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Old Feb 09, 2013, 10:04 AM
leadfeather is offline
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Help!

How to make selectable 90/180 servo, or stretcher with expo.


I've recently become interested in Ultrabatics...ultra aerobatic slope flying...very cool.

One feature that makes the glider do extreme tricks is to move the flying elevator +/- 180. Check out the video below.

I have been thinking of different ways to accomplish this elevator movement, but every method (usually mechanical set ups) have trade offs and most often the large 180 throw results in less resolution during normal flying.

1) I've seen servo stretching mods whereby a resistor is soldered in series with the pot of the servo. My idea is to make this extra resistance selectable. What I'd like to do is by flipping a Tx switch, I can go from a standard servo operation to 180 servo operation. Is there a simple way to do this?

2) Is there a way to do this automatically (no switch flip) so that when the servo gets to the end of it's normal travel it automatically goes to the 180 mode electronically...release a little pressure on the elevator stick and back to regular servo mode?

3) A non linear servo stretcher with adjustable expo ( adjustable non linearity)

Any help will be greatly appreciated. I know there are some electronic geniuses out there, hoping one of you sees this thread.

The Flow - Afternoon Winds (2 min 12 sec)
Last edited by leadfeather; Feb 09, 2013 at 01:21 PM.
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Old Feb 09, 2013, 11:27 AM
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It's called Dual Rates and Expo. It's a function of the transmitter. The servo still has the same travel at all times, it just isn't all being used all the time.

Andy
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Old Feb 09, 2013, 12:02 PM
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Originally Posted by AndyKunz View Post
It's called Dual Rates and Expo. It's a function of the transmitter. The servo still has the same travel at all times, it just isn't all being used all the time.

Andy
Not good enough.

What I'd like is something like a non linear servo stretcher combined with external expo...in one device.
Last edited by leadfeather; Feb 09, 2013 at 01:20 PM.
Old Feb 09, 2013, 05:43 PM
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Why not good enough?

I can set up a model to do exactly what you see using nothing but standard, unmodified servos and a transmitter with the ability to provide either dual rates or ELE > ELE mixing with a switch.

Use of expo would make it act very suddenly with extreme deflection while not affecting normal flying. In fact, I can use DX8 or DX18 to kick suddenly into that mode automatically.

Please provide a detailed explanation of why you think it's necessary to do it electrically.

Andy
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Old Feb 09, 2013, 06:38 PM
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Originally Posted by AndyKunz View Post
Why not good enough?

I can set up a model to do exactly what you see using nothing but standard, unmodified servos and a transmitter with the ability to provide either dual rates or ELE > ELE mixing with a switch.

Use of expo would make it act very suddenly with extreme deflection while not affecting normal flying. In fact, I can use DX8 or DX18 to kick suddenly into that mode automatically.

Please provide a detailed explanation of why you think it's necessary to do it electrically.

Andy
What I'm after is 180 control surface deflection of the elevator while maintaining fine control in the middle of the stick and without using dual rates and while using a simple radio such as a DX6.
Old Feb 09, 2013, 07:58 PM
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Do you have any experience with microcontrollers? I'm thinking modding the signal but the expo can easily be done on any computer radio and gives you even more precision in the fine range.
Old Feb 09, 2013, 07:59 PM
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Originally Posted by AndyKunz View Post
Why not good enough?

I can set up a model to do exactly what you see using nothing but standard, unmodified servos and a transmitter with the ability to provide either dual rates or ELE > ELE mixing with a switch.

Use of expo would make it act very suddenly with extreme deflection while not affecting normal flying. In fact, I can use DX8 or DX18 to kick suddenly into that mode automatically.

Please provide a detailed explanation of why you think it's necessary to do it electrically.

Andy
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Originally Posted by leadfeather View Post
... using a simple radio such as a DX6.
Simple as you said but limited. Basic feature on other TX example futaba multi point curve. So AndyKunz pretty much nailed
If its all about the money Devo7e+deviationtx

Ps Tx module will need modding for full range or swap out for another devo8s telemetry still cheap mind. Still up in the air as which way is best.
Old Feb 09, 2013, 08:35 PM
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Originally Posted by leadfeather View Post
What I'm after is 180 control surface deflection of the elevator while maintaining fine control in the middle of the stick and without using dual rates and while using a simple radio such as a DX6.
Your DX6i has expo and it can mix ELE > ELE.

Problem solved. Just learn how to program the radio.

On the D/R and Expo screen, set your expo very high (+70 or maybe more).

On the Mix screen, set Mix 1 to mix Elevator to Elevator at 100%. Select the switch to control it.

Max out the elevator servo travel (125% I think is as high as it goes).

I would do it with the same switch for both the D/R and mix so I can fly easier around neutral when I want. Not sure if the DX6i allows that, but it would be my desired method.

You will probably need to adjust the linkages in your aircraft to handle the extra deflections. You'd have to do that anyway.

Enjoy!

Andy
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Old Feb 09, 2013, 10:43 PM
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Quote:
Originally Posted by AndyKunz View Post
Your DX6i has expo and it can mix ELE > ELE.

