Aerocomm 2.4GHz Transceiver

[Hell-e-Guy]

Hi Guys,

Has anyone tried the Aerocomm 2.4GHz module for R/C Control ?

http://www.aerocomm.com/rf_transceiver_modules/ac4424_24ghz_rf_transceiver.htm

I Know UAV projects use it for telemetry.
Looks promising...frame rate of 8ms should be sufficient...
I know spektrum is using a diversity method with two antennas at the RX...
how do you think the FHSS will behave in an open field and a closed gym ?
Is Spektrum's method really superior to FHSS or is it just done for patent reasons to be unique ?

Any comment will be appreciated.

[Hell-e-Guy]

Any Ideas on this.....?????

[Nicetie]

"I know spektrum is using a diversity method with two antennas at the RX...
how do you think the FHSS will behave in an open field and a closed gym ?
Is Spektrum's method really superior to FHSS or is it just done for patent reasons to be unique ?" snip

The Spektrum TX is actually sending two separate signals (both containg the same information), so this isn't diversity, but redundancy. There are two
receivers in the airborne package each on a different frequency which is
determined at TX startup. The servos are controled by the RX with the
strongest signal or by both RX if both signals are good.

They claim their method (DSS) is superior to FHSS due to it's abillity to detect and amplify
the signal while improving the signal to noise ratio. I've read elsewhere that this
method actually does work. The whole thing is unique and the reports of excellent range
and freedom from glitching keep coming in the RADIO section of this BB.
That's all I know about it. The Spread Spectrum Sourcebook by the ARRL
describes these SS systems and other SS modulation techniques
Ken K5MBV

[rclinks2002]

hell-e-guy,
I am in the process of building a way to control an airplane using a RC-PC interface, radio modems and servo controller. The radio modems I am currently using are for control only and data transmission is almost impossible because of only 9600 baud data rate. I have looked at the aerocomm modules and I will consider them if we need a higher data transfer rate...

Second note, through mouser the price is for one module right? Thanks

Ben Mitchell

[Osprey WannaB]

Hey Ben,
u say u are interested in using Rc-Pc interfaces, well so am i, but i dunno where to start.. do u have any links that could help me get started on my own project?? here is a link to my discussion:D..
http://www.rcgroups.com/forums/showthread.php?t=496861
:D
JAMIE

[rclinks2002]

With regards to links....hmm.

well I bought a servo controller from: http://www.picobotics.com/Products.html and ordered the pico pic (49.95)

Then I bought the joystick interface program from : http://www.ryonix.com/software.html ($18)

Then a PC interface for my hitec radio that i made....


Then I am using some surplus radio modems from the mars rover project, but will probably upgrade to the aerocomm sooner or later.....

I am still waiting on the radio modems right now so I dont really even know if this will work yet. Conceptually it does work....

Ben

[Osprey WannaB]

Thanx for that ben,
I'm sure this design of urs will work if u make it right:D
I will look in to this setup... Please let me no if it works or not..
Jamie

[Hell-e-Guy]

rclinks,
What modems are u using ? 2.4GHz ?
what brand ?

I want to try other modems before I buy the aerocomm (around 100$ as piece).

[rclinks2002]

hell-e-guy,
I am using the motorola rnet 9600 radio modems. They are actually the ones used on the mars rover, but they were also widely used in other fields. I got my pair for 150 off of ebay. I believe that they operate on 439mhz band, which I believe is a commercial licensed band. I need to do more research on this. I still havent been able to figure out how to overcome the problem of RTS and CTS on the modems without having to use a computer in the plane. I believe that the CTS on the receiving modem can be tied to logic low (gnd) and then it will always be in receive mode, this inhibits transmitting data back to the ground through the modem. I was thinking that I may be able to put a oscillator on both the ground and air modem that will switch between RTS and CTS at a fast rate which will allow me to use the modems much like a standard dial up internet modem, where the switching rate is far faster than the transfer rate of the bits in the modem. I assume that this will allow me to transmit and receive at the same time...I havent proven this theoy yet though. Sorry for the long reply....

Ben Mitchell

[Hell-e-Guy]

If you have a micro-controller integrated into your project it's no problem to implement the whole RS232 protocol (with CTS,RTS,DTR ect.) Just means more I/O's.
You can check in the modem's manual if it can work with no flow control at all.
This will eliminate the need for the extra lines.

