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HelicopterRadio - Servo - Gyro - Gov - Batt › A better servo idea?
12-11-2004 07:33 AM  13 years agoPost 1
www.stef.comrrNovice - Alameda, CA USA - My Posts: All  Forum  Topic

Hello all, what do you think about this for a linear servo design for just about all RC applications, but especially heli CCPM etc... I drew the diagram to just illustrate the basic concept, so disregard porportions. Any thoughts -stef


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12-11-2004 09:47 AM  13 years agoPost 2
Colibri

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It looks interesting. There are a few problems to be solve like preventing torque on the ball ends otherwise the might just pop off and the size of it may be a concern too.

I saw this last week:

This used on a Futaba S-148 servo. But the idea is compatible with all servos.

It can be bought here: E-Clec-Tech

Tim

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12-11-2004 11:36 AM  13 years agoPost 3
Crusty

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N51 degrees 29.823 minutes W3 degrees 16.133 minut

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looks good, But you want to look at a more secure attachment of the non moving end as there is an obvious torque componant on that end..I dont think a ball link would be sufficiant
good idea if you can make it smaller/ work better than a simple rack and pinion

...Crusty

I am dsylexia of borg..resistance is fruity...your arse will be laminated

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12-11-2004 01:01 PM  13 years agoPost 4
Al Magaloff

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I think a usable linear servo, will be our next "greatest thing since sliced bread." addition to this sport.

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12-11-2004 02:33 PM  13 years agoPost 5
rstacy

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Rochester, NY

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Stef,
The servo that you drew already exists today.
As I recall they were $600 a piece.

I purchased the conversion that TVhalter mentions.
It works but the drag is tremendous and it still isn't linear in true sense of linear movement.
All this does is put a lever on the same rotary output.

I agree that a true linear servo is just over the horizon.
I also predict that Mike Mas will take full credit for it because he asked for a linear servo in RM a while back.

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12-11-2004 04:32 PM  13 years agoPost 6
www.stef.com

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Thanks for the thoughts everybody, great feedback -stef

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12-11-2004 06:02 PM  13 years agoPost 7
Al Magaloff

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Ray, I remember those servos. As I recall, they were about 1"x2"x4" in dimension, or something huge like that.

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12-11-2004 09:03 PM  13 years agoPost 8
rstacy

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As I recall, they were about 1"x2"x4" in dimension, or something huge like that.
They were and I cant remember where I saw them but they are out there and most likely will lead the way to a better, more affordable servo for hobby.

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12-12-2004 04:49 AM  13 years agoPost 9
rstacy

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It's the right idea.
Just needs to be scaled

CLD Motor Specs in Brief:

Brushless direct drive technology

1180 Lb. Peak Force

180 In/Sec

40G Acceleration

Strokes up to 20 inches

CLD Features:

Single moving part – integral bearings

Compact size (about the size of a blender)

Brushless direct drive technology

Unmatched Programmability

UL Recognized

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12-12-2004 06:07 AM  13 years agoPost 10
docloc

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What would stop the shaft from being pulled out under load? Say like a pitch servo, loaded it would pull it or push depending on positive or negative pitch. I think the current needed to hold it would be huge.

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12-12-2004 08:01 AM  13 years agoPost 11
Al Magaloff

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Yeah! For those "can't get enough" guys, three of these babies on your eCCPM machine should do it.

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12-12-2004 09:29 AM  13 years agoPost 12
www.stef.com

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Alameda, CA USA

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No current would be required to hold the servo position. The arm shaft is threaded, as well as the inside of the motor armature, giving a mechanical advantage in the push/pull direction.

Torque would definitely be an issue. I didn't think about that. What about splitting the rotor in two so you have two counter rotating armatures? -stef

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12-12-2004 02:47 PM  13 years agoPost 13
Crusty

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Not to be too pessimistic but This whole "I need a linear servo for linear output is barking up the wrong tree, the swash output describes an arc as does he washout levers, as do the balls on yer grips...linearity in a helicopter control system is a pipe-dream

I am dsylexia of borg..resistance is fruity...your arse will be laminated

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12-12-2004 03:14 PM  13 years agoPost 14
Colibri

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While its true that you can solve every non linearity in a helicopter it would solve some if the eCCPM interaction problems.

@rstacy
QUOTE]and it still isn't linear in true sense of linear movement.[/QUOTE]

Why isn't it truly linear? For every degree of turn on the servo shaft there is an equal linear movement of the slider or am I missing something?

Tim

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12-12-2004 03:29 PM  13 years agoPost 15
Al Magaloff

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TV, it's the same as with a servo arm installed. When you are at 90 degrees to the servo body, the amount of movement is quickest, and as you go away from center on either side, the movement slows down.

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12-12-2004 06:06 PM  13 years agoPost 16
www.stef.com

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Alameda, CA USA

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Aside from the torque issue with the above design, I really like the idea of snapping the servo on, or having a floating servo. I think it would really simplify the setup process to not have to worry about where the servo's throw is at neutral, (as the throw is linear) and to just mount one ball to the frame of the helicopter, and your basically done. What do you all think about this aspect? -stef

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12-12-2004 06:16 PM  13 years agoPost 17
Al Magaloff

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Stef, there's a lot of load put on the mounting though.

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12-12-2004 09:42 PM  13 years agoPost 18
Colibri

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TV, it's the same as with a servo arm installed. When you are at 90 degrees to the servo body, the amount of movement is quickest, and as you go away from center on either side, the movement slows down.
Check the image:

With this 'band' wrapping around the wheel it is always like the connection is made at 90 degrees to the horn.

With a standard horn/ball connection the problems is that for a given number of degrees movement the ball moves in both X and Y direction. In this case the effect you describe happens. But with this wrapping 'band' the direction is always 90 degrees to the servo wheel and always moving with the same proportion to the angular movement of the wheel.

For example let's assume the connection point (where you can mount the ball) moves 1cm for the first 90 degrees of the servo wheel. From looking at the picture you can easily see that it will also move 1cm for the second 90 degrees. It is pure linear.

Tim

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12-13-2004 04:59 PM  13 years agoPost 19
gigi

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Port-au-Prince, Haiti

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Old Multiplex or Graupner servos...

Way back in the eighties, A friend of mine had a german radio set, and the servos had two arms side-by-side, which traveled length-wise in opposite directions. It was like a regular servo, but the rotary output drive a pinion, and was located in the center of the servo. This pinion in turn drove the two racks, one on each side.

Benefits were in-line actuation, compactness, and for ailerons installations in trainers, you just ran one push-rod to each aileron.

I seem to recall they were neither very fast nor very powerful. But I think that would be the way to go with the idea of a linear actuator. The original poster's idea is excellent, but is far more complex, and will be more expensive by an order of magnitude.

Of course, who would've thought people would pay $20 to send a package overnight when the post office would do it for $2, and take a couple of days longer... So maybe for a select few, his idea is the better one.

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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12-13-2004 09:06 PM  13 years agoPost 20
Colibri

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You mean these:

Apparently these are as old as the road to Rome. I wonder why we don't see them a lot more today.

Tim

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HelicopterRadio - Servo - Gyro - Gov - Batt › A better servo idea?
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