Problem solved. Just learn how to program the radio.

On the D/R and Expo screen, set your expo very high (+70 or maybe more).

On the Mix screen, set Mix 1 to mix Elevator to Elevator at 100%. Select the switch to control it.

Max out the elevator servo travel (125% I think is as high as it goes).

I would do it with the same switch for both the D/R and mix so I can fly easier around neutral when I want. Not sure if the DX6i allows that, but it would be my desired method.

You will probably need to adjust the linkages in your aircraft to handle the extra deflections. You'd have to do that anyway.

Enjoy!

Andy
Didn't work.

I used my Dx7. Mixed elevator to elevator, travel set at 150% both directions and expo at 100%.

The result. No extra travel from the mix. The radio seems to truncate the output at 150% max.

Expo is reduced by the mix. I triple checked that the on and off switch (flap) controlling the mix was actually on and off and not misread for the test. I checked both the graphic (servo monitor) display and a servo hooked up to the Rx to confirm both the stretch and expo effects.

Net result, mixing elevator to elevator does not add any maximum servo travel and it reduces expo.
Last edited by leadfeather; Feb 09, 2013 at 10:54 PM.
Old Feb 09, 2013, 10:50 PM
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Do you have any experience with microcontrollers? I'm thinking modding the signal but the expo can easily be done on any computer radio and gives you even more precision in the fine range.
There is not enough expo built into my Dx7 or Dx6 for what I need to do. If I could use a programmable throttle or pitch curve in the DX7 to control the elevator I might at least get the expo effect (or in other words elevator stick response) I'm looking for. Need to look at the manual to see if this is possible.

I'm thinking about using an programmable chip between the Rx and the servo to accomplish the stretching and the expo I want.

Thanks all for the suggestions.

ps. Dohhhh, why not just plug the elevator into the throttle port of the Rx (slave throttle to elevator) and try the throttle curve....big maybe. If it works, being in heli mode means I have to do some other mixing to get flaperons, but that should be do-able.
Last edited by leadfeather; Feb 09, 2013 at 11:16 PM.
Old Feb 09, 2013, 11:35 PM
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Did some more testing. Using the throttle curve to control the servo worked in part. Using the throttle stick to control the servo got me much more expo. If a 7 point curve was available instead of a 5 point curve it would have worked better still. I had to not use the exponential smoothing option in this mode. When I did, the curve became totally flat in the mid range.

Slaving throttle to elevator stick did not work as hoped. The radio just sums the signal from the elevator and throttle. What i really need is to be able to reassign throttle to elevator stick. I don't see in the manual where this is possible to do on the DX7.
Last edited by leadfeather; Feb 09, 2013 at 11:48 PM.
Old Feb 10, 2013, 12:51 AM
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If you use PIC ,it is here
http://www.waitingforfriday.com/inde...ervo_Processor

change 90 ----> 180.

RC Servo Processor (1 min 57 sec)
Old Feb 10, 2013, 02:01 AM
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Quote:
Originally Posted by leadfeather View Post
why not just plug the elevator into the throttle port of the Rx (slave throttle to elevator) and try the throttle curve....big maybe.
Sadly, that won't work.

Quote:
I'm thinking about using an programmable chip between the Rx and the servo to accomplish the stretching and the expo I want.
That is probably the best solution. I have previously developed an ATV circuit using the PIC12F675, which increases throw up to 200%. With a bit of modification to the code I have managed to get a curve that is normal up to 80%, then accelerates to give up to 200% throw in the last 20%.

The circuit is a generic one that I use for various projects. In this case the LED and 1st servo output are not required.
Old Feb 10, 2013, 06:34 AM
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This is the kind of thing I had in mind.

I have some experience with the Arduino processor ( the Pro Mini ). Used it in multicopter and VTOL projects. The code looks very similar.

A few questions, I hope they don't sound to dumb but I'm outside my expertise when it comes to this kind of project.

1) I've never made a circuit board. Do I have to build this one from scratch or can I buy the board with components ready to program?

2) What interface device do I need for the programming? for the Arduino I use something called an FTDI interface.

3) Is there support for the programming? Debugging, algorithms etc.?

Thanks for your help.
Old Feb 10, 2013, 06:38 AM
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Sadly, that won't work.

That is probably the best solution. I have previously developed an ATV circuit using the PIC12F675, which increases throw up to 200%. With a bit of modification to the code I have managed to get a curve that is normal up to 80%, then accelerates to give up to 200% throw in the last 20%.

The circuit is a generic one that I use for various projects. In this case the LED and 1st servo output are not required.
Are there enough ports for two inputs. It might be nice if one of these devices would control the elevator and the rudder in the same way at the same time.

The curve you describe would probably work very well for this application. "With a bit of modification to the code I have managed to get a curve that is normal up to 80%, then accelerates to give up to 200% throw in the last 20%."

How is the chip flashed?

Thanks for the help.
Last edited by leadfeather; Feb 10, 2013 at 06:44 AM.


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