smirkracing

iTrader: (19)

Hey all - here's a really bizarre problem I could use your help diagnosing.

Situation: pretty new Arrma Granite developed a problem on its 10th battery pack. The problem is that the servo moves clockwise in a slow, jerky fashion. The servo moves counterclockwise perfectly - no problem at all. This problem can be reproduced over and over.

My troubleshooting: I thought perhaps the servo was "bad" and took everything apart to replace it. On a whim, I thought I'd try the servo in a different rig, different radio, and to my surprise, the servo worked perfectly. I tested this over and over, and there were no problems. Then, I thought perhaps there was some kind of problem with the receiver, so I took a known-good servo and plugged it in. That servo worked perfectly. Then, just to be complete, I took apart the problem servo, and there was no damage at all to any of the gears. I repeated the testing and had the same results - the servo works perfectly with the one transmitter/receiver, but has a problem in only one direction (clockwise) with the other transmitter+radio.

Any ideas? I've never seem a gremlin quite like this. The servo seems to be physically intact, it works in a different rig, and it only has a problem in one direction when paired with its original kit.

I'd appreciate any advice or troubleshooting tips. I've tried everything I can think of so far. Of course I can just replace the servo (which is what I will do in the short term) but I'd like to understand what is causing this problem so I can resolve that issue.

Thanks!

billdelong

iTrader: (33)

Just a guess, but it might be worth replacing the servo connector... the pins in each Rx might be slightly different thickness to where one Rx works fine and the other may not be getting as good of a connection.

Werty Yui

Was the servo wet at any point?

smirkracing

iTrader: (19)

Bill thanks. I tried multiple different (known good) servos in the suspect receiver and they all worked fine. So the pins might be a problem but it seems unlikely.

Thanks Werty. No the servo was never wet.

1995 Monster T

Do both receiver's workr with the good transmitter? I suspect the old transmitter is bad?

Andy Koback

iTrader: (280)

Sounds like there could be a binding issue in the truck your trying to use it in. With the bull cups removed from the servo, are you able to manually turn the wheels by hand in both directions without any issues? May be binding in one direction only. Worth checking.

smirkracing

iTrader: (19)

I used two different radiosets, so I can't test the suspect transmitter or the suspect radio. However, both are working fine with the new servo I installed.

The truck is a-ok - I moved the wheels when it was taken apart. The problem is visible even when the servo is removed completely from the truck - I just tested it while holding it in my hand.

gigaplex

iTrader: (2)

Do you have a voltmeter? Try checking the output voltage from the BEC/receiver as the servo moves, the servo might be browning out.

PDR

iTrader: (31)

For completeness, could you list out the make/model of each component? ServoA, ServoB, receiverA, receiverB etc...

smirkracing

iTrader: (19)

I do have a voltmeter, so I'll give this a try. However, this was the stock servo that came with an RTR kit, so odds of a brownout should be low. I installed and aftermarket servo (currently in the truck) which has far higher specs (more than 2x) and that one is working fine.

I can look up the parts, but basically, here's the run down:
Vehicle 1: Arrma Granite 4x4 (all stock). This is the vehicle which was having problems with the servo
Vehicle 2: Associated ProsSC10 (all stock). This was the known-good vehicle (everything working well).
Additional servo: Trackstar 20kg 8th scale servo

The radios and servos in question are the stock units that come with the models above (mostly rebrands or just low-spec RTR stuff). The arrma servo in particular gets no love, but even that component is working just fine in another vehicle. It only fails when paired with its original components (and that too, in one direction only).

All combinations of servo / radio above worked properly, EXCEPT the pairing of the stock arrma servo with the stock arrma radio set. I am currently using the stock arrma radio with the Trackstar receiving and it is working with no issues.


(The only reason I'm even posting this question is that the specific problem is so unusual and (so far) inexplicable. I am not worried about the components themselves and they are all getting replaced as they fail anyway.)

billdelong

iTrader: (33)

This is a very good point... it's not uncommon for the potentiometers (POT) to go bad on older radios.... many name brands have replacement steering assemblies which include the POT.


Another way to check for a bad pot is to swap out the servo with another known good servo and see if it also glitches with the radio that might have a bad POT.

smirkracing

iTrader: (19)

I can't test that particular thing, because the two radiosets are totally different and incompatible.
However, I currently have a different (known good) servo installed with the "bad" radio, and everything is working just fine. So I don't think the "bad" radio is actually bad in general. There is some kind of specific problem that only arises when the 'bad servo' and the 'bad receiver' are paired, and that too in only one direction.

Both the 'bad servo' and 'bad receiver' are working fine as long as they are not paired with one another.

I will perhaps take some video. It is quite a gremlin.