RunRyder - TX/RX eCCPM Output Test Results

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Radio - Servo - Gyro - Gov - Batt > TX/RX eCCPM Output Test Results

AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

Servo variations are another can of worms. You can compensate for feedback pot nonlinearities, easy enough, but dynamic nonlinearities are quite something else.

Wolfgang

07-08-2005 Over year old.

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seattle_helo
Key Veteran
Location: Seattle, WA USA

Quote
You know, with an on-board device, one could even completely compensate for servo variations. For example, each servo could have its own, say, 10-point curve for correcting non-linearities. I foresee a small on-board device (again, about the size of a TJ Pro) with a seperate programming unit. - John

I wonder if Joel from Helitronix is following this thread. He might be just the guy to create something like this.

07-09-2005 Over year old.

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JKos
Elite Veteran
Location: City of California in the state of Maryland

> but dynamic nonlinearities are quite something else.

Agreed.

> The Parallax units are very nice

Yes, but not something you would really want to use for production as they cost about 15-20 times more than just buying the necessary parts and processor.

Also, the instruction set does not seem to support measuring pulse lengths on two or three pins at the same time. This would be necessary for our purposes.

- John

07-09-2005 Over year old.

AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

By the way John,

Quote
Here is a quick run down of how the various PCM rx output the pulses

Thanks for that info. I saved it to my info cache.

Wolfgang

07-09-2005 Over year old.

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Helitronix
Senior Heliman
Location: Marlborough, MA - USA

I just saw the thread. The Helitronix Mixer captures, computes and outputs a new frame all within 20ms with some room to spare. The latency from the input to the output side is less than a single frame.

I chose to output the servo data sequentially and it works quite well. I made a prototype version that outputs all servo data simultaneously, but found no particular practical reason to do that. I fly JR equipment, and their PCM receivers output the data sequentially. That works for me and serves as a good model for what works.

Of course the mixer could be made smaller. With surface mounted parts, it could be made the size of a postage stamp, dominated by the servo wire footprint. I've thought about doing that, but I'll stick to the through hole parts for now since it's easier for me to assemble myself that way. If you think the mixer is expensive now, add to that the price of the 3rd party labor to do the surface mount assembly in ultra low quantity! Then they'd be priced out of sight for everyone.

Of course, if you know of a good board assembly place than can build a surface mounted board very inexpensively at low volumes, please do contact me. I do this development work for fun on the side. It's not my day job. I could use some "inside" information on the manufacturing side of things to make that aspect affordable and less time consuming for me.

Joel-

07-09-2005 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

> The Helitronix Mixer captures, computes and outputs a new frame all
> within 20ms with some room to spare. The latency from the input to
> the output side is less than a single frame.

Joel,
Welcome to the discussion!

20 ms is more than a frame for all the radios except JR SPCM which is right at 20 ms. Can it handle sub-13 ms frame times w/o missing frames?

What is the timing resolution of your mixer? I assume it can measure simultaneous pulses from the receiver, correct?

What is your latency from the last pulse captured to the output pulses?

- John

07-09-2005 Over year old.

Helitronix
Senior Heliman
Location: Marlborough, MA - USA

Quote
20 ms is more than a frame for all the radios except JR SPCM which is right at 20 ms. Can it handle sub-13 ms frame times w/o missing frames?

The short answer is "yes", but it's more complicated than that because the mixer is designed differently than your paradigm suggests. The mixer operation is not slaved to the data from the input frame. The output stage runs asynchronous to the input stage and maintains a periodic refresh to the servos no matter what is coming in on the input side. It does not wait for all channels within a frame to complete before calculating a new frame because when you're using gyros, the frame timing can be irregular. If you waited for all inputs within a frame, you'd unnecessarily delay the output stage.

The interesting thing about frame times varying from brand to brand is that all of the servos appear to work well with the JR equipment, which has the standard 20ms frame time. JR receivers will never update the servos at a 13ms interval, yet they still work just fine with all the servos. I am not aware of any evidence that suggests there is a practical problem with a 20ms update rate for the all but the "super servos" that need the faster rate.

Quote
What is the timing resolution of your mixer? I assume it can measure simultaneous pulses from the receiver, correct?

Yes. It has to. Because you can't count on synchronous cascading outputs from the receiver. That would have made life much simpler.

Quote
What is your latency from the last pulse captured to the output pulses?

I can't quote you a precise answer because the input mechanism is decoupled from the output mechanism in order to capture input from a variety of real world radio systems. That being said, the processing and output stage execute in approximately 13ms.

Joel-

07-11-2005 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

Joel,
Thanks for the info!

One thing faster frame rates gives on the Stylus is lower latency. The servos don't mind being updated more often. I suppose for you mixer, the small reduction in latency of letting the computation and output run at its fastest (13 ms vs 20 ms) isn't an issue on a scale heli to which your product is mainly marketed.

- John

07-11-2005 Over year old.

