Smoothing out the throttle servo
 

I have a Futaba 3pks and savox SB-2274SG throttle servo. My problem is that when I barely press the trigger on my transmitter, the throttle servo jumps to about 20% throttle. From there the range is smooth. It is just when I first press the throttle trigger and I mean I am barely pressing on it. If there is any one who has had this problem it would be nice to know how to fix it. The servo is brand new so I don't think that is the problem. Any help is much appreciated.

Really? Are you sure its new?

Yea. Just pulled it out of the packaging from a main hobbies

Set throttle expo to -15 and try.

I tried doing that as well. I even tried to specify on the throttle spectrum where to decrease the throttle expo. I have literally been looking through the menu on my futaba 3pks and messing with everything associated with the throttle servo. I keep coming up empty. At this point I have manually adjusted the linkage so that the servo horn just barely touches the set screw

Change out that servo with another and try. If it's still doing the same thing on the other servo, it's definitely yr tx. If it is ok, the. It's yr servo.

Some radios have a feature where you can set the throttle servo to jump to a predetermined position when the throttle is engaged to eliminate the initial slop in the mechanical carburator linkage on nitro cars.

When you just touch the throttle trigger, the servo immediately jumps to the predetermined position and then operates normally (smooth) from that position on.

Your problem sounds very much like that.

Maybe your radio is set with that?

X2

Futaba calls this feature TH-ACCEL I would check that setting on your Tx and if its not already set to 0%, turn it down to 0% FWRD and 0% BRAK so you will have smooth linear operation around neutral instead of jumping away from neutral.

I will check that when I get home and let you guys know if it work

Kotton, I am going through the exact same thing at the moment with my Futaba 3pk. Was speaking with an experienced racer last night and he reckons it sounds like the potentiometer (POT) is on its way out in the throttle.

He gets his handset serviced every two years to help sort these problems out. My handset is nearly 7 years old and never been serviced once!

Tonight I have gone into the ADJUSTER setting to try and realign where neutral is for the throttle...................will let you know how it goes!

Checked the th-accel. It is set at zero for both forward and brake. I honestly don't have a clue of how to fix this issue

BINGO!!!

After two weeks of changing servo's, carbs and trying different engines this looks like it has fixed it.

Go to Menu page 3 and the last option is ADJUSTER
Then choose Throttle.

At that point in neutral my reading was 35%. I very slowly pulled the throttle until the dial read 0% and pressed OK. Then moved onto full trigger and brake which ended up reading 125% and 146% then held the + and - to set it.

Went out to the car and took of the air filter to check the carb. With all electrics on the carb was open (around 35% the original neutral setting) so whipped off the servo arm and repositioned it and reset my EPA. (previously 30% EPA for throttle was giving the full 60 degree servo movement) This is now up to 50% and the action appears to be nice and smooth through the full throttle range, no initial jumping.

I am a happy bunny, hope it works for you

I have a Sanwa MT4, yes its a different radio but they may have similar functions.
On mine I can adjust the throttle & brake curve, so setting the throttle curve to a negative % slows down the thottle movement, then at 50% (also selectable) throttle pull, the throttle opens slightly faster than the first half of the trigger pull.
It just applies the first part of the throttle opening a little slower depending on how its set so when only applying a very small amount of throttle, you only get a small amount. I haven't tried it while driving yet as I have only just finished a rebuild but I have had a look & tried it out & it seems like it should work well.

I would reset everything to default values and see what happens. Then if the problem still exists I would swap out servos and see if the problem follows the servo or if it only happens with the throttle channel.