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Old 12-07-2008, 05:13 AM   #1
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Default Weird electrical / servo problem ?????

I have a RC8 using - JR Tx and JR RS310 Rx, 2 x Hitec HS645MG's, still running a Rx pack of 4x AA's (yes I know , hump pack coming soon). Today I was the only one not on 2.4GHz and I've never had interference at this track (as it is pretty remote).

Today my failsafe (a GV) kept coming on at random. Car would just go full brakes now and then. I thought no probs, it is very tight in the Rx / batt box so it is just hitting something and pressing the little button on it. So stuff it, I removed it. Weird thing was, I sometimes also lost steering servo at the same time but NOT always.

The buggy ran fine for a very short while, but then it was worse. It would lose the throttle servo completely every 10sec or so. The car would just stop dead, I would move the trigger fingr and nothing..... always for about 5sec of nothing, then away it would go and it would run fine for 10 sec or so then same thing.

Then heart attack: it died and was sitting at idle, as I walked towards it i pulsed the throttle and it would not rev. Just as I grabbed it to pick it up (thank god) the throttle came on halfway (ish) and stayed there. I would have had a runaway at half throttle, but I already had hold of the wing and I shut it down.

My thoughts:

(1) it was not the failsafe (derrrr).. eliminated that one right?
(2) it could be throttle servo, but it is 15 tanks old. It should not be stuffed?
(3) could be the Rx but how would I know? The Rx has awesome range and never failed before... it is also new (15 tanks) and if it dies why woudl the car got o zero throttle every time it becomes unresponsive? I don't have a throttle return spring.
(4) the battery wiring is OLD and was taken from another car. Could it be that the batt pack wires are broken so are intermittently failing on jumps n bumps? That would activate the failsafe... BUT after I removed the failsafe IF the voltage dropped to nil the servos woudl stay where they are..... again, as above, it is more like the throttle centres (goes back to idle) and then refuses to respond for 5 sec. If voltage went to zero for a little while the servo would stay where it was until power came back,right?

what should I check and in what order should I eliminate things?
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Old 12-07-2008, 05:26 AM   #2
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I just had a similar situation, I upgraded to 2 7955 hitec servos and those 2 servos when pulling hard at the same time would cause my battery voltage to drop just enough to make them glitchy. I am running lipo and was running castle creations regulator, I switched to a better/ stronger regulator(MIP) or is it (MPI) any how no more problems at all. Special thanks Frank @ Hobby Town for his quick suggestion as to how to remedy the situation.
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Old 12-07-2008, 06:05 AM   #3
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Thanks man... but no help.. maybe I should have mentioned that under load (both servos) my pack voltage is like 5.7V so it is not a lack of power thing.

Also it is not a glitch: the buggy will stop dead and sit at idle.... throttle does nothing: i will pull throttle on and off 5 times with no response.. After a few sec it will run 100% normal, and then 10 sec later it does it again. And again, and again
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Old 12-07-2008, 06:27 AM   #4
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Try unplugging your fail safe sometimes they intefere and cause problems or you might have a bad fail safe. Just make sure you have some fresh batteries in if that does not work check your wires on your switch in the reciever box some times those wires can get freyed. and wile you are at it check your servo wires also. Hope that helps.
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Old 12-07-2008, 06:39 AM   #5
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is the plug on your batterys simply lose? sounds alot like a problem i had and it was just the metal was not getting a good contact. i could squeeze the plug and it would come back to life
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Old 12-07-2008, 06:56 AM   #6
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i agree it can be a loose connector ...and thats what it sounds like....

you can tape up all your connectors with electrical tape to make sure they stay put
also do not discount the fact that lower grade hitech servos are not that good ....so it may need to be sacked i like that word thanks for reminding me .......i had the same serv o way back when do the exact same thing ....
when you have an electrical glitch it can be
loose wires
wires passing close to metals
shorted wires
bad batteries
bad switch
bad rx
bad servo
in that order i would think servo or wires from what you explained

i mean im thinking of others but you got a bad servo or a bad connection or a bad switch .....

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Old 12-07-2008, 07:13 AM   #7
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I have had this happen a couple of times and the cause was different for each instance. In one instance, the receiver was actually intermittently bad. After shutting everything down while trying to diagnose the problem, all would seem well after turning it back on. Then, a few minutes later, it would happen again. I found the problem by taking everything out of the car and running the electronics on the bench. A couple of jolts to the receiver after it was operating for a bit and the problem revealed itself.

In other instances, I found that the wires would back out of the battery and servo connectors ever so slightly. I really had to look hard to find those. Oddly enough, it was always the black wire that was the culprit and was caused by a worn or defective retaining mechanism for the socket inside the connector.

A friend of mine had a wire on one of his servos that was worn through and randomly touched his servo tray. He also had to completely take his electronics out and give them a good going-through.

And then there are switches. Switches are great when they work but when they go bad they really suck and cause all kinds of havoc...nuf said there.
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Old 12-07-2008, 10:08 AM   #8
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The 1st thing I would try is get the eciever pack and when you install it take out the radio tray and inspect everything and maybe get a new switch too if that was the part you said was from an old car.
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