[rclinks2002]

hell-e
At the current time I dont have a microprocessor in the plane...I am not that skilled in the ways of them...haha. I thought that I may be able to bypass the RTS and CTS with a jumper on the computer. I havent had any luck with this. I ordered a manual for my particular modems but it hasnt come yet. I would like to incorporate a microprocessor but I dont know how I would go about doing it. Ideally I would like to be able to transmit the telemetry back to the ground with the radio modem rather than having to use a seperate transmitter for the telemetry. (currently I have the eagle tree systems telemetry unit; very nice unit I must add) For the servo controller I have a picobotics controller pico pic 30 or something like that, running a piece of software written by ryonix. Do you have any ideas for micro controllers? Thanks

Ben Mitchell

[Hell-e-Guy]

8 bit Micro's are a lot of fun...easy to program...and the newer ones have a lot of peripherals like A/D, D/A, Comparators, Internal voltage reference, Hardware UART....
and the list goes on.
The preferred micro-controller on the web is the MICROCHIP PIC which has a free development software (in assembly language), but you can also download a C or BASIC
compiler and write the code with a higher level language.
With little search you can find a programming software and hardware schematics.
The next ones are the ATMELTINY and MEGA which I have little experience with.
worked with them in a former job for a couple of month and was very pleased...
Only because of bad local Support we switched to MICROCHIP.
The micro-controller i am now using is the CYPRESS PSoC. It is not very popular in the
hobby electronics market, but it has several unique features.
All in all I recommend the MICROCHIP PIC to start with.
If you have any more questions I will gladly be of service...

[rclinks2002]

I ordered and put together a PIC programming board, and have yet to use it..haha
I was wondering if it were even possible to program a chip that will bypass the RTS and CTS functions on rs232 devices? Also is there a way to externally add an address to packets of information that are sent out of the computer?


Also how about a failsafe, that will isolate all the inputs for the servos, and activate a gear switch.... (its actually to isolate servos from the receiver while still maintaining the voltage)

Basically to shut off the servos from the receiver (while its receiving corrupt data) and activate a return autopilot.

(Its late, I will elaborate/clarify later....)

thanks
Ben

[INewton]

I don't understand why you are using the Aerocomm 2.4GHz module rather than the Aerocomm 900 MHz module. The range is much greater, 4X. And you don't need 2 receivers to solve the multi-path problems.

Is the issue interference from cell phone towers?

[Hell-e-Guy]

INewton, I can't use the 900MHz version in my part of the world due to strict regulations on the 900 band.
rclinks, the RTS and CTS lines are only buffer control lines. if an RX buffer on either side is full it need to let the other side know not to keep transmitting.
You can easily Monitor and generate these signals with a PIC.
when you want to send info flag with the RTS line (don't remember if you need to take it high or low) and wait for the CTS acknowledge from the modem and then send the data.
Also a fail-safe system can be made to monitor incoming signals, and generate an output when one/some/all signals are corrupted.
You will need to use the internal timer to clock the input pulse and see if it's corrupted/logical with some kind of algorithm and them make the decision if to activate the fail-safe or not.

Hope this gives you a lead for now...

[rclinks2002]

Hell-e
With regards to the "Monitor and generate these signals with a PIC." Implying the RTS and CTS, is there a particular book or website you would reccomend for me to look at. I am not all that versed in PICs. I was looking at PIC books on Amazon.com and I received mixed results about the quality of the majority of the books they have...

Also I have looked into doing a failsafe circuit and have found a circuit and code that will do only one servo per circuit. I was wondering if I could use something like a 32 pin PIC to allow me to use a single PIC for about 10 servo I/Os, or does a PIC that has multiple 12F675s inside (much like 8pin logic circuits) exist? Thanks

Ben

[Hell-e-Guy]

Hi Ben,
Multiple CPU in one package is reserved for the BIG BOYS... PIC micros come in a wide variety of sizes. This means that you can have more I/O Pins but less flash memory...a lot of flash memory but less peripherals. You pay for everything they put in.
For a prototype I always take a large Micro (a lot of flash memory, a lot of RAM and all the available peripherals) to start with...Write the program...Debug it...optimize the code for size...and then find the specific micro I really need.
You can have the PIC serve multiple servos, but 10 servos I am not sure...10*2 milliseconds is 50Hz, that is exactly the optimal rate the servos like to
get their pulses... I haven't tried to send a servo pulses in a lower frequency.
I think you can (up to a certain extent) but probably with a price of lower torque.
I don't think a book is necessary as a starting point...you can find a lot of web sites dedicated to Pics.
What you need to do first is download a code (HEX file) that you know works,
that does something stupid like light a LED. and try to burn it into your PIC
. This is the "Hello World" of embedded programming. It will give you confidence that your burning hardware is working properly. Then start to write a code and to compile it.
Your first tries will take a while, but then all becomes a piece of cake.
Don't hesitate to ask for help...

