Deadband Measurement
I was curious how the deadband measurement is made by the ServoXciter EF. My guess is ... since it can measure current consumption (to 10ma resolution) it starts varying the servo's input pulse width from a known point until it detects a rise in current consumption. The current consumption would imply that the servo's controller has commanded the motor to move. Is this right, or is some other method used? Also, what is the minimum deadband that can be measured? And finally, I sometimes run my servos on a 5-cell pack in my gliders. Would you know if a servo's deadband will change with a different supply voltage? Thanks, Lance

You are pretty much right on-target with your assumptions. The deadband alternates the output pulse between 1500 microseconds and 1500 + the selected value on the screen. For example if you rotate the knob to 10 microseconds the output is alternated between 1500 microseconds and 1510 microseconds. When the servo current rises above the threshhold limit set in software the text below the deadband value changes to "ACTIVE". This is the point at which the servo actually begins to move electrically. (You should make sure that the ACTIVE text remains active at this deadband for a least a few seconds, because sometimes you may see one slight movement that causes the display to show ACTIVE but then the servo stops moving). Depending on the servo, you may not actually see the servo horn "jittering" when the the display shows "ACTIVE" because of the amount of "slop" present in the gear train. You can continue increasing the deadband value until you see the servo horn start to move. This would show you the amount of physical amount of deadband in the servo. Your last question is intriguing. I have never tested for differing deadbands on the same servo under various voltages. I will perform some tests today and post my results here later tonight. Thanks for the questions!

Thanks for the info! I think this means the minimum deadband that can be measured is 1 us because the resolution on the servo pulse display is 1 us, is that correct? Regarding the 5V and 6V deadband tests, I'm looking forward to seeing your results. One reason I'm interested in getting a ServoXciter EF is to be able to measure deadband on analog and digital servos. I just read that its possible to run the servo off a battery pack by using a Y-harness so I assume that's the way you'll run the test. However, I noticed the manual says the current measurement capability is disabled when powering the servo off an external pack. I hope this doesn't mean the 6V deadband can't be performed? Lance

Okay, Lance, here is what I came up with after testing 10 servos I had close at hand.... *The deadband values listed are the maximum value that did not cause the servo to jitter It is interesting to note that the deadband stayed the same for all of the relatively newer model servos, while some of the older Futaba model's deadbands increased by 1 or 2 microseconds at the 6.0 volt test. But for the most part I would say that the deadband of the servo wil stay consistent over their voltage range. This was an interesting test to perform - thank you for planting the seed! Oh, and yes, the minimum deadband that can be measured by the ServoXciter is 1 microsecond. Alan

Awesome Alan. Thanks for posting your test results and for the answers! I don't use standard-sized servos, but the JR 527 seems to have a relatively small deadband for a non-digital servo. In fact, that jives with the claim made at jrradios.com: 527 Standard Servo Overview You can rely on the 527 sport servo for trouble-free, accurate operation, and sophisticated SMT construction makes it a real value. This standard servo features wider spaced output support (similar to the 8231) for reduced radial free play –– to maintain tight tolerances in year-after-year use. In addition, the 527's electronics dramatically improve the servo's deadband –– now 1/3rd that of the previous generation servo. The result: more accurate servos provide more precise flying. In contrast, the GWS S3002 has a fairly large deadband. I'm not saying deadband is the one figure of merit to judge all servos by, but I'd guess the GWS is a poorer performer. This is a cool use for the ServoXciter! Lance

On this subject, I have a question. What if the dead band is always active and will not go to the dashed lines like usual. I was checking one today when it quit working in flight and then worked fine on the ground. Was wondering if this could confirm a possible bad servo? Bob Anniston, AL

The deadband measurement on the ServoXciter EF is current-based. So if you have dialed the deadband down to the minimum and it still shows ACTIVE - the servo may be drawing more current than normal. Check the servo in the current measurement mode and see what the idle current draw is.

Tell Tale Signs of a Failing Servo
Hi! I'm from Manila, Philippines and got myself a ServoXciter a few months back.. Being into the aerial photography business, servo failure is a NO-NO so I do extensive pre-flight checks prior any AP work.. What I used to do before I got the ServoXciter is a touch test on the tail servo after 5 minutes of hovering to see if it's overheating.. now with the ServoXciter, what's the best and right way to use your product to find tell tale signs of a servo that is about to fail? I recorded my servos' deadband readings.. Is one tell tale sign getting a different reading from the actual manufacturer's deadband rating? or ACTIVE does not hold well on deadband rating? i.e. deadband rating is 4 and holds "ACTIVE" steadily then on any future test when ServoXciter Deadband set to 4 again, same servo, and ACTIVE does not hold steadily is that a sign? Any other tell tale signs I should know using ServoXciter? Pardon my ignorance on this, I just want to find out how I can max out the use of my ServoXciter and do AP work SAFELY. :D

Being into the aerial photography business, servo failure is a NO-NO so I do extensive pre-flight checks prior any AP work.. What I used to do before I got the ServoXciter is a touch test on the tail servo after 5 minutes of hovering to see if it's overheating.. now with the ServoXciter, what's the best and right way to use your product to find tell tale signs of a servo that is about to fail? I recorded my servos' deadband readings.. Is one tell tale sign getting a different reading from the actual manufacturer's deadband rating? or ACTIVE does not hold well on deadband rating? i.e. deadband rating is 4 and holds "ACTIVE" steadily then on any future test when ServoXciter Deadband set to 4 again, same servo, and ACTIVE does not hold steadily is that a sign? Any other tell tale signs I should know using ServoXciter? Pardon my ignorance on this, I just want to find out how I can max out the use of my ServoXciter and do AP work SAFELY. Some of the best evaluation is performed by using the slow sweep mode to check for any erratic movement which could indicate the the servo's feedback pot is becoming dirty. A dirty pot will cause servo position error which could lead to a crash. Center position repeatability (use the one-touch center) is another good check. If the servo doesn't center in the same position each time (from both directions) then this could indicate a dirty feedback pot or mechanical (gear) slop or wear. Static current checks can also be used to check for abnormal operation - if the servo begins drawing more current at a static position this could indicate that the servo is fighting a binding condition or that it is having difficulty maintaining its position. In either case increased current draw can indicate pending servo failure - or at least increased system current draw could drain receiver pack battery power and create unexpected shortened flight time. You could perform the test with a known load. The deadband check could be used to determine if your servo has changed electrically for some reason. If you have evaluated deadband on a servo for a substantial period with basically the same values and then you begin detecting much different deadband values it would cause me to be suspicious of that servo. I can't say what the specific failure mode would be, but I wouldn't want to be in the air when I did find out. Using the standard drive mode while applying slight pressure with your hands on the servo horn can be used to check for worn or stripped gears which could yield binding or slipping while in flight. I hope some of these checks answer your question. Alan

Alan! Thank you so much for that very informative post! The exact answers I was looking for! Cheers! Clement