servo issues - twitching

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My guess is that the twitching is due to poor ground connection somewhere. I have only noticed twitching one single time, for a short moment.
I have however noticed that often when my car stops and won't start again, there's no spark. It could be the CDI, but I think it is a wire or bad connection issue, possibly the connector to the sensor. I will replace that connector.
I also put an extra earth wire from the spark plug to the cdi, since I felt that the ground connection between the spark plug and the plug cap was not good. That seemed to make quite a difference.

On the other hand I have understood that these CDI's are also used on RC helicopters, and then one would assume they need to be very reliable. But maybe there are some quality differences in those.
 
I have the exact same problem. No spark after the car stops.
I have a condition which makes it hard for me to pull-start it all the time, so I'd love if someone came up with a
electrical start for it.

My suspicion fell on the connectors as well (I've made a thread about it here) - The original connectors does not seem up to the job imo.
I would prefer something stronger - with both leads connected to a common platform, so that you're not able to push out or bend them independently.

I have not tried the extra ground connector on the spark plug cap, but I noticed the cap didn't look to sturdy and have often wondered if it was secured correctly or not. I believe the way the cap is built, it can be hard to keep a constant connection at all.

I fished around after some new connectors but I got no answer here, so I guess I'll just buy a bunch and try them out it it comes to that.

I think the biggest problem with the CDI is the way it's been placed in the batterybox - you're forcing a unnatural bend on the spark plug wire,
and you need to move the CDI each time you're reaching for the batteries. You're begging for problems this way.
Martin Haas made a battery box modification which seems better than the original choice.
I still would prefer it if the CDI was placed with even less bends to the wire.
I tried placing the CDI in an alu box between the rear wheels which seems to work fine.. in theory.. Again, I can't remember how it went after that.

I have now returned my car back to the shop for them to look it over.
 
I got some new water tight high quality connectors in about the same dimesion as the originals, from Digikey, check the numbers below out at Digikey. Don't forget the pins and stuff.

I always place the CDI so that the spark plug cable goes from the CDI box directly out of the box, without any bends. The two wires in the other end goes in under the Radio on/off switch.

I ran the car at standstill yesterday, wheels in the air. It ran fine for about one tank, then suddenly just stopped, like someone shut it off. Then it had the start stall problems. I switched spark plug to a cleaned one, and then it ran fine again.

151-1170-ND CONN RCPT 3 WAY BLACK 22-28AWG

151-1181-ND 3 WAY PLUG BLACK
 
Thank you very much - those connectors looks like the kind I wanted.

So you have modified the battery box?
It seems more logical for the sensor wires to enter the battery box where the servo is mounted, instead of going all around to the back as it is original.

It all seems familiar.
I have also had problems the other way - suddenly the car takes off - full throttle.. I can just watch and hope it hits something soft.


You changed to a cleaned spark plug.. How did the one you replaced look?
A spark plug should be really dirty to stall the car with no warning.. One would think you would notice some hickups from the engine first.
But since most of my experience with gasoline engines comes from 1:1 and not RC - perhaps I shouldn't come to a conclusion so fast.
 
That your car takes off on its own can be due to a completely different issue that i have noticed.
Take a look at your throttle servo linkage. The small steel rod should exit from the top of the throttle horn, not underneath which I have noticed it does on many pictures of the Octane, it should also be positioned above the screw that attaches to the carburettor arm, not underneath. If this steel rod is located underneath, it can get stuck in a couple of places. I bet that is what is happening to yours.

I have not modified the battery box (yet). I just put the CDI in with the spark plug cable facing rear.

The spark plug looks almost like new when I take them out. Generally you can see that the isolator looks wet or shiny, and that's the thing, it gets what is called "fouled", which means that it gets a cover of "something" on the isolator between the tip giving off the spark and the ground side. This more or less invisible cover conducts electrical current and makes the spark weaker. This is a well known phenomena. It can come from too much oil in the gas and not getting the spark plug up to heat. When the spark plug gets hot enough, this cover burns away.
It seems to me, that I need to change the spark plug after every tank. I clean the spark plug using a spot sand blaster. Just inserting the end of the plug into the hole of the sandblaster and run for a while. Then I brush the plug thoroughly with a steal brush, not to get any blasting sand into the engine.
 
