servo: radial to linear motion???  
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All Forums >> Radios, Batteries, Clubhouse and more >> RC Radios, Transmitters, Receivers, Servos, gyros >> servo: radial to linear motion???
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servo: radial to linear motion??? - 7/22/2008 11:15:59 PM   
Capt Jim


 

Posts: 1111
Joined: 4/14/2002
From: Boca Raton, FL, USA
Status: online 		I have an application that could benefit from a more linear push rod actuation. Is there any clever way to reduce the typical arc produced by a standard servo arm?
I do not need a lot of torque or speed but I do need a full inch of push rod movement.
Thank.


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RE: servo: radial to linear motion??? - 7/23/2008 12:35:36 AM   
fizzwater2


 

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From: Paola, KS, USA
Status: offline 		Use a really long arm, and reduce the amount of radial throw with your transmitter - less radial action would give you a more linear response.

Many years back you could get servos with both a rotary output, and two "rack" outputs in the same servo. There was an internal gear that drove the racks, sort of a rack and pinion design. You might rig up something like that external to a servo.



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RE: servo: radial to linear motion??? - 7/23/2008 12:41:01 AM   
TLH101



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Status: offline 		http://www.e-clec-tech.com/lisekits.html
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCJG6
If that don't work, try laying the servo on it's side. That's what I do when I need a linear motion (like 1 servo to actuate a very short Y shaped push rod).

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RE: servo: radial to linear motion??? - 7/23/2008 1:21:54 AM   
Campgems


 

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quote:

ORIGINAL: TLH101

http://www.e-clec-tech.com/lisekits.html
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCJG6
If that don't work, try laying the servo on it's side. That's what I do when I need a linear motion (like 1 servo to actuate a very short Y shaped push rod).


I've got to keep these in mind. They don't look like they will work for Capt Jim though as they only have 3/4" travel vs the 1" he needs.

Capt, you could use a long servo arm, and then use expo to flaten out the movement in relation to the stick. I don't know if it would work for you or not. The only other thing would be to find a rack and gear and mount the gear on a servo wheel. You would have to build a trough for the rack though.

Another answer is to use one of the linear actuators for Robotics. The Cal Poly Aerospace guys were out to the field last month with a big parasail and a cage below with a DA50 engine. The thing was radio controled The pull handles for control was handled by a couple linear actuators having about 4 to 6" of stroke. They amplified it what a long arm so the actual pull was 12" or more

Unfortunatly, the first flight wasn't the best. I don't know where they got the acuators, and the college is in summer mode now.

Don

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RE: servo: radial to linear motion??? - 7/23/2008 2:28:24 AM   
sfsjkid



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Status: offline 		Servo City has actuators that look similar to the Cal Poly ones.

http://www.servocity.com/html/servo_actuators.html

Also, back in the days when mixing was not available, one option to set up a y-tail was to put one servo (rudder) on a sliding tray and have another servo (elevator) actually move that tray. You wouldn't need the second servo, and it would require some space, but you'd probably would be able to get your inch movement by adjusting the lenght of the actuating servo arm.

Good luck!

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RE: servo: radial to linear motion??? - 7/23/2008 3:12:45 PM   
BarracudaHockey



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Status: offline 		Hehe yea, I had a glider with the sliding servo arrangement.

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RE: servo: radial to linear motion??? - 7/23/2008 3:40:05 PM   
sfsjkid



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quote:

ORIGINAL: BarracudaHockey

Hehe yea, I had a glider with the sliding servo arrangement.


Watch out that is a sure sign of how long one has been in the hobby and age .

I had another thought, in this case where only one servo is needed, one could set up the servo to move itself on the servo tray.

