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Old Feb 14, 2010, 05:33 PM
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Warbirds Rule's Avatar
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"Understanding Spektrum and Futaba Low Voltage Claims" video

I'm sure this has already been posted somewhere on the forum but I couldn't find it so here goes. Spektrum posted a video on their website demonstrating the low voltage handling and recovery capability of their system vs. Futaba FASST. It essentially shows the Spektrum system operating down to the same identical voltage before the servos stop working (approx. 3.2V I believe) and then recovering faster (by milliseconds) than the Futaba. Just wondering if this has been discussed as generally when I read this forum the consensus seems to be that the Spektrum systems "brown out" sooner than Futaba and recover slower. However, this test conducted by the Spektrum crew shows quite the opposite results. Does this prove that all the internet chatter about Spektrum being "inferior" in this regard has been a "bunch of bunk" as the engineer in the video states or is it actually due to some testing inconsistencies between the test Spektrum and those that others have conducted?

Spektrum website here:
http://www.spektrumrc.com/#

Video of test on Youtube here:
http://www.youtube.com/watch_popup?v=PwnM9pBH9QM#t=233

Thanks,

Sean
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Old Feb 14, 2010, 05:39 PM
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Nevermind......I did another search and found that you guys talked about it way back in October. I'll go back and read through the old threads.

Thanks,

Sean
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Old Feb 14, 2010, 05:41 PM
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Here's another thread that you can read about it.
http://rc.runryder.com/helicopter/t537735p1/

Doug.
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Old Feb 14, 2010, 05:52 PM
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Leesburg, VA
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Thanks. Wow, those guys really take their radio brands seriously over there.

Sean

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Originally Posted by DougV View Post
Here's another thread that you can read about it.
http://rc.runryder.com/helicopter/t537735p1/

Doug.
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Old Feb 14, 2010, 06:35 PM
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Pretty much MOST of the strong opinions expressed here or in any other group are "bunk".

Especially when it comes to 2.4 specific RF issues. 2.4 RF technology is unfortuantely so complex that only maybe 0.1% of anyone here compeltely understands it to be able to give any sort of rational opinion. Everything else is whatever a person descides they want to believe

The only people I've seen have any problems with brownouts or blackouts are people with shickingly dodgy power setups. I've even seen people fly with 4 cell packs that measured "in the yellow" on an LED power meter and went "Meh" and tossed the plain up again only to have it crash 5 minutes later. Then comes all the posts about XXX brand destroyed my plane :/
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Old Feb 15, 2010, 12:35 PM
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Originally Posted by Warbirds Rule View Post
[]It essentially shows the Spektrum system operating down to the same identical voltage before the servos stop working (approx. 3.2V I believe) and then recovering faster (by milliseconds) than the Futaba. []
I personally tested my Futaba RX to work with a voltage as low as 2.6V.

http://www.rcgroups.com/forums/showt...88#post7443588

Quote:
I've even seen people fly with 4 cell packs that measured "in the yellow" on an LED power meter and went "Meh" and tossed the plain up again only to have it crash 5 minutes later.
No problem for Fasst, it even works with one defective cell:

http://www.rcgroups.com/forums/showp...8&postcount=77

And with a flat battery, too:

http://www.rcuniverse.com/forum/m_61...tm.htm#6489050

I just noticed, that Spektrum's video nicely shows how their RX quits at a higher voltage than the Fasst RX:
http://www.youtube.com/watch?v=PwnM9pBH9QM#t=2m25s

It is clear that the servos stop responding at the same level, as they are identical. But that does not mean, that the RXes stopped delivering a valid signal.
But look exactly at 2m25s at the LEDs of both systems: At 3V, the Spektrum LED goes out, whereas the Fasst LED is still green, meaning that the RX is still fuctioning, and Spektrum is not.
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Old Feb 15, 2010, 12:42 PM
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Hey Julez,
Yeah, after I read some of the threads others pointed me to it seems the Spektrum video was essentially showing the low voltage cutoff point of the servos rather than the cutoff point for the Futaba receiver. I guess if all servos shut down at 3.1 or 3.2V it would be a moot point as to who's receiver functions below that level. I assume some servos will work below that level though? Some also suggested that the Futaba receiver used in the test was an older version which explained why the Spektrum receiver reconnected faster. Do you know if the new Futaba receivers connect faster than the one in the video?

Thanks,

Sean


Quote:
Originally Posted by Julez View Post
I personally tested my Futaba RX to work with a voltage as low as 2.6V.

http://www.rcgroups.com/forums/showt...88#post7443588


No problem for Fasst, it even works with one defective cell:

http://www.rcgroups.com/forums/showp...8&postcount=77

And with a flat battery, too:

http://www.rcuniverse.com/forum/m_61...tm.htm#6489050
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Old Feb 15, 2010, 01:14 PM
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Yes, all FASST receivers available right now will reconnect faster than that old R606FS receiver. and another thing that was not mentioned is that at 3.8 volts the FASST receivers will warn you of low voltage by the way of F/S the throttle channel only, so you can land your model.

