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Analog versus Digital servos

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Roy Hill 310/09/2019 19:23:11
138 forum posts
97 photos

Hello chaps. I need your help. A dear friend, who understands the 'black art' of modern radios, in checking my 35 meg Futaba Tx and Rx which have stopped working. He tells me that he needs to test them but I need to give him an analog servo because the digital one is not compatible! Can some-one please explain this to me, because I have never encountered this problem before. Thank you.

Peter Christy10/09/2019 19:45:18
1666 forum posts

I would be very wary of letting anyone who displayed such a poor grasp of RC systems anywhere near my radios!

"Analog" servos (poor terminology, but it will have to do) will only work with low-frame rate radios. ALL 35 MHz radios are low frame-rate. The 10KHz channel spacing doesn't allow enough bandwidth for high frame rate.

"Digital" servos (again, poor terminology) will work with both low and high frame rate systems. Only spread spectrum radios are capable of high frame rate, and most default to low frame rate to avoid damaging analog servos inadvertently connected.

The only time you will find high frame rate on a 35 MHz radio is in the output of a high-end gyro - usually only employed on helicopters.

In other words, "digital" servos (except very expensive tail-rotor servos) will work happily with high or low frame rates. "Analog" will only work with low frame rates, and can be damaged if connected to a high frame rate radio.

Find yourself a proper service engineer! Mike Ridley springs to mind!



kc11/09/2019 11:59:34
6207 forum posts
169 photos

I am sure Peter is right. Anyone with RC experience would surely have an analogue servo to hand.

But any 35 Mhz system will be quite old now and I would question whether it's worth paying to have it mended, 2.4 systems are so cheap now. Reliabiliity is surely everything in RC planes. If you must continue with 35 Mhz then it's likely that someone would give away a Futuba Rx or Tx that works well. Most of my club members have cupboards full of 35 mhz unused now but working. I would just ask around if there is anything going spare.

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