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I noticed in your film in an earlier post, OWi, that your throttle linkage is probably not mounted in a good way, take a look at these photos I took of my setup, before and after fixing it.
In the top photo below, when you give gas, the pusher on the steel rod can get in contact with and get stuck on the plastic housing underneath, that might cause your car taking off. And as you can see, you have contact also at zero throttle, where the red arrow shows.
In the photo below, everything runs clear.
DSC_0882.JPG DSC_0878.JPG
 
F-Type said:
I noticed in your film in an earlier post, OWi, that your throttle linkage is probably not mounted in a good way, take a look at these photos I took of my setup, before and after fixing it.
In the top photo below, when you give gas, the pusher on the steel rod can get in contact with and get stuck on the plastic housing underneath, that might cause your car taking off. And as you can see, you have contact also at zero throttle, where the red arrow shows.
In the photo below, everything runs clear.
View attachment 1145 View attachment 1146
Click to expand...
You are missing a piece of rubber that goes between the two pieces of metal with the set screws, refer to part number 108948.
 
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So, the exploded view is showing the completely wrong thing here, apparently an early prototype version.
When looking at photos on the internet, I can't spot a rubber piece an any of the few photos I've found.
And in the photo on HPI's website for this part number, I can't identify which piece should go in between!?

108948_108948_01_314_235.jpg
 
a simple fix is to use a couple pieces of fuel tubing, it is cheap and works well....
 
Sure, finding some rubber is not the issue, I think ;) But do you mean there should be a piece of rubber between the metal part that is fixed to the "rod" (the "pusher") and the metal part that is fixed to the arm on the carburetor which the rod passes through (that the "pusher" is pushing onto)? Or elsewhere?

What part in the picture is the actual rubber piece?

ANyone with a photo perhaps, showing this rubber piece?
I did find a couple of photos via google showing this part of the car, but I could not identify any such rubber in those. They seemed to look like mine, with the difference related to the problem I mentioned above.
 
does it really matter so much how the "factory" does things designed by some engineer who probably doesn't even do the hobby? I have run my own style linkages on a few of my nitro vehicles and had much success with doing so... a bit of forethought is needed to design the linkage and all but it is not rocket science....
 
I don't see any problems with my linkage. But I was told a piece is missing. So, to understand what is missing and what use it might do, seeing how it was thought to begin with might help. Then I can decide if I want to do something about it.
So yes, since engineers usually have a thought with that they do, good or bad, considering how the "factory" did it and why is always a good start, IMO.
 
F-Type said:
I don't see any problems with my linkage. But I was told a piece is missing. So, to understand what is missing and what use it might do, seeing how it was thought to begin with might help. Then I can decide if I want to do something about it.
So yes, since engineers usually have a thought with that they do, good or bad, considering how the "factory" did it and why is always a good start, IMO.
Click to expand...

Hopefully this helps, also when I got my truck back from HPI the CD I was flipped around so the solid part of the ignition wire was coming straight out of the battery box essentially reversed as it was from the factory...this may fix the twitching issues.IMG_20150617_235703.jpg
 
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Thanx for the photo, I have not seen a rubber part like that on mine.
I also notice your linkage is underneath both the throttle horn and the screw on the carburetor side. Mine was like that, and tended to get stuck as it got in contact with the plastic housing underneath. I switched, as I mentioned earlier in thread, so it is on top instead, and it works fine. I also notied that is how it is depicted in the manual. Though there is a totally different kind of linkage there.

I have also noted that the range of the throttle movement does not quite match the full throttle range of the carburetor. However, as I am still struggling with break in (or maybe a faulty CDI) I have not dug deeper into that, yet.
 
