than trying to press against the servo when it's working?

[barnyard]

check the pcb on the inside of the endbell is connected (red led should come on when the motor is running) This pcb has all the caps on it that help to get rid of the majority of the electrical noise created by the motor.

if the led doesnt turn on check the contact strips to the pcb if these are good get a new pcb

also try another endbell on the motor (it doesn't have to be a V2 the important thing is to make sure the caps are there)

[Fiddybux]

Okay...done.

The PCB seems to be ok....all making contact and the PCB itself isn't burned out.

I can't check the red LED at the moment as the motor is basically inoperational on account of the fact the brushes ain't connected up and I've just snapped a motor wire!

[bert digler]

Originally Posted by barnyard

check the pcb on the inside of the endbell is connected (red led should come on when the motor is running) This pcb has all the caps on it that help to get rid of the majority of the electrical noise created by the motor.

if the led doesnt turn on check the contact strips to the pcb if these are good get a new pcb

also try another endbell on the motor (it doesn't have to be a V2 the important thing is to make sure the caps are there)

the motor has nowt to do with servo adjustment common physics say that the servo has slipped ie new gear set i have never known a servo to move unless gear set has stripped or has lost its centre due to motor talkbak it dont happen more likely cause interfence or receiver failure but i would check the gear set

[tc2k]

Solder that brush together, resistance in it must b high with a tiny strand all thts left

[Northy]

You are experiencing electrical noise from the motor affecting your servo. It IS NOT the servo gears.

Check the pcb as Barnyard says, also clean the contacts on the pcb and to it with some motor cleaner on a cotton bud, skim and re-brush the motor, also clean out the slots between the comm segments.

The motor brush shunts carry some current, but not all of it, some is conducted through the brush holder (tube) directly to the brush.

The snapped (or partially snapped) brush shunt has not sent electricity through the chassis to the servo.

It's a dirty motor causing this, nothing else. As long as there is copper left on the comm it is fixable and not bin fodder.

G

[Fiddybux]

Hey thanks Northy. I strongly suspect the servo wasn't at fault on account that I gave it a good testing to try and get it to slip...but it didn't.

It is good to know that electrical noise can do this to a servo as well.

It would be a shame to bin the motor because it's a real belter, so I'll get it all cleaned up and give it some TLC as you suggest - fingers crossed it will fix the problem.

Cheers.

[Fiddybux]

Hehe...turns out that after I cleaned all the motors up, fitted new brushes and all that....the problem turned out to be something much simpler.

The steering post was slipping and when I looked deeper into the problem I found that it was actually glued on and the teeth are all mangled underneath!

Anyway, I glued it back on again for now...this seems to be the only way forward until I can get some spares...and everything is all good!

Let this be a lesson - even if it doesn't look loose - check it anyway!