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Old 02-12-2015, 08:58 PM   #1
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Questions?? Mini-Z Servo keep spinning and spinning and spinning

My AWD Mini-Z ran into a wall and the steering instantly went to full left lock making a struggling sound. Turning it on and off did nothing.

Removing the servo cover, everything was still intact and not binding. I then removed the servo motor and potentiometer to inspect their connections. With the car and transmitter on, the servo motor rotates continuously in one direction. No transmitter steering input or trim is shown through the servo but the throttle functions correctly. When the transmitter is turned off, the servo motor stops.

Here is my servo motor and new potentiometer I installed to try fixing the problem:



I have completed the following troubleshooting items, none were successful:
-Replaced the potentiometer with one from a Losi Micro-T servo (in picture)
-Adjusted both potentiometers to see if there was a difference
-Tried a new Transmitter & Transmitter Batteries
-Tried new radio crystals
-Replaced the car batteries
-Installed a new antenna on the car
-Re-soldered the servo motor
-Checked all wire connections

None of these options have changed the problem at all.

Thoughts:
Maybe I cannot find the correct position for the potentiometer?
Maybe the board has become faulty, but why when hitting wall?
Possibly a bad servo motor but it takes the command from the board so I don't believe so. I have a 3 wire micro servo that I could possibly hook up but I am not sure how.

Any help would be greatly appreciated, thanks!
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Old 02-12-2015, 10:29 PM   #2
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got a photo of the other side of the board?

Im viewing that as an AM board which makes me think there might be a small micro adjust dial for the steering on that opposite side near to where the steering fets. That could have been bumped out of alignment....
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Old 02-13-2015, 09:12 AM   #3
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What you are having right now i have been there several times!

If the servo motor spins in one direction it's fine. It runs. It's up to the potenciometer to keep that continous on a small range!

-Have you sure the Miniz potenciometer was bad? And not the teeth on the gears somewhere?
-The 2 wires are right on the 3 pot legs?
-Changing to another pot from other rc could not work...or could be reserved on the minz...(wires...)
-In AWD miniz that sympton sometimes is the servo saver that feel off the place...check it closelly...it could be just that! (never use the alloy one, stick to plastic, it's the thing with a spring that looks like a bridge)
-Make sure every plastic pins in in place inside the servo cage...they are more important then meets the eye!

I have more then a thousand miniz/xmods photos i could look into them to see if that pot on AM 27mhz is right...


-I don't remember right, but one in the picture for a Mr01 is wrong with the stock radio that haven't steering reverse

When everything is on place motor will stop and only go when remote goes left or right but the fisically stuff must the on the car and not on the hand...or servo motor will just spin if i remember right!

And looking at the picture, are you sure the left fet of the steering is not burnt? By the looks it seens it got a classic hole burn...but could be just dirt in there that pic does not clear...

Quote:
Originally Posted by small=breakable View Post
My AWD Mini-Z ran into a wall and the steering instantly went to full left lock making a struggling sound. Turning it on and off did nothing.

Removing the servo cover, everything was still intact and not binding. I then removed the servo motor and potentiometer to inspect their connections. With the car and transmitter on, the servo motor rotates continuously in one direction. No transmitter steering input or trim is shown through the servo but the throttle functions correctly. When the transmitter is turned off, the servo motor stops.

Here is my servo motor and new potentiometer I installed to try fixing the problem:



I have completed the following troubleshooting items, none were successful:
-Replaced the potentiometer with one from a Losi Micro-T servo (in picture)
-Adjusted both potentiometers to see if there was a difference
-Tried a new Transmitter & Transmitter Batteries
-Tried new radio crystals
-Replaced the car batteries
-Installed a new antenna on the car
-Re-soldered the servo motor
-Checked all wire connections

None of these options have changed the problem at all.

Thoughts:
Maybe I cannot find the correct position for the potentiometer?
Maybe the board has become faulty, but why when hitting wall?
Possibly a bad servo motor but it takes the command from the board so I don't believe so. I have a 3 wire micro servo that I could possibly hook up but I am not sure how.

Any help would be greatly appreciated, thanks!
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Last edited by targetingxmod; 02-13-2015 at 09:26 AM.
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Old 02-14-2015, 11:12 AM   #4
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Thanks for the responses! I re-installed the mini-z potentiometer and then assembled the servo back into the vehicle. Again same problem.

Please note, new pictures have been uploaded below.

I just ran a test on the potentiometer: I used a voltmeter and checked the volatage on the potentiometer. With no steering input: 1.0V (even with the tx off). With the tx on and steering input given, the voltage was still 1.0v. Knowing already that the tx is good, I am now wondering if the receiver is the problem which is strange since the throttle still functions with the tx.

About the screw dial on the back of the board, I really hoped this would do something but it had no effect.
Because the pot is wired as it was when it was correct, I believe it is wired correctly still.
The plastic pins are good, only one is a bit loose.
I don't really know anything about fets. I was able to scrape the stuff off of the top so I don't think it was a burn hole.
I just tried a new motor and it moved the same as the the normal servo motor.

Next step, maybe replace the FET's?
What is the screw on the back supposed to do? It moves freely but doesnt move in and out.

Thanks!!!






Last edited by small=breakable; 02-14-2015 at 01:52 PM.
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Old 02-14-2015, 05:46 PM   #5
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The area labeled "vr2" is a micro adjust for steering centering...in AM devices they sometimes needed to set the steering center by using both the board item as well as the TX dial.

If what you say is correct and you've tested for pot function:

1. Set TX "st trim" to 0-center
2. power tx
3. power rx/chassis and with very slight movement try using vr2 dial with a flathead driver and see if you get any response difference.

tagrgetingxmod does have some valid points as well...it seems you have covered both our queries though.

One other option which is a bit left field:

When i used to do 2.4Ghz/asf swaps into AM chassis I would sometimes get the motor leads backwards and i would get a similar "full throttle locked steering". I realize that in your case this was caused by an impact but you might consider swapping the motor leads to see if that does anything.
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Old 02-14-2015, 06:21 PM   #6
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Really good points everyone, thanks for all of the help! I have tried the screw adjustment also to no avail lol. New plan: I am scrapping the electronics and will be using my brushless, lipo, 2.4ghz setup from my Losi project with a different motor all with the help of manufacturing a carbon fiber chassis at my schools shop to make room.

Again, I really appreciate all of the feedback that was given, thank you!
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Old 02-20-2015, 10:22 AM   #7
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A word of caution: Be sure to keep your build as light as possible. The Losi BL esc and motor are underpowered for this size of application and are prone to meltdown if stressed. I built an aftermarket RWD platform with this same power unit and didnt get very far before it cooked its drive fets.

Kyosho are now making brushless systems for the AWD package so if you have a kyosho specific ASF TX you could make the swap with no issues.
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