[rclinks2002]

Ok so I have figured out how I am going to do the fail safe.....Easy and simple...I will just go ahead and use multiple PICs. I am quite baffled about using a PIC to control the RTS and CTS lines.
After alot of looking I have seemed to confuse myself more. Correct me if I am wrong, but here is what I thought of. So the PIC would have the RTS and CTS lines connected to it. The pic (using the timer function) would constantly be waiting for a RTS signal from the modem, then when it gets a signal it would then activate the CTS. It would then wait for the RTS line to clear (Negative) and then deactivate the CTS line...Am I on the right track? or totally lost? Would this set up work in the opposite direction also?

Is there a way to add a RTS buffer to a transmit line? like if I wanted to connect the rs232 output from my GPS to a PIC and transmit serial data back to the ground?

Thanks

Ben

[Hell-e-Guy]

Hi,
Take a look at: http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html#anchor1155404
I hope it will help to clear the picture.
The DCE is the modem and the DTE is the PIC.
When you have data to transmit from the PIC you assert the RTS line low.
When the modem can handle the task, it will assert low the CTS line and this will let you know that you can send the data at the required baud rate.

[glloq2]

Hi,
Take a look at: http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html#anchor1155404
I hope it will help to clear the picture.
The DCE is the modem and the DTE is the PIC.
When you have data to transmit from the PIC you assert the RTS line low.
When the modem can handle the task, it will assert low the CTS line and this will let you know that you can send the data at the required baud rate.


Hell-e-Guy,

What about your idea of using the Aerocom 2.4 GHz FHSS industrial modules or any other similar (And cheaper....) systems made by Siemens, ABB or Alsthom ????

I was also thinking about doing that.

Dont be impressed by the boasts of Spektrum, their system is sure more clever than the antiquated standards we have now but it is NOT a proper spread spectrum system, it is just a redondant dual frequency scanning system with TX digital ID which just happens to operate on 80 chanels of the 2.4 GHz FHSS frequency band.
Have a closer look at it and you will not be really impressed.

Many people all over the world used this exact principle on the existing RC bands (35,40,41 and 72 Mhz) just by modifying existing scanning TX's (Basically by putting 2 RF modules and 2 antenas on the same TX) and using 2 standard scanning reicievers.
Those scanning TX modules and receivers exist since many years and they also have unique TX ID.
Most of the big manufacturers have them and I am sure you can buy them at you LHS....

How Spektrum can patent this simple and already widely used technique is beyond me, the patent laws and regulations in the US must be even weirder than what I though possible.....

Your idea of using the real FHSS modules is far much better (But more expensive than Spektrum's "patented" simplistic system) and should work very well.
As you said, those systems have a thruput of about 800 Kb/s so it should not be difficult to figure out a protocol to transmit the relatively low ammont of data required at a speed and resolution sufficient to emulate or far exeed the existing systems, Spektrum included.
Your limitation will certainly be the speed and accuracy of the existing servos which are a throw back from the 20th century anyway and are also overdue for a change to a more modern technology derivated from existing industrial control systems.
Those modules are sure fast enough to satisfy Jason Krause or Quique Somenzini, let alone the rest of us "dumb thumbs"...

I have already used those modules for industrial applications and the link is extremely robust, even in places like electric powered ships or power plants as well as places with a tremendous lot of traffic on the same band and channels.

I used tem also for the radio remote control of a big 350 tonnes gantry crane used for precise postioning of heavy loads. It had 8 proportional functions with 16 bits resolution each and a whole lot of digital IO's. According to the crane operators, the feel from the radio remote was just as good as the feel fom the hard wired joysticks in the main crane cabin.
The link was extremely robust because you do not want to lift 350 tonnes with a dodgy radio link.....The laws and regulations would not allow it anyway.

This was a REAL FHSS radio control link and I am just laughing when I read on Spektrum web site that FHSS is "old technology" and "not suitable for RC applications"......What about my crane then, in 5 or 6 years of operation, it should have killed many people and I should be in jail for life, not writing this blah blah....

