Controlling a Helicopter with a Computer on the Ground

[HelicopterBoy]

I am part of a Autonomous helicopter club, currently we have everything setup on the helicopter to start recording in flight data.

The problem now is getting the data that we need. To do this we need to run “Frequency Sweeps” essentially get the servos to move back and forth at a certain rate.
I hope to be able to tie into the buddy box connection on my transmitter and be able to pull the trainer switch and let the computer send the control inputs to the servos. Has anyone ever tried to receive signals from the computer?? All of the Flight Sim adapters allow you to send signals to the computer, can this be reversed? I am worried since it all runs on PPM modulation it appears the computer can recive this so I am assuming it can send to?? Thanks for the help.

[sesat]

This is trivial. If you're using Linux with GCC, I'll help the best I can.


Ram.

[HelicopterBoy]

That would be great, I do currently have a computer running on linux. In fact all of the data collection software is linux. So what is the best way to get started??

[sesat]

I'm sorry I shouldn't have made it sound so easy. You will need to add RTOS patches or the jitter will make the signal unusable. For me, I'd need to start with a clean install. I'm unsure but maybe there are more options for 2.6.x users. I didn't think of your case that you're already doing lots of stuff with the computer.

If it easier, consider using a slave microcontroller do perform the PWM output, and talk to the microcontroller using the serial port. This would be the most reliable option. The more I think about it the better it sounds, why waste dedicating a whole computer to the task when a microcontroller will do.


Ram.

[Arp]

PWM, as in "pulse width modulated"?
Like a servo control signal?

Could a servo controller intended for robots... by any chance be suitable for generating this?

[danstrider]

Yeah, I know exactly what you want to do. I have a friend working on a Hitec Laser 4 interface. He wants to read what the transmitter is sending to the plane. I am guessing that the "frequency sweeps" as something different than the others here have taken to mean it. If you can clarify what you mean a bit, I'm sure others can help. For now, here's a bunch of Hitec Laser 4 (and others) pc-serial interface cable information. I'd love to get a link to your organization's website if you have one!
Dan

GENERAL INFORMATION
Hitec buddy box connector pinout:
http://www.welwyn.demon.co.uk/buddy.htm

Hitec Laser 4 manual: (just for reference)
http://www.horizonhobby.com/ProdInfo/Files/hrc156721-manual.pdf

How a Buddy Box works:
http://webpages.charter.net/rcfu/HelpsHints/BuddyBox.html


DIY CABLES
All about making your own interface cable:
http://www.heliguy.com/nexus/fmsinterface.html

More info about making your own interface:
http://webpages.charter.net/rcfu/ConstGuide/FSC.html

You get the idea about making your own cable, not too bad:
http://www.soldcentralfl.com/flyingpenguin/rcstick.htm


COMMERCIAL CABLES
Commercial serial-TX interface:
http://www.tti-us.com/sim/prod-ser.html

Another commercial interface:
http://www.helihobby.com/html/fms_interfaces.html

USB interface (if serial not good):
http://www.acehobby.co.nz/ossb2/root/OSSBEC1/showitem.asp?PID=52310


Once it's to the port, I'm not sure what you'll see. You might paruse this forum of other simulator programmers to see what comes out those lines:
http://n.ethz.ch/student/mmoeller/fms/index_e.html

[HelicopterBoy]

Thanks for all the links and ideas. All of the cables are designed to send the transmitter signals to the computer, However I want to go the other way. I need to send signals from the computer to the controller. Instead of trying to control a simulator on the computer, I need to controll the helicopter with the computer.

sesat, what kind of cables are you using to connect the computer and transmitter? Also you say PWM output, isnt this different that PPM and doesnt the transmitter need a PPM modulated signal?? I may be way off here correct me if im wrong. Thanks again for all the help.

[danstrider]

>>The pulse train from the slave unit is interpreted by the RF section of the master unit and a particular amplitude or frequency variation is generated to represent the pulse train. The radio signal is carried to the antenna and radiated from the transmitter.<<

You can SEND data through a buddy box cord too. If you plug into the "master," then you SEND data to the master that will be transmitted to the vehicle when the master's trainer switch is toggled.

Think of how a buddy box works. Each plugs into the back but only one is powered. If you plug into a non-powered transmitter, then the cord will tell you what the sticks are doing. If you plug into a powered transmitter, then the cord will send stick data to the transmitter.

There are two different signals you're talking about. One: servo signal. Two: transmitted signal btw RX and TX. Both use square waves to transfer data, but the purpose is different. A servo signal is Pulse Width Modulation, that is, the width of the pulses represent a position the servo should hold. One pulse represents the position. For the RX/TX signal, multiple servo waves are combined into a pulsetrain. This pulsetrain includes a squarewave for each servo. So a single PPM pulsetrain contains multiple servo PWM pulses. Does that help at all?

There are a lot of servo resources on the web that have graphs and demos and better explainations. It would be good to get confirmation of what I said anyhow, since miscommunicating here is easy.

Dan

[HelicopterBoy]

http://www.tti-us.com/shop/product_info.php?products_id=40 I think this will do just what I need.

[chopperguy]

Hey guys i'm looking for some help with setup of the carvec system on a helicopter it's a additude control system any one from edmonton alberta canada..?
thanks brendon
email info@hovercamm.com

[meb48]

If I understand your problem, it seems that with a little poking around the transmitter's pcb with an o-scope probe, you should be able to find where the transmitter signal is just before it is sent into the RF modulator; intercept it here, and modify it with the computer to your heart's content. The trainer port is one place to start --- this is where you'll find all channel data in a single output stream.
Once you have that, an MCU or computer can massage the data however you like. Then, send it along to the RF modulator in the transmitter. It won't do much for your transmitter's warranty, but it will solve your problem.

[Cerberus]

Are you trying to map the poles and zeros of the UAV platform? i.e. perform a frequency analysis so you can design a pole placement controller... I think you may encounter more than one problem attempting this with a PC, especially on a UAV in flight... your much better off performing some first principles physical modelling and using that for designing your controller.

PID should be sufficient for most applications.