Servo stretcher

31 posts in this topic

Posted

Hi,

I'm fairly new to RC-electronics, but had a great time building some of the circuits on this site. (Thx Mr RC-CAM!)

Now I'm searching for something what seems to be fairly uncommon. And that's a Servo Stretcher. Mind you, not the one where you have to hack the servo's electronics by adding a few resistors or replacing the pot by a pair of resistors, but a separate circuit which can be placed between the RX and the servo.

I've searched noumerous sites, but came out empty-handed. One time a thought I'd found it, but it turned out to be a dead link.

Has anyone a link to such a circuit or could kickstart me in the right direction so I can try and design it myself?

All help will be greatly appriciated.

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Posted (edited)

Hi, Kilrah

45 Swiss francs for a pic that stretches the input signal ...

those are gangsters !!! :blink::blink::blink:

Jevis ... can you ( or have a friend who can ...) program a small pic ( say 12F 629 or 675 for a common one ... or a 16F628 ) ??? :unsure:

Could you also tell me How Much you'd like to stretch the signal ... cause, there's in one of my drawers, a ready to burm application called "The magic Box" that permits to trim with push buttons all ( useful :D ) parameters of a couple of servos ... will eventually need to modify the stretching ( as is, you can add or substract 254 µs to max positions ... )

There's one input and two contra-rotative outputs ...

That was intended to use two mechanically coupled servos or drive two separate elevator or flaps surfaces with two servos ... ( matching the travels )

Or use to drive a bomb bay ... on a scale plane !!! ( For that ... I have simpler !!! )

It's a bit over what you want ... but it exists ... as a free download :rolleyes:

Alain

Edited by Acetronics

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Posted

Thanks for the link Kilrah, but as Alain already mentioned, I also think there's a quick buck made that way. Yesterday I also found an online shop selling a ready build circuit. But where's the fun in that?

Alain,

That sounds perfect! If I read it well, it's programable per servo you connect it with.

I've noticed that, when altering the servo's electronics, there's alway's a slight diference per servo in the value of resistors you have to use in both directions to get max travel without wrecking the gears 'cause you're pushing the limits of the pot.

Am I right that this is still something to be aware of when you use a external servo stretcher?

Programming PICs is no problem. So with a schema and software I'll be more than happy!

At first it's just to open retracts scale-like with standard proportional servo's.

But as many of us do, in the end we always want more. So do I ;).

It would be great being able to experiment with it.

If the program code is opensource it will help me understand an thus serve my learningcurve in programming pics. But that's in the category 'Nice to have! :D.

First and foremost I need a working external servo stretcher which can be homebuild. The required stretching will be the pot's limits I think!? But more than 180 is not realy usefull, for that will give the max linear movement (to e.g. a rod).

Are you willing/able to provide me with the necessary links?

Jevis

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Posted (edited)

Hi, Jevis

There's no problem for any Hobbyist use of these files ...

the only point I want to raise ( very important !!! ) is to be sure the pot is the closest to its middle postion for the neutral : that's the must for having a maximum travel.

Also verify the limiting "bit" on the output gear allows the max travel ( must be placed along the great axle ( length ) of the servo.

For programming PiCs ... I use most of time PbP Pro ( the best Time /efficiency ratio available ) ... cause I better fly than lose my last hair :D .

So, If you have access to this Compiler, source files will be helpful ... otherwise, It's rather difficult to follow Uncompiled Hex files obtained with PbP :blink:

Now, I just need a private address to post you those files ... ( More room than allowed here ... :rolleyes: )

Alain

PS: your link is full of goodies ... Especially the pan Cam base ( for Mr Cam's fans, of course !!! )

Re PS: For info ... also have a look here : http://www.rc-float-flying.rchomepage.com/...o%20Trimmer.htm

Edited by Acetronics

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Posted

Hi, Kilrah

45 Swiss francs for a pic that stretches the input signal ...

those are gangsters !!! :blink::blink::blink:

Kilrah is the owner of the Gangster cie... :P:D:lol:

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Posted (edited)

:lol:

Yesterday I also found an online shop selling a ready build circuit. But where's the fun in that?

