Author Topic: Servo mod for continuous rotation  (Read 3121 times)

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Offline Adityav95Topic starter

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Servo mod for continuous rotation
« on: December 26, 2010, 10:17:44 PM »
I have posted pics on the HS-425BB servo that i planning to modify for continuous rotation.

I guess in this servo all that is required is to remove the physical stop and then glue the pot head.

Q: I'm fine with removing the physical stop but i have a problem with gluing the pot head. How do u center the servo/pot head? according to this post( http://www.societyofrobots.com/robotforum/index.php?topic=4921.0 ), what i understood was that "centering a servo" did not mean the average of the rotating angles on both sides. Could someone pls tell me how to "center" the servo? ???

After the servo is centered, all that is left is gluing the pot head. Is that right? ???

Thnx  :)

Offline VegaObscura

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Re: Servo mod for continuous rotation
« Reply #1 on: December 26, 2010, 11:15:52 PM »
Well you don't just have to glue it, you also have to cut it off.

Offline Adityav95Topic starter

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Re: Servo mod for continuous rotation
« Reply #2 on: December 27, 2010, 12:20:24 AM »
@vegaObscura: U mean cut off the pothead or cut of the physical stopper? I thought the pot head must be glued and the physical stopper must be cut off. ???

Offline Conscripted

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Re: Servo mod for continuous rotation
« Reply #3 on: December 27, 2010, 12:32:00 AM »
To center the potentiometer you need to send a signal to tell the servo to go to the center position. While the servo is being commanded to the center position you adjust the potentiometer until the motor stops moving. That is the center position. Glue it in place. Make sure you don't move it while applying the glue.

Remove the physical stop, reassemble and you are finished.

Conscripted

Offline VegaObscura

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Re: Servo mod for continuous rotation
« Reply #4 on: December 27, 2010, 12:39:52 AM »
I'm not sure about this particular model of servo, but I do know with the Hitec HS-311 servos I've used you have to cut off the pot head and glue the 'stub' into place so it doesn't move.  But I recommend you listen to conscripted and not me.

Offline Adityav95Topic starter

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Re: Servo mod for continuous rotation
« Reply #5 on: December 27, 2010, 12:50:56 AM »
@Conscripted: K after sending the signal to center, what do u mean adjust the potentiometer? do u mean twist it left and right?  ??? If that is the case, then i guess, when u twist the pot, at a particular angle the servo will stop moving. Is that correct? Well I'm totally confused.

@VegaObscura: Yeah, people told me the HS-425BB was the easiest servo to modify, that's why i got it. I remember to have seen somewhere that the HS-311 is rated 3/10 for difficulty but the HS-425BB is rated just 1/10.

Thnx for ur help guys.

Offline Conscripted

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Re: Servo mod for continuous rotation
« Reply #6 on: December 27, 2010, 08:46:00 AM »
@Conscripted: K after sending the signal to center, what do u mean adjust the potentiometer? do u mean twist it left and right?  ??? If that is the case, then i guess, when u twist the pot, at a particular angle the servo will stop moving. Is that correct? Well I'm totally confused.

That is it exactly.

Offline Adityav95Topic starter

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Re: Servo mod for continuous rotation
« Reply #7 on: December 27, 2010, 10:32:28 AM »
thank u so much Conscripted and VegaObscura for ur help!  :)

@ conscripted: Then, in that case can i just command the servo to keep sweeping left & right? Instead of commanding it to center as in that case i would have more time to adjust the pot.....so when the servo keeps sweeping, i'll just rotate the pot to get it rotating continuously.
« Last Edit: December 27, 2010, 10:54:56 AM by Adityav95 »

Offline Conscripted

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Re: Servo mod for continuous rotation
« Reply #8 on: December 27, 2010, 03:15:30 PM »
@ conscripted: Then, in that case can i just command the servo to keep sweeping left & right? Instead of commanding it to center as in that case i would have more time to adjust the pot.....so when the servo keeps sweeping, i'll just rotate the pot to get it rotating continuously.

I'm not sure what you would accomplish by continually sweeping the servo left and right. It does that during normal operation. I think if you understood how a servo works a little it might clear up some of your confusion.

A servo is a gear motor with some built in control electronics. The control electronics are what allows the servo to go to 20 degrees when commanded and stop. The same control electronics will allow it to go to 50 or 70 or 90 or -90 degrees. It can do this because it gets feedback from the potentiometer. The pot is connected to the gears on the servo horn. When the servo horn moves so does the pot. In order to allow a servo to turn 360 degrees you must remove the mechanical stop. You also must "trick" the control electronics. You do this by telling the servo to go to the center position and then adjust the pot till the motor stops moving.

The servo will always think it is in the center position. If you tell it to got to 45 degrees it will keep turning until the pot says "HEY DUMMY YOU ARE AT 45". Because we glued the pot in the center that will never happen and the servo will continue to spin. The same thing happens if we tell it to go to -45 (but it will spin the other way).

Conscripted
« Last Edit: December 28, 2010, 06:05:16 AM by Conscripted »

Offline Adityav95Topic starter

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Re: Servo mod for continuous rotation
« Reply #9 on: December 27, 2010, 10:20:26 PM »
oh! now i get it. I never knew all this, thank u so much for the description. Helped a lot!  :)

 


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