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Thursday, July 26, 2012

Video Reviewer Suffers Crash After a Typical DSM-X Brownout

Horizon Hobby forced their user base to buy all-new radio equipment when they switched to DSM-X from their admittedly shoddy DSM-2 standard. 

Spektrum and JR brand DSM-X receivers with “QuickConnect” were supposed to limit the number of crashes caused by receiver reboots in the air.  Why there is a need for a receiver to reboot in the air remains an unanswered question.  DSM-X was also supposed to fix routine frequency conflicts causing crashes when more than a few radios are operating.

It didn’t work. 

Brownout-induced crashes continue as “a fact of life” for those who have been slow to switch from DSM to a more modern 2.4 standard.

DSM-X Brownout and Crash at 4:30 mark.

In typical European business model fashion, Spektrum/JR engineers lay 100% of the blame on their customers:

“The #1 problem encountered by DSM fliers: inadequate power supply. Unlike PCM, where servos get "crunchy" at voltages as low as 2.5 volts, the digital system used in DSM shuts down at 3.2 volts. 99% of fliers have no problem, but when you do, it's a toughie. New QuickConnect software allows restoration of your radio link the instant voltage is restored.” 

They consider themselves the customers’ savior, by offering “QuickConnect” to patch their own critically unsafe design flaw (but only if the bus voltage magically rises, fixing the root problem on its own). 

For those unfamiliar with Horizon Hobby’s defunct receiver design, power from an e-powered motor battery flows in the following order of precedence:

   1. To the motor(s)
   2. To the servos and electric accessory bus
   3. To the radio receiver
 

Using a modern receiver design, such as Hitec SPC, the priority for e-power goes:

   1. To the radio receiver 
   2. To the motor(s)

  
3. To the servos and electric accessories

Using only leftover servo bus power as the sole source of receiver power is an obviously inept design paradigm left over from the days when dedicated receiver packs, grafted into the servo bus, were the only source of electric power in an RC aircraft.  

News Flash!  Today we have big things called motor batteries.

e-Powered planes and helicopters, in particular, have a very current draw so it isn’t surprising that any components downstream from the motor will often get shortchanged.  Thus e-powered DSM models tend to crash, a lot.  Additionally, a stuck servo or electric accessory like a landing gear, or even a fried motor or a bad dedicated BEC can cause servo bus power to fall below the 3.2 Volts required for DSM receivers to stay awake, causing a certain catastrophic crash. 

Despite numerous bandaid releases, like QuickConnect, Spektrum engineers still fail to recognize the root cause of their problem:  an unrecognized and erroneous assumption that a dedicated receiver pack remains the only form of power in an electric airplane today, and the corresponding false requirement to power the radio receiver from the servo bus instead of directly from the higher power motor battery. 

In other words, the crash in the video was caused by low intellect. 

I suppose electric planes with high powered motor batteries are so new that Horizon Hobby engineers haven’t had a chance to analyze them.  Until they figure out e-power, avoid dangerous DSMX radios.

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