Accelerator Jams at full throttle

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Pearforth

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Hi all
I am now chief mechanic to my my Grandsons latest hobby nitro cars which he received a Schumacher Swift 2 for Christmas. This car has been a problem from day 1 when the pull starter broke a spring which I managed to repair to keep things going, unfortunately the spring did break again but not before a major calamity occurred when the throttle jammed on and car went straight through a substantial timber gate at full speed. We have now lost considerable confidence in the control of this car and my question to the forum is has anyone encountered similar problems and what do we do to put it right. I have tested the batteries and they each have 1.4 volts + , plus I have done some running test on a wooden block firstly testing all the controls without the engine running which they worked perfectly. With engine running the servo unit seemed to have a mind of it's own when the engine was revved up it just went straight to full throttle and refused all attempts to push it back the only thing that worked was to stop the engine at which time the throttle went back to normal.
 

reighard53

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did you adjust the throttle trim?

could be the batterys in the controller. it happened to my 18mt

also there could be an interference in the radio try switching the crystals in the reciever and transmitter.
 
Last edited:

flm_savage

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so when you had it on a test bench and cranked up the engine, it still went to 100%?


what radio gear are you using?
 

beason

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i had a buggy that would do something similar. It was a bluebird servo and when the rig was running it would start acting stupid. fried 2 receivers before i figured out it was the servo. the vibration of the engine running is causing it to glitch.
 

Candyman

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There could be a few reasons for this. But the 2 things I would check first are the servo travel and the throttle linkage. Turn the radio equipment on and just cycle the throttle. Watch the linkage and servo horn when you get near full throttle. Look to see if there's any unusual hitches in the movement when you get near full. There may be a chance that the servo continues to try to push even after the carb is fully open, and sometimes that can bind the servo so it won't easily return. If the radio has End Point Adjustment, adjust it so that the maximum throttle throw occurs exactly when the carb is fully open.

Also, how far away from you was the car when it took off? It may be possible that there was a radio glitch, interference or temporary loss of signal. That can send a rig running off at full throttle.

Ultimately, this is a good example for all of us and immediately shows us all the need for a Throttle Return Spring and a Failsafe.

EDIT: Just read a little more of your post. If the servo starts freaking out when the car's running, it may be an RF glitch. The most common cause of this on a nitro car is metal vibrating against metal. See if there are any places where metal chassis plates may be rubbing against screwheads or anything like that. Try to run out as much of the receiver antenna as you can through the antenna tube. That will limit it's possible susceptibility to the RF stuff. But ultimately see if there's some metal rubbing somewhere.
 
Last edited:

Pearforth

RC Newbie
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Sticking throttle at full revs.

Many thanks to all those who answered my question on the sticking throttle at full revs and the ideas put forward that might find a solution to the problem. As yet I haveN'T had a chance to make any further progress but when I have I will report back with the results.

The question asked about what type of radio control equipment is being used it is Response SW 27 MHz.

The other question on how far away was the control from the car when it went wrong it was about one metre which rules out the problem of long distance radio control.

Any more ideas keep them coming they all help.
 

RC Addict

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Like Candyman said: A failsafe is a MUST. If you don't have one yet GET ONE immediately. Radio interference may not be the cause of your problems right now (but I am willing to bet you it IS) but no one should run without one. I know from experience!
 

Rolex

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Candyman is also correct about the chance of binding if the servo linkage exceeds the needed distance. That's the first thing you should check. Do a lot of testing with the rx and tx on, but the engine off, till you can locate the cause of the problem.
If it doesn't have a problem with the engine off, then you have vibrating metal, loose crystal or bad connection in the receiver.
 

qaart

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my ofna car would go 50 feet and start doing this. the car ran away 5 times at least
i bought a traxxas rx and tx works great
 

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