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Author Topic: Servo modification problem HELPPPPPP MEEEEEEEE  (Read 2730 times)

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Offline cyclopediatechtilonTopic starter

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Servo modification problem HELPPPPPP MEEEEEEEE
« on: January 11, 2009, 06:56:12 AM »
I have a problem with modifying my servo motors
I took 2 3k3 resistors and chopped off the potentiometer instead of desoldering it
then i soldered the two resistors with the right arrangement on the remaining sticks of the potentiometer jutting out
but when i test the values of the resistors with multimeter the sum of both shows 1.6 readng whereas it should show 6.6
with one side and the centre it shows readings between 2.5 and 3.5
Whats wrong PLSSSSSSSSS HELPPPPPPPPPPPPP
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Offline cosminprund

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #1 on: January 11, 2009, 07:55:09 AM »
Your 3k3's are somehow in parallel: 3k3's in parallel would give 1k6. Check the sides, they're somehow communicating.

Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #2 on: January 11, 2009, 09:59:09 AM »
ok thks
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Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #3 on: January 12, 2009, 09:56:55 AM »
no sides are not communicating i tested with the "BEEP" test in the multimiter
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Offline cosminprund

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #4 on: January 12, 2009, 10:21:35 AM »
Take two more 3k3 resistors, wire them up serially and measure with the multimeter: you'll get 6k6
Now put the same two resistors in parallel: you'll get 1k6. I can't imagine how you might have linked them up but you only get 1k6 from two 3k3 resistors if you link them up in parallel.

Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #5 on: January 13, 2009, 09:56:44 AM »
yes but then i think there is some resistance in the circuit of the servo
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Offline frodo

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #6 on: January 13, 2009, 09:59:30 AM »
but you want resistance in the circuit, thats why you are adding 3.3K resistors isn't it?
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Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #7 on: January 15, 2009, 06:45:47 AM »
Alllllll IDEAS ARE WELCOME
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Offline D1g1talDragon

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #8 on: January 17, 2009, 01:10:15 PM »
Take a look at my post here: http://www.societyofrobots.com/robotforum/index.php?topic=6363.msg48034#msg48034

I was trying the same method in HS-311 servos the other day, and decided it was just too touchy about resistor values and such.  So I replaced the resistors with a small screw terminal 25 turn potentiometer.  The part number is in my post above if you'd like to order a few from DigiKey.

The end result was very, very pleasing.  I took advice from Ro-Bot-X and drilled out a small hole through the side of the servo casing to stick the pot screw through, and now I can adjust to any and all voltage sources to almost perfectly zero on the fly while mounted to my bot.  Using a 25 turn makes the calibration much less sensitive, so it's easier to tweak compared to the touchy stock pot, and you don't have to worry about drilling out your gearing, just have to cut off the plastic stop.  I'm ordering more for all of my future servo mods, hope this helps you as well.

-Jeff-

Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #9 on: January 23, 2009, 09:28:22 AM »
but i have desoldered and broken my pot.
It cant be a problem with my servo cause i did it with my other servo too and the
results came same
so with my resistors the servo pot moves a little forward even though it is not
supposed to because the signal i gave was the center servo hex file
PLLLLLLS HELP
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Offline frodo

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #10 on: January 23, 2009, 12:01:33 PM »
maybe the moving of the servo a bit is it centering? just a thought
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Offline cosminprund

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #11 on: January 23, 2009, 02:08:50 PM »
Put some pictures with your soldering here.

I've done two servos, first with your technique (replace the servo pot with two resistors) and then I replaced the two resistors with an 25 turn potentiometer, as advised by D1g1talDragon and following Ro-Bot-X's suggestion of drilling a hole in the servo so the pot screw is accessible from outside. In both cases I got the expected resistance when measuring across the connections. I suspect there's a problem with your circuit, other ways I can't imagine how you got the values you measured.

Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #12 on: January 25, 2009, 11:35:43 AM »
Frodo, i modded the servo so it is not centering
cospirund, do you mean that the shop is faulty?? :-\ no offence
Then hows it a problem with my servos circuit?
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Offline cosminprund

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #13 on: January 25, 2009, 11:52:00 AM »
cospirund, do you mean that the shop is faulty?? :-\ no offence
Then hows it a problem with my servos circuit?

What shop ??? I don't expect any problems with the servo circuit, I expect problems with your modifications to the servo circuit. If there are no problem with your modifications to the circuit and there are no problems with the circuit itself then it's working - but I guess it's not, since you're still asking questions... Putting some pictures on the forum might help the smart people over here figure out what's wrong. Really, you're not offering enough information for anyone to help you out. You didn't specify your servo model (you should have placed that in the subject line as it's very important and would have sparked the interest of anyone else that has modified the same servo).

This is all you sad about your problem:
Quote
I have a problem with modifying my servo motors
I took 2 3k3 resistors and chopped off the potentiometer instead of desoldering it
then i soldered the two resistors with the right arrangement on the remaining sticks of the potentiometer jutting out
but when i test the values of the resistors with multimeter the sum of both shows 1.6 readng whereas it should show 6.6

And then you added:
Quote
but i have desoldered and broken my pot.

Hope this helps and hope you'll fix your problem.

Offline HDL_CinC_Dragon

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #14 on: January 25, 2009, 12:27:40 PM »
Cyclo the one and only existent explanation for those results are in fact that the resistors are somehow in parallel. There HAS to be some way that they are in parallel with each other. Desolder them and desolder the contacts you snipped off(dont do that...) from the pot so you have fresh through holes. Then solder the resistors in again being EXTRA careful. Use only enough solder to fill the holes and hold the resistors.

I use .032" diameter 60/40 solder because I can very easily and accurately control how much solder im applying to the joint since .032" is extremely small. I got a pound of it from AllElectronics.com :)
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Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #15 on: January 25, 2009, 11:40:58 PM »
Conspirund, about the circuit
I did not modify it
Just sniped off the potentiometer and left three sticks of it,
then soldered the resistors
I dont know how to post pics here
and the model of the servo is not known by anyone because it is some indian model
called VS-2
I bought those servos cause they are very similar to hitec hs-311s
anyways thanks for helping me out ;D

and dragon,
i could not desolder the potentiometer because it was very tough,
so i thought about this idea
anyways, ill try to desolder it or will get help
sounds good
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Offline cosminprund

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #16 on: January 26, 2009, 01:47:56 AM »
Conspirund, about the circuit
I did not modify it. Just sniped off the potentiometer and left three sticks of it, then soldered the resistors

Did you measure the resistons from the previous pot before desoldering/cutting it? Was it the usual 5k pot? Did you identify the "middle pin" of the pot? On my servo it was simple, the middle pin was soldered to the board in the middle - but I don't think that's a requirement.

I don't know how to post pics here

Do you have a camera (or can you borrow a camera)? Once you have the JPG on your computer you simply attach it to the forum post, just as you'd attach any other file.

and the model of the servo is not known by anyone because it is some Indian model called VS-2

I'm pretty sure you're not the only Indian one around here.

Offline cyclopediatechtilonTopic starter

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Re: Servo modification problem HELPPPPPP MEEEEEEEE
« Reply #17 on: January 30, 2009, 09:25:02 AM »
Well it was the usual 5k pot and i measured the resistors

The servo is just a random one which is available in an electronics store

I will be posting pics soon
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