pic: VEX High Reduction Gearbox

[MrForbes]

Originally Posted by Madison

I think the makes it reasonably possibly to accelerate the larger wheel to the speed of light.

If not for that pesky friction....

[Andrew Schreiber]

Originally Posted by squirrel

If not for that pesky friction....

Also inertia

Someone please correct me if I am wrong but wouldn't you be fighting a force of 1/12(mass)(3*radius^2 + height^2) * 244140625 Newtons to get it started? Now, maybe if you put a crazy long lever arm on the small wheel's shaft you could over come that.

Of course, even that number is almost nothing compared to the real number because you would have to account for starting the gears rotating too. This could be an interesting problem for more advanced students, What is the max length of a lever arm you could attach a 100 kg weight to and still not have the large wheel move? Have them run it both ways.

But very cool John.

[Kevin Sevcik]

What I want to know is what the backlash is at the input gear. It has to be several thousand full revolutions of the input shaft. Which amuses me to no end, given I'm usually working with gearheads that measure backlash in minutes of arc....

[daltore]

Now try replacing all those medium gears with the large gears.

[Andy Baker]

Cool gearbox, JVN!

We had a guy call us this past summer, wanting to use a Toughbox and a low power motor to slowly move a parabolic solar panel so that it follows the sun.

So... we found a small gearmotor package from Dayton, and used that as an input to the Toughbox. We bench tested this assembly and found out that the output shaft of the Toughbox was doing 1 revolution in about 18 minutes. Of course, this is much faster than the Earth is spinning, but it was a good way to use a very low power motor to move a 12 foot long solar panel.

AB

[Rupnick]

Now lest see you "back-drive" that!

[Bannanakin]

Have you seen the mini jet engines that are in the fancy rc planes? Some of those spin up to around 150,000 rpm. At that rate it would take a little over a day to turn the wheel.

[Eugene Fang]

Originally Posted by Bannanakin

Have you seen the mini jet engines that are in the fancy rc planes? Some of those spin up to around 150,000 rpm. At that rate it would take a little over a day to turn the wheel.

That is, before the thing starts melting or grinds itself into pieces...

[Libby K]

Wow. This is just plain cool. =]

[Mr. Freeman]

Originally Posted by Andrew Schreiber

What is the max length of a lever arm you could attach a 100 kg weight to and still not have the large wheel move? Have them run it both ways.

It's going to move the large wheel if you apply any torque to the small wheel at all, the amount of torque just determines the acceleration, which will be tiny for any reasonable amount of mass. The only thing that might actually stop the entire thing from rotating is the friction in the bearings, which I don't think is very large.

[Andrew Schreiber]

Originally Posted by Mr. Freeman

It's going to move the large wheel if you apply any torque to the small wheel at all, the amount of torque just determines the acceleration, which will be tiny for any reasonable amount of mass. The only thing that might actually stop the entire thing from rotating is the friction in the bearings, which I don't think is very large.

Thanks, you can tell it has been a while since physics.

[dlavery]

Heh - very cool. If you could "drive" the big wheel from the Earth to the Moon (at apogee, the approximate distance is 251,968 miles), the little wheel would turn only 4.1629 times.

-dave



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[Rich Kressly]

Originally Posted by dlavery

Heh - very cool. If you could "drive" the big wheel from the Earth to the Moon (at apogee, the approximate distance is 251,968 miles), the little wheel would turn only 4.1629 times.
-dave

Say we're driving on the big wheel to Mars ... how many little wheel turns?

[dlavery]

Originally Posted by Rich Kressly

Say we're driving on the big wheel to Mars ... how many little wheel turns?

At closest approach (such as during the perihelic opposition in August 2003) the Earth-Mars distance can be as small at 34,646,418 miles. In that case, the little wheel turns 572.418 times. During conjunction, such as the one just ending this week, the distance can be approximately 247,821,000 miles. In that case, the little wheel turns 4094.437 times. I would find that number to be excessive, so for a Mars transportation application I would want to add on at least one more 12:60 reduction stage.


-dave



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[AdamHeard]

Originally Posted by dlavery

At closest approach (such as during the perihelic opposition in August 2003) the Earth-Mars distance can be as small at 34,646,418 miles. In that case, the little wheel turns 572.418 times. During conjunction, such as the one just ending this week, the distance can be approximately 247,821,000 miles. In that case, the little wheel turns 4094.437 times. I would find that number to be excessive, so for a Mars transportation application I would want to add on at least one more 12:60 reduction stage.


-dave



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I would like to thank both John and Dave for finally making me understand how far away mars is