Well it looks like after the real first time i get to do some bashing on my Octane the steering servo goes out. Won't turn left or right sitting on the ground. You can pick it up and it will turn both ways. Charged the batteries checked the wire and the servo saver and it does the same thing. Also check to make sure there was no dirt or rocks stuck in the steering linkage. Any other suggestion. Or can anyone point me i the right direction on a new servo.
 
Mark Walters said:
Well it looks like after the real first time i get to do some bashing on my Octane the steering servo goes out. Won't turn left or right sitting on the ground. You can pick it up and it will turn both ways. Charged the batteries checked the wire and the servo saver and it does the same thing. Also check to make sure there was no dirt or rocks stuck in the steering linkage. Any other suggestion. Or can anyone point me i the right direction on a new servo.
Click to expand...

I know you said you checked your servo saver, but the problem you describe screams loose servo saver. If you are driving the savage does the steering work, even a little? Are you running a receiver hump pack (5 cell)? Stock servo?
 
Yes it turn a little and its the stock 5 cell battery and stock servo. The sevro save is turning. It also took a tumble down a 10 foot hill front to back and landed on its wheels
 
So i tried the tighten up the servo saver and found this while i was looking at it to take it apart. I was wonder if this is cracked. If its not how do i get to it?
upload_2015-8-5_12-17-43.png

upload_2015-8-5_12-21-35.png
 
It's tough to tell with those pictures. Though there does appear to be cracking. That would be a good reason for the issues you are seeing. I would recommend pulling out the servo saver and taking a closer look. There are two screws inside the electronics box (under your gas tank), on the bottom. There are two screws holding it to the bottom bumper/skid assembly. And then the screw that holds the arm to the servo.

If the plastics are indeed damaged the replacement kit is the following:
http://www.hpiracing.com/en/part/85058

Though there does appear to be some very cheap servo saver assemblies on ebay (including the metal parts).
 
I got my servo twitching. So what the fix? I was tried to separate the CDI and looks like the twiching is gone. But honestly I don't want to separate the CDI and battery box.
 
deephis said:
I got my servo twitching. So what the fix? I was tried to separate the CDI and looks like the twiching is gone. But honestly I don't want to separate the CDI and battery box.
Click to expand...


If proximity causes twitching, then you need to isolate. Since you are unwilling to move them apart, shielding is likely your answer. You could replace your cabling with cabling that has shielding built in. Or you could get metal braid tape or wire loom. Another possibility is to simply construct a metal container around one or both of the components.
 
X said:
If proximity causes twitching, then you need to isolate. Since you are unwilling to move them apart, shielding is likely your answer. You could replace your cabling with cabling that has shielding built in. Or you could get metal braid tape or wire loom. Another possibility is to simply construct a metal container around one or both of the components.
Click to expand...
If shielding could eliminate twitching 100%,I will do that. But I don't know how. Do you have any pic a DIY shielded wire?
In the end I would do move them apart if it's easier than shielding.
hmm...can I do shielding with aluminum tape?
 
deephis said:
If shielding could eliminate twitching 100%,I will do that. But I don't know how. Do you have any pic a DIY shielded wire?
In the end I would do move them apart if it's easier than shielding.
hmm...can I do shielding with aluminum tape?
Click to expand...

Might do it for you, depending on severity of the EMI and how thoroughly you cover the wire. Any openings are a potential issue. I tend to use copper tape. Many a times have I been in EMI testing and used rolls of that stuff.....haha.

Something like the following still has good flexibility:
http://solutions.3m.com/wps/portal/...abric-Tape-X-7001?N=8704974+3294000672&rt=rud

Or braid (wire loom) like the following:
http://www.alphawire.com/en/Products/TubingAccessories/FIT-Wire-Management/Braid/1239
 
Anything that could possibly be an emitter or a receiver of interference. Definitely the CDI leads and servo leads. Bundle them up by device and location they travel to. Basically wrap stuff until you take care of the issue......haha.
 
Looks like could be some time to find the issue:rolleyes: haha
The other way if I want move them apart the CDI, where is the better location to secure it? I saw somewhere in this forum he put the CDI behind the rear shock tower.
 
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