Stretch0069

A friend of mine passed away and I bought his old R/C stuff. In the lot was a car that he had started building. It has a K/B 3.5 that drives the rear wheels directly. Clutch bell drives a large gear connected to the rear solid axle. Posi.

I had to complete it by making an upper deck to mount the fuel tank, Rx, and the two servos.

Everything is made from aluminum. The Rx is a Futaba FP-R102J. The receiver worked fine in an electric car from Tamiya.

I finally got everything put together and started it up. Once running, though, the servos get real twitchy. At one point, the throttle went wide open. Not good since I was trying to get the carb setup.

Anybody have any ideas???

'preciate the help.

PS-if pics would help, I can get some.

BUGGIES_R_US

You know..

My Car's throttle servo twitches uncontrollable every time I go to my friend's house.

Worse.. it wont even respond to the radio.. and the fail safe doesnt kick in either.

IT scares me that there is a possibility of this happening anytime when I'm driving!

But when I'm in/around my home..its perfectly fine.


Minor twitching is either 1) metal contact in the car or 2) interference.

I've heard that wrapping the RX in a mylar bag helps. I've yet to try it.
ram

Stretch0069

I did some searching and found stuff that pointed toward the metal to metal contact, but I'm not real sure what it all entails.

The chassis upper plate (where everything is mounted) is bolted directly to the lower chassis. Is there any way to isolate the upper from the lower? What do I need to isolate to solve the problem??

Sorry about all the questions. This is my first home-built car.

I had the runaway again. This time I saw that the battery came disconnected. THAT was scary. Glad I had it on the box. I think I'll RTV it so it doesn't come out again.

Thanks for the help.....

dbow

My Feedback: (1)

You will have to troubleshoot the problem with metal to metal contact. Usually its not something that is bolted tight, its metal to metal contact that is in motion from the vibration of the engine.

Sometimes you can take a screwdriver and touch the head of the engine and the whole radio system will start glitching.

You will just have to check each area with the radio on to get a response.
Also take note if it only glitches when the engine is on.

Wrap your rcvr in foam and isolate the ant from any metal, make sure it is not running along the chassis. it needs to be in a tube and lifted up and away from the chassis. The excess ant can be wrapped and tied or taped to the top of the rcvr, this way you will only have enough ant to clear the top of the ant tube.

Also secure your battery pack so it does not fall out, it needs to be held down very tight with zip ties or some other way.

Once you do all this, place the rcvr in a ballon to keep it clean.


Dbow

Stretch0069

Thanks for the input. I'll get on that in the next few days and post the results.

Thanks again....

Smalls

Buggies,

Is there a Ham Radio around your friends house?

I hear they can cause interference.

mortonmr

I'd love to see some pics of this thing, I've been kickingf around the Idea of a scratch built for quite a while and it would be cool to get Ideas from!

Thanks and good luck
MRM

Stretch0069

Sorry about the lateness of this reply. I've been indulging in my other fav pastime....guns. Funny...the problems with this car almost caused a merging of the two hobbies.
Since its been raining here the last couple days, I've gotten back on this car. Think of this car as an RC10 made of aluminum and a .15 nitro motor. I originally had another smaller aluminum deck that held the servos, tank, etc. Well...I got the elec-deck isolated from the rest of the car, but I still get the twitch. I tested by turning on the Rx and Tx. I then took an allen wrench (you can use anything metal) and rubbed it on the servo linkage to the motor. As I would move the wrench, the servos would twitch. I haven't started it up yet to see how it will run, but my guess it will twitch pretty bad. The original elec-deck was made of a rubbery plastic about 1/8th inch thick. I think I'm going to use the same material and see what happens.

I'll try to get some pics this weekend and post them. It ain't pretty though. [sm=spinnyeyes.gif]

I have a bit of aluminum laying around. If I stick around in this country, I'm thinking of building some crazy "cars".

28ga

I've had problems with twitchy servos in the past and most times it is the crystal set, or mis-matched radio and transmitter. You said the Rx is a Futaba FP-R102, what transmitter are you using? Is the crystal set within a channel or two from what the radio is marked as? Do you have another channel you can try? Another factor can be florescent lights. Is the bench you are working on lit with fluorescent lights?

Just some things to try!

Stretch0069

The Tx and Rx were bought together. They came out of an old electric Tamiya car.

I DO have a flourescent light. Hmmmmm.......I'll try this stuff outside.....at least while the sun is shinning. Screwey weather as of late.

crooper

Ham radios DO cause interference. I used to live near a guy who had a big Ham radio antenna on his house. I could tell when he was using it because my car got all twitchy and was relatively uncontrollable.

As for isolating the top plate from the bottom -- couldn't you attach it with nylon screws and put nylon bushings/spacers where the posts meet the lower plate?

drf

Fluorescent lights are nasty sometimes but it could be something else as well. check it outside to see it is still glitching. If it it it could be the crystal even if both are the exact same frequency. If you hit a crystal quite hard you can damage it internally and its freqyency might skew. Since the equipment is old I would bet that the crystals had a couple of nasty knocks in the past. Since crystals are cheap put a new set in and check again.
I get a lot of twiches on my car all the time. I dont know exactly from where it is but it only happens when I am near to the car. If I am closer than about a meter the car glitches- not too much but it does. If I get a bit far away it work fine! The Rx and Tx are about 12 years old and had a LOT of beating during their life and where cheap stuff anyway.

Stretch0069

Sorry about the lateness of this reply. I did a check outside and I still get the twitchiness.
That was about all I got done before Pop went in for double bypass. This week I'll try to find some different mounting material and see what happens. I'll try to get some pics.
I'm still trying to get it figured out.........

zoomin

same thing is happening with me, i also have some older model futaba AM rx and its gettin twitchy, first time it went to WOT scared the **** outa me, car just jumped up and i caught it with my foor (from the looks of it this thing is FAST), this was in my basement but i noticed sometimes when i move the ignitor around when its on or i touch it to the head then it gets titchy, whats a mylar bag? one of those static free computer part bags??? anyone here sucessfully running an AM radio on a gas RC car? i wanna play with this thing soon.

if i figure somethin out i'll let you know.

thanks
victor