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[BarryM]

I want to increase the operating arc of three servos up to about 170 deg. and I know that this is covered eleswhere on the forum by inserting extra resistors into the servo internals. However, this is not always practical with all servos (at least not for me).   I know that external servo stretchers are available commercially but can anyone come up with a DIY circuit?

Thanks for any input.

Barry M

[BarryM]

I'm told that this is a circuit diagram for a servo stretcher. Unfortunately Spanish is not one of those languages I picked up except for "dos cevezas por favor". Can anybody help with http://www.estradamejido.com/L/servo.pdf

 ???  ???

Barry M

[Martin (Admin)]

This any use?  http://www.uoguelph.ca/~antoon/gadgets/servos/servomod.html



Or, what about one of these?

http://www.servocity.com/html/180o_servo_stretcher.html

[BarryM]

Thanks for that but:-

The internal mods I am reluctant to try because of the fiddly soldering iron work and the Servo City ready built item I had also found but 3 x $14.95 plus P&P is a bit too pricey just yet. After all, looking at the unit, how complex is that bit of circuitry? I did find another almost identical looking  unit on sale - at $43!

I am surprised that nobody has come up with this as a home-brew in one of the mags but thanks again for trying anyway.

BarryM

[Faraday's Cage]

Barry,

Have you thought of going down the mechanical route with this one.

Replace the servo arm with a large cog which in turn could mesh with a slightly smaller cog to which you could attach your function.

Large cog turns with servo operation and secondary cog will travel further due to smaller size giving you more degrees of throw.

I did this with a small camera module to obtain 180 degrees travel.

Terry.

[BarryM]

Terry,

Yes, that's an alternative I have considered and one I might end up with.  I've used SHG for reduction boxes although their gears with grub screw locking are a bit bulky for this job. Muffet's may be a better bet although I'm open to info on alternative suppliers. Any ideas?

Barry M

[Faraday's Cage]

Barry,

Think that I got my gears from Hobby's. Came in pack of about 20 with 4 or 5 different sizes.


Terry.

[BarryM]

Terry,

Thanks for that. I've found that Maplins also do a range of MFA gears and I will have a look when I'm allowed to get down from this step ladder (decorating  ::)) Seems servo stretchers will have to be put on hold until someone produces them over here.

Cheers!  :)

PS. I've since been told that the Spanish instructions for the servo stretcher construction (see link above) also assume that you have the means to program the chip  :'(

[BarryM]

Well, I went the gearbox route and expanded the operating arc with the unfortunate side-effect of also doubling the speed of the output. To slow it all down I'm fitting a servo slow obtained from www.welwyn.demon.co.uk/sslow/sslow.htm                  It's all getting very complicated...  ::)

[ukengineman]

Probably too late to help now but this guy seems to provide just what you want, a module to stretch and optionally slow your servo movement.
http://www.kleefeld.freeserve.co.uk/model/barry/pic01/rc_servo.htm
Alan

[OMK]

I'm working on such a unit as we speak. Can be made from easy-to-get components and no need for chip programming.
In the meantime, a simple method to increase servo throw - albeit quick 'n' dirty - would be to replace the appropriate stick potentiometer inside the transmitter. Most R/C transmitter pots are rated at 5,000 Ohms, but doubling that value to 10K-ohms would increase the throws somewhat.

[OMK]

Addendum:

>>Can anybody help with http://www.estradamejido.com/L/servo.pdf.

Sure.
I've just had a look at this site and noticed that the chap has included the Hex code. I've got plenty of PIC chips, so if it's any help I can build and pre-program it for you.

[BarryM]

Thanks lads but I've already given up on increasing the resistance (see first post) and am about to test run the gearbox plus servo slower. The consolation for me is that my way works out a bit cheaper than the other solutions proposed. (Look after the bawbies..    ) However, I'll certainly file away the info for possible future use. Thanks again.

Barry M

PS The servo slower I chose has two outputs and thus can be used instead of a Y-lead to feed two servos. Included this info in case it's any use to others.

[HS93 (RIP)]

If you can speak Kermit.

http://bateaux-alain.chez-alice.fr/course180.html

Peter