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twinturbostang

180 Degree servo mod

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Hey guys. I'm very close to finally having a decent wireless video setup on my planes. It should be up in the air sometime this week. I have mounted the camera on a pan servo. Eventually I will have a pan/tilt setup, and hopefully also have Killrah's head tracking system. But for now I figured I'd start out with just a basic pan (baby steps right? :) ).

But since it is an unmodified servo, I'm getting about 90 degrees of pan (45 each way from center). So I'm curious, what exactly is involved in "modifying" the servo so it will move through 180 degrees of motion? I've heard of some people tearing their servos apart. And I know Killrah has a plug in harness with a PIC. I think I like this better actually, since I don't have to rip the servo apart. So what is it that the PIC changes? Standard servo signal is usually 1ms to 2ms pulsewidth. Is that just changed to 0.5ms to 2.5ms for twice the range? I wasn't sure if the servo could "read" the added range or not. But then I don't know how else it would work.

Thanks,

Brian

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Exactly, it does nothing more than this. I store stick neutral position at powerup (to avoid moving the center point), and then each time I get a pulse from the receiver I subtract that offset, multiply by 2, re-add offset and generate corresponding pulse. That's it :)

Every analog servo I've tested accepts that. Digital ones will be more likely to check pulse validity and thus not to tolerate signals that are too far from the standard.

Fine adjusting to the servo's mechanical end points (which are not always symmetrical by the way) is then done using the TX's end point adjustment function.

The module will become available along with the tracker :)

Edited by Kilrah

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A simple hardware solution for extending the servo throw is to "pad" the feedback pot with some resistors. The actual value will vary, but start off with a 1.2K *series* resistor in the outside legs of the pot (2 resistors total). Be sure that your hack never allows the motor to stall (due to the mechanical limits inside the servo).

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Thanks guys.

Kilrah: At one time you said you'd be willing to send me the source or BIN for the PIC. Is that still the case? I can purchase the PIC's from Digikey probably. I don't currently have a way of writing the BIN to the PIC though. So I will have to build or puchase a PIC writer.

Mr.Rc-Cam: So both resistors go in series with each other between the two outer legs of the pot? I'm not sure I understand how to wire it. BTW, How do you fit all that inside the servo body? I'm using a Hitec HS55 and it looks pretty crowded in there. :)

Edited by twinturbostang

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The servo's feedback pot has three leads. You would introduce a series resistor into each of the outside leads (do not add one to the center lead). There should be room inside the servo for the two 1/8W or 1/4W resistors.

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The method that Mr.rc-cam tell is exactly what I do. It's easy with standard servo, I do it also on sub-micro servo, but it's harder. First, to determine the good resistor, I cut the two outside leg of the pot, and sold wire that extend outside the servo body, I close the servo and adjust the pot at zero ohm.

I plug the servo in a receiver and I move the rudder stick at each end, I turn one pot and the other pot untill the max is found. I remove the pot. and measure the value in ohm of each one and install the closest value( but not higher) inside the servo on the servo pot. leg.

You can add a washer between the horn and the servo case. you tight the screw untill all loose of the horn is remove.

Don't use tiny servo on glow engine plane, you need standard servo for this.

Happy to see you are vey interested in this hobby, you will like it I fly yesterday and today over a beautifull park with an artificial lake, it was awesome :) I dream about it all the day. I made a video, it's available (in poor quality...) here:

http://www.youtube.com/watch?v=mbTvv-xG1Xc

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Thanks guys. I've already hot glued the servo into the top of the wing, so I'm not sure if I'll be able to pull it apart or not.

I flew FPV today! This is maybe the third time so far. Been several months since the first few times. I've finally got a real Tx/Rx setup now (cheap setup before). Today, I flew with a BlackWidowAV 50mW Tx, and it did ok. Some static and drop-outs though. I was hoping to use this on my park flyer due to the low weight. Maybe some tweaks here and there will help (eg: antenna design). I also have a 600mW Tx, that I'm hoping will be really good. I know people have flow well over a mile away with this Tx, so it should work good for me.

