Gearbox Construction

[JoelP]

Originally Posted by sparksandtabs

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?

The pressure angle is the angle in which teeth between two gear contact each other. 14.5 pressure angle gears are smoother but have a lower load capacity. 20 pressure angle gears are less smooth but have a higher load capacity.

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

With the angled teeth helical gears have higher load capacity because there is more contact area between teeth. Also since the angled teeth gradually engage each other, helical gears run smoother and quieter. However since there is some sliding action between the teeth, there is some loss in efficiency. The efficiency also decreases as the angle of the gear increases. In addition to the loss of friction, the angled teeth also create axial thrust forces so you have to use thrust bearings with them and it also creates more efficiency losses.

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

Minimize the number of stages of reduction through gears and chain because you lose efficiency with each interaction between gears or between chains and sprockets.

4.) How do you determine the efficency?

You can use benchmarks to determine the efficiency. I know that some people use an overall gearbox efficiency of 81%. Others prefer to determine the efficiency through each stage of reduction. Some benchmarks I've found are:
Spur gears - 95%-98%
Chain/Belt - 95%-98%
Bevel gear - 90%-95%

5.) How do you make it run quitely?

Lower pressure angle and lower diametral pitched gears tend to run smoother and quieter. I've also read that adding .002" to the center-to-center distance between gears allows the gears to run smoother and quieter. Lubrication also helps.

Sorry, but I don't know the answers to your last two questions, but I hope this helps you. I'm also working on designing a custom gearbox for my team and its great to see other people interested in this type of thing too. Good luck with your gearbox project!!