Axel Diameters

Hey guys, I need some help.

I need to find out the width (diameter) of a standard Robot axle.

The kind that go with these wheels:

3/8" Bearing
1/2" Bearing


As listed in the middle of that webpage, you can order either a 3/8" or 1/2" diameter bearing. Therefore, your shaft would be either 3/8" or 1/2".

There are many teams that utilize 3/8" shafts. There are equally as many teams that utilize 1/2" shafts. As a point of reference, the kit chassis is designed to work with 3/8" shafts (or bolts…)


thanks homie

We use 3/8"

If you use Grade 8 bolts, 3/8" works fine.

1293’s used 3/8" threaded rod for two seasons with no complaints at all. (After some personal experience with my omnidrive project, however, I’d be inclined to make the switch to bolts.)

I prefer 1/2" shaft, it is smaller and saves that precious weight.

Isn’t 3/8 less than 1/2?

minor details. :stuck_out_tongue:

Only in metric… :slight_smile: :stuck_out_tongue: :slight_smile:

As another point of reference, 1519 used standard (grade 3) bolts on their 2005 robot for the non-drive wheels and had problems with the axles becoming bent. (We never did get around to switching the grade 3 bolts out for grade 8 bolts, primarily because we had added about 0.75" of thread by hand and didn’t want to do that on grade 8 bolts!)

I would think that 3/8" grade 8 bolts would work fine for most FRC robot drive axles.

hahhaha thats what i was thinking :rolleyes:

If you use 3/8, make sure it is steel.
If you go to 1/2, you can use aluminum - this is our typical shaft size and material.

3/8" shaft must be supported on both sides, you can probably do without the extra support with 1/2". In 2005 we used 3/8" shaft with the skyway wheels, and slowly the axles bent upwards. They would be fine if it was just our robot driving around on the flat surface, but it had to content with other robots weight some of the times, and being leaned back onto 2 wheels for getting it up onto the cart, etc… Luckily, we just had to undo some bolts, take off some shaft-locks, and slide out the old axles, put new ones in, put wheel and shaft locks on, tension up the chain, and tighten the bolts back up.

I highly recommend using 3/8" grade 8 bolts with the KOP frame and Skyway wheels.

we used the high traction robot wheels and they work very good with our design. the only thing im having trouble wiht is trying to figure out how much bigger the hole needs to be where the shaft goes into the side plates

If it’s a powered axle in bearings, you’ll need to bore press fit holes large enough for the bearing outer diameter. If you’re using a dead axle and you’re not intent on being too precise (which seems to be the case), you ought to be fine by drilling out the hole with a drill bit the same diameter as your axle and then opening it up slowly by hand using a deburring tool or the like.

233 uses 1/4" diameter axles

Do yourself a favor and always use grade 5 or 8 bolts or something better anywhere you can. Forget threaded rod and any of that mystery metal stuff, unless it is very large.

Although heavy, we’ve more often than not used 5/8" driven axles with bearings on each end. 4 years, never a single drivetrain failure. This is using regular shaft with a keyway, which is not, to my knowledge, heat treated in any way.