Doug.
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Old Feb 15, 2010, 01:15 PM
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What good is that if I do not have a motor!

I know, I could drop the flaps or something but isn't the failsafe only good on the one channel or is it assignable?
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Old Feb 15, 2010, 01:25 PM
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Originally Posted by Fly2High View Post
What good is that if I do not have a motor!

I know, I could drop the flaps or something but isn't the failsafe only good on the one channel or is it assignable?
Well, its better than just lockout everything, on the 6 and 7 channnel rx's its fixed to channel 3 only, but on the 8 and 14 I think its assignable.

Doug.
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Old Feb 15, 2010, 01:30 PM
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Quote:
Do you know if the new Futaba receivers connect faster than the one in the video?
Hi!

The R606FS I tested down to 2.6V needed 0.3s to boot and 0-0.5s to connect.
I never owned any other Fasst RXes I did tests with, so I can't comment on the reboot performance of the newer ones.
But I guess it's a moot point anyhow: With a low voltage performance that good, Fasst RXes never need to reboot in the first place.
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Old Feb 15, 2010, 01:36 PM
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Quote:
Originally Posted by Julez View Post
Hi!

The R606FS I tested down to 2.6V needed 0.3s to boot and 0-0.5s to connect.
I never owned any other Fasst RXes I did tests with, so I can't comment on the reboot performance of the newer ones.
But I guess it's a moot point anyhow: With a low voltage performance that good, Fasst RXes never need to reboot in the first place.
That rather misses the point.
Voltage can drop to zero if there is any sort of intermittent contact in the system (like a bad switch), or if a BEC chip is operating at the edge of its heat limit.
This is when reboot times become important. Servos will pick right back up when the power is restored.

Pat MacKenzie
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Old Feb 15, 2010, 02:45 PM
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A BEC chip at it's limit lowers its voltage gradually, and does not abruptly cut off. When my last BEC shut down because of a shorted servo, my Jeti system reported a voltage drop before everything finally shut down.
When I flew Fasst and had a BEC overheat, I still had intermittant control, and was able to land the plane in one piece.

Of course it is possible to construct a scenario where a 0.5s difference in reboot time will be better than a 0.5V difference in low-voltage tolerance, but in most cases, it will be vice-versa.
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Old Feb 15, 2010, 07:36 PM
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Hi Julez,
I had a cold solder joint fail in an MPI HD switch harness this past year. The model had an R607FS receiver. The failure made itself apparent just after take off. Who sez 2.4Ghz systems don't glitch. The bottom line was I was able to land safely and do the troubleshooting on an intact model, found the problem very fasst
Pete
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Old Feb 16, 2010, 02:08 AM
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This video seems to do as much harm as good to the Spektrum brand... Have you guys looked on the Spektrum website and read they're description of their DSSS radio link? They get pretty close to saying that it's better than the Futaba FASST system without actually saying it. The problem is that what they're comparing their signal to isn't actually how the FASST system works, so it's completely irrelevant except for to those that don't know any better, playing off their ignorance for self promotion.

Quote:
There are two main broadcast methods that spread spectrum manufacturers can utilize. One format is called Frequency Hopping Spread Spectrum (FHSS). With an FHSS system, the transmitter transmits a narrow band signal and rapidly jumps from one frequency to the next, spending a few milliseconds on each frequency. Originally, Spektrum engineers started their development with FHSS-based systems because they were relatively easy and inexpensive to develop. However, they soon discovered that FHSS had several limitations that would prevent it from being the optimal solution for RC. While more difficult and costly to develop, our engineers began experimenting with Direct Sequence Spread Spectrum (DSSS) and optimized the modulation scheme to overcome critical response and re-link issues. DSSS systems transmit on a single selected frequency but on a very wide band. Only a small portion of that band is used for specially encoded information. In addition, DSSS offers an increase of processing gain for significant improvements in range. With years of development and testing, the DSSS modulation scheme was optimized for RC car and airplane use, and Spektrumīs DSM 2.4GHz Spread Spectrum Technology was born. DSSS provided engineers and hobbyists with the safety, security, and locked-in feeling that is necessary to maintain total and complete control in any vehicle or aircraft.
I've actually seen this referenced in this forum as why Spektrum radios are better than Futaba radios.

Don't get me wrong. I don't have a problem with Spektrum, and I think their radios are more than adequate, though I do prefer Futaba myself. I just don't like false implications in advertisements.

It reminds me of the Mac vs. PC ads, and I know that just about everyone uses this method of advertisement. I just don't like it.
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