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HelicopterRadio - Spektrum DSM › SPM4649T Warning. Do not use in helicopters
03-31-2017 05:15 PM  7 months agoPost 1
ticedoff8

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Morgan Hill, CA. USA

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The Spektrum engineer in charge of designing the SPM4649T says that it is not suitable for helicopters - only quad-copters.

The SPM4649 is a cute little receiver that came out about 4 months ago.

This warning is related to the facts that there were many compromises made in the design and testing of the unit, and many of those compromises are cropping up in the form of units that are DOA, burned out on initial power up, failures in flight and use of 2S LiPo voltages.
But, I am not sure why they would be reliable enough for quad-copters.

The unit is labeled for use at 4.8v to 8.4v - it tends to burn out at higher voltages (above 7.5v)
It is a single receiver with no options to add satellite receivers.
It does not have capacitors to filter voltage spikes.

The reason this came up is because MSH created software for their Brain 2 / iKON 2 that makes them integrate with the SPM4649T as a flight controller.
For this reason, Spektrum sold a sh!t-ton more of these units than they expected and (apparently) a majority of them to helicopter guys for use with the MSH Brain 2 / iKON 2 gyros.
And, a lot of these units failed in the helicopters
Personally, I had two burn out on the bench when I initially powered them up using a 2S LiPo (not freshly charged. Voltage measured after the units burned out at 7.9v)

On the Brain 2 / iKON 2, MSH uses the bi-directional SRXL serial connection to map and decode all available channels from the Spektrum transmitter (up to 20) to functions on the gyro and relays telemetry data gathered from Hobbywing or Castle Creations Edge / Talon ESCs and the internal logs of the gyro back to the transmitter in real time.

Now, the Spektrum developers have told the world that the SPM4649T was never design for helicopters.

The next Spektrum receiver that will get the bi-directional SRXL interface is the AR6600T (with telemetry). And there is no expected date for that new firmware

If you have a SPM4649T on a helicopter, you may be living on borrowed time.
If the heli is in the 550 to 700 range, it could kill someone when the SPM4649T takes a dump.
Take it off the heli and call Horizon Hobby to return it.
They will also confirm what is in this post.

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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03-31-2017 05:58 PM  7 months agoPost 2
CostaRicaHeli

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Costa Rica, Central​America

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Already returned mine - NIB

Thanks for the heads up. After reading many posts on other forums I decided not to even open mine. Returned it to dealer NIB. Not worth the risk. Let's hope Spektrum steps up with the development. If not, I'm afraid I will have to switch to Jeti. I've been looking for a reason, and maybe I've found it!

Franz

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03-31-2017 06:16 PM  7 months agoPost 3
EEngineer

rrProfessor

TX

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Here's the link to the Specification for Spektrum®
Bi-Directional SRXL.....

https://www.spektrumrc.com/ProdInfo...cifications.pdf

According to Spektrum:

"This document is intended for engineers to develop accessories that leverage the SRXL protocol. It
assumes an intimate knowledge of how the Spektrum systems work."

In Section 6, paragraph 2, Spektrum says:

"This protocol is only for products developed after May 2016."

"The Spektrum engineer in charge of designing the SPM4649T says that it is not suitable for helicopters - only quad-copters."

Who is he and where is that statement posted? Just to check out everything he said, so nothing is taken out of context...

Is this an issue only when trying to connect "legacy" h/w to this new protocol?

Logo 600SXs, 800XX, TDR IIs

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03-31-2017 09:28 PM  7 months agoPost 4
hrc37

rrApprentice

Derry, PA

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Jeti!

CostaRicaHeli,

I've flown/owned just about every radio out there over the last 40 years and I have to say that Jeti (I have the DS-16) is the best I've used so far. I currently also own a dx9 for my Blade/Eflite BNF stuff and have owned a dx18 in the past and they are nice/good radios also but it's tuff to beat a Jeti. Mark

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04-01-2017 02:26 AM  7 months agoPost 5
ticedoff8

rrKey Veteran

Morgan Hill, CA. USA

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Who is he and where is that statement posted? Just to check out everything he said, so nothing is taken out of context...
I sent you a PM with the link to his statements on a different website.

I will not be publishing his name.

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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04-01-2017 04:26 AM  7 months agoPost 6
ticedoff8

rrKey Veteran

Morgan Hill, CA. USA

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Is this an issue only when trying to connect "legacy" h/w to this new protocol?
The MSH Brain 2 / iKON is relatively new - Feb '16.
The code on them has evolved quickly due to MSH being dedicated to the RC Heli hobby

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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04-01-2017 04:28 AM  7 months agoPost 7
EEngineer

rrProfessor

TX

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Thanks for the PM...I don't blame you.

Wondering if they're maxed out the capabilities of the RF processor with all the new telemetry and such....or that with more and more telemetry, they've had to make changes that render it incompatible with legacy h/w....

Time will tell, I guess.

Logo 600SXs, 800XX, TDR IIs

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04-01-2017 05:05 AM  7 months agoPost 8
ticedoff8

rrKey Veteran

Morgan Hill, CA. USA

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The SPM4649T is supposed to be designed for lots of various telemetric parameters being downlinked to the transmitter from the "Flight Controller".

As an "Engineer", you probably know all there is to know about serial communications protocols. As long as the start and stop bits line us and the checksum match, the data will flow.

Attaching a Brain 2 or an iKON 2 to a Jeti or Futaba receiver doesn't seem to cause those receivers to fail.

More importantly, when I hooked up a 2S LiPo to bind to the transmitter the first time, I didn't even have the Brain 2 connected to the SPM4649T - it just smoked.

The reality is that Horizon Hobby / Spektrum has made a clear statement on their web site:

Do Not Use The SPM4649T on Helicopters.

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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04-01-2017 05:22 AM  7 months agoPost 9
EEngineer

rrProfessor

TX

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"As long as the start and stop bits line us and the checksum match, the data will flow."

Yes, but those two bits slow things down....if they could implement a synchronous bit stream(with a clocking signal), data can be transferred much more rapidly.

Also, being asynchronous, the UART rx has to oversample to determine exactly when the start/stop bits "start"(leading edge and such).

Hopefully Spektrum will get it figured out.

Logo 600SXs, 800XX, TDR IIs

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HelicopterRadio - Spektrum DSM › SPM4649T Warning. Do not use in helicopters
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