Nomadio_Dave
Posts: 26
Joined: 3/12/2005
From: Upper Pittsgrove,
NJ, USA
Status: offline
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quote:
ORIGINAL: rsilvers
This came out because of talk and promotion about output power and latency.
Here is what I found:
For range I put both units 20 feet in the air on a platform, and then walked away until I found a range for each where they would reliably work. I did not try to find a range where I could get the servo to move barely, but rather, where they worked reliably (likely in contrast to how a manufacturer rates them). Both antennas were vertical.
The Spektrum DSM was 636 feet.
The Nomadio was 531 feet.
I believe both claim about 3000 feet.
Sounds like a solid test... and it sounds like you've got some problem with the Sensor, OR you're running 1.x software. There is a very big difference in practical range through the evolution of our software. And in fact, the older software runs in DSSS mode only, nearly identical to Spektrum's "DSM" (I think they use a slower link and longer spreading code, which might, in fact, yield longer range in some cases, as you get a slightly higher protocol gain).
I don't THINK we've ever claimed over 1000ft... but I'm not in marketing. I've never run working Nomadio hardware that benchmarked less than over 1000ft, though your distance is always going to be somewhat location dependent -- I do most of my testing around my farm (26 acres) and the neighbors. I've calibrated the road out back (about 1/2 mile in length), and when I need more distance, I go down US RT 40, which has these handy mile marker posts along the highway (but I do lose line of sight after about 3400ft). I've typically seen about 2100ft with "nomal" Sensor gear along RT40, to the point where the link isn't mostly there, though that's my typical Sensor test with the Sensor up on the mailbox and with me holding the car -- you'd see a bit less with the car on the ground. I usually do drive tests with the military/robotics stuff out to 1000ft or more; it's impossible to actually drive my mini-T even a significant fraction of that 2100ft.
Anyway, that's my test setup; I don't see anything wrong with yours, either. Different results could be explained as more noise in your area, or something different about that Sensor. Read on.
quote:
ORIGINAL: rsilvers
How can I explain the Nomadio having less range when Nomadio says it has between 7.5 and 10 times the output power?
(Nomadio claims either 75 or 100mw output while the Spektrum is 10mw).
You only get a real 75mW or so when running the frequency hopping software.
quote:
ORIGINAL: rsilvers
There is a DSSS concept called processing gain: The processing gain is a measure of immunity to noise. The more the band spread of the signals, the higher the gain. Spektrum set up their data rate to allow for an 18dB processing gain over the FHSS that Nomadio uses. That means a 10mw implementation may have more range than a Nomadio 75mw FHSS system (it could be equal to an 80mw FHSS system). I had posted this weeks ago, and my hypothesis appears to be correct. Nomadio is probably hoping that people will assume that their greater power output equals more range when it fact it mostly likely only results in more power consumption.
Good in theory, no so good in practice. Nomadio systems are always DSSS -- that's actually a hardware protocol in the chip we use (the same chip family, in fact, as the Spektrum does). You can vary the size of the spreading code, either 32-bits or 64-bits, but that's always in the protocol. Our older software, as mentioned, only ran DSSS mode. The 2.x software added frequency hopping on top of DSSS, but the DSSS processing gain is always there.
quote:
ORIGINAL: rsilvers
No doubt if others test the range they will get different but similar numbers. In any case, do not assume anything about range without doing the test side by side.
Yup -- you can't have any real A/B comparison of systems unless you tests, and multiple tests, along the same course under the same conditions.
quote:
ORIGINAL: rsilvers
I also measured the data rate and latency of a Spektrum DX3 and Pro receiver system using a Tektronix TDS-220 100 Mhz bandwidth digital oscilloscope.
The data rate being sent to the servo from the Spektrum 'receiver' is 20ms per frame, or 50 updates per second.
The data rate being sent to the servo from the Nomadio 'receiver' is 10ms per frame, or 100 updates per second.
(For comparison, JR PCM radios are approx 46 updates per second for Z mode, and 47 for S mode per channel. Standard FM PPM systems are about the same.)
The advanage here goes to the Nomadio -- 100 frames per second is excellent and how it should be done (I feel that anything in the 80 to 120 frames per second range is ideal).
You may also notice that the Nomadios fire all servos at once; so there's no additional delay between, say, steering and throttle. There is, however, some additional processing delay on the Sensor for buttons vs. pots; the steering and throttle are hard-wired to servo channels but highly optimized. Everything else (at least in the current software) runs via "soft keys", and will have additional latency over the optimized channels. I don't know just how significant it might be. I also don't know if Spektrum is firing all servos at once, as we do, or in series, as most analog receivers will do.
quote:
ORIGINAL: rsilvers
The Nomadio salesman said that the Spektrum system had about 15ms of latency inherent in the transmission, and another 30ms of latency provided by the transmitter encoding the controls. That would be 45ms. I was not able to duplicate those numbers.
Nope... whoever said that is confused. 45ms is largely undriveable at any normal R/C speeds... believe me, we weren't always fast. Our initial robotics control system was essentially too slow for real R/C driving, and some of our early test people pointed this out in interesting ways.
quote:
ORIGINAL: rsilvers
For the Nomadio I found that latency was always between 13.0 and 16.0ms so that is about 14.5ms average or 2ms (1/500 of a second) less than the Spektrum's average.
This will vary by software release (newer releases are faster), and of course, whether you pressed a button or a potentiometer. I think you're pressing a button here, which as mentioned will be slower than steering or throttle.
< Message edited by Nomadio_Dave -- 11/6/2006 9:01:41 AM >
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All Forums >> RC Cars, Buggies, Trucks, Tanks and more >> RC Car Radio Equipment >> 2.4Ghz RC range and latency measurements. 
2.4Ghz RC range and latency measurements. - 
Your welcome to test a React
