Gearmotors/Servos - Really basic question

Hi,
If I get a servo and remove everything form inside it except the motor and the gears will it work as a gearmotor??
If so, can anyone recommend a really cheap servo I can use as a gear motor, preferably one that has matching servo wheels...
Thanks
gareth
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gareth wrote:

Most of the premade wheels are for Futaba-spline servos. So, get a Futaba, GWS, Cirrus (in-house brand of Hobby People mail order), or other servo that has a Futaba-compatible spline. Of the makes, GWS and Cirrus are probably the cheapest.
-- Gordon
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I assume you are talking about hobby servos ? If so, it depends on *exactly* what you mean by "remove everything form inside it except the motor and the gears". If you mean you remove ALL electronics and reconnect the motor then yes, you will have a gear motor. But if you leave the little circuit board in that is connected up to the standard 3 wire servo connector, then you will still have a servo that requires some form of PWM to drive it.
I have a feeling these links might help you out:
http://www.lynxmotion.com/images/html/smodh2.htm http://www.acroname.com/robotics/info/ideas/continuous/continuous.html
Also, check out the chapter "Working With Servo Motors" in the book, "Robot Builder's Bonanza" by Gordon McComb. I like the 2nd edition.
Good luck ! JCD
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Yes, you can gut the electronics, remove the physical stop, and use it as a gearmotor.

I'm partial to the Hitec line, but Futaba is also good. Select your wheels first, and then you should have no trouble finding a compatible cheap servo. Off the top of my head, LynxMotion.com has wheels for Hitec servos (get the HS-311, which should cost you under $10), and BudgetRobotics.com has wheels for Futaba servos.
HTH, - Joe
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That will work, but most people don't do what you suggest. Instead, they modify the servo for continuous rotation. This gives you a motor with a variable speed drive for cheap. Granted, it's not the best VSD. But it works. I think Hitec makes the best low-price hobby servos. Some are more easily modified than others. ServoCity.com has some good guidelines on their web site. They also sell all sorts wheels that will attach to them.
BRW
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That will work, but most people don't do what you suggest. Instead, they modify the servo for continuous rotation. This gives you a motor with a variable speed drive for cheap. Granted, it's not the best VSD. But it works. I think Hitec makes the best low-price hobby servos. Some are more easily modified than others. ServoCity.com has some good guidelines on their web site. They also sell all sorts wheels that will attach to them.
BRW
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Yes, but you may need to remove the moulded "stop" on the final gear to get 360 degree rotation.
Deep.
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Hobby Engineering sells servos without the electronics in them. http://www.hobbyengineering.com/H1210.html
-Kit
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Excellent, thanks for all the replies.
I'm thinking it would be a lot easier to build robots in the US (I'm in the UK) - all the shops seem to be there!!!
The only place I've foundis Technobots.co.uk who have a good range but seem to be about twice the price of US stores :o(
Oh well....
Gareth
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Hobby Engineering says on their website that they will ship international. But they don't give the shipping cost.
There is also Solarbotics (www.solarbotics.com) that sells the same thing. They are in Canada, but they have shipped stuff to me (in the US), so I would think they would also ship to the UK. -Kit
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Didn't realise Hobby Engineering would ship to the uk, will look into that.
I knew Solarbotics did but unless you pay $40 it takes 4-6 weeks and isn't insured or tracable....
Gareth
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gareth wrote:

That servo is made by GWS (but is a special item). Try www.gws.com.tw for UK-based dealers, then see if they happen to carry it. You never know.
-- Gordon
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Thanks Gordon. They don't seem to carry that special server, oh well.
Final question on this subject...I read somewhere that servos aren't very consistent when it comes to speed. I was hoping to create a four wheel drive robot with one servo driving each wheel but if they all run at different speeds it's not going to work very well!!! :o) Is this true??
Thanks
gareth
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gareth wrote:

They aren't any more/less consistent than any open loop motor. You might used encoders to control the motors on opposite sides, and make sure there is sufficient wheel slippage for the motors on the same side. That seems to work well.
-- Gordon
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O.K. I lied - another question...
How do you get wheel slippage with a wheel attatched to a servo?
Ta
Gareth
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gareth wrote:

A wheel surface that doesn't "grip" the road too much. A medium to hard plastic might be good. A real soft rubber would probably not be.
This is the kind of thing thing where you know the problem when you see it.
-- Gordon
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That's funny -- I'm in the US, and I've often thought the same thing about the UK. There are a LOT of robotics/electronics resources in the UK, often carrying things we can't easily get here in the states. Unfortunately, I don't collect those links, so I can't point any out to you... but keep looking, they're certainly there.
Best, - Joe
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Other UK stores that you may wish to check out are:
http://www.active-robots.com / http://www.milinst.com/index.htm http://www.robot-electronics.co.uk / http://www.britishrobotics.com / http://www.totalrobots.com /
I Know what you mean about the price though, but now that the exchange rate between the $ and the is so fantastic (if you live in the UK that is :-) its quite often cheaper to order from the states.
The other place that I have bought things from is ebay. there are loads of component suppliers on ebay, (you can get some really cheap servos shipped from Hong Kong) you can get lots of component packs/materials/tools etc quite cheap on ebay, its now pretty much my main source of components.
hope this helps,
Lee.
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