Westcoast Drive bearing + axle retention

FIRST General Forum
1

Simple question. I am aware of several solutions but wanted to see if there was a consensus as to how those who do a westcoast drive style base retain their axle and bearings. “E” clips against fanged bearings might be one method.

Does anyone have close up images or CAD as to how they might do it?

I am talking about something like this

2

Thread the ends of your axles, use bolts and washers.

3

I’ll second screw and washer on the end of the shaft.

My team also used high-strength shaft collars, and we never had a problem with them. They were more expensive and harder to access than the screw and washer method though.

4

https://drive.google.com/open?id=0BxWVPt_Kq4XxZGV1UTlKZWc4cXM

I third that. It’s obviously heavier than the clips, but it’s less complex if you don’t have the resources. :slight_smile: Here is a picture of our drive base, sorry for the fuzzy photo.

5

This.

Best solution by far.

Be sure to loctite the bolts if you do this, though, or they will come out.

6

There are 5 common ways to retain axles and retain things on axles in FRC that I can think of.

  • Clamping Shaft Collars
    This is the easiest to manufacture, but you have to buy and keep shaft collars on hand. Also, the shaft collars can become loose at critical moments.
  • Snap Rings
    These are often sold as “external retaining rings.” You have to machine a groove into the end of the shaft for these to fit into and you need a set of pliers to remove and install the rings; but once these are installed they are a very reliable solution that are easy to remove. But relocating a groove is pretty tricky if plans change.
  • E-Clips
    Very similar to snap rings, these are often sold as “side mount external retaining rings.” These also require a groove to be manufactured into the shaft. Technically, you can install and remove these with a set of normal pliers or by hand, but it’s much better to just buy the tool that accompanies them. E-clips’ biggest advantage over snap rings is that they can be installed radially, while snap rings must be installed axially. However, I prefer snap rings because the groove for an E-clip must be considerably deeper for the same size shaft.
  • Push Rings
    These are the deforming rings often seen on CIM shafts holding pinions in place. They’re easy to install and remove, but the rings can wear down and become loose after repeated removal and installation.
  • Bolt & Washer
    Seriously. Just do this unless it’s on an abnormally hollow shaft or something.
7

Triple Helix uses McMaster 98585A109

Our machining procedure is attached.

grooveProcedure.pdf (142 KB)

8

We forgot to loctite half the bolts on our comp bot and they still never came out. I was pretty surprised.

9

Also, if you end up tapping the shaft for a retention screw, try to keep the tapped portion of the shaft away from the highly loaded portion of the shaft.

https://www.youtube.com/watch?v=5uyiT904ZBc

2363 lesson learned 2015 - Gmail - On the Doc Ock arm mishap.pdf (343 KB)

10

I’ll throw another hat in the ring for bolts and washers. We typically use 1/4-20 bolts, very short, only half inch or less, and corresponding washers. If you have access to a lathe drill the hole out that way and then use a standard tap set to thread the hole. Like others have said, make sure you use the metal-metal loctite or you can end up with wheels on the floor when it matters most.

If we were to switch to another method it would be the snap rings, but the bolts typically tend to be easier to assemble and maintenance.

11

For the sake of redundancy, we use both bolts/washers and 1/4" wide shaft collars to retain our wheels. Is it absolutely necessary to have both? No. But I’d rather not risk it on a system as essential as the drive base.

12

One of the worst things you can do is put E-clip grooves in the middle of a shaft. We did that one year to skip the need for spacers, and we were just shredding axles all year long until we switched to spacers. Other then that, all suggestions in this thread are good. One of my favorites currently is to use ThunderHex, and just tap the existing hole to accept a 1/4-20 bolt. Silly easy to use, reliable and easy to change if need be. C-clips are cool, and much better then E-clips, but they’re a lot of work that is unnecessary for drive axles nowadays. However, on other subsystems I still prefer C-clips for space reasons.

13

We have been using E clips for years. It’s easy to make the shafts if you have access to a lathe and a cutting tool to make the groove. I prefer them over the normal external retaining rings because they are easier to install and you don’t have to round off the end of the shaft.

Quoted for truth. Never put a groove for a retaining clip on a part of the shaft that transmits torque. It’s like putting a giant “cut here” label on the shaft. Only put them on the ends.

14

254 uses snaprings on both ends of the shafts to retain the sprockets and wheels.

15

Thanks for all the replies. Tap and bolt seems to be the most common. We have done that in the past, and will continue.

16

Ok, so did you experience any issues with the washer & bolt method that made you want to look at alternate options? Or just wanting to get more info?

17

We use a tapped 10-24 and washers on the wheel side, and a 1/2 E-clip on the interior side. With all the electronics and mechanisms, it’s far easier to pull an E-clip then get a hex wrench inside and remove bolts and washers. We tap a full 1/2" of threads and use the Locktite Blue.

We only use 7075 hex stock in our shop.

Nikcole makes reasonably priced groving inserts of different widths with both 1/2" holders for BXA, and 3/8" holders for AXA or bench top sized lathes. Easy way to cut proper width E-clip or C-clip groves.

18

We’ve done both snap rings and bolts in the past. We’ve had a problem with snap rings popping off with enough lateral force. Since we’ve switched to bolts and washers, we haven’t had any issues. Also, changing wheels is much faster with bolts than snap rings. We haven’t used lock-tite on our wheels and haven’t had much issue. Might not be a bad addition.

19

We never had any issues with washer and bolt. It just didn’t look as elegant as smaller snap rings or clips. So yea, just wanted to hear what a lot of others do in case I was missing something. Given the reliability and simplicity as others have stated washers and bolt makes the most sense for drive axles.

20

Way back in the day, Mean Machine used to use all steel shaft collars, until we realized one of our robots had ober 7 lbs of them.

Now we use snap rings and grooves because they are the smallest, lightest, and most reliable solution. I also personally think they are faster and easier to machine than a drilled and tapped hole. You can honestly do it without even having a lathe. We used to do it with a drill press and a hack saw.

It’s also a groovy solution.