Spektrum A7200BX and dual rate3s

Tomhintz

Member
I have my AR7200BX set in transmitter mode (Parameters, menu B) so I can use dual rates/expo in the radio. I set up rudder, elevato0r and aileron dual rates to the udder switch with position 0 being 100%, position 1 being 80% and position 2 being 60%. When I hold a control on an airplane and flip through the dual rates there is a noticeable change in the control surface. If I hold a control on the helicopter, say aileron for instance and flip through the dual rates nothing appears to happen. The amount of control does not look like it changes. This is all with the motor not running, just controls.
My question is should I see a change in control movement as I do on an airplane or does the AR7200BX handle this differently for helicopters?
 

pvolcko

Well-Known Member
D/R should impact how much pitch will be imparted to the blades. But it will not be the same as on a plane. It won't be as dramatic as on a plane control surface where 100 might be +/-30 degrees of throw and 50 might be +/- 15 degrees of throw.

By changing to lower D/R settings on the 7200BX you are effectively limiting the maximum roll rate it will attempt with a full stick position. So, in flight, if you do a full stick right ail roll at 100% D/R it will roll at some rate (lets say it's 360 degrees/second, ie. 1 rev per second). At a D/R of 50% that full stick ail roll will now be substantially slower, perhaps 180deg/sec or .5 rev/sec.

On the bench, lower D/R should at some point translate into less pitch thrown. The problem is that it is stationary so the 7200BX will still dial in a great deal of pitch until it actually starts rolling in the direction it is trying to make it go. If you want to see this, try a substantially lower D/R just as a test. Prhaps 40% or even 20%. This should force it's hand and result in less pitch deflection on the bench, despite it being stationary. However, on the bench, the ptich deflection between 100% and 20% D/R will not translate into a typical linearish reduction in pitch deflection. If you were able to measure pitch deflection while in flight, though, it would very much translate into a more or less linear reduction in average pitch deflection.

Another way to see this on the bench is to place the heli on a rotating surface (maybe a lazy susan) use rudder D/R set to 100% put in a stick input and then spin the heli in the direction of rudder input and look at the blade deflection when it comes around to you. Note it. Then set D/R 20 and then spin it again. You should see a substantial difference in blade pitch. You should also see the pitch increase as the rotations slow down.
 

Tomhintz

Member
Pasul,

That makes sense. It is also easier to see it when you get down to like 20% or so.
Thanks a lot. Now I can relax and wait until I get to the field to fly it and try the different settings in real time.
 

pvolcko

Well-Known Member
Just remember to set back to 100% or whatever you want to fly at. 20% will probably result in a crash. :)
 

Tomhintz

Member
Just remember to set back to 100% or whatever you want to fly at. 20% will probably result in a crash. :)

Never left the dual rate screen before putting the DR back to where I want it. I already had an "incident" with zeroed out dual rates and won't make that mistake again!
 
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