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Author Topic: Question on modifying HS 311 servo  (Read 6168 times)

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Offline airman00Topic starter

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Question on modifying HS 311 servo
« on: October 02, 2007, 07:20:46 PM »
Yes I have read admins tutorial and searched the forum....
I need to modify an HS-311 servo for continuous rotation( not for the 50 bucks robot,  :P).
I have found a few ways to do it and don't know which one to do.

In admins tutorial it says to leave the pot in the servo and glue it.

On this website it says to take out the pot and leave it on the outside http://www.ge.uiuc.edu/s-burns/HS311hack/


And on this website it says to remove the pot and replace it with two 2.2k resistors http://www.seattlerobotics.org/guide/servohack.html


Also, someone told me that you can just cut out the pot and leave all the wires disconnected. Just one cut across the wires going to the pot.


Which modification is the easiest to do and which one is the best to do? ( and which ones are really bad to do )
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Offline Ro-Bot-X

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Re: Question on modifying HS 311 servo
« Reply #1 on: October 03, 2007, 12:36:53 AM »
Parallax modified servos have a small adjustable pot instead of the original one, mounted verticaly, that is with the axle of adjusting horisontal and have a small whole on the side of the servo that allows you to adjust it with a scewdriver.
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Offline Steve Joblin

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Re: Question on modifying HS 311 servo
« Reply #2 on: October 03, 2007, 06:12:25 AM »
I would assume that the "best" method depends on how much "drift" will occur over time (that is, how much the pot may move it's position due to the robot moving, shaking, vibrating, and jolting due to crashes).

The idea of mounting the pot in an easy to reach place makes adjustments pretty easy.

I've also read about replacing the pot with resistors (though I have never tried it myself), and would think that this approach eliminates any "wandering".

I don't think the "cut out the pot" works since the servo circuit needs the resistance that the pot creates as a comparison.

I haven't seen any articles comparing the merits of each modification technique, but seems like it would make for interesting reading!!! Maybe I'll be a few servos one day, do some testing, and write an article for SOR!


Offline airman00Topic starter

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Re: Question on modifying HS 311 servo
« Reply #3 on: October 03, 2007, 06:17:48 AM »
I guess I'll do the resistor method , seems the easiest/ best
makes sense, since if you would turn the pot to a certain position it would have the same resistance all the time, so also if you remove th epot and replace it with rsistors, the resistance will be the same all the time.
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Offline Rebelgium

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Re: Question on modifying HS 311 servo
« Reply #4 on: October 03, 2007, 09:43:34 AM »
If you leave the pot in and glue it , you'll have to make sure it's not mechanically connected to the motors any more. - good solution

If you leave the pot hanging out of the side you'll have some "drift" over time due to bumps, and it will entangle in other wires etc. - This is just a low qualtiy solution.

Solder out the pot and replace it by two identical R's - good solution

Leave the wires hanging unconnected. - not true, won't work.

Quote
I haven't seen any articles comparing the merits of each modification technique, but seems like it would make for interesting reading!!! Maybe I'll be a few servos one day, do some testing, and write an article for SOR!
It's way to simple to write an article about  :D ;)
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Offline Ro-Bot-X

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Re: Question on modifying HS 311 servo
« Reply #5 on: October 03, 2007, 10:53:10 AM »
I did the couple resistors mod on a pair of Futaba 3004 servos and one of them had a little backward movement when a 1.5 ms signal was on. So I had to tweak the signal and found that it would stand still at 1.55 ms.
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Offline airman00Topic starter

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Re: Question on modifying HS 311 servo
« Reply #6 on: October 03, 2007, 11:38:10 AM »
Yea I'm guessing that I'll use the HS-425BB because you only need to remove a plastic clip from the pot and remove the stop tab.

Also, ill probably use an LCD to display the pwm to the servos and ill use a button to make the pwm go higher , once I see that it stopped I just check the LCD for the pulse.
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Offline Steve Joblin

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Re: Question on modifying HS 311 servo
« Reply #7 on: October 03, 2007, 11:51:19 AM »
Yep... I guess that is the difference... do you want to modify your programming code to "center the servo", or do you want to make a mechanical modification to "center the servo"...

I did the couple resistors mod on a pair of Futaba 3004 servos and one of them had a little backward movement when a 1.5 ms signal was on. So I had to tweak the signal and found that it would stand still at 1.55 ms.

Offline Admin

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Re: Question on modifying HS 311 servo
« Reply #8 on: October 08, 2007, 11:04:05 AM »
I subscribe to the glue the pot method ;D

All the robots Ive made use this method - its the quickest and easiest method.

 


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