Gearbox Construction

[John Gutmann]

Looking at somethings online I was thinking about how to make a really good gear box, and especially after looking at those pics of the segway gearbox in thread I was wondering about a few things.

1.) What is the biggest difference between 14.5 and 20 degree pressure angle gears, and how do you determine what the angle on the gear is?

2.) Significance of helictal gears. Why use a gear with angled teeth?

3.) How do you make a gearbox with a high efficency?

4.) How do you determine the efficency?

5.) How do you make it run quitely?

6.) Correct spacing for gears?
6.1.)Is the paper spacing method sufficient for a sliding mount?

7.) Best type of bearing to use?
7.1.) how does a sealed differ from the rest?
7.2.) how does a shielded differ from the rest?
7.3.) How does a unshielded differ from the rest?
(eviroment of use and characteristics of use, which one is best for speed o rlow friction, ect...)

I have found some of the answers else where but the sources differed in the information for alot of these questions, so I decided to ask the experts.

Note: I may end up creating a white paper out of this information.