RunRyder - Plug-in 2.4GHz modules! - Continued

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Radio - Servo - Gyro - Gov - Batt > Plug-in 2.4GHz modules! - Continued

Ace Dude
Elite Veteran
Location: USA

New plug-in 2.4GHz modules! - Continued

I'm not sure what, if anything, closing the thread below accomplished

http://www.runryder.com/helicopter/t283568p1/

so in the spirit of research, development, and education I decided to continue it in a new thread. I just don't think one individual's behavior should ruin it for everyone.

09-19-2006 07:06 PM

kookboy
Key Veteran
Location: Vancouver, BC -up north and Seattle, WA down south

Xtremepowersystems

http://www.xtremepowersystems.net/xtremelink.php

Link above

... But honey it was only $$$

09-19-2006 07:53 PM

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

Continued from previous thread...

>> If you are worried about the effect of sequential pulses on
>> the "feel" of the system, I guarantee 100% an asynchronous host-to-
>> XtremeLink frame setup is much worse than that due to repeated
>> frames and a random latency evenly distributed between
>> base_latency and (base_latency + 20 ms). Those two will be much
>> worse than the effect of sequential output.

> There are no latency issues with an asyncronous system.

This simply cannot be true! Let me demonstrate this fact graphically.

Assumptions: transmitter PPM frame "rate" of exactly 22 ms, XtremeLink frame "rate" of exactly 20 ms (actual pulse outputs to servos, not the RF link)

As can be seen, there is a variable latency penalty due to asynchonous operation.

It gets even "uglier", if you will, when a frame must be repeated by the XtremeLink system because the transmitter has not made another "update" before the XtremeLink receiver must make an output.

- John

MSH Protos

09-19-2006 10:17 PM

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

It would probably be best that if you just used the link to the page instead of posting the information in a thread. What you have posted is already out of date, and the information will change likely several times before the final release.

Jim Drew, CEO/President - Xtreme Power Systems

09-19-2006 11:13 PM

HOMEPAGE

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

John, I understand what you are saying. Draw your diagram with our unit sending/receiving data every 10ms instead of every 20ms. We are actually updating the data more frequently by converting the frame data from 22ms (or whatever it might be) to a fixed 20ms. When there is an "overlap", which does occur, the data was the last known data but we are still way ahead in the frame refresh.

Jim Drew, CEO/President - Xtreme Power Systems

09-19-2006 11:22 PM

HOMEPAGE

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

Mr. Drew,
It does not matter, nor really make much sense, that your system sends data every 10 ms but only outputs data every 20 ms. It does not change either diagram.

Please show graphically how sending data every 10 ms helps this issue.

- John

MSH Protos

09-19-2006 11:30 PM

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

Sorry, but I don't have time to draw diagrams for you.

Sending the data every 10ms means that we have redundancy, and paves the way for new radio systems with faster frames, giving higher resolution and faster response times. It also reduces the overlap. When you calculate the overlap, you will see it is infrequent. As stated before there is no way around this if you need to skew the frame to fit between other frames being sent to other units. We have to be able to hold off the PPM frame as long as necessary for the time slicing to function.

You are concerned that the overlap period is going to cause a problem. It doesn't, we have been flying it this way since May. Consider that PCM frames are 28.75ms and nobody is complaining about response times, even though frames occur only 35 times per second and not 50 times per second like typical PPM. Also consider that a digital system collects the entire frame and sends it all at once, so the frame is off by as much as one entire frame (typically 1/2 frame).

Jim Drew, CEO/President - Xtreme Power Systems

09-20-2006 01:58 AM

HOMEPAGE

Ace Dude
Elite Veteran
Location: USA

From the previous thread:

Quote
That stinks! Why would they do that on a brand new product!

I bet they didn't catch it until recently and now they're rushing to get the product out the door and don't want to invest the time rith now to fix it.

09-20-2006 02:16 AM

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

Mr. Drew,
> we have been flying it this way since May

On what? Have you had your system flown by advanced helicopter pilots on top end helicopters?

Using the above example, your receiver would output a repeated frame every 10 tx frames or every 220 ms. That is ~4.5 repeated frames per second! You don't think a heli pilot doing 3D is going to feel that?

I believe you would find that your "requirement" of 40 users on one "band" is much less important than the ramifications of an asynchrounous setup in real world use.

You've quoted your system as being 100 mW. At that level for a mobile device at 2.4 GHz, the FCC requires 20 cm of separation between the antenna and any part of the body. How do you plan to get around this as your module is obviously going to be much closer to body parts than this?

Thanks,
John

MSH Protos

09-20-2006 10:45 PM

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

The Spektrum system has a 22.5ms frame. Most radios use a 22.0ms frame. That means you are only getting 44.4-45.5 frames per second. Even if we repeated 4.5 frames, we are still outputting data more often, so it doesn't really matter. Can anyone tell the difference? Absolutely not. A human can not recognize a physical difference in motion that is less than 25ms. We are well under that, and we are merely repeating the same data. You have to remember that every digital radio system collects the entire packet and then updates the frame. This means that you can be anywhere from 5.0ms to 17.75ms behind the actual transmitter stick movement. If you send the data packets in realtime as they are decoded, the worst you can be is 2.25ms behind.

Our FCC approval requires less than 10cm separation. The Spektrum system is suppose to use 100mw for the transmitter (10mw for the receivers) and they apparently have no FCC issues, and their antenna is closer to the holder's body than ours.