IMHO, you should go ahead with the Aerocom modules and apply for a patent, if they ganted it to those Spektrum guys, they must also grant it to you....

[Hell-e-Guy]

glloq2,
Thanks for the confidence builder...after a short research I too think that FHSS is the way to go!!!
I am now experimenting with very simple and cheap 2.4GHz IC's...200us hopping time and virtually no latency (Aerocomm modules have 8ms Time frames), the work is a bit more difficult because I have to write a simple protocol and it's stack.
My plan is to enjoy both world's FHSS and channel diversity. The IC I am working with now can be configured to transmit at two separate frequencies the same data in a very short time!!!

I didn't like the Aerocomm modules' size and price! way too big...and at around 100$ a piece it seemed too expensive.

The work should be very simple with aerocomm, but the final product will be quite large.

[mat01]

Hi ...

Just to say, in the UK Cool Components, (www.coolcomponents.co.uk) are about to start offering the Laipac TRF2.4G Transceiver.

This has some pretty impressive specs, and could be used for both telemetry and control, with additional room for sound or picture transmission.

Cheers.

[glloq2]

Mat01,

It looks Ok but it do not seem to be a FHSS unit, it looks like just a standard GFSK transceiver.

Hell e guy,


What is the progress on you FHSS project ??????
I have ordered the Aerocom modules and I now wait for them to arrive.
If you have had any kind of results, pse let me know

[Hell-e-Guy]

glloq2,
I started experimenting with very simple 0dbm transceivers. I am now writing the code to interface them. After I finish I will start boosting the TX to 20dbm.
The 100$/pc. for the aerocomm looked too much...

[rclinks2002]

Have a look at this.....

I think I will rig up something (with a cmos to rs232 converter) that will allow me to upload GPS waypoints from the ground....I guess it could also be used to control a park flyer or something. (it is FM)

http://www.abacomdirect.com/PLL-FM-Transmitter-Module-RFTQ1-P93402C23630.aspx

[glloq2]

glloq2,
I started experimenting with very simple 0dbm transceivers. I am now writing the code to interface them. After I finish I will start boosting the TX to 20dbm.
The 100$/pc. for the aerocomm looked too much...


Good to see that you are progressing.

Once you are ready to boost your power up, dont forget that a good antena is much better than more RF power.
I am not impressed at all by the commercial 2.4 Mhz antenas available, it is very easy on this frequency to make a very good omnidirectional gain antena which is still very compact.
My long experience as an amateur radio operator shows that for range and reliability of the radio link, more db's gains on the RX and TX antenas are much more efficient than more kilowatts on the TX power stage.....


As soon as I receive my modules, I will just try to validate the FHSS concept by using an existing transmitter ( Graupner MC 24) and just replacing the original HF module by the Aerocom with a proper 2.4 Ghz home made gain antena (About 10 db gain).
On the reciever side, I will try with one Aerocom only, also with a gain antena and use an existing reciever without quartz for decoding to the servos.

The idea is just to use existing standard PPM or PCM signals to modulate the TX and decode that on the reciever side to feed the servos.

What I really want to try for the moment is just replacing the present unreliable 35/40 or 72 Mhz VHF FM radio link by a robust FHSS 2.4 Mhz one and see how it goes regarding actual feel, range, speed and resistance to heavy QRM.

If this works OK, I will then figure out a different concept with radio link based on FHSS redondent TX's / RX's (possibly with RX diversity) and a completely digital control system on the TX and the RX based on existing mini PLC's and mini remote I/O's on some kind of industrial bus (CAN bus or Profibus).

All the components exist for all the above (At a very reasonable price) but they are relatively big and heavy and need a 12V or 24V DC supply.
The coding would be dead simple using standard PLC code or ladder logic.
On the TX side, using digital encoders rather than pots on the joysticks should be no problems and implementing the required mixings and bells / wistles on a PLC is easy.

The main problem would be converting the exiting RC servos, gyros, ect..... to REAL digital operation all the way from the TX joysticks to the servo. This should be possible with a bit of "surgery" and by using standard automotive components.

With the power of the latest industrial / automotive controls components, it would be possible not only to implement a much better and more robust system than anything existing at present (Including Spektrum, of course....) but it would be bi directional and have a wide pass band, thus making all kinds of real time data / video telemetry links very easy and reliable.

Anyway, I soon retire and I need something to keep me busy

73's DE YC6WDB