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Old Apr 18, 2005, 04:52 PM
Who needs a pilot??
danstrider's Avatar
Alexandria, VA
Joined Jul 2002
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switch between manual/autopilot?

I'm trying to build a switching mechanism for manual vs autopilot flight so I can have manual control for takeoffs/landings and give control to the autopilot for piloting where the ground isn't so close :-)

Does anyone have a circuit schematic for such a safety switch or a link to commercial boards? I can give more details of my personal requirements, but I don't want to limit responses!

Thanks for the help, and I figure others here will also benefit from the circuit too!

Thanks!
Dan
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Old Apr 18, 2005, 05:03 PM
Gotta make the doughnuts
Toledo Express, Ohio, United States
Joined Oct 2004
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Cam Man's project should be able to turn something on and off if it's a soft button.

http://www.rc-cam.com/project1.htm

If not, you can use a silicon diaode with it to open and close a cicuit. You'd need two of them I believe, one to open, and one to close.
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Old Apr 18, 2005, 05:11 PM
Who needs a pilot??
danstrider's Avatar
Alexandria, VA
Joined Jul 2002
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I'm not sure if the mechanical switch will work for pwm (it might, I have concerns in the switching time the servo would spaz or something). I found a prototype circuit, but it wasn't confirmed yet to work.... there has to be something out there that can do this.

I have toyed around with AP before, triggering cameras etc. The best solution came down to programming a basic stamp or buying a prism switch. Gotta be a commercial board........

Dan
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Old Apr 18, 2005, 05:37 PM
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What exactly are you trying to switch? The signal from the receiver to your controller?
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Old Apr 18, 2005, 05:40 PM
Who needs a pilot??
danstrider's Avatar
Alexandria, VA
Joined Jul 2002
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Yeah, exactly that. Switch input from a receiver (i.e. manual mode) to a computer (i.e. autopilot mode).

Dan
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Old Apr 18, 2005, 05:49 PM
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Well one way that it's often done, as you know, is to have the output of the receiver be an input to the computer. In manual mode you have the computer simply pass the signal on to the servos, in autopilot mode, you don't have to turn the signal off, you just have the computer ignore it and issue its own signals to the servos. Of course in that case manual mode is still in some ways dependent on the proper operation of your computer.

As for switching the PWM signal itself, like you I'd wonder if a mechanical switch might not work very well, given the noise it would introduce. I suppose you could try it and see what happens. I don't know of any commercial switches that would do it, but your circuit looks pretty good.
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Old Apr 18, 2005, 05:50 PM
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Dallas Tx USA
Joined Apr 1999
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I can't put my hands on it right now, but there is a two op amp circuit that switched over at the 1.5ms range. It was typical to use these circuits to start and stop motors before ESC's became popular (now I'm showing my age ). Use the output to drive a micro 5 volt relay. I did this to dissable my AOA controller on the first version, as I didn't have the code 100% stable.

Today, I'd just code it into the PIC I was already using or use a standalone PIC to switch the control. At a buck or less each, the PIC solition is cheaper than a relay.

In PBP, it's dirt easy.

test control port for high, loop (re-test) if high.

PULSIN port,value

test value for over/under 1.5ms

branch as needed from test.

Jump/include correction code lines or drive relay, FET's, photo couplers or what ever as desired.

This process works well on my slip/skid project where I must shut off the sensor input for launching a sailplane.

Another 'hammer' for the thumb tack is to use a servo to move a mechanical switch. I've done that too on the AOA project.

Gary
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Old Apr 18, 2005, 06:04 PM
Who needs a pilot??
danstrider's Avatar
Alexandria, VA
Joined Jul 2002
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In this case, I can't pass the signal through the autopilot (for reasons beyond the scope of the question), though I did think of that too.

I have a sinking feeling about the mechanical relay, so I'm going to seek different solutions before I try the relay....

Programming a pic seems robust enough. I'll look into that for a bit to see if I can figure out the specifics.

If you can remember that two op-amp circuit, I'd really love to see the schematic!

Thanks for the input guys.

