Servo pass through?

[Xnaron]

I am building a UAV control system based on a Linksys wrt54gs linux router running OpenWRT. I have a thread going in the UAV section...anyhow I am looking to build a backup control system and want to use a traditional RC transmitter and receiver. I need a device that will allow each servo to have two inputs. One from the RC receiver and one from my UAV controller board. One of the channels on the receiver would be a switch that would turn control of the servos over to the UAV controller and then back to the receiver when switched back. Anyone know of a device out there that can do this?

I suppose I could build a circuit that would just switch the servo control signal wires between the uav controller and the receiver using some type of relay or IC. I could build something using reed relays...is there a better way?

Thanks,
Brendin

[Miami Mike]

How about something like a 74HC157 (http://www.robotstore.com/download/45428.pdf), with the select pin controlled by a pc board salvaged from a bad servo?

[vintage1]

Sure. Mikes found the right SWITCH. Taking a sprare channel and using it to drive it is a little more complex.

You need a timer and a latch of some sort.

Use the servo pulse to clock a D type latch, and a simple RC with a diode on one data input coming from the servo pulse.

A short pulse will be at affectively '0' when the negative edge comes..a long pulse will be at '1'

[Acetronics]

Hi,Xnaron

I think such devices already exists in the " ready cooked " version. That is found when using two receivers for safety ( BIG Models 50 lbs + ).

F. Thobois ( Home.nordnet ....) published one DIY version 20 or 25 years ago, based upon a couple of CD 4519 ...

Alain

[Gary Warner]

I suppose I could build a circuit that would just switch the servo control signal wires between the uav controller and the receiver using some type of relay or IC. I could build something using reed relays...is there a better way?

Thanks,
Brendin

I used a reed relay on my AOA project because I wanted a hard-wire solution to getting around my PIC controller. It worked well and it gave me the peace of mind that no matter what the PIC did, I still had a fool-proof way of getting around it.

This was about 9 or 10 years ago. I now have confidence in my PIC's to handle the pass-through process without using a relay.

Gary
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[Xnaron]

How about something like a 74HC157 (http://www.robotstore.com/download/45428.pdf), with the select pin controlled by a pc board salvaged from a bad servo?

Thanks... I haven't worked with TSOP or SOP packages before. Are there sockets for these things or would I have to have a circuit board and surface mount it? I suppose I might be able to find another similar version in a DIP...

[JimDrew]

Does Canada have laws regarding unmanned vechicles? What you are proposing is a federal offense in the U.S. You are not allowed to have any type of "unmanned automated guidance system" on any flying aircraft. With technology today, its as simple as a palm pilot, gps unit, and interface for board to fly something anywhere in the world... you just can't fly it in U.S. air space.

[Mr.RC-CAM]

R/C servo switch discussion: http://www.rcgroups.com/forums/showthread.php?t=360746

[Miami Mike]

And to think that I looked through all the logic chip types yesterday and picked out the 157 as a suggest for Xnaron. I wish I had realized that you guys had recently gone through all of this.

I still say a servo pc board and a failsafe receiver could do the switching of the select line, but maybe I'm wrong about that for some reason. I've never tried it.

[Mr.RC-CAM]

I suppose I might be able to find another similar version in a DIPDIP is not going to be a problem.

I still say a servo pc board and a failsafe receiver could do the switching of the select line, but maybe I'm wrong about that for some reason. I've never tried it.You can do that. In Xnaron's case, he is using a hacked LinkSys Wi-Fi router as the remote control system, so he will have several layers of protection for ensuring that the Mux chip is controlled with good predictability.

[Miami Mike]

I was just reading about the new Spektrum DX6 (http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=SPM2460) radios, and it seems that many folks are interested in pushing them past the recommended range limit. It's natural to want to use such an interference-free system for purposes other than just a close-in helicopter or park flyer, but who knows for sure if it will work reliably?

It occurs to me that any solution that comes out of this discussion or that other UAV thread (http://www.rcgroups.com/forums/showthread.php?t=360746) could be applied toward practical range test experiments with the DX6 system. A 72 Mhz fail-safe receiver could be installed in a plane along with the DX6 system and rigged to be ready to take over control as soon as the 72 MHz radio was turned on.

[Nicetie]

JimDrew, I didn't know about the Federal law against unmanned aircraft. Can you point me to the source of this info ...maybe on the internet?
Are there exceptions made for experimental systems? I know some people
have had government grants to develop UAV's.