New to servos

I'm new to using servos and have a couple questions:
How do you usually connect the servo to the object you want to move?
I want to use a 555 circuit to move a servo to an angle and keep it there. I've never done any circuitry either and am looking for some instructions or tips...
Thanks
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snipped-for-privacy@gmail.com wrote:

I'm not sure you can easily control a servo with a 555 timer.
ttyl, --buddy
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Buddy Smith wrote:

I think the OP is talking about a RC (radio control) servo.
Too bad the OP failed to mentioned that.
google found this:
http://www.tkk.fi/Misc/Electronics/circuits/servo10v.html
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Yes, I meant a RC servo, sorry.
Thanks for the link. Do you connect these together and put them in a box or connect them to some sort of board?
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snipped-for-privacy@gmail.com wrote:

Ok, What is it your trying to do ??
( connect what together ?? )
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I'm trying to do what is in that link you gave me. In the big picture, I'm trying to control a servo so it will rotate a touch screen out of the dash of my car; up to viewing angle. So, I will want to have it run either when I give power to it or switch it on and then stop at the specified angle and then again go back down when it is switched off or cut power.
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snipped-for-privacy@gmail.com wrote:

So, do you know how to build electronic circuits ? (Solder wire and chips)
Do you think your RC servo will move the LCD display ?
An RC servo has about 270 degree movement, will that move the LCD to where you want it ??
This sounds like more then your initial request.
Have you built the hardware that holds the LCD display yet ?
Do you have any pictures ?
donald
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No, I don't know how to build circuits - I guess that is really what I want to understand. I understand the concept behind using the 555 ic with the servo, just not sure how to build the entire thing.
I'm pretty sure my servo will move the LCD - it's a small touch screen that weighs just over 1 lb.
I really only need the servo to move the LCD setup about 90 degrees, which should not be a problem with this servo (it moves about 180 degrees).
I just got the basis of the hardware done for the screen today. I still have to clean it up and put padding in it and such (it's made of aluminum and thus both light weight and has sharp edge, etc.). I made the pivot point out of a hollow aluminum rod which brings me to my other question right now: how will I go about attaching the servo to the end of the rod to turn it? But, that was not intended to be answered here, but would be very helpful.
Thanks for your help.
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snipped-for-privacy@gmail.com wrote:

You need a strong servo for this, unless your touch screen is very small and light. Most weigh at least 9-10 ounces, and several weigh a pound or more.
The GWS S06 servos come with a version that offers some 110 oz-in of torque. That might be a minimum for you, as long as the servo is merely rotating the display about its center, and not actually lifting it.
You can spend a lot of money on servos, and the stronger ones are bulky. Have you considered not doing it the "Star Trek" way (which is cool, I admit), and use dashpots instead? You can get surplus dashpots for maybe $5 each. With springs from the hardware store they'll provide a smooth gliding action of opening the LCD into view. You then push it back manually into a locked position.
-- Gordon
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I've looked into using an actuator already and found that the servo would be the best way to do it because of the size. Something much bigger would not fit into the space I have available. I'll be the first to admit if this doesn't work I'll back up toward something less active, something more like you suggested using a spring and a latch or something similar.
The servo I have is rated close to that 110 oz-in, so it might do the job...
Thanks
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Gordon McComb wrote:

To throw some math at the problem, if the screen weighs one pound and measures eight inches from the rotation axis, the servo will initially have to lift the full weight of the screen at the center of gravity, or 4 inches * 16 ounces = 64 oz-in minimum torque. A plain-vanilla hobby servo is about 50 oz-in, so he'll need to look at larger ones that offer more torque.

I don't think he's rotating around the center. But the 110 oz-in servo could do the trick, if the screen isn't heavier than we're guessing.

Some of the standard (non-digital) servos, in the 1/4 scale range, are actually pretty cheap for 100+ oz-in. I'm of course looking at http://www.servocity.com which has pretty much everything a servo user could want. Including shaft adapters, to address his earlier question about mounting the servo to a pivot tube.
One more consideration: this is a touchscreen, and when the screen is being poked the servo will be fighting back. Also, the same thing will be happening during acceleration and deceleration. One too-hard of a jab or braking and the servo gears could be stripped out. Using a servo of course means that to keep the screen upright, the servo would need to be powered at all times. Otherwise the touchscreen will flop over the first time it's poked.
I like the dashpot idea, actually. Might provide a little bit of shock protection.
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Using math, it looks like I will need more torque if my setup stays the same:
24 oz * 5.5 in. from pivot point to top of touch screen = 132 oz-in.
As for the stability of the servo, I think it will do the job beacause I'm planning on keeping it powered, and if I get one that has metal gears it should be fine, correct?
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snipped-for-privacy@gmail.com wrote:

For servos, there's no real guarantee on longevity. They are designed for high performance over short durations, maybe a 20 minute flight. I don't have numbers on hand but I had thought they were usually under 50 hours expected usage. The gears aren't the only factor, other wear parts include the potentiometer and the motor itself, which is usually driven as hard as possible.
Please also realize that the servo is going to try to snap your screen to the vertical position in about a quarter second. Unless you have some kind of programmed proportional sweep of the servo input, you are going to risk breaking the LCD or even launching it who-knows-where.
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On 19 Jan 2006 09:54:29 -0800, snipped-for-privacy@gmail.com wrote:

If you are just looking for open/close action, you could use the geared motor from a $8 6v B&D cordless screwdriver from walmart, and a motor reversing circuit. Some simple diagrams for circuits at the bottom of the below page. Use limit switches to stop the action on each end of movement.
http://www.geocities.com/zoomkat/switch.htm
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snipped-for-privacy@gmail.com wrote:

When you do the mechanical design on this, it would be a good idea to design it so that the screen rests on something in both the open and closed positions. If the servo is supporting it in either position in a moving car, you will probably see double the forces you calculate for a stationary system due to bumps and vehicle dynamics. The vibration will also beat things up over time.
Good Luck, Bob
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Well, this seems to be turning into something more iffy and more complicated than I expected. At this point I kind of just want to scrap it and go with something I can just manually open. Maybe the auto open idea is more of a pipe dream.
Thanks for all your comments, I'll have to think about it.
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Hey,
The electronics isn't too hard -- except that you appear to be a novice. One thing to think about: if you turn the power off, how will the servo close? You really need to have the logic control the power so that you can keep the power on long enough to move the servo and then turn itself off. Also as somebody pointed out you have to ramp the servo so that you don't try to move the screen too fast. Not hard to do if you do it in software.
The real battle is the mechanical side. Even something like mounting the screen to the servo will be difficult. Most RC servos I've seen just have a nylon horn with small teeth on the *inside* diameter. Not exactly a strong mechanical connection. Plus as others have mentioned you'll want some sort of locking mechanism. I've seen screens that do what you're trying to do, and although I didn't look inside, I would suspect that they use geared DC motors with limit switches. (Look inside a CD-ROM tray and see how that works, same exact thing.) Those motors are much stronger (think a cordless drill) and more reliable, and you can control the velocity by changing the gearing appropriately.
If you think you can handle the mechanics, the electronics is something you could get a friend (or maybe even someone here) to help you make.
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snipped-for-privacy@gmail.com wrote:

Do a Google search for "servo tester" and "servo 555" (both without quotes) There are many examples of building a 555-based tester for R/C servos. I remember seeing some that were pretty basic, including explanations on how to assemble the board. These testers are simple enough that you can create them on a basic solder board that you can buy at Radio Shack.
The first hit I got doing a search for "servo 555" is this one:
http://wolfstone.halloweenhost.com/TechBase/svoint_RCServos.html
Seems to have a lot of what you're looking for.
-- Gordon
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snipped-for-privacy@gmail.com wrote:

Don't know about a 555, but these guys sell chips to control RC servos from a computer. http://www.ferrettronics.com / They've been bought out, but the new guys still sell the old stuff
--
Pat



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Seems to me a worm gear setup with limit switches would be the desirable situation. Worm gears, if properly lubed, last a long time and resist external forces once they are turned off. A simple double relay circuit can be wired to handle the logic with a push of a button and cause the motor to retract by pushing the same button again. A power mirror motor gotten from a junk yard would probably do the trick. If not that - go for a power antenna motor. (note - a power antenna motor often has the proper relay already supplied - but the stops may need to be adjusted).
I don't think you want a hobby servo motor because of what others have said - they are expensive, they are always on, they require supporting electronics. On the other hand... when worm driven motors stop they STOP. There is no more power needed to maintain their position. There is a great resistance to move in either direction. This configuration is what I would use for your suggested application.
You can adapt these motors to servo electronics - but they are a bit sluggish and power hungry when used this way.
Bart
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