Would anyone potentially be interestered in a commercial switch for 8 channels? My contact that sent me the circuit above is looking to eventually make a small pcb for the purpose.

Dan
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Old Apr 18, 2005, 06:31 PM
York Electronics
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Dallas Tx USA
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Quote:
Originally Posted by danstrider
In this case, I can't pass the signal through the autopilot (for reasons beyond the scope of the question), though I did think of that too.

I have a sinking feeling about the mechanical relay, so I'm going to seek different solutions before I try the relay....

Programming a pic seems robust enough. I'll look into that for a bit to see if I can figure out the specifics.

If you can remember that two op-amp circuit, I'd really love to see the schematic!

Thanks for the input guys.

Would anyone potentially be interestered in a commercial switch for 8 channels? My contact that sent me the circuit above is looking to eventually make a small pcb for the purpose.

Dan
I wouldn't worry about the relay. The most you'll get is a one frame 'glitch' in the transition. Hardly a reason to crash.

I don’t have a schematic available from here. Try to fallow this:

First op amp: one input is 1/2VDD (reference), the other input is from the receiver. Output to low-pass filter (LPF).

Second op amp: one input is threshold adjustable reference (fixed once the value is known). The other input is the LPF output from the first amp.

As time 'on' increases from the receiver, output on amp one climbs. Once it's over the threshold reference voltage of the second op amp, the second op amp toggles its output. Reverse logic for decreased 'on' time from receiver.

One big problem can be dropped frames, from weak signals or RFI. They can screw with the RC time constant of the LPF. Using a low enough LPF can reduce the chances of there being a problem, while slowing down the response time of the command to change state.

Gary
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Old Apr 18, 2005, 07:08 PM
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Here is a link to a commercially available one

http://www.microboticsinc.com/servctrl.html#TOP

I think it is about $450...which is about $400 more than what is would cost to make a similar one yourself. Anyways, that link should give you some ideas about how to build one. Buying all the servo connectors is the expensive part.

Matt
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Old Apr 18, 2005, 07:14 PM
Who needs a pilot??
danstrider's Avatar
Alexandria, VA
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Ouch! $450! Well, I took a look and it's beast robust for what I'm looking to do! But it is indeed good reference at this point.

I took a good hard look at the circuit I posted above and I think there was a mistake. I've contacted my source and told him, but it'll be tomorrow before he gets back to me about it. I'll post what he thinks.

Still chewing on your opamp idea Gary. At first glance I see how it works; will need more thought to grasp it fully. Thanks for the post though!

Dan
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Old Apr 18, 2005, 07:55 PM
York Electronics
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Dallas Tx USA
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Here's the basic circuit. Don't ask for the values of the components - I'm not an engineer . I can't find a copy of the original schematic on the web.

Gary
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Old Apr 18, 2005, 07:58 PM
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Dallas Tx USA
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Oops, forgot the file.. - senior moment.
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Old Apr 18, 2005, 08:24 PM
Tom Para
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Cincinnati, Ohio, United States
Joined May 2003
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What AP board are you using that does not have on/off control channel?
http://www2.towerhobbies.com/cgi-bin...&I=LXCJD6&P=ML
Tom
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Old Apr 20, 2005, 03:38 PM
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These two diagrams illustrate what I think are possible solutions for what you want to do. If there's enough interest, I can design either or both.

The first diagram shows a simple setup. You would choose a receive channel to control the selection of R/C Receiver or UAV Controller to the servos. There are easy ways to implement the control logic, but they may prove troublesome in the presence of glitches or temporary loss of signal.

The second configuration would use a Microcontroller to decode the R/C Receiver outputs (deglitching, loss of signal detect, etc.). Servo outputs are generated by the Microcontroller as well. The UAV controller would be able to read the R/C Receiver's outputs, and provide its own servo settings. The Microcontroller would still monitor one of the R/C Receiver channels to determine which device has final control the servos.

Interfacing the UAV Controller to the Microcontroller would be through a serial, I2C, or other connection. This eliminates the need for the UAV Controller to generate servo pulse timings.

Let me know what you think...

--Jay
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