Gearmotors/Servos - Really basic question

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

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

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

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

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

Yes, but you may need to remove the moulded "stop" on the final gear to get
360 degree rotation.

Deep.

Hobby Engineering sells servos without the electronics in them.
http://www.hobbyengineering.com/H1210.html

-Kit

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

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

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

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

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

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

O.K. I lied - another question...

How do you get wheel slippage with a wheel attatched to a servo?

Ta

Gareth

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

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

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.