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Is there such thing as a super slow servo?

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Old 07-25-2006, 11:28 PM
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Fastenjaw
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Default Is there such thing as a super slow servo?

Hi everyone =) This will be my first post! This looks like a good place to ask about servos so here I am!

Now while I am not exactly very deep into RC material, I do own some RC items. One of those is a bag filled with servos of about 30 or so working servos. However all those servos may not work for the task of my new project. The problem? Load and speed requirements.

I am basically trying to control the movement of 2 rods that are about 4 feet long. They dont weigh much as they are made of a light material. But the load of moving each rod is a bit too high for a standard servo. So I need high torque servos. The other thing is its going to be used for a loooong time. So the servo needs to have a long life span. The last and most important thing is speed. The servos need to control the rods very slowly. So fast servos are out. A slower speed servo with quality gears would work well as it would be best suited for the job. I am not too concerned with the price. I just want to know what kind of long life slow servos I would need. This is where you guys come in. I read that slow servos are unpopular, and thus, hard to find. If you guys know of any that will work well and can handle alot of load without much fuss or wear, please let me know. I did think about the idea of taking a servo apart and using the electronics to control a more durable motor scheme. I am not sure if that is fully possible. I hear alot about servos breaking and failing. I would like it if that didnt happen anytime soon for this particular project.

Thanks for reading

Fastenjaw
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Old 07-26-2006, 12:43 AM
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Campgems
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Default RE: Is there such thing as a super slow servo?

If I needed more toque, and slower speed, I would gear the output shaft, IE replace the horn with a gear and build a mount for a mating gear. A standard servo will not work because of the limited travel, but a winch servo might just fill the bill. It has around two or three turns on the drum which could be replaced with a gear and if you setup a 9 to 1 gear ratio, you could get a load of torque and a lot slower output on the final shaft. a 9 to 1 ratio would give you about 120 degrees of movement for a three turn winch servo at 9 times the torque.

Now, is a servo what you realy need, or do you need a stepper motor with driver?

Don
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Old 07-26-2006, 01:39 AM
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Default RE: Is there such thing as a super slow servo?

The link below maybe of use for your project.

http://servocity.com/html/robotzone_servos.html

Hitec programmable digital servos can be programmed to be veerrrry slow too.... I'd suggest something like Hitec's 5995TG premium coreless digital with titanium gear train...
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Old 07-26-2006, 01:54 AM
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Default RE: Is there such thing as a super slow servo?

I have roughly a 4 inch mounting space to work with so I dont know about the use of a winch. I didnt really give those much thought as I assumed they are very big and bulky. I want to use servos because the rods need to be synchronized. Using the controller with both servos assures me that, unless theres some kind of error, it will be where I want it to be when I want it. The range of the servo could be as low as 60 degrees of travel. Maybe lower for the other 2 rods I have. I heard about super servos and even found some info off of them. But they seem a bit big and fast for the job. Robbing a servo of the parts and adapting it to a geartrain that has the speed I want is the best alternative I can think of since I have not found any servos that are real slow and small yet. The only thing with that is I would need to find half a dozen matching gear sets to do it for all the rods I have. I think I may find a toy that can work well and buy a couple of em for the geartrains. That would take time to setup as opposed to an already made servo. But if I dont turn up anything soon, those cheap toy's at the local toy store may very well be my new project.

I think stepper motors are a bit complicated to run. I could look into them as a possibility. The thing is that the rods need to move at the same time. If one gets out of sync from the other, it may cause problems. The rods are in seperate housings but the wires run to the same board. I think it might be a bit complex for me to synchronize 6 stepper motors as opposed to 6 servos that are adjusted.
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Old 07-26-2006, 07:41 AM
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Edwin
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Default RE: Is there such thing as a super slow servo?

Try this place. Lots of gizmo's.
Edwin

http://www.pololu.com/products/gearbox.html
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Old 07-26-2006, 02:47 PM
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Fastenjaw
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Default RE: Is there such thing as a super slow servo?

Thanks guys! This info is quite helpful. I have found some servos on ebay for 100 which may work well. I'll keep up my search for servos. Thanks again!

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Old 07-26-2006, 03:20 PM
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Default RE: Is there such thing as a super slow servo?

I don't know if you can buy servos that are specifically slow, but you can buy modules that they plug into to make them slow down.
Some have adjustable times that they move the servo.
They are used in such instances as aircraft retracts and flaps to give them a more scale appearance when operated, rather than moving at unrealistic fast speeds.


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Old 07-26-2006, 03:21 PM
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Default RE: Is there such thing as a super slow servo?

The speed of the servo would depend on how fast you change the control pulse width - the rating you see for a servo is the maximum travel speed for a given amount of movement.
I'm not too sure just how synchronized multiple servos would be for very precise movement. The servo position is controlled by a variable width pulse, and the pulses need to be sent continuously in order to operate the servo (just one pulse will not work). It takes several pulses to get a servo to move to the intended position.
Stepper motors and stepper motor drivers are fairly small these days, and can be moved very precisely - they are used in almost all inkjet printers for both paper movement and print head movement, so old printers are a convenient source of parts.
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