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Can Servos Be Indexed for a Specific Arm?

Old 07-06-2011, 06:51 AM
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SeamusG
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Default Can Servos Be Indexed for a Specific Arm?

Just curious - if you have a servo arm that is not at 90 degress to the servo body can the servo gears be adjusted (or indexed)so that the arm is at 90 degrees?

Please, please - no replys like "why would anyone want to do this? Just use your radio's sub trim to make the necessary adjustment".

OK- you can cut-n-paste it if you want

Old 07-06-2011, 08:33 AM
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onewasp
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Default RE: Can Servos Be Indexed for a Specific Arm?

No but sub trim on your Tx will work . That is what it is for .

This assumes you have tried reversing the servo arm as many if not all splines are odd numbers so that
changing the servo arm mount either 90 degrees at a time (circular arm or four armed ) or 180 degrees at a time
(two armed servo arm) will alter the final orientation .

Yeah, it's hard not to inject humor .....................
Old 07-06-2011, 08:55 AM
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Default RE: Can Servos Be Indexed for a Specific Arm?


ORIGINAL: SeamusG

Just curious - if you have a servo arm that is not at 90 degress to the servo body can the servo gears be adjusted (or indexed) so that the arm is at 90 degrees?

Please, please - no replys like ''why would anyone want to do this? Just use your radio's sub trim to make the necessary adjustment''.

OK - you can cut-n-paste it if you want [img][/img]

Back in the 80's, we had servos that required the pots to be cleaned and centered, manually. Most modern servos have sealed pots, so you can't change the Neutral point that way. With Hitec Digital servos, you can use a Hitec programmer to reset the Neutral point.

Changing the Gear position won't do what you want.

A JR Matchbox will allow you to change the Neutral point.
Old 07-06-2011, 11:45 AM
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Default RE: Can Servos Be Indexed for a Specific Arm?

Thanks. I was just wondering. Some guys were stressing on getting a full 150% travel which is not possible if you use sub trim.
Old 07-06-2011, 06:37 PM
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Default RE: Can Servos Be Indexed for a Specific Arm?

If you use Futaba servos you can rotate the arm to the next arm and one of them will line up.
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Old 07-06-2011, 06:43 PM
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Default RE: Can Servos Be Indexed for a Specific Arm?

If you are willing to open the servo, you can disengage and adjust relative position of the gears to the position of the shaft that you would like, with no adverse consequences.

You will have more of a fine adjustment by playing with the gears that are closer to the motor of the servo, because one full turn of any of those is just a little fraction of a turn of the output shaft.

The servo is just a reversible motor, a train of gears and a feed back to inform the motor how far it has moved the gears (potentiometer actuated by the gears).
Old 07-06-2011, 09:04 PM
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Default RE: Can Servos Be Indexed for a Specific Arm?


ORIGINAL: Lnewqban If you are willing to open the servo, you can disengage and adjust relative position of the gears to the position of the shaft that you would like, with no adverse consequences. You will have more of a fine adjustment by playing with the gears that are closer to the motor of the servo, because one full turn of any of those is just a little fraction of a turn of the output shaft. The servo is just a reversible motor, a train of gears and a feed back to inform the motor how far it has moved the gears (potentiometer actuated by the gears).
Many servo do not have teeth all the way around on output gear and incorporate a keyway
to fit on to pot drive one way only.
Also to avoid jamming on mechanical stops on either side of most case tops, the plastic stops need
to be cut away to provide greater than usual rotation.
refer sub section
"Servo - Modify for Retracts, Swing, Number of Turns, Ganging, Reverse & Continuous Rotation"
at Alan's Hobby, Model & RC FAQ Web Links(quick search = Ctrl+F)

Alan T.



Old 07-07-2011, 08:20 AM
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Default RE: Can Servos Be Indexed for a Specific Arm?

Alan - thx for the link! 'preciate it.
Old 07-07-2011, 12:08 PM
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Default RE: Can Servos Be Indexed for a Specific Arm?


ORIGINAL: Lnewqban

If you are willing to open the servo, you can disengage and adjust relative position of the gears to the position of the shaft that you would like, with no adverse consequences.

You will have more of a fine adjustment by playing with the gears that are closer to the motor of the servo, because one full turn of any of those is just a little fraction of a turn of the output shaft.

The servo is just a reversible motor, a train of gears and a feed back to inform the motor how far it has moved the gears (potentiometer actuated by the gears).
How can the servo arm be adjusted by moving some gears if the servo arm has a direct connection to the potentiometer? And we all know that the potentiometer is what locates the servo around it's circular path?

The only way I see to "index" a servo arm as asked by the thread starter is by removing and rotating the arm to find a better arm that fits the splines on the output shaft, or using another arm althogether. Utimately you might have to use sub-trim which will reduce the amount of servo travel.

ORIGINAL: SeamusG
Thanks. I was just wondering. Some guys were stressing on getting a full 150% travel which is not possible if you use sub trim.
Why do you need 150% of servo travel anyway? What about using a longer arm?

If your answer includes the words "resolution", then you might have to look at your receivers and servos to make sure that the resolution that you are looking for is actually achievable with your system. Not all receivers and servos can reach the resolution of the newer types of transmitters. Other than that, how much more resolution do you think you are getting over 100% servo travel? And what about the translation between circular motion and linear motion? We could be here discussing for hours.......

Rafael
Old 07-07-2011, 12:21 PM
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Default RE: Can Servos Be Indexed for a Specific Arm?

100% travel, in the Tx, does not give you the full 60deg of servo arm movement, on either side of neutral.
Old 07-07-2011, 02:27 PM
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Default RE: Can Servos Be Indexed for a Specific Arm?

I was told by an Aero-Works tech that he wanted as much of the 150% pie as he could get. He's flying 3D on big planes. I might hazard a guess that at 150% the load will be spread over over more gear teeth than when using 100%. Just an uneducated guess mind you.

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