Jul 1, 2007

Anyone for a Knob Wheel?



Despite these wheels being in the education kit, the retail kit and the education resource set, I don't see them used in many models. That could be because I don't get out much, or it could be that their slipperiness makes them less suitable than conventional gears. (I used them in pairs while building Alpha Rex, but the knobs kept disengaging from each other).

Knob wheels provide more surface contact than a regular gear, hence more torque (theoretically). But I haven't seen many around.

Can anyone point us to models on the web or in NXTlog that use these wheels? They look too good to just lie in the box.

19 comments:

Robotica said...

they are good to go around the corner, take a look at the gripper on the cover of the book :)

Rick Rhodes said...

Martyn,

I'm looking at the book cover's gripper at 400% magnification, and I don't see the knob wheels. Perhaps they're obscured by other parts?

Rick

David Levy said...

They are also used on the motor module of the Lego Edu Base vehicle

You can see one of them on the front cover. Look at the swinging arm. There are actually two there that convert the gear direction by 90 degrees.

I'd be interested in knowing why the designer chose those gears as well.

My guess is that they provide better torque esp. at higher speeds.

Rick Rhodes said...

David and Martyn,

I still don't see it, but I'll take your word for it. (I'm looking at the first draft of the cover. Maybe something is cropped or I'm looking in the wrong place).

I do see the one on the Lego Ed base vehicle. I never noticed it before.

Rick

Robotica said...

Rick,

I must admit the current cover picture, does not show them.

But they are used.
so maybe you just will have to wait a little longer until the book is available.

Martyn

Rick Rhodes said...

The folks over at nxtasy.org have heard my cry, and have posted a great robot using knob wheels as critical parts. Look just above the ultrasonic sensor for the knob wheels:

http://www.youtube.com/watch?v=K6u7pn62Zz0

Thanks!

Rick

Mr Mandrake said...

They work very well when you want a lot of torque to go through a 90 degree bend without teeth slipping. I use them quite a lot. For example in my NXT roadster at http://mrmandrake.wordpress.com/2007/01/27/nxt-roadster/ . If you look at the picture of the underside at the bottom of the page you will see how I used them for the steering and to link to the engine's chain drive.

Sivan said...

See my transmission car for a good use of these: http://www.tau.ac.il/~stoledo/lego/ShiftingGears/

To shift gears, I needed to
shift the angle of rotation by
90 degrees, and bevel and crown
gears just kept slipping. They
were not able to transfer enough
torque. The knob gears do a
great job here without slipping.

In a normal configuration
(no 90 degree turn), I don't
think you need them. The normal
gears don't slip much. But
the bevel and crown gears do,
and that's were you need the
knob gears (that's what they
are called).

Rick Rhodes said...

Mr. Mandrake,

Ah, yes....I plainly see the knob wheels in the undercarriage of your roadster. A beautiful model, too, by the way.

Rick

Rick Rhodes said...

Sivan,

An amazing transmission and a GREAT video.

Where can I get those yellow knob wheels featured in your model? ("Knob wheels" is common parlance in our part of the world, even though the wheels function as gears).

Rick

Rick Rhodes said...

Sivan,

I read your post more carefully and now see where you got the yellow knob wheels: 8421, the Mobile Crane.

Rick

Fernando said...

At the link bellow, you can see all the sets where this 'Technic Knob Wheel' is included.

http://www.bricklink.com/catalogItemIn.asp?P=32072&in=S

Fernando said...
This comment has been removed by the author.
Rick Rhodes said...

Thanks, Fernando.

I was aware that the knob wheel was included in many manufactured models. I just hadn't seen it in many homemade models.

Obviously, lots of people have found creative uses for this wheel. And I considered it an "orphaned" part. :)

Rick

Brian Davis said...

Another useful application of these is gearing at *arbitrary* angles, not just as spur gears (no change in axle angle) or crown/bevel gears (90° shift in axis). With the odd angles that are possible under studless design, I suspect this may be used more frequently.

--
Brian Davis

Sivan said...

Thanks for the compliment Rick.

Sorry I didn't see your question ealier. Yes, they are from the mobile crane.

pehrlich said...

Heres a good model that uses knob wheels (not by me):
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=145292
take a look at the in progress folder!

I'm definitely a believer in knob wheels, even with a perfect frame the 12z bevel gears' teeth will bend and click, especially under power from the NXT motors.

Rick Rhodes said...

Perlich,

Impressive photos!

The two pairs of knob wheels add a large amount of torque, I assume.

Rick

Julian said...

my idea for a differential XL, works nice.

http://www.brickshelf.com/gallery/masterprogram/DifferentialXL/diff_xl_center.bmp

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