Yeah well, it's obviously not for those who want to program PICs themselves, as you said those wouldn't want to buy something ready-made anyway :P

However, most of the people out there don't know a thing about electronics, and those are very happy when someone takes the time to develop and produce what they need ;)

It was primarily meant to be bundled with the full system, but you'd be impressed at the number of people who will place an international order for little details like a $5 Y-cable they don't find at their LHS... At least I am! :blink:

Edited by Kilrah

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Posted (edited)

Hi, Vrflyer

That's also called "ServoMax" ...

http://feretphilippe.neuf.fr/

and it really does a Max !!! :D ...

Alain

Hi, Kilrah,

<< but you'd be impressed at the number of people who will place an international order for little details like a $5 Y-cable they don't find at their LHS... At least I am! >>

I Sadly know all that ... as I am a "non-commercial" ( component costs !!! )furnisher for members of our scale nats champions !!!

And understand there are here HUNDREDS of designs that have been made ... from batt couplers to lighting systems including PPM fail-safe systems .

May be you've heard from a twin jetcat powered french Airbus ( Will Morbin http://www.mes-avions-rc.net/ ) ??? ... Electronics designs come from here !!!

Alain

Edited by Acetronics

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Posted

Hi Alain,

T'has been a while. Sorry for that. Don't wanna create the impression of ingratitude. :unsure: Electronics ain't the only field which can be challenging. Bill's failure of an OS are giving me sleepless nights the past few days (speaking of losing your last hair ;)). Drivercaused BSOD's: a real nightmare! :angry: But that's a topic for another forum.

I can handle the sourcecode. Have PicBasicPro as well. Besides basic language I also have a C compiler. Using MPLAB and C it's more of a homematch for me. But still am to much of a rooky with PIC programming to have a real opinion which is more practical in the long run. Have read several pro's and con's on the matter.

I'm keen on having a look at the sources so I've send you my mailaddress. :rolleyes:

'Maximas tibi gratias' so far for taking the time and effort Alain! tfr1mt2.gif

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Posted

Hi, TwinTurbo

This one is more honest ... ( ~ 12 Euros or 18 Swiss francs for a comparison ).

Just one thought : It's not trimmable ... :rolleyes:

Alain

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Posted (edited)

Hi,

Finally found THE simple thing !!! :D:D:D

http://www.estradamejido.com/L/servo.pdf

Alain

... in spanish he tells the same as I !!! :

" y no habrá que pagarle a rc tech los 30 euros que pide, con 10 teneis bastante " :rolleyes:

Edited by Acetronics

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Posted

" y no habrá que pagarle a rc tech los 30 euros que pide, con 10 teneis bastante " :rolleyes:

Ou encore: pourquoi payé 30 piastres quand tu peux l'avoair pour un p'tit 10 piastre.

Effectively is cheaper that way, but most of the people don't know how to program PIC. Thanks to peoples like RC-Tech who made it for us. With patience it's always possible to find it somewhere cheaper, but many don't have patience.

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Posted

Hi, Vr

T'aurais pas quelques actions là dedans ??? ... par le plus grand des hasards ???

Well, Seriously

This is a good thing to raise our World's main deasease : life would be sooo easy if every one didn't try to build it's own thing in its own corner ...

just to claim " I DO EXIST AND I DID IT BY MYSELF "

no matter the cost or waste involved.

... Just a thought of an old Aeromodeller having seen 40 years of stupidity around.

Alain

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Posted (edited)

This is a good thing to raise our World's main deasease : life would be sooo easy if every one didn't try to build it's own thing in its own corner ...

just to claim " I DO EXIST AND I DID IT BY MYSELF "

Is that really a disease? I'd actually encourage people to do that. To stay a bit in the subject, if I had found a servo stretcher that had the features I needed 2 years ago, made by that guy in his corner I'd have heard of, I'd simply have bought it from him instead of bothering making one myself. Too bad, it wasn't really of an interest back then. Or the guy didn't shout loud enough.

So now I spent some time making one I could use, there could be other people in the same situation as me at the beginning who'll be happy to find it. It actually seems there are.

Duplicate that as needed for each other item.

If nobody was doing stuff in their corner a lot of things we're using daily wouldn't be around.

Edited by Kilrah

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Posted (edited)

Hi, Kilrah

We'll close that slippy subject, cause you make money from that, and me, I do that for fun.

We can't agree wich each other ... that's impossible. :P

But, When flying my planes at the field, I hear the ONLY first question of young ( and less young ! ) people about models :

" HOW MUCH DOES IT COST ??? "

I'd want to cry !!! :(

That only mean they do not know anymore to use their brains or arms ... just can give a credit card number or sign a cheque. :blink:

That's really THE Deasease ... but you'll never accept to tell it !!!

