Originally Posted by
pkoury
Pylonracr I disagree with your methodology. For maximum servo torque and resolution the closer to the center of the servo horn the better. Using the 5 degree arc of slop in the servo gear train example the linear movement of a connection point located closer to servo center will be less than the linear movement of a connection point farther out.
I once built a training aid using two protractors and bell crank mounted pointers attached to identical servos mixed to the elevator channel on my computer radio. One servo was set up with the shortest servo arm and the longest bell crank connection to give one inch of throw. The other was set up with the longest servo arm and the bell crank connection that also gave one inch of throw. All connections were made using ball links for slop free connections. Care to guess which set up gave the least amount of slop at the end of the pointer? Care to guess which one gave the most precise and smooth response to trim input?
Pkoury
I find your test results quite interesting, and I am quite curious to see more. When I became a competent enough pilot to require accurate servo linkage I researched the best method and found what has been considered the best arrangement for the past 25 years or so. Use the longest servo horn possible, with the corresponding length control horn to achieve the needed control surface travel. This simply provides the most linear pushrod travel for any given control surface travel, thereby minimizing the effect of any linkage play. Applied servo torque, of course, remains the same as you still use the same servo travel to obtain the same control surface travel. This method has been used by nearly every TOC, IMAC, and pattern competitor for over 20 years.
Now you have evidence that proves there is a better way. Will you please share it with us? I am very interested in high resolution photos of your test. What test instrumentation was used? What were the differences between the Control Subject and the Test Subject? How were the tests documented? I admit I never built a bench model to test this. I had one of my grad students in theoretical physics model the test in 3D Force/Vector plotting software and document the results. We tested using servo arm lengths of 1/4", 1/2", 1" 1 1/2", 2", and 3" while introducing linkage play of .030". The results were staggering to say the least. With the shortest servo arm the free travel at the control surface was over 2 degrees, and with the longest arm the movement was less than 0.01 degrees. Now, if there is a better way, there are hundreds of competitive pilots, myself included, that would like to know how to achieve better control surface resolution.
Please share your testing and documentation with us so we can all improve our aircraft.
Scott