When a Futaba 9C is operating in PCM mode I assume a given channel/servo has some number of possible positions as a control input is moved from one extreme to the other, e.g. 0 to 1024. But the 9C has the ability to provide a high rate beyond the normal 100%. Does this mean that when the rates are set at 100% that the number of servo positions are something less than 1024 to provide the positions needed to go to a higher rate like 130%? If that is the case is it better to always have your high rate set above 100% to take advantage of the increased servo positions and granularity.

Hi 8178,

If you are asking if you can somehow get more resolution than 1024 from this in PCM mode, the answer is no. Just moving the rates to 130%, will still only give you 1024 resolution, or the same amount of steps, it cannot increase. If you are looking for finer resolution, you would need to check the 14MZ which offers 2048.

I hope you find this information helpful. You can also reach our Futaba support technical team at 217-398-8970, or via fax at 217-398-7721.

Sincerely,
Krysta
Lead Futaba Customer Service and Programming Technician
Futaba Service Center USA

Thanks Krysta. Yes, I know there can only be 1024 steps. I wanted to verify that the 1024 steps must be present at the 130% setting and something less than 1024 steps when set at 100%. Therefore there would be advantage to always having the high rate setting above 100% to take advantage more steps and better granularity. At 100% it would be 1024 less 30% at each end direction for only 409 steps available?

With the PCM Systems, you always have 1024 steps (or 2048 with the 14MZ) in your total travel. For example, from full "UP" elevator with full "UP" trim, to full "DOWN" elevator with full "DOWN" trim you have 1024 steps. This is the same whether you have the total throw at 100%, 80%, or 130%. With smaller percentages, the steps are smaller, but you still have 1024 steps.

This may sound like you get better resolution when you decrease the percentage. That's not really so. Suppose you want your elevator to have a travel of +/- 20 degrees. If your system's set up for ATV at 100%, then you adjust the position of the pushrod on the servo and control horn to get the +/- 20 degrees. Hoping for better resolution, though, you move the ATV to 75%. That also reduces servo throw. However, by the time you adjust your servo/pushrod/control surface geometry to get the +/- 20 degrees of control surface movement, the 'size' of the steps seen by the control surface is the same as before. You've reduced the servo throw in your ATV, but then had to increase control surface throw by moving out on the servo arm and in on the control horn. The geometry 'expands' the 'compression' you performed in the radio.

For almost all purposes, the only reason you'd want regular ATV at something other than 100% for normal travel is to fine-tune the endpoints of your control surfaces' travel.

Thanks Bill! I end up getting this same question from time to time but I've never seen an "official" answer.

Thanks Bill! That’s how I originally thought it worked but after watching how my servos changed endpoints as I dialed in more than 100% on my high rate I got thinking how complex it would be for the radio to encode a larger value to each step real time. Some amazing computer power and logic there!

Bill,
That is a very interesting answer.
I will have to see how to best apply that knowledge on my models.
To get the best servo resolution you would have max servo movement
TO do this, you would need to go to max ATV. If max ATV will reduce the resolution of each step, then what is the end result on the servo?

I do appreciate the insight. I would have never thought PCM worked this way!
Again, thanks!

So how does the reciever know to decode certain steps (those at 50% ATV) to less of a servo angle than other steps (those at 100% ATV)?

In other words, if I have ATV set to 50%, and send "1024" to the reciever (say full UP), how does it know to send half the pulse width to the servo (compared to the pulse width it would send to the servo if you had ATV set to 100%)

Thanks

That’s what I was having a hard time comprehending but apparently the RX must decode the change in step value!