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RE: servo: radial to linear motion??? - 7/23/2008 3:50:23 PM   
Capt Jim


 

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From: Boca Raton, FL, USA
Status: online 		I really like those linear conversion kits. That would do the trick...I would just have to modify things to get happy with only 3/4" motion.
Until I get a couple of those little gismos in the mail, I may just have to lengthen the pushrod so that the radial excursion is no longer an issue.
Back to the bench...
Thanx everyone.
jim
Just to make things a little more clear....or maybe not. The application is for a (2 stage) multiple release mechanism. Banner tow/drop, parachute drop, etc etc.
The push rod that causes the release must operate within a small...3/8" diameter tube. When the servo is mounted close to the mouth of the tube, the radial motion of the servo arm causes the push rod to rub the inside wall of the tube. By moving the servo away significantly, the angle created by the radial motion is reduced at the mouth of the tube. It makes the installation less compact, but still workable.

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RE: servo: radial to linear motion??? - 7/23/2008 8:24:10 PM   
Dsegal


 

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quote:

ORIGINAL: TLH101


If that don't work, try laying the servo on it's side. That's what I do when I need a linear motion (like 1 servo to actuate a very short Y shaped push rod).


That doesn't make a lot of sense to me- no matter what the attitude of the servo the motion of the output arm will still be rotary and not linear.


< Message edited by Dsegal -- 7/23/2008 10:17:38 PM >

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RE: servo: radial to linear motion??? - 7/24/2008 12:22:18 PM   
Hibrass



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Status: offline 		Dave,

It does indeed if you think of it in this way... With the Y rod in the horizontal plane and the Server Vertical there will be deflection left and right on the Horzontal plane as the servo rotates and moves the Y rod back and forth... If the Y rod was connected to say a pair of Elevators you would see a change in deflection on one half compared to the other depending on what point the servo is at during its travel..

Now if the same setup as above is used but the servo is now horizontal i.e. on its side, the left to right deflection will be change to up and down deflection. since the Y rod is still the Horizontal plane the up and down deflection will have no impact on the Elevator halves deflection...

I'm using the very same setup in a 27% Midwest Cap 232 and it works great and I only need one really big servo... LOL In this case a S9152..

I hope this long winded explantion helps..

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RE: servo: radial to linear motion??? - 7/24/2008 1:29:20 PM   
TLH101



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quote:

ORIGINAL: Hibrass

Dave,

It does indeed if you think of it in this way... With the Y rod in the horizontal plane and the Server Vertical there will be deflection left and right on the Horzontal plane as the servo rotates and moves the Y rod back and forth... If the Y rod was connected to say a pair of Elevators you would see a change in deflection on one half compared to the other depending on what point the servo is at during its travel..

Now if the same setup as above is used but the servo is now horizontal i.e. on its side, the left to right deflection will be change to up and down deflection. since the Y rod is still the Horizontal plane the up and down deflection will have no impact on the Elevator halves deflection...

I'm using the very same setup in a 27% Midwest Cap 232 and it works great and I only need one really big servo... LOL In this case a S9152..

I hope this long winded explantion helps..


Exactly. I learned this many years ago, when trying to set up the flaps on a GP Cherokee. The flap push rod "yoke" was very short. When I would hook up the flaps with the servo up right, the deflection from servo wheel rotation made the flaps uneven. After turning the servo on it's side the, the deflection was in the vertical plane and the flaps were more synchronized.

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RE: servo: radial to linear motion??? - 7/24/2008 2:48:08 PM   
GBR2


 

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From: Snohomish, WA, USA
Status: offline 		While I can see that putting the servo on its side would not make the rod move from side to side any longer, the movement of the rod is still non-liner in its travel.

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RE: servo: radial to linear motion??? - 7/24/2008 3:09:07 PM   
Silent-AV8R



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From: SOCAL, CA, USA
Status: offline 		Laying the servo on it's side will still result in non-linear motion. The pushrod will move up and down instead of side to side. And the throw will still be non-linear.

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RE: servo: radial to linear motion??? - 7/24/2008 3:22:16 PM   
TLH101



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Status: offline 		OK............

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