End of File.

Regards

Alain

Edited by Acetronics

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Posted

Oh, said that way I agree.

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Posted

I'm independant, me too I do FPV for fun only, I made no money with it.

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Posted (edited)

Hi,

Let's be POSITIVE !!! :D:D:D

I made some tests with my " Magic Box" ... max disposable travel is only ~ 140° ... <_<

That permitted me to see servos without any "internal trimming" can accept 500 to 2500 µs signals ... as a MAXIMUM. :huh:

One must take care not to reach the mechanical limits ... otherwise a gentle smoke could be exhausted from the servo !!!

So, I re-wrote the program ... :(

Now, we can shrink the output pulse from 500 to 2500 µS !!! And that with standard transmitter settings ( 100% dual rate )

very close to 180° with my futaba Servos ( 3001 and 9201 tested ). A neat 180° would need an internal adjustment of the output gear and/or pot ( for symmetry ).

Note Output travel can also be reduced in the same ratio !!! ( an as-is feature !!! )

The Trimming strep is 10µS and positionning resolution 2µS ... makes 100 Trimming Steps - and no visible steps when moving.

Three leds help for programming and run : a red one to show signal lost or servo side ( when programming ), a green one to show everything Ok or pushbuttons steps ... and a bicolor one to show where we are with the pushbuttons ( increase, decrease or 100% servo travel ).

There's also a Fail-Safe included :) : locked to neutral ... unlocking occurs automatically when a neutral position is received for 1/3 second without any glitch.

Now, here it is ...

Alain

PS: as some room was left ... I also made it fit the retract servos requirements ( two positions with switch and fail-safe at an extremum ... )

Two jumpers permit All the programming ... and system learn values by itself, so it's compatible w/all pos. signal radio brands !!!

Edited by Acetronics

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Posted (edited)

Surprising tests ...

While testing my servo stretcher with different servos ... :unsure:

I looked at the Mechanical Neutral vs Electrical neutral, to verify no mechanical issue involved.

Surprising results :blink: : my graupner ( JR ...) servos have approx 1.50 ms mechanical neutral ... quite normal !!!

But Futaba servos ( mine are a bit old - S 9201, S 3001 ..., S 148 ) ... ALL show a 1.30 ms mechanical neutral. ( NO !!! Robbe brand is not dead !!! )

If someone could confirm for other servos/brands ... would be nice.

Reason ??? "streching " Graupner servos do not show issues ... but For Futaba ones ( W Graupner TX ... 1.5 ms Neutral ) , some trickery is necessary, like reprogramming those servos neutral on the TX to ... 1.30 ms !!! :rolleyes:

Alain

Edited by Acetronics

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Posted

Hi,

Finally found THE simple thing !!! :D:D:D

http://www.estradamejido.com/L/servo.pdf

Alain

... in spanish he tells the same as I !!! :

" y no habrá que pagarle a rc tech los 30 euros que pide, con 10 teneis bastante " :rolleyes:

Oh NO! Finally found a DIY servo stretcher which I have been searching high and low for and it's in Spanish! Can any kind soul do a translation? (There's free beer at the Livingston Inn for the translator.) ;)

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Posted (edited)

You need PIC programming hardware, do you have that?

BTW, I just finished upgrading mine's software. It now stores the R/C's center position instead of reading it at powerup (depending on the setup it could be very annoying to have to center the stick/control each time), and lets the user offset the servo's position to compensate for the differences between "electrical" and mechanical center.

Edited by Kilrah

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Posted

PIC programming hardware? No - but hard, wary, determination not to pay a penny more that necessary. She Who Must Be Obeyed is already raising an eyebrow at the cost of the latest project...

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Posted (edited)

Hi, Barry

<< not to pay a penny more that necessary>>

Pure Scottish breed ... I see !!! :D:D:D

<< There's free beer at the Livingston Inn >>

Is this Inn the one you are supposed to bring your beer and glass ... some kind of Spanish Inn ??? :unsure:

Hi, Kilrah

If you need some more ideas ... just give a call !!! :P

Alain

Edited by Acetronics

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Posted

>If someone could confirm for other servos/brands ... would be nice.

1.5mS the universal standard, in multiplex mode 1.6mS.

the normal min is 1.0mS and max is 2.0mS.

most analog servos accept much more and much less,

this will give you more travel, but there is a tradeoff: RESOLUTION.

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