It's really an amazing feel, flying FPV. Since I'm still very new to this, I had a friend hooked up via buddy box in case I lost signal or got disoriented. It's really dificult at first to judge distances and speeds. I imagine that is something that gets better with more "goggle" time. :)

Edited by twinturbostang

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Cool :D

Yes it of course gets much better with some time. After a few hours it becomes totally natural, you don't ask yourself questions anymore ;)

I had the same probs with this 50mw. I've dropped it after noticing my 10mW was much more reliable and would offer me twice the range... maybe a receiver sensitivity thing?

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Very strange that a 10mW kit would be better than a 50mW kit. But as you said, it could be the quality of the components. However, all my stuff came from BlackWidowAV.com which I believe is top notch stuff. Where I flew (at work) has some, shall I say, sensitive areas that are not supposed to be photographed. So I can't upload any video of it. But I will try to get some FPV video up from a different field.

As for the flying. Yes, I know it will get better with more practice. I've played plenty of flying games on the computer, so I have no problem "faking 3D". But the big thing is situational awareness. Knowing exactly where you are. AND, knowing how far you are from objects in view, and your current altitude. That's really tricky. I've seen FPV videos of people doing Split-S maneuvers (for instance), and I thought for sure the plane was going to pile straight into the ground. However, after the maneuver was complete it was obvious there was plenty of altitude. I think that kind of thing just takes a lot of practice to become familiar with.

I have a wider angle lense that I am going to try next time out. I believe that will help with situational awareness. Being able to pan the camera definitely helps. But I guess I'm realizing that the less you have to do to orient yourself, the better.

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The first time I fly(flied?) FPV, I remember it was easy to get disoriented because I never seen the field from the sky. I came back and fly the planes without goggle but record a video of the field. When I came back at home, I watched several time the video until I knew detail that could help me for orientation. The second FPV flight was a lot easier.

( just for info...)

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I know the field I'm flying at pretty well. The problem was figuring out my exact position. But I think a wider angle lens will help. Right now I'm flying with a 60 to 70 degree lens I believe. I've got a 90 degree that I'm going to put on it for the next flight though. I may also need to tilt the camera down a few degrees so that more of the ground is in view.

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BTW, here is my setup...

GWS E-Starter

400F brushless outrunner

APC 6x4E

ThunderPower 3S 2000 LiPo

Camera: KT&C S226 (I think)

Tx: BlackWidow 2.4GHz 50mW

Rx: BlackWidow 2.4GHz, 6dbi whip

Camera & Tx Power:

2S 480mAh LiPo, LM7805 5V regulator (no caps installed)

Rx & Goggles Power:

3S 730mAh (or 2000mAh) LiPo pack

Next time out (hopefully today), I'm going to try it with the standard 3dbi whip. I believe I had too much altitude on the first flight, and was above the beam of the 6dbi whip antenna. The 3dbi will give me less maximum range, but more coverage vertically. I have a GP patch that I may try at some point. I'm also wondering if my Tx power is a problem, running it directly off a 7805 regulator. A switching DC-DC regulator would probably be better, but I have to locate one. The project box from All Electronics described here http://www.rc-cam.com/dc-dc.htm is out of stock. I could also add the capacitors to the 7805 as described on the same page. I'm assuming that helps clean up the power output. Not sure if that will make a difference or not, but it may be worth trying.

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Well, bad news. I attempted to go up today at lunch time. But had NO video feed at all. I checked and re-checked all connections but just couldn't figure out what was going on. So came back and looked at the camera,tx,rx on the bench. First thing I did was to try and get a video signal from the camera to my computer monitor (it has a composite IN), and then I was going to check the tx/rx. Well, I couldn't even get a video signal on the monitor. It looks like my camera may be toast. I'm going to do some more testing of wire continuity and voltage levels. Will know more after that...

