source of largish gears?

Posted by Joe Strout on April 18, 2007, 10:48 pm

I have two largish (15 cm) surplus Pittman motors, which I'm trying to
cram into a circular shell 24 cm across in order to power the two
primary wheels (for a differential-drive robot). Obviously I can't just
lay them out side by side; I'm going to have to have one motor in the
front, and the other in the back, which means connecting to the wheels
via gears, chains, or belts.

Of these options, I like gears best and chains least. But now I'm at a
loss -- where would I find reasonably-priced gears beefy enough to suit
these motors? I'm expecting this to be a fairly heavy robot, which is
why I'm glad to have such strong motors. The axle-to-axle span of these
gears only needs to be about 4 cm, but it's no good if they're skinny
little axles that introduce an obvious weakness compared to the rest of
the system -- the gears built into the motor assemblies are all 5 mm
thick or more.

So, in brief: I need (for each wheel) a pair of gears with a total
radius of 4 cm or so, and a thickness of 5 mm or more. (I'll also need
fitting shafts and bearings, but presumably those are easier to find
than the gears themselves.) Any suggestions?

Thanks,
- Joe

Posted by Pogo on April 19, 2007, 12:24 am

> I have two largish (15 cm) surplus Pittman motors, which I'm trying to =

> cram into a circular shell 24 cm across in order to power the two=20
> primary wheels (for a differential-drive robot). Obviously I can't =

just=20

> lay them out side by side; I'm going to have to have one motor in the=20
> front, and the other in the back, which means connecting to the wheels =

> via gears, chains, or belts.
>=20
> Of these options, I like gears best and chains least. But now I'm at =

a=20

> loss -- where would I find reasonably-priced gears beefy enough to =

suit=20

> these motors? I'm expecting this to be a fairly heavy robot, which is =

> why I'm glad to have such strong motors. The axle-to-axle span of =

these=20

> gears only needs to be about 4 cm, but it's no good if they're skinny=20
> little axles that introduce an obvious weakness compared to the rest =

of=20

> the system -- the gears built into the motor assemblies are all 5 mm=20
> thick or more.
>=20
> So, in brief: I need (for each wheel) a pair of gears with a total=20
> radius of 4 cm or so, and a thickness of 5 mm or more. (I'll also =

need=20

> fitting shafts and bearings, but presumably those are easier to find=20
> than the gears themselves.) Any suggestions?
>=20
> Thanks,
> - Joe

Hey Joe. The best source I have found so far is Stock Drive Products, =
found at: https://sdp-si.com/eStore/ . They're the *only* place I have =
managed to find both matching timing pulleys and belts so far.

McMaster-Carr is also a good place to look & get educated, if nothing =
else: http://www.mcmaster.com/. So is Stock Drive.

Hope that helps !
JCD

Posted by John Nagle on April 19, 2007, 3:13 am

Pogo wrote:

>>So, in brief: I need (for each wheel) a pair of gears with a total
>>radius of 4 cm or so, and a thickness of 5 mm or more. (I'll also need
>>fitting shafts and bearings, but presumably those are easier to find
>>than the gears themselves.) Any suggestions?
>>Thanks,
>>- Joe

>
>
> Hey Joe. The best source I have found so far is Stock Drive Products

SDP is more for small stuff. As you move up in size, you
go to Boston Gear (www.bostongear.com).

Take their "Gearology" on line course:

http://www.bostongear.com/pdf/gearology/all_gearology-chapters.pdf

If you take the quizzes and pass, they send you a "Gearology"
certificate.

John Nagle

Posted by Joe Strout on April 19, 2007, 10:45 am

> SDP is more for small stuff. As you move up in size, you
> go to Boston Gear (www.bostongear.com).

Thanks for the tips, guys. Boston Gear looks like they may have some
nice stuff, but geez, I've never seen a company make it so difficult
even to find out exactly what products they have. Fortunately there's a
local distributor nearby -- I'll go in today and look at a catalog.

Best,
- Joe

Posted by Gordon McComb on April 19, 2007, 11:26 am

Joe Strout wrote:

> So, in brief: I need (for each wheel) a pair of gears with a total
> radius of 4 cm or so, and a thickness of 5 mm or more. (I'll also need
> fitting shafts and bearings, but presumably those are easier to find
> than the gears themselves.) Any suggestions?

This is where a good local surplus outfit comes in handy. Most areas
have at least one, but they don't always stand out. You gotta go looking
for them.

Failing that, check out the surplus mail order like AmSci, H&R, C&H,
etc. I like to buy assortments, if they're cheap enough, for the junk
box. I've never had to buy a new gear from SDP, Boston, or their ilk.

Lastly, venture into ye good olde hobby store, and check out the
replacement gears for electric R/C airplanes and cars (like the Traxxis
E-Maxx). These are going to be molded nylon, but well made. I use a
Traxxis replacement gear that retails for about $3 in stores in my 360
turret: product:

http://www.budgetrobotics.com/shop/?shop=1&cat=157

They do have some with larger diameter, but the thickness is about what
you're looking for.

-- Gordon

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