AirWolfRC
rrProfessor
Location: 42½ N, 83½ W

Well, one thing for sure, if you have a pulse that is delayed a whole frame, you WILL have slew or latency or both whether you take the pulses as they come or try to re-sync. them after the fact.

Wolfgang

07-11-2005 Over year old.

HOMEPAGE

Helitronix
Senior Heliman
Location: Marlborough, MA - USA

Quote
Well, one thing for sure, if you have a pulse that is delayed a whole frame, you WILL have slew or latency or both whether you take the pulses as they come or try to re-sync. them after the fact.

By definition, any device the performs signal processing to implement a transform function such as this one, must insert some non zero amount of latency into the output stage. That simply is the nature of the beast.

Simply having control signal latency isn't the problem. That latency must be high enough so that it creates a discernable difference in flight behavior in order for it to be a problem. I'm not going to make a claim that you can or cannot detect a 13ms latency in your control inputs. That might be like arguing that tubes make better amplifiers than transistors, or that vinyl records give a better sound than CDs. Each side has its proponents.

Of course, the latency that provides that "just noticeable difference" in response is going to be different for each pilot + helicopter combination.

Joel-

07-12-2005 Over year old.

z11355
rrMaster
Location: 10000 is enough time wasted.

Quote
tubes make better amplifiers than transistors

HE|_|_ YEA!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

07-12-2005 Over year old.

HOMEPAGE

Britflyer
Veteran
Location: Derby, England

Can anybody tell me which channels are used for eCCPM on the Futaba PCM 1024 ??

In terms of swashplate dancing with rapid collective changes, which is better the JR SPCM or Futaba PCM 1024 format ??

Thanks

Paul

------------------------------------------------------------------

Climb-out.com
CSM
Hyperformance RC
Flightpower

07-28-2005 Over year old.

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JKos
Elite Veteran
Location: City of California in the state of Maryland

OK, here you go... Results for the Futaba 9ZWC2. About the same as the 9C and the 14MZ with an R149DP receiver.

- John

08-03-2005 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

This just in... Test results for the Hitec Eclipse 7 with a QPCM receiver.

I must say that I'm a bit surprised. The Eclipse 7 with QCPM is actually very well behaved! As good as the Airtronics Stylus. And the separation between Channel 1 and then Channels 2 and 6 (which have simultaneous output pulses) is only 2 ms.

Here is the Eclipse 7 with an FM receiver.

- John

08-22-2005 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

I don't have any further plots right now, but do have some observations to make.

Every radio I've tested (Airtronics Stylus; Fubata 14MZ, 9C, 9ZWC2; Hitec Eclipse 7; JR 8103, 9303, 10X) except the Futaba 9CS and 7C exhibit full change of all channels in one frame behavior in PPM mode. This is a good thing although the time spread of the pulses coming out can cause slight swashplate tilt during fast collective moves. All PPM/FM receivers and all JR PCM receivers have sequential pulse output.

The JR 8103 and 10X behave exactly the same as the 9303 in PCM mode.

The Spektrum DX6 system exhibits full change of all channels in one frame. The channel output is the same as all JR receivers and all FM receivers... Sequential pulses. The behavior is good although it is a bit disappointing that JR/Horizon/Spektrum had a chance to do it "right" and have channels 2, 3, and 6 have simultaneous output pulses but they didn't.

- John

MSH Protos

01-19-2006 Over year old.

jzeller
Senior Heliman
Location: Victoria, MN - USA

Is this 7C and 9CS slow ramp present in non-eCCPM mode as well? It seems like incredibly bad behavior that makes the radio fairly worthless for high performance applications. Nobody runs servos with a move time of 0.3s+!

03-01-2006 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

I haven't posted here for a while partly because the radios have been getting better at eCCPM. Here's a quick take on some current radios.

Spektrum DX7... Excellent eCCPM performance.

Futaba T6EX 2.4 GHz... Just OK eCCPM performance. Like the 9C Super and 7C, it has slew rate limiting on collective, aileron, and elevator inputs when in eCCPM mode. Data gets split between frames.

JR 9303 with Spektrum module... Excellent eCCPM performance.

- John

MSH Protos

08-04-2007 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

A video of a FASST module in a 9C has been posted at http://www.runryder.com/helicopter/t373402p1/.

- John

MSH Protos

09-14-2007 Over year old.

superpin
Heliman
Location: Solna - Sweden

I actually posted it here att RR first and someone copied the link to the Freak. Here is the original thread: http://www.runryder.com/helicopter/t373402p1/

//Ola, not so happy FASST owner...

09-14-2007 Over year old.

JKos
Elite Veteran
Location: City of California in the state of Maryland

superpin,
Thank you. Somehow I totally missed your posting of it here on RR. I corrected my post.

I'm sure we all hope the FASST module for the 12 and 14 series will be better than that.

- John

MSH Protos

09-14-2007 Over year old.

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