Servo Extentions and Jitter
by John Thompson

I have done some testing with various servo extension configurations
trying to determine the best method to eliminate the “jitter” you get
with the JR servos when using long extensions and I thought your readers
may be interested. I have always had problems with JR servo jitter on
long extensions and when I was trying to rig up my new 40% Giles, I
decided I just had to do something different. The Radio I used was a JR
10SX with 4721 servos. The following reflect different configurations
and the test results.

Case one: Standard extensions four feet long made of ribbon cable
connected directly to receiver using a 4 cell pack into the receiver.
Results: unacceptable jitter

Case two: Same as case one but with a 5 cell pack. Results:
unacceptable jitter

Case three: Standard extensions made of ribbon cable four feet long
connected to an EMS optical isolator (Glitch Buster) with 5 cell pack
driving servos separately from receiver. Results: unacceptable jitter

Case four: Same as case three but with only a short extension (< 1foot)
to determine if it was the extension length or the fully charged 5 cell
pack. Results: Rock solid

Case five: Same as case three but with 22-gauge ribbon cable shielded
in braided sheath (floating). Results: Rock solid

Case six: Same as case five but directly into receiver with standard
four cell pack driving receiver and servos. Results: Rock solid

Case seven and eight: Same as case five and six but with unshielded but
twisted 22-gauge wire. Results: Rock solid.

Conclusions:
It is not the high voltage of the five cell pack that causes the
jitter.
Twisted or shielded 22 gauge wire seems to eliminate all jitter.
Optical isolators do not seem to help with this kind of EMI problem.