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Mar 03, 2019, 03:01 PM
Non Fragosus
jackcutrone's Avatar
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Programming HiTec servo for Spektrum RX/TX question

Didn't know where else to post this. I am putting together a 35% Aeroworks Extra 260. I am at the point of mounting the rudder servo, a HiTec HS 7950TH servo which will be used for a pull-pull set-up. I am also using the HiTec HFP-20 programmer which I have used before. But I ran into something I am curious about.

I used the programmer to set the center point for the servo and then used it to set the end points, all according to the manual's instructions. I arbitrarily set the end point travel to give me about 45 degrees of servo movement right and left. I then plugged the servo into the receiver and powered up both the transmitter and the receiver. I am using a Spektrum DX9 TX generation 2. With the rudder stick full right and full left, I only get about 20 degrees of movement right and left, I checked both the servo travel and the dual rates in the transmitter and they are both set at 100%.

When I used a y harness to plug both the servo and the HFP-20 into the RX, (a Spektrum 9030T nine-channel RX) and then set the HFP20 to measure pulse width, and moved the rudder stick full right and full left. In each direction it showed 397 milliseconds difference from center (1500): left showed an 1103 pulse width and right an 1897 pulse width.

So with all that prelude, my question is this: if I set the end points to give me about 45 degrees of movement each way, and the servo travel and dual rates are both at 100% in the TX, shouldn't that give me 100% of the travel to the end point and thus 45 degrees of movement each way instead of roughly 20 degrees? I know I can go back and reset the end points with the HFP 20 to increase the movement with the TX full l-r rudder, but I am curious as to why I am only getting partial movement toward the end point if both travel and DR are at 100%.
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Mar 03, 2019, 06:27 PM
AndyKunz's Avatar
You would need to set the transmitter to either 125% or 150% for the full 45 degrees.

Spektrum generates pulses of 1100us to 1900 at 100%, 1000 to 2000 at 125%, and 900 to 2100 at 150%.

Mar 03, 2019, 07:05 PM
Non Fragosus
jackcutrone's Avatar
Thread OP
Thanks Andy. Good information to know.
Mar 06, 2019, 02:29 PM
Fully Sending It
Xpress..'s Avatar
When you use a Hitec programmer to set end points, you are reprogramming the brain in the chip to command the servo to that specific position at either 900Ķs or 2100Ķs. Therefore, you need to open up your transmitter dual rates and end points until it outputs those signals at the extremes.

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