Re: Bevel/Miter Gear Mounting Distances
 

The argument to tangent is the pressure angle of the teeth, not the pitch cone angle. tan(20°) is around 0.36 resulting in a reduction in your figures by a factor of 3.

Re: Bevel/Miter Gear Mounting Distances
 

Axial Bearing Load = (Torque / radius avg) tan (20°) sin(45°)
= (Torque/0.463) (.364) (.707)


Axial Gear Force = 172 (Ounce*In) * (.364)(.707) / 0.463 in
= 95.6 oz or 5.9 lbs

With a Swerve drive gear reduction, this is still a substantial force on a small FR6ZZ

Re: Bevel/Miter Gear Mounting Distances
 

One counter example is 1640, who has been re-iterating their swerve modules for the last few years and have one of the most fully developed systems (in my opinion). They still incorporate thrust bearings into their modules. It's only about $3.50 per bearing, so not really a large resource cost.

Anyone designing swerve modules should check out their wiki, it's a fountain of information. http://wiki.team1640.com/index.php?t...XI_Drive_Train

Re: Bevel/Miter Gear Mounting Distances
 

Much smaller than the thrust loads applied to the bearings in all traction wheeled skid steers.

Re: Bevel/Miter Gear Mounting Distances
 

If you're particularly worried about the thrust loads and you're using the Vex miter gears...you'll notice they already include a small shoulder on the back side for a standard sized 0.0625" thick thrust bushing. Adding this bushing will not modify the mount distance.

They don't advertise this feature but it's there. :)

Re: Bevel/Miter Gear Mounting Distances
 

Are thrust bearings required behind the bevel gears? No. Some teams have not used them and it will work. Our justification for them is long term protection from wear. Our robots rack up hours and hours of run time from many events, driver practice and demos. They are cheap failure protection. Also note that there are some very large dynamic loads. This years game was very tame for drive trains. And then there was 2014. We have never had any failures in this part of the module. We will always use thrust bearings. We do not use radial ball bearings on the vertical. We use needle bearings and the thrust bearings. The drive shaft is 4140 steel. We have contemplated going with a 7075 drive shaft with radial ball bearings. Have always questioned the durability of a 7075 shaft in this application. We try to maintain tight tolerances on the bevel gears. That said we have 1 module that is about .023" off on the vertical bevel. It's been bouncing around since 2013 and still works. Just beginning to have very slight wear. No matter how a team chooses to do the bevel gear and bearings the 1 most important thing for teams to do is design the lower module so that it does not "rack". Racking will lead to wear and failure.