Jim Drew, CEO/President - Xtreme Power Systems

09-21-2006 12:07 AM

HOMEPAGE

Angelos
Key Veteran
Location: nr Oxford, OX11, UK

Quote
Using the above example, your receiver would output a repeated frame every 10 tx frames or every 220 ms. That is ~4.5 repeated frames per second! You don't think a heli pilot doing 3D is going to feel that?

I’d like to support the above statement with this example.

Modern gyros are capable of well over 500deg/sec. At roughly 45 frames per second this relates to over 10deg yaw rotation per frame. At competition flying 10 deg difference at the stopping of the tail can make a lot of difference between winning and loosing. If the pilot is unfortunate enough to be on a repeated frame the tail stopping will be 10+ deg wrong. And the chance of this happening is 1 in 10!

-Angelos

Spartan RC R&D - Visit us at our local club www.helicollective.org.uk

09-21-2006 01:23 AM

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

If you look at the existing systems, they do not update as fast as we are doing. Look at Futaba 9CHP radio with PCM. That only updates 34.782 times per second, clearly much less frequent than our 50 times per second, even if we in fact repeated 4.5 frames. Does anyone complain about using this or any other PCM radio that has 28.75ms frames? I will have to calculate the amount of wrap that actually occurs with our system, as I believe it is less than 4.5 frames. In the absolute worst case scenario, we are the same speed (with higher resolution) than any other system running a 22ms frame (and still faster than the Spektrum at 22.5ms frame). Now, if the radio runs at 20ms, then we are dead on at 50 times per second.

Jim Drew, CEO/President - Xtreme Power Systems

09-21-2006 04:39 AM

HOMEPAGE

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

> The Spektrum system is suppose to use 100mw for the transmitter
> (10mw for the receivers) and they apparently have no FCC issues,
> and their antenna is closer to the holder's body than ours.

How can you say the Spektrum antenna is closer than your antenna? The Spektrum's antenna is the last couple inches of the antenna sticking out the top of the case. That puts it at least 12 inches from the user's body and about 6 inches hands. Your antenna sticks out the back of the transmitter and would be about 6 inches from the user's body. The users fingers will also be much closer than 6 inches if they wrap fingers around the side of the transmitter, as the majority of flyers do.

How much research have you done on the effects of various radio channel/servo update characteristics on eCCPM helicopter swashplate motion? Mr. Drew, even subtle differences have visible on the bench and feelable in flight effects. Futaba PCM1024 causes noticeable "swashplate dancing." JR SPCM causes a little less. ATX PCM is extremely good and Futaba G3 is perfect. A variable delay and repeating frames will have an impact.

If you care about your system's use in the helicopter world, please have it tested by some really good pilots. But, I suppose, as you said, "This system was designed for us guys that have $10,000 or more invested in a plane..." you may not really care about the heli market.

Best of luck with your system.

- John

MSH Protos

09-21-2006 05:27 AM

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

One of my friends is an expert helicopter pilot. He has flown just about every time of helicopter made over the last 20 years. He will be flying various helicopters with our system for testing.

I can make an option to use the transmitter's exact frame rate, but I am telling you that using a faster frame is NOT going to cause a problem, in fact, it makes the system much more reliable in case there are drop outs. You seem to be stuck on this point, and it really is not going to be an issue - for real.

My transmitter is nowhere near 6 inches to my body when flying. That would be like holding it nearly against your chest and trying to fly. Our antenna is on the backside of the transmitter, not sticking up and pointed at you.

Jim Drew, CEO/President - Xtreme Power Systems

09-21-2006 05:32 AM

HOMEPAGE

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

Mr. Drew,
Most heli pilots fly with a neck strap and the bottom of the radio rests against the abdomen. Like this:

Your antenna would be pointed down at the ground and about 6" from the abdomen. Some pilots even have the radio angled more towards the ground so your antenna would get even closer. I have also seen numerous FAI airplane pilots fly with this type of "hold."

- John

MSH Protos

09-21-2006 06:04 AM

seattle_helo
Key Veteran
Location: Seattle, WA USA

As illustrated by John's post above, when I fly my helis I use a neck strap and the TX rests on my abdomen. I would agree that is a very common arrangement.

nick

09-21-2006 06:53 AM

HOMEPAGE

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

Even in this position, with the bottom of the transmitter touching your stomach, and due to the placement of the antenna, we are still within the recommended safe zone. We are not concerned about this.

Jim Drew, CEO/President - Xtreme Power Systems

09-21-2006 02:55 PM

HOMEPAGE

longhair
Heliman
Location: Beaver Falls, PA

This is a very interesting product and I understand both sides of the camp on the frame overlap. I have been doing RF and electronics for 14 years as my livelihood and choose not to use PCM on my helis nor my pattern planes. I think you'll find people will decide what is best for them or at the least acceptable to them.

I have to ask how you getting past FCC type acceptance. Last time I checked using a module such as yours in another manufacturer’s transmitter was a violation of FCC regulations unless the manufacturer issues a type acceptance of the device.

09-21-2006 08:36 PM

XPS
Senior Heliman
Location: Lake Havasu City, AZ USA

We were told that the FCC does not require this for 2.4GHz radio modules.

Jim Drew, CEO/President - Xtreme Power Systems

09-21-2006 08:49 PM

HOMEPAGE

Professorwiz
Veteran
Location: Livonia, Michigan - USA

Ok all this has led me to the question when can we expect to see these on the market?

09-21-2006 08:58 PM

HOMEPAGE

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