:angry::(

edit: Well, voltage levels look good. Continuity looks good. 7805 regulator gets warm when powered up. I can feel some heat from the camera too. Yet no video signal. :(

Edited by twinturbostang

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The TX will run off the 7805 with no prob. I had it along with a cam that draws around 180mA when I was using it. Don't bother with switchers.

Regarding FPV flight, I've never really had problems to locate myself. I can arrive at a place don't know at all and fly with no probs...

At the beginning I wasn't using a servo either, that was a bit too much to get used to at the same time. Then I started with a 3-position switch, then linear cursor, then rudder mix. Once you try it you can't do without anymore, but steps are the way to go :P

Be careful with wide angles. They need the same to get used to, and the ground appears farther than it really is...

First choose an angle you decide you'll be using the most and fly a lot with it. Then if you change and get back to that one you'll be at ease immediately.

Try to find a place that is not too flat and clean. Like if you have tall trees you can easily say if you are over them, at the middle,... while you get acquainted to the FOV.

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Yes, I also have soldered/hotglued the power-supply-components to my airwave-tx-module directely.... it works fine and saves a lot of space and a little more weight (you dont need the pcb).

The Audiomodule is done as a "plug-in"-connector to stick between cam and tx... this was a first try but also works fine... I will redo it even smaller, but I think I keep the plug-in-style rather than fixing the board/components to the tx. This gives the option to use it or leave it out for even more weight-saving...

Greets,

Marcus

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Well, bad news. I attempted to go up today at lunch time. But had NO video feed at all.

Check with a strong magnifier.

My story: I recently found that one of my dead camera have one tiny capacitor with microscopic crack in the solder, I try to move it , and it broke easily. I removed a cap same size from another circuit, and luckly it regain life.

The cap was locate on the side where the screw from the bracket are fixing. I removed bracket and to not loose the screw I put them in the camera hole. Wrong, the screw without bracket was too long... :(

Or try to push on parts when camera is power up, perhaps you will locate a bad solder.

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Well, it's not the camera. Finally got it working. I didn't have the proper connector at the time to run the video signal from the camera to my monitor, so I had it rigged up. But I guess there was a bad connection somewhere. Anyway, it works with my 600mW transmitter. But as soon as I swap to the 50mW Tx, it stops working. It's strange too because the LED on the Tx board turns on and the unit gets warm. But no video. <_< I've sent an e-mail to BlackWidow. Hopefully either they have some other diagnostics that I can run, or they will replace it.

BTW, wow that 7805 gets HOT when the 600mW Tx is plugged in. I may have to go with a switching regulator just to keep the heat down.

Edited by twinturbostang

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That obviously won't help :blink:

I was having problems with the channel selector at one point too, when I noticed it got forced and the tracks on one side had been torn... :unsure:

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Quick clip so far: http://www.twinturbostang.com/rc/E-Starter..._clip_small.wmv

Sorry, no fancy music, and I had to cut the video together to avoid showing certain areas where I'm flying. ;) This is about the 5th time for me flying first person.

I'm swamped this week. But maybe sometime next week I'll have some more video.

Edited by twinturbostang

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Hi there.

Just a warning to servo-modders out there - servos can get twitchy if you adjust the pot throw to get that 180 degrees by putting 1-2K resistors at either end; you may also have to decrease another resistor - often about 100K - running from one end of the pot to a small electrolytic capacitor, which adjusts the time-constant of the feedback i.e. how quickly the motor settles to zero (rather than over-shooting, reversing and over-shooting, and so-on). Replacing this with something between 47k & 82K I've found can settle this, although some servos just won't settle!

The 'UK experience' is limited by a strict 10mW transmit limit, and after trying various YAGIs for the receiver, I'm currently flying a Sanyo Xacti VPC5 solid-state camcorder to avoid dropouts on playback. Yes, on a 2-axis mount controlled by head movement; it is a bit cumbersome!

Kilrah - I documented my last version at http://myweb.tiscali.co.uk/splat - have you documented your work with head position feedback that someone mentioned on this board? I hope to update my page in the autumn...

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