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Kilrah

Corona receiver performance analysis

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Some of you might know of those inexpensive synthesised receivers found at hobbycity.

Firstly, I wanted to install one of the small 4 channel ones in my Multiplex Fox. Unfortunately, I had lots of glitches even at very short distance (<50m), and had to give up on it and replace it with the bigger brother - the 8ch one. It was the second smallest I could find around.

The range problem was gone (I flew reliably up to 700m, didn't try more). I didn't investigate a lot on that, but it seems the 8ch has power supply filtering that is absent on the 4ch one - in conjunction with my Turnigy 7A BL ESC, I could measure strong RF noise on the RX power supply line ranging up to 50MHz+. The same ESC on the 8ch RX and the noise would stop at about 16MHz.

What interested me here is in flight performance. Range and stability was good, but I felt like there were pretty large servo "steps". I had just received that nice servo tester with pulse length display, that also allows measuring an incoming pulse, so decided to put it to good use straight away and test the receiver and servos.

The 3.6gr servos showed to have steps approx every 4us. By comparison, a common Futaba S3001 has one every 2us.

The most interesting part was however the receiver - and it confirmed all I could see in flight. The steps are very large (11us), and centering isn't reliable.

:)

I now got a nice little ACT DSL4top "true" receiver ;)

Edited by Kilrah

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I haven't tried the HobbyCity Rx's, but I have tried a couple other low end DSP based models. I found the same thing (low resolution, poor operation).

I suspect that if you put a scope on it you will also see excessive jitter too. Have you looked inside the Rx to see which microcontroller is used? If you have, is it a low end 4MHz 8-Bit'er?

My very first DSP Rx purchase was one that warned me to be careful about these things. It had all sorts of problems. I ended up reverse engineering it to see what was going on (details are posted in this old thread at post 129: http://www.rcgroups.com/forums/showthread....92#post2993392). I tried another low cost R/C Rx later on and the poor operation was enough to send me back to the good (more expensive) stuff. I've avoided the cheap Rx's ever since. :)

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I haven't scoped it yet, but don't think there would be any jitter (as you can see in the video the meter updates its display every frame), and the servos are perfectly quiet.

I haven't taken them apart either, but I have a 4 channel one that seems to have died (won't lock to a signal anymore when scanning), so it will see a cutter from too close pretty soon :)

In the opposite the tiny ACT RX is very good, even allows 4 freely programmable mixes to be programmed into it, allows choosing which channels have to be sent to the 4 headers, and more... yes it's more expensiv, but not a lot compared to the benefit. OK, you lose the synthesiser, but oh well...

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Don't know if you fellows are aware of this site but he seems to put a lot of work into testing the Hobby King and other systems. Might be worth a look to see what he's been doing with the cheap Chinese stuff.

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Umm didn´t know about the resolution of that receiver, I have one prepared to use with my new Mikrokopter. Users in our forum have had lots of problems with the act dsl 4 in terms of range, not my case, I´ve never had a sigle problem with that little receiver, and I did have with the ACT DSL 8 on my Telemaster. Oposite from that users have had great performance in range with the Corona DSP 8 channels.

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If you're using it on the MK, I would assume that you would pick the PPM signal between the demodulator and decoder. So you wouldn't notice the problem, as it's most likely induced by the decoder's firmware.

No problems with the DSL4 either